NAVAL OPERATIONS AND SEAMANSHIP
NAVAL OPERATIONS AND SEAMANSHIP NAVA 302
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Date Created: 10/19/15
CHAPTER 2 RADAR OPERATION RELATIVE AND TRUE MOTION DISPLAYS GENERAL There are two basic displays used to portray target position and motion on the PPI s of navigational radars The relative motion display portrays the motion of a target relative to the motion of the observing ship The true motion display portrays the actual or true motions of the target and the observing s ip Depending upon the type of PPI display used navigational radars are classi ed as either relative motion or true motion radars However true motion radars can be operated with a relative motion display In fact radars classi ed as true motion radars must be operated in their relative motion mode at the longer range scale settings Some radars classi ed as relative motion radars are tted with special adapters enabling operation with a true motion display These radars do not have certain features normall associated with true motion radars such as high persistence CRT screens RELATIVE MOTION RADAR Through continuous display of target pips at their measured ranges and bearings from a xed position of own ship on the PPI relative motion radar displays the motion of a target relative to the motion of the observing own ship With own ship and the target in motion the successive pips of the target do not indicate the actual or true movement of the target A graphical solution is required in order to determine the rate and direction of the actual movement of the target If own ship is in motion the pips of xed objects such as landmasses move on the PPI at a rate equal to and in a direction opposite to the motion of own ship If own ship is stopped or motionless target pips move on the PPI in accordance with their true motion Table of Contents Orientations of Relative Motion Display There are two basic orientations used for the display of relative motion on PPI s In the HEADINGUPWARD display the target pips are painted at their measured distances in direction relative to own ship s heading In the NORTHUPWARD display target pips are painted at their measured distances in true directions from own ship north being upward or at the top of the PPI 260 270 28 25 HAWnuiml 29 150 HM MM u o 50 0 10 w ulurml 2 mu I Heading flash 3 n ll7 my 391 o m N o o n u I 3 WWW m m l m 09 17 003 i I 09 4 06 081 on NV 0 3 m a wini mqu L I 0quot 0 6 08 0 Figure 21 Unstabilized HeadingUpward display In gure 21 own ship on a heading of 270 detects a target bearing 315 true The target pip is painted 045 relative to ship s heading on this HeadingUpward display In gure 22 the same target is painted at 315 true on a NorthUpward display While the target pip is painted 045 relative to the heading ash on each display the HeadingUpward display provides a more immediate indication as to whether the target lies to port or starboard Stabilization The NorthUpward display in which the orientation of the display is xed to an unchanging reference north is called a STABILIZED display The HeadingUpward display in which the orientation changes with changes in own ship s heading is called an UNSTABILIZED display Some radar indicator designs have displays which are both stabilized and Heading Upward In these displays the cathoderay tubes must be rotated as own ship changes heading in order to maintain ship s heading upward or at the top of the PPI 0 0 9 3 n quotInniwuiin 7 Kw quotwt3 4 Fig Heading flash c o m m ea my NA 0 a m x a 09 m 00 lIIHIynquotilllllvpluyu 9 e 061 091 on o Figure 22 Stabilized NorthUpward display Table of Contents TRUE MOTION RADAR True motion radar displays own ship and moving objects in their true motion Unlike relative motion radar own ship s position is not xed on the PPI Own ship and other moving objects move on the PPI in accordance with their true courses and speeds Also unlike relative motion radar xed objects such as landm asses are stationary or nearly so on the PPI Thus one observes own ship and other ships moving with respect to landm asses True motion is displayed on modern indicators through the use of a microprocessor computing target true motion rather than depending on an ils extremely long persistence phosphor to leave tra39 Stabilization Usually the true motion radar display is stabilized with NorthUpward With this stabilization the display is similar to a plot on the navigational chart On some models the display orientation is HeadingUpward Because the true motion display must be stabilized to an unchanging reference the cathoderay tube must be rotated to place the heading at the top or upward Radarscope Persistence and Echo Trails High persistence radarscopes are used to obtain maximum bene t from the true motion display As the radar images of the targets are painted successively by the rotating sweep on the high persistence scope the images continue to glow for a relatively longer period than the images on other scopes of lesser persistence Depending upon the rates of movement range scale and degree of persistence this afterglow may leave a visible echo trail or tail indicating the true motion of each target If the afterglow of the moving sweep origin leaves a visible trail indicating the true motion of own ship estimates of the true speeds of the radar targets can be made by comparing the lengths of their echo trails or tails with that of own ship Because of the requirement for resetting own ship s position on the PPI there is a practical limit to the degree of persistence see gure 23 Reset Requirements and Methods ecause own ship travels across the PPI the position of own ship must be reset periodically Depending upon design own ship s position may be reset manually automatically or by manually overriding any automatic method Usually the design includes a signal buzzer or indicator light to warn the observer when resetting is required 0 10 20 350 o w 3K m 330 UV v 198 Electronic bearing 97 cursor interscan sgt 6amp6 270 280 hint Hm 16 quotn a quot u u m M H W i 005 i 06f 08 39 0 Figure 23 True motion display A design may include North South and EastWest reset controls to enable the observer to place own ship s position at the most suitable place on the PPI Other designs may be more limited as to where own ship s position can be reset on the PPI being limited to a point from which the heading ash passes through the center of the PPI The radar observer must be alert with respect to reset requirements To avoid either a manual or automatic reset at the most inopportune time the radar observer should include in his evaluation of the situation a determination of the best time to reset own ship s position Table of Contents Ran e setting examples for Radiomarine true motion radar sets having double stabilization are as follows Type CRMNTD75 32cm and Type CRMN2D30 10cm Relative motion range settings True motion range settings 1 2 6 39 12 1 2 6 16 and 40miles and 16 miles Maximum viewing times between automatic resets in the true motion mode are as follows Speed Range setting Initial view Viewing time knots mi s ahead miles minutes 20 16 26 66 12 6 975 41 8 2 325 24 8 1 16 16 The viewing time ahead can be extended by manually overriding the automatic reset feature Modes of Operation True motion radars can be operated with either true motion or relative motion displays with true motion operation being limited to the short and intermediate range settings In the relative motion mode the sweep origin can be offcentered to extend the view ahead With the view ahead extended requirements for changing the range scale are reduced Also the offcenter position of the xed sweep origin can permit observation of a radar target on a shorter range scale than would be the case with the sweep origin xed at the center of the 1 Through use of the shorter range scale the relative motion of the radar target is more clearly indicated Types of True Motion Display While xed objects such as landmasses are stationary or nearly so on true motion displays xed objects will be stationary on the PPI only if there is no current or if the set and drift are compensated for by controls for this purpose Dependent upon set design current compensation may be effected through set and drift controls or by speed and coursemadegood controls When using true motion radar primarily for collision avoidance purposes the seastabilized display is preferred generally The latter type of display differs from the groundstabilized display only in that there is no compensation for current Assuming that own ship and a radar contact are affected by the same current the seastabilized display indicates true courses and speeds through the water If own ship has leeway or is being affected by current the echoes of stationary objects will move on the seastabilized display Small echo trails will be formed in a direction opposite to the leeway or set If the echo from a small rock appears to move due north at 2 knots then the ship is being set due south at 2 knots The usable afterglow of the CRT screen which lasts from about 112 to 3 minutes determines the minimum rate of movement which can be detected on the display The minimum rate of movement has been found to be about 112 knots on the 6 mile range scale and proportional on other scales The groundstabilized display provides the means for stopping the small movements of the echoes from stationary objects This display may be used to obtain a clearer PPI presentation or to determine leeway or the effects of current on own ship 1n the groundstabilized display own ship moves on the display in accordance with its course and speed over the ground Thus the movements of target echoes on the display indicate the true courses and speeds of the targets over the ground Groundstabilization is effected as follows 1 The speed control is adjusted to eliminate any movements of the echoes from stationary targets dead ahead or dead astern 1f the echoes from stationary targets dead ahead are moving towards own ship the speed setting is increased39 otherwise the speed setting is decreased The coursemadegood control is adjusted to eliminate any remaining movement at right angles to own ship s heading The coursemadegood control should be adjusted in a direction counter to the echo movement Therefore by trial and error procedures the display can be ground stabilized rapidly However the display should be considered only as an approximation of the course and speed made good over the ground Among other factors the accuracy of the groundstabilization is dependent upon the minimum amount of movement which can be detected on the display Small errors in speed and compass course inputs and other effects associated with any radar set may cause small false movements to appear on the true motion display The information displayed should be interpreted with due regard to these factors During a turn when compass errors will be greater and when speed estimation is more dif cult the radar observer should recognize that the accuracy of the ground stabilization may be degraded appreciably The varying effects of current wind and other factors make it unlikely that the display will remain ground stabilized for long periods Consequently the display must be readjusted periodically Such readjustments should be carried out only when they do not detract from the primary duties of the radar observer While in rivers or estuaries the only detectable movement may be the movement along own ship s heading The movements of echoes of stationary objects at right angles to own ship s heading are usually small in these circumstances Thus in rivers and estuaries adjustment of the speed control is the only adjustment normally required to obtain ground stabilization of reasonable accuracy in these con ned waters N V Table of Contents PLOTTING AND MEASUREMENTS ON PPI THE REFLECTION PLOTTER The re ection plotter is a radarscope attachment which enables plotting of position and motion of radar targets with greater facility and accuracy by reduction of the effect of parallax apparent displacement of an object due to observer s position The re ection plotter is designed so that any mark made on its plotting surface is re ected to a point directly below on the PPI Hence to plot the instantaneous position of a target it is only necessary to make a grease pencil mark so that its image re ected onto the PPI just touches the inside edge of the pip The plotter should not be marked when the display is viewed at a very low angle Preferably the observer s eye position should be directly over the center of the PPI Basic Re ection Plotter Designs The re ection plotter on a majority of marine radar systems currently offered use a at plotting surface The re ection plotters illustrated in gures 24 and 25 are designs that were previously used aboard many navy and merchant ships and may still be in use The curvature of the plotting surface as illustrated in gure 24 matches but is opposite to the curvature of the screen of the cathoderay tube ie the plotting surface is concave to the observer A semire ecting mirror is installed halfway between the PPI and plotting surface The plotting surface is edgelighted Without this lighting the re ections of the grease pencil marks do not appear on the PPI Marking the Re ection Plotter The modern at plotting surface uses a mirror which makes the mark appear on not above the surface of the oscilloscope as depicted in gure 2 5 In marking the older at plotter shown in gure 25 the grease pencil is placed over the pip and the point is pressed against the plotting surface with suf cient pressure that the re ected image of the grease pencil point is seen on the PPI below The point of the pencil is adjusted to nd the more precise position for the mark or plot at the center and leading edge of the radar pip With the more precise position for the plot so found the grease pencil point is pressed harder against the plotting surface to leave a plot in the form of a small dot In marking the plotting surface of the concave glass plotters the point of the grease pencil is offset from the position of the pip Noting the position of the re ection of the grease pencil point on the PPI a line is drawn rapidly through the middle of the leading edge of the radar pip A second such line is drawn rapidly to form an which is the plotted position of the radar target Some skill is required to form the intersection at the desired point Cleanliness The plotting surface of the re ection plotter should be cleaned frequently and judiciously to insure that previous markings do not obscure new radar targets which could appear undetected by the observer otherwise A cleaning agent which does not leave a film residue should be used Any oily lm which is left by an undesirable cleaning agent or by the smear of incompletely wiped grease pencil markings makes the plotting surface dif cult to mark A weak solution of ammonia and water is an effective cleaning agent During plotting a clean soft rag should be used to wipe the plotting surface PLOTTING ON STABILIZED AND UN STABILIZED DISPLAYS Stabilized N orthUpward Display Assuming the normal condition in which the start of the sweep is at the center of the PPI the pips of radar targets are painted on the PPI at their true bearings at distances from the PPI center corresponding to target ranges Because of the persistence of the PPI and the normally continuous rotation of the radar beam the pips of targets having reasonably good re ecting properties appear continuously on the PPI As targets move relative to the motion of own ship the pips as painted successively move in the direction of this motion With lapse oftime the pips painted earlier fade from the PPI Thus it is necessary to record the positions of the pips through plotting to permit analysis of this radar data Failure to plot the successive positions of the pips is conducive to the much publicized RADAR ASSISTED COLLISION Through periodically marking the positions of the pips either on the glass plate implosion cover over the CRT screen or the re ection plotter mounted thereon a visual indication of the past and present positions of the targets is made available for the required analysis This analysis is aided by the HEADING FLASH HEADING MARKER which is a luminous line of the PPI indicating ship s heading Table of Contents Observer s position Observer s position Semireflecting mirror Reflected images Radar pip Figure 24 Reflection plotter having curved plotting surface Table of Contents Observer39s position Observer39s position Flat plotting surface Re ected images Radar pip Figure 25 Reflection plotter having flat plotting surface Table of Contents 41 2 270 0 20 o 0 16 30 1quot w 350 o 10 quotMW 310 50 W 3A 20 a a m 33S quot MM quotWW H44 Jo nan90 c N I 9 n7 9 law 39539 ia w o a 5 an E 5 5 Q m w uV Dgelmwl nlrm39uu mwwv ggx 019v 0 3 7 0610810 Wm L De I wwwmm 1 l 9 011 001 06 0 Figure 26 Effect of yawing on unstabilized display Unstabilized HeadingUpward Display Plotting on the unstabilized HeadingUpward display is similar to plotting on the stabilized NorthUpward display Since the pips are painted at bearings relative to the heading of the observer s ship a complication arises when the heading of the observer s ship is changed If a continuous grease pencil plot is to be maintained on the unstabilized HeadingUpward relative motion display following course changes by the observer s ship the plotting surface of the re ection plotter must be rotated the same number of degrees as the course or heading change in a direction opposite to this change Otherwise the portion of the plot made following the course change will not be continuous with the previous portion of the plot Also the unstabilized display is affected by any yawing of the observer s ship Plots made while the ship is off the desired heading will result in an erratic plot or a plot of lesser accuracy than would be afforded by a stabilized display Under severe yawing 330 340 350 0 370 U Alumni Him uh 0 a m 350 o m WWWla 3 mhmm 20 U 9 ac u WM 3 o in I a i n h a 39e E 55 E N y 2 1 250 739 13 a 7m 0 e oquot a quotquotHrmpmmmunu 7 one l i w 06 x 061 cm on 08 w WV I V 091 v 0 l 091 Figure 27 Effect of course change on unstabilized display conditions plotting on the unstabilized display must be coordinated with the instants that the ship is on course if any reasonable accuracy of the plot is to be obtained Because of the persistence of the CRT screen and the illumination of the pips at their instantaneous relative bearings as the observer s ship yaws or its course is changed the target pips on the PPI will smear Figure 26 illustrates an unstabilized HeadingUpward relative motion display for a situation in which a ship s course and present heading are 280 as indicated by the heading ash The ship is yawing about a heading of 280 In this case there is slight smearing of the target pips If the ship s course is changed to the right to 340 as illustrated in gure 27 the target pips smear to the left through 60 ie an amount equal and in a direction opposite to the course change Thus to maintain a continuous grease pencil plot on the re ection plotter it is necessary that the plotting surface of this plotter be rotated in a direction opposite to and equal to the course change 42 Table of Contents 35 0 0 10 A0 20 60 a NANA li1iLu4l 3o 5 u A 0 4 7 51W 44 o o o 399 0 N 4 a 3 392 o 5 10 2 9 go 2 9 o 3 g e 2 32 o 3quot 00270 cc 6 o 3e 70 0quot 08 m m x Dog17im 9 cc 06 I OBI a Figure 28 Stabilized displayfollowing course change Figures 28 and 29 illustrate the same situation appearing on a stabilized NorthUpward display There is no pip smearing because of yawing There is no shifting in the positions of the target pips because of the course change Any changes in the position of the target pips are due solely to changes in the true bearings and distances to the targets during 0 o 1 0 3 33mliiLS 7 33 N Mu f0 it w Iq v 0 o 390 0 9399 o 66 07 o e 0 N o m Hm oomquWWIIIN HHu 9 09 a 061 081 0L1 0 Figure 29 Stabilized display preceding course change the course change The plot during and following the course change is continuous with the plot preceding the course change Thus there is no need to rotate the plotting surface of the re ection plotter when the display is stabilized I Table of Contents 43 RANGE AND BEARING MEASUREMENT Mechanical Bearing Cursor The mechanical bearing cursor is a radial line or cross hair inscribed on a transparent disk which can be rotated manually about its axis coincident with the center of the PPT This cursor is used for bearing determination Frequently the disk is inscribed with a series of lines parallel to the line inscribed through the center of the disk in which case the bearing cursor is known as a PARALLELLINE CURSOR or PARALLEL INDEX see figure 210 To avoid parallax when reading the bearing the lines are inscribed on each side of the disk When the sweep origin is at the center of the PPI the usual case for relative motion displays the bearing of a small well de ned target pip is determined by placing the radial line or one of the radial lines of the cross hair over the center of the pip The true or relative bearing of the pip can be read from the respective bearing dial 50 o 10 3 0 3 mimtm 2 o m hm mamWI m u 6 WWIquotUHnmluuquot m9 0quot a 06 09 OH 0 Figure 210 Measuring bearing with parallelline cursor Variable Range Marker Range Strobe The variable range marker VRNI is used primarily to determine the ranges to target pips on the PPI Among its secondary uses is that of providing a visual indication of a limiting range about the position of the observer s ship within which targets should not enter for reasons of safety The VRM is actually a small rotating luminous spot The distance of the spot from the sweep origin corresponds to range39 in effect it is a variable range ring The distance to a target pip is measured by adjusting the circle described by the VRM so that it just touches the leading inside edge of the pip The VRM is adjusted by means of a range crank The distance is read on a range counter For better range accuracy the VRM should be just bright enough to see and should be focused as sharply as possible Electronic Bearing Cursor The designs of some radar indicators may include an electronic bearing cursor in addition to the mechanical bearing cursor This electronic cursor is a luminous line on the PPI usually originating at the sweep origin It is particularly useful when the sweep origin is not at the center of the PPI see gure 23 Bearings are determined by placing the cursor in a position to bisect the pip In setting the electronic cursor in this manner there are no parallax problems such as are encountered in the use of the mechanical bearing cursor The bearings to the pips or targets are read on an associated bearing indicator The electronic bearing cursor may have the same appearance as the heading ash To avoid confusion between these two luminous lines originating at the sweep origin on the PPI the design may be such that the electronic cursor appears as a dashed or dotted luminous line Another design approach used to avoid confusion limits the painting of the cursor to that part of the radial beyond the setting of the VRM Without special provision for differentiating between the two luminous lines their brightness may be made different to serve as an aid in identi cation In the simpler designs of electronic bearing cursors the cursor is independent of the VRM ie the bearing is read by cursor and range is read by the rotating VRM In more advanced designs the VRM range strobe moves radially along the electronic bearing as the range crank is turned This serves to expedite the reading of the range and bearing to a pip Table of Contents Interscan The term TNTERSCAN is descriptive of various designs of electronic bearing cursors the lengths of which can be varied for determining the range to a pip lnterscans are painted continuously on the PM the paintings of the other electronic bearing cursors are limited to one painting for each rotation of the antenna Thus the luminous lines of the latter cursors tend to fade between paintings The continuously luminous line of the interscan serves to expedite measurements In some designs the interscan may be positioned at desired locations on the PM the length and direction of the luminous line may be adjusted to serve various requirements including the determination of the bearing and distance between two pips OffCenter Display While the design of most relative motion radar indicators places the sweep origin only at the center of the PPI some indicators may have the capability for offcentering the sweep origin see gure 211 The primary advantage of the offcenter display is that for any particular range scale setting the view ahead can be extended This lessens the requirement for changing range scale settings The offcentering feature is particularly advantageous in river navigation With the sweep origin offcentered the bearing dials concentric with the PPI cannot be used directly for bearing measurements If the indicator does not have an electronic bearing cursor interscan the parallelline cursor may be used for bearing measurements By placing the cursor so that one of the parallel lines passes through both the observer s position on the PPI sweep origin and the pip the bearing to the pip can be read on the bearing dial Generally the parallel lines inscribed on the disk are so spaced that it would be improbable that one of the parallel lines could be positioned to pass through the sweep origin and pip This necessitates placing the cursor so that the inscribed lines are parallel to a line passing through the sweep origin and 50 10 35 3 n x Pa 30 H mu n u I m39 m m W 3 5 w wow0 Range ring m w 09 quotquotlquot l 09 061 gm 0L1 Figure 211 Offcenter display Table of Contents 45 Expanded Center Display Some radar indicator designs have the capability for expanding the center of the PPI on the shortest range scale 1 mile for instance While using an expanded center display zero range is at onehalf inch for instance from the center of the PPI rather than at its center With sweep rotation the center of the PPI is dark out to the zero range circle Ranges must be measured from the zero range circle rather than the center of the PPI While the display is distorted the bearings of pips from the center of the PPI are not changed Through shifting close target pips radially away from the PPI center better resolution or discrimination between the pips is afforded Also because of the normal small centering errors of the PPI display the radial shifting of the target pips permits more accurate bearing determinations Figure 212 illustrates a normal display in which range is measured from the center of the PPI Figure 213 illustrates an expanded center display of the same situation Figure 212 Normal display Figure 213 Expanded center display Table of Contents RADAR OPERATING CONTROLS POWER CONTROLS Indicator Power Switch This switch on the indicator has OFF STANDBY and OPERATE ON positions If the switch is tuIned directly from the OFF to OPERATE positions there is a warmup period of about 3 minutes before the radar set is in full operation During the warmup period the cathodes of the tubes are heated this heating being necessary prior to applying high voltages If the switch is in the STANDBY position for a period longer than that required for warm up the radar set is placed in full operation immediately upon turning the switch to the OPERATE position Keeping the radar set in STANDBY when not in use tends to lessen maintenance problems Frequent switching from OFF to OPERATE tends to cause tube failures Antenna Scanner Power Switch For reasons for safety a radar set should have a separate switch for starting and stopping the rotation of the antenna Separate switching permits antenna rotation for deicing pquoses when the radar set is either off or in standby operation Separate switching permits work on the antenna platform when power is applied to other components without the danger attendant to a rotating antenna Special Switches Even when the radar set is off provision may be made for applying power to heaters designed for keeping the set dry In such case a special switch is provided for tuIning this power on and off Nate Prior to placing the indicator power switch in the OPERATE position the brilliance control the receiver gain control the sensitivity time control and the fast time constant switch should be placed at their minimum or off positions The setting of the brilliance control avoids excessive brilliance harmful to the CRT on applying power The other settings are required prior to making initial adjustments of the performance controls Table of Contents 47 PERFORMANCE CON TROLS INITIAL ADJUSTMENTS Brilliance Control Also referred to as Intensity or Brightness control The brilliance control which determines the overall brightness of the PPI display is rst adjusted to make the trace of the rotating sweep visible but not too bright Then it is adjusted so that the trace just fades This adjustment should be made with the receiver gain control at its minimum setting because it is dif cult to judge the right degree of brilliance when there is a speckled background on the PPI Figures 214 215 and 216 illustrate the effects of different brilliance settings the receiver gain control being set so that the speckled background does not appear on the PPI With too little brilliance the PPI display is dif cult to see39 with excessive brilliance the display is unfocused Reproduced by Courtesy of Decca Radar Limited London Figure 215 Normal brilliance Reproduced by Courtesy 01 Decca Radar LimiletiV London Reproduced by Courtesy of Decca Radar Limited London Figure 214 Too little brilliance Figure 216 Excessive brilliance Table of Contents Receiver Gain Control The receiver gain control is adjusted until a speckled background just appears on the PPI Figures 217 218 and 219 illustrate too little gain normal gain and excessive gain respectively With too little gain weak echoes may not be detected39 with excessive gain strong echoes may not be detected because of the poor contrast between echoes and the background of the PPI display In adjusting the receiver gain control to obtain the speckled background the indicator should be set on one of the longer range scales because the speckled background is more apparent on these scales On shifting to a different range scale the brightness may change Generally the required readjustment may be effected through use of the receiver gain control alone although the brightness of the PPI display is dependent upon the settings of the receiver gain and brilliance controls In some radar indicator designs the brilliance control is preset at the factory Even so the brilliance control may have to be readjusted at times during the life of the cathoderay tube Also the preset brilliance control may have to be readjusted because of large changes in ambient light levels Reproduced by Courtesy of Decca Radar Limited London Figure 217 Too little gain Reproduced by Courtesy of Decca Radar Limited London Figure 218 Normal gain Reproduced by Courtesy of Decca Radar Limited London Figure 219 Excessive gain Table of Contents 49 Tuning Control Without ship or land targets a performance monitor or a tuning indicator the receiver may be tuned by adjusting the manual tuning control for maximum sea clutter An alternative to the use of normal sea clutter which is usually present out to a few hundred yards even when the sea is calm is the use of echoes from the ship s wake during a turn When sea clutter is used for manual tuning adjustment all anticlutter controls should be either off or placed at their minimum settings Also one of the shorter range scales should be used PERFORMANCE CONTROLS ADJUSTMENTS ACCORDING TO OPERATING CONDITIONS Receiver Gain Control This control is adjusted in accordance with the range scale being used Particular caution must be exercised so that while varying its adjustment for better detection of more distant targets the area near the center of the PPI is not subjected to excessive brightness within which close targets may not be detected When detection at the maximum possible range is the primary objective the receiver gain control should be adjusted so that a speckled background is just visible on the PPI However a temporary reduction of the gain setting may prove useful for detecting strong echoes from among weaker ones Fast Time Constant FTC Switch Differentiator With the FTC switch in the ON position the FTC circuit through shortening the echoes on the display reduces clutter on the PPI which might be caused by rain snow or hail When used this circuit has an effect over the entire PPI and generally tends to reduce receiver sensitivity and thus the strengths of the echoes as seen on the display Rain Clutter Control The rain clutter control provides a variable fast time constant Thus it provides greater exibility in the use of FTC according to the operating conditions Whether the FTC is xed or variable it provides the means for breaking up clutter which otherwise could obscure the echo of a target of interest When navigating in confined waters the FTC feature provides better de nition of the PPI display through better range resolution Also the use of FTC provides lower minimum range capability Figure 220 illustrates clutter on the PPI caused by a rain squall Figure 221 illustrates the break up of this clutter by means of the rain clutter control Reproduced by Courtesy of Decca Radar Limited London Figure 220 Clutter caused by a rain squall Reproduced by Courtesy of Decca Radar Limited London Figure 221 Break up of clutter by means of rain clutter control Table of Contents Figure 222 illustrates the appearance of a harbor on the PPI when the FTC circuit is not being used Figure 223 illustrates the harbor when the FTC circuit is being used With use of the FTC circuit there is better de nition 0 G t t i Reproduced by Courtesy oi Decca Radar Limited Landon Figure 223 FTC in use Reproduced by Courtesy oi Decca Radar Limited Lcndcn Figure 222 FTC not in use 51 Table of Contents Sensitivity Time Control STC Also called SEA CLUTTER CONTROL ANTICLUTTER CONTROL SWEPT GAIN SUPPRESSOR Normally the STC should be placed at the minimum setting in calm seas This control is used with a circuit which is designed to suppress sea clutter out to a limited distance from the ship Its purpose is to enable the detection of close targets which otherwise might be obscured by sea clutter This control must be used judiciously in conjunction with the receiver gain control Generally one should not attempt to eliminate all sea clutter with this control Otherwise echoes from small close targets may be suppressed also Figures 224 225 and 226 illustrate STC settings which are too low correct and too high respectively Reproduced by Courtesy of Decca Radar Limited London Figure 225 STC setting correct Reproduced by cour esy of Decca Radar L39m39ted London Reproduced by Courtesy of Decca Radar Limited London Figure 224 STC setting too low Figure 226 STC setting too high Table of Contents Performance Monitor The performance monitor provides a check of the performance of the transmitter and receiver Being limited to a check of the operation of the equipment the performance monitor does not provide any indication of performance as it might be affected by the propagation of the radar waves through the atmosphere Thus a good check on the performance monitor does not necessarily indicate that targets will be detected When the performance monitor is used a plume extends from the center of the PPI see gure 227 The length of the plume which is dependent upon the strength of the echo received from the echo box in the vicinity of the antenna is an indication of the performance of the transmitter and the receiver The length of this plume is compared with its length when the radar is known to be operating at high performance From Radar and Electronic Navigation 4th Ed Copyright 1970 GJ onnenberg Used by permission Figure 227 Performance monitor plume Any reduction of over 20 percent of the range to which the plume extends when the radar set is operating at its highest performance is indicative of the need for tuning adjustment If tuning adjustment does not produce a plume length Within speci ed limits the need for equipment maintenance is indicate With malfunctioning of the performance monitor the plume appears as illustrated in gure 228 The effectiveness of the anticlutter controls can be checked by inspecting their effects on the plume produced by the echo from the echo box 7 From Radar and Electronic Navrganon Ath Ed Copyright 1970 Gl s nnenberg Used by permission Figure 1quot plume when r Table of Contents 53 Pulse Lengths and Pulse Repetition Rate Controls On some radar sets the pulse length and pulse repetition rate PRR are changed automatically in accordance with the range scale setting At the higher range scale settings the radar operation is shifted to longer pulse lengths and lower pulse repetition rates The greater energy in the longer pulse is required for detection at longer ranges The lower pulse repetition rate is required in order that an echo can return to the receiver prior to the transmission of the next pulse At the shorter range scale settings the shorter pulse length provides better range resolution and shorter minimum ranges the higher power of the longer pulse not being required Also the higher pulse repetition rates at the shorter range scale settings provide more frequent repainting of the pips and thus sharper pips on the PPI desirable for short range observation On other radar sets the pulse length and PR must be changed by manual operation of controls On some of these sets pulse length and PR can be changed independently The pulse lengths and PRR s of radar sets installed aboard merchant ships usually are changed automatically with the range scale settings LIGHTING AND BRIGHTNESS CONTROLS Re ection Plotter The illumination levels of the re ection plotter and the bearing dials are adjusted by a control labeled PLOTTER DIMMER The re ection plotter lighting must be turned on in order to see re ected images of the grease pencil plot on the PPI With yellowishgreen uorescence yellow and orange grease pencil markings provide the clearest images on the PPI39 with orange uorescence black grease pencil markings provide the clearest images Heading Flash The brightness of the heading ash is adjusted by a control labeled FLASHER INTENSITY CONTROL The brightness should be kept at a low level to avoid masking a small pip on the PPI The heading ash should be turned off periodically for the same reason Electronic Bearing Cursor The brightness of the electronic bearing cursor is adjusted by a control for this purpose Unless the electronic bearing cursor appears as a dashed or dotted line the brightness levels of the electronic bearing cursor and the heading ash should be different to serve as an aid to their identi cation Radar indicators are now equipped with a springloaded switch to temporarily disable the ash Fixed Range Markers The brightness of the xed range markers is adjusted by a control labeled FIXED RANGE MARK INTENSITY CONTROL The xed range markers should be turned off periodically to avoid the possibility of their masking a small pip on the PPI Variable Range Marker The brightness of the variable range marker is adjusted by the control labeled VARIABLE RANGE MARK INTENSITY CONTROL This control is adjusted so that the ring described by the VRM is sharp and clear but not too bright Panel Lighting The illumination of the panel is adjusted by the control labeled PANEL CONTROL MEASUREMENT AND ALIGNMENT CONTROLS Range Usually ranges are measured by means of the variable range marker On some radars the VRM can be used to measure ranges up to only 20 miles although the maximum range scale setting is 40 miles For distances greater than 20 miles the xed range rings must be used The radar indicators designed for merchant ship installation have range counter readings in miles and tenths of miles According to the range calibration the readings may be either statute or nautical miles The range counter has three digits the last or third digit indicating the range in tenths of a mile As the VRM setting is adjusted the range is read in steps of tenths of a mile The VRM control may have coarse and Table of Contents ne settings The coarse setting permits rapid changes in the range setting of the VRM The ne setting permits the operator to make small adjustments of the VRM more readily For accurate range measurements the circle described by the VRM should be adjusted so that itjust touches the inside edge of the pip Bearing On most radar indicators bearings are measured by setting the mechanical bearing cursor to bisect the target pip and reading the bearing on the bearing d39 1 1a With unstabilized HeadingUpward displays true bearings are read on the outer rotatable dial which is set either manually or automatically to ships true heading With stabilized NorthUpward displays true bearings are read on the xed dial With loss of compass input to the indicator the bearings as read on the latter dial are relative Some radar indicators designed for stabilized NorthUpward displays have rotatable relative bearing dials the zero graduations of which can be set to the heading ash for reading relative bearings Some radar indicators especially those having true motion displays may have an electronic bearing cursor and associated bearing indicator The electronic cursor is particularly useful When the display is offcentered Sweep Centering For accurate bearing measurement by the mechanical bearing cursor the sweep origin must be placed at the center of the PPI Some radar indicators have panel controls which can be used for horizontal and vertical shifting of the sweep origin to place it at the center of the PPI and thus at the pivot point of the mechanical bearing cursor On other radar indicators not having panel controls for centering the sweep origin the sweep must be centered by making those adjustments inside the indicator cabinet as are prescribed in the manufacturer s instruction manual Center Expansion Some radar indicators have a CENTER EXPAND SWITCH which is used to displace zero range from the center of the PPI on the shortest range scale setting With the switch in the ON position there is distortion in range but no distortion in the bearings of the pips displayed because the expansion is radial Using center expansion there is greater separation between pips near the center of the PPI and thus better bearing resolution Also bearing accuracy is improved because centering errors have lesser effect on accuracy with greater displacement of pips from the PPI center When center expansion is used the xed range rings expand with the center However the range must be measured from the inner circle as opposed to the center of the The use of the center expansion can be helpful in anticlutter adjustment Heading Flash Alignment For accurate bearing measurements the alignment of the heading ash with the PPI display must be such that radar bearings are in close agreement with relatively accurate visual bearings observed from near the radar On some radar indicators the heading ash must be set by a PICTURE ROTATE CONTROL according to the type of display desired Should there be any appreciable difference between radar and visual bearings adjustment of the heading ash contacts is indicated The latter adjustment should be made in accordance with the procedure prescribed in the manufacturer s instruction manual However the following procedures should prove helpful in obtaining an accurate adjustment 1 Adjust the centering controls to place the sweep origin at the center of the PPI as accurately as is possib e 2 In selecting an object for simultaneous visual and radar bearing measurements select an object having a small and distinct pip on the PPI 3 Select an object which lies near the maximum range of the scale in use This object should be not less than 2 nautical miles awa 4 Observe the visual bearings from a position as close to the radar antenna as is possible 5 Use as the bearing error the average of the differences of several simultaneous radar and visual observations 6 After any heading ash adjustment check the accuracy of the adjustment by simultaneous radar and visual observations Range Calibration The range calibration of the indicator should be checked at least once each watch before any event requiring high accuracy and more often if there is any reason to doubt the accuracy of the calibration A calibration check made Within a few minutes after a radar set has been turned on should be checked again 30 minutes later or after the set has warm ed up thoroughly The calibration check is simply the comparison of VRM and xed range ring ranges at various range scale settings In this check the assumptions are Table of Contents 55 that the calibration of the xed range rings is more accurate than that of the and that the calibration of the xed range rings is relatively stable One indication of the accuracy of the range ring calibration is the linearity of the sweep or time base Since range rings are produced by brightening the electron beam at regular intervals during the radial sweep of this beam equal spacing of the range rings is indicative of the linearity of the time base Representative maximum errors in calibrated xed range rings are 75 yards or 15 percent of the maximum range of the range scale in use whichever is greater Thus on a 6mile range scale setting the error in the range of a pip just touching a range ring may be about 180 yards or about 01 nautical mile Since xed range rings are the most accurate means generally available for determining range when the leading edge of the target pip is at the range ring it follows that ranging by radar is less accurate than many may assume One should not expect the accuracy of navigational radar to be better than plus or minus 50 yards under the best conditions Each range calibration check is made by setting the VRM to the leading edge of a xed range ring and comparing the VRM range counter reading with the range represented by the xed range ring The VRM reading should not differ from the xed range ring value by more than 1 percent of the maximum range of the scale in use For example with the radar indicator set on the 40mile range scale and the VRM set at the 20mile range ring the VRM range counter reading should be between 196 and 204 miles TRUE MOTION CONTROLS The following controls are representative of those additional controls used in the true motion mode of operation If the true motion radar set design includes provision for ground stabilization of the display this stabilization may be effected through use of either set and drift or speed and course madegood controls Operating Mode Since true motion radars are designed for operation in true motion and relative motion modes there is a control on the indicator panel for selecting the desired mode Normal Reset Control Since own ship is not xed at the center of the PPI in the true motion mode own ship s position must be reset periodically on the PPI Own ship s position may be reset manually or automatically Automatic reset is performed at de nite distances from the PPI center according to the radar set design With the normal reset control actuated reset may be performed automatically when own ship has reached a position beyond the PPI center about two thirds the radius of the PPI Whether own ship s position is reset automatically or manually own ship s position is reset to an offcenter position on the PPI usually at a position from which the heading ash passes through the center of the PPI This offcenter position provides more time before resetting is required than would be the case if own ship s position were reset to the center of the PPI Delayed Reset Control With the delayed reset control actuated reset is performed automatically when own ship has reached a position closer to the edge of the PPI than with normal reset With either the normal or delayed reset control actuated there is an alarm signal which gives about 10 seconds forewarning of automatic resetting Manual Reset Control The manual reset control permits the resetting of own ship s position at any desired time Manual Override Control The manual override control when actuated prevents automatic resetting of own ship s position This control is particularly useful if a critical situation should develop just prior to the time of automatic resetting Shifting from normal to delayed reset can also provide more time for evaluating a situation before resetting occurs Ship s Speed Input Selector Control Own ship s speed and course being necessary inputs to the true motion radar computer the ship s speed input selector control permits either manual input of ship s speed or automatic input of speed from a speed log With the control in the manual position ship s speed in knots and tenths of knots can be set in steps of tenths of knots Set and Drift Controls Set and drift controls or their equivalent provide means for ground stabilization of the true motion display When there is accurate compensation Table of Contents for set and drift there is no movement of stationary objects on the PPI Without such compensation slight movements of stationary objects may be detected on the PPI The set control may be labeled DRIFT DIRECTION the drift control may be labeled DRIFT SPEED Speed and Course Made Good Controls The radar set design may include speed and course made good controls in lieu of set and drift controls to effect ground stabilization of the true motion display The course made good control permits the input of a correction Within limits of about 25 to the course input to the radar set The speed control permits the input of a correction to the speed input from the underwater speed log or from an arti cial dummy log Zero Speed Control In the ZERO position the zero speed control stops the movement of own ship on the PPI in the TRUE position own ship moves on the PPI at a rate set by the speed input Table of Contents 57 Table of Contents APPENDIX A EXTRACT FROM REGULATION 12 CHAPTER V OF THE IMO SOLAS 1974 CONVENTION AS AMENDED TO 1983 THE REQUIREMENT TO CARRY RADAR AND ARPA Ships of 500 gross tonnage and upwards constructed on or after 1 September 1984 and ships of 1600 gross tonnage and upwards constructed before 1 September 1984 shall be tted with a radar installation Ships of 1000 gross tonnage and upwards shall be tted with two radar installations each capable of being operated independently of the other Facilities for plotting radar readings shall be provided on the navigating bridge of ships required by paragraph g or h to be tted with a radar installation In ships of 1600 gross tonage and upwards constructed on or after 1 September 1984 the plotting facilities shall be at least as effective as a re ection plotter An automatic radar plotting aid shall be tted on 1 Ships of 10000 gross tonnage and upwards constructed on or after 1 September 198439 Tankers constructed before 1 September 1984 as follows a If of 40000 gross tonnage and upwards by 1 January 1 N 985 b If of 10000 gross tonnage and upwards but less than 40000 gross tonnage by 1 September 198639 3 Ships constructed before 1 September 1984 that are not tankers as follows a If of 40000 gross tonnage and upwards by 1 September 198639 b If of 20000 gross tonnage and upwards but less than 40000 gross tonnage by 1 September 198739 c If of 15000 gross tonnage and upwards but less than 20000 gross tonnage by 1 September 1998 ii Automatic radar plotting aids tted prior to 1 September 1984 which do not fully conform to the performance standards adopted by the organization may at the discretion of the administration be retained until 1 January 1991 iii the administration may exempt ships from the requirements of this paragraph in cases where it considers it unreasonable or unnecessary for such equipment to be carried or when the ships will be taken permanently out of service within two years of the appropriate implementation date 367 Table of Contents EXTRACT FROM IMO RESOLUTIONS A222V II A278V II A477XII Performance Standards for Navigational Radar equipment installed before 1 September 1984 INTRODUCTION The radar equipment required by Regulation 12 of Chapter V should provide an indication in relation to the ship of the position of other surface craft and obstructions of buoys shorelines and navigational marks in a manner which will assist in avoiding collision and navigation It should comply with the following minimum requirements Range Performance The operational requirement under normal propagation conditions when the radar aerial is mounted at a height of 15 meters above sea level is that the equipment should give a clear indication of Coastlines At 20 nautical miles when the ground rises to 60 meters At 7 nautical miles when the ground rises to 6 meters Surface objects At 7 nautical miles a ship of 5000 gross tonnage whatever her as ec At 2 nautical miles an object such as a navigational buoy having an effective echoing area of approximately 10 square meters At 3 nautical miles a small ship of length 10 meters Minimum Range The surface objects speci ed in paragraph 2a ii should be clearly displayed from a minimum range of 50 meters up to a range of 1 nautical mile without adjustment of controls other than the range selector Display The equipment should provide a relative plan display of not less than 180 mm effective diameter The equipment should be provided with at least ve ranges the smallest of which is not more than 1 nautical mile and the greatest of which is not less than 24 nautical miles The scales should preferably of 12 ratio Additional ranges may be provided Positive indication should be given of the range of view displayed and the interval between range rings Range Measurement The primary means provided for range measurement should be xed electronic range rings There should be at least four range rings displayed on each of the ranges mentioned in paragraph 2cii except that on ranges below 1 nautical mile range rings should be displayed at intervals of 025 nautical mile Fixed range rings should enable the range of an object whose echo lies on a range ring to be measured with an error not exceeding 15 per cent of the maximum range of the scale in use or 70 meters whichever is greater Any additional means of measuring range should have an error not exceeding 25 per cent of the maximum range of the displayed scale in use or 120 meters whichever is the greater Heading Indicator The heading of the ship should be indicated by a line on the display with a maximum error not greater than 1 The thickness of the display heading line should not be greater than 05 Provision should be made to switch off the heading indicator by a device which cannot be left in the heading marker of position Table of Contents Bearing Measurement Provision should be made to obtain quickly the bearing of any object whose echo appears on the display The means provided for obtaining bearings should enable the bearing of a target whose echo appears at the edge of the display to be measured with an accuracy of 1quot or better Discrimination The equipment should display as separate indications on the shortest range scale provided two objects on the same azimuth separated by not more than 50 meters in range The equipment should display as separate indications two objects at the same range separated by not more than 25 in azimuth The equipment should be designed to avoid as far as is practicable the display of spurious echoes Roll The performance of the equipment should be such that when the ship is rolling 10 the echoes of the targets remain visible on the display Scan The scan should be continuous and automatic through 360 of azimuth The target data rate should be at least 12 per minute The equipment should operate satisfactorily in relative wind speeds of 100 knots Azimuth Stabilization Means should be provided to enable the display to be stabilized in azimuth by a transmitting compass The accuracy of alignment with the compass transmission should be within 05 with a compass rotation rate of 2 rpm The equipment should operate satisfactorily for relative bearings when the compass control is inoperative or not tted Performance Check Means should be available while the equipment is used operationally to determine readily a signi cant drop in performance relative to a calibration standard established at the time of installation Anticlutter Devices Means should be provided to minimize the display of unwanted responses from precipitation and the sea Operation The equipment should be capable of being switched on and operated from the main display position Operational controls should be accessible and easy to identify and use After switching on from the cold the equipment should become fully operational within 4 minutes A standby condition should be provided from which the equipment can be brought to a fully operational condition within 1 minute Interference After installation and adjustment on board the bearing accuracy should be maintained without further adjustment irrespective of the variation of external magnetic elds Sea 0r Ground Stabilization Sea or ground stabilization if provided should not degrade the accuracy of the display below the requirements of these performance standards and the view ahead on the display should not be unduly restricted by the use of this facility Siting of the Aerial The aerial system should be installed in such a manner that the e lciency of the display is not impaired by the close proximity of the aerial to other objects In particular blind sectors in the forward direction should be avoided 369 Table of Contents Performance Standards for Navigational Radar equipment installed on or after 1 September 1984 Applic ation This Recommendation applies to all ships radar equipment installed on or after 1 September 1984 in compliance with Regulation 12 Chapter V of the International Convention for the Safety of Life at Sea 1974 as amended Radar equipment installed before 1 September 1984 should comply at least with the performance standards recommended in resolution A222VH General The radar equipment should provide an indication in relation to the ship of the position of the other surface craft and obstructions and of buoys shorelines and navigational marks in a manner which will assist in navigation and in avoiding collision All radar installations All radar installations should comply with the following minimum requirements Range performance The operational requirement under normal propagation conditions when the radar antenna is mounted at a height of 15 meters above sea level is that the equipment should in the absence of clutter give a clear indication of Coastlines At 20 nautical miles when the ground rises to 60 meters At 7 nautical miles when the ground rises to 6 meters Surface objects At 7 nautical miles a ship of 5000 gross tonage whatever her aspect At 3 nautical miles a small ship of 10 meters in length At 2 nautical miles an object such as a navigational buoy having an effective echoing area of approximately 10 square meters Minimum Range The surface objects speci ed in paragraph 312 should be clearly displayed from a minimum ran e of 50 meters up to a range of 1 nautical mile without changing the setting of controls other than the range selector Display The equipment should without external magni cation provide a relative plan display in the head up unstabilized mode with an effective diameter of not less than 180 millimeters on ships of 500 gross tonnage and more but less than 1600 gross tonnage 250 millimeters on ships of 1600 gross tonnage and more but less than 10000 gross tonnage 340 millimeters in the case of one display and 250 millimeters in the case of the other on ships of 10000 gross tonnage and upwards Nate Display diameters of 180 250 and 340 millimeters correspond respectively to 9 12 and 16 inch cathode ray tubes The equipment should provide one of the two following sets of range scales of display 15 3 6 12 and 24 nautical miles and one range scale of not less than 05 and not greater than 08 nautical miles or 1 2 4 8 16 and 32 nautical miles Additional range scales may be provided The range scale displayed and the distance between range rings should be clearly indicated at all times Table of Contents Range measurement Fixed electronic range rings should be provided for range measurements as follows Where range scales are provided in accordance with paragraph 3321 on the range scale of between 05 and 08 nautical miles at least two range rings should be provided and on each of the other range scales six range rings should be provided or Where range scales are provided in accordance with paragraph 3322 four range rings should be provided on each of the range scales A variable electronic range marker should be provided with a numeric readout of range The xed range rings and the variable range marker should enable the range of an object to be measured with an error not exceeding 15 per cent of the maximum range of the scale in use or 70 meters whichever is greater It should be possible to vary the brilliance of the range rings and the variable range marker and to remove them completely from the display Heading indicator The heading indicator of the ship should be indicated by a line on the display with a maximum error not greater than 1 The thickness of the displayed heading line should not be greater than 05 Provision should be made to switch off the heading indicator by a device which cannot be left in the heading marker of position Bearing measurement Provision should be made to obtain quickly the bearing of any object whose echo appears on the display The means provided for obtaining bearing should enable the bearing of a target whose echo appears at the edge of the display to be measured with an accuracy of or better Discrimination The equipment should be capable of displaying as separate indications on a range scale of 2 nautical miles or less two similar targets at a range of between 50 and 100 of the range scale in use and on the same azimuth separated by not more than 50 meters in range The equipment should be capable of displaying as separate indications two small similar targets both situated at the same range between 50 per cent and 100 of the 15 or 2 mile range scales and separated by not more than 25 in azimuth Roll 0r pitch The performance of the equipment should be such that when the ship is rolling or pitching up to 10 the range performance requirements of paragraphs 31 and 32 continue to be met Scan The scan should be clockwise continuous and automatic through 360 of azimuth The scan rate should be not less than 12 rp m The equipment should operate satisfactorily in relative wind speed of up to 100 knots Azimuth stabilization Means should be provided to enable the display to be stabilized in azimuth by a transmitting compass The equipment should be provided with a compass input to enable it to be stabilized in azimuth The accuracy of alignment with the compass transmission should be within 05 with a compass rotation rate of 2 rp m The equipment should operate satisfactorily in the unstabilized mode when the compass control is inoperative Performance check Means should be available while the equipment is used operationally to determine readily a signi cant drop in performance relative to a calibration standard established at the time of installation and that the equipment is correctly tuned in the absence of targets 371 Table of Contents Anticlutter devices Suitable means should be provided for the suppression of unwanted echoes from sea clutter rain and other forms of precipitation clouds and sandstorms It should be possible to adjust manually and continuously the anticlutter controls Anticlutter controls should be inoperative in the fully anticlockwise positions In addition automatic anticlutter controls may be provided however they must be capable of being switched off Operation The equipment should be capable of being switched on and operated from the display position Operational controls should be accessible and easy to identify and use Where symbols are used they should comply with the recommendations of the organization on symbols for controls on marine navigational radar equipment After switching on from cold the equipment should become fully operational within 4 minutes A standby condition should be provided from which the equipment can be brought to an operational condition within 15 seconds Interference After installation and adjustment on board the bearing accuracy as prescribed in these performance standards should be maintained without further adjustment irrespective of the movement of the ship in the earth s magnetic eld Sea or ground stabilization true motion display Where sea or ground stabilization is provided the accuracy and discrimination of the display should be at least equivalent to that required by these performance standards The motion of the trace origin should not except under manual override conditions continue to a point beyond 75 per cent of the radius of the display Automatic resetting may be provided Antenna system The antenna system should be installed in such a manner that the design ef ciency of the radar system is not substantially impaired Operation with radar beacons All radars operating in the 3cm band should be capable of operating in a horizontally polarized mode It should be possible to switch off those signal processing facilities which might prevent a radar beacon from being shown on the radar display Multiple radar installations Where two radars are required to be carried they should be so installed that each radar can be operated individually and both can be operated simultaneously without being dependent upon one another When an emergency source of electrical power is provided in accordance with the appropriate requirements of Chapter 111 of the 1974 SOLAS convention both radars should be capable of being operated from this source Where two radars are tted interswitching facilities may be provided to improve the exibility and overall radar installation They should be so installed that failure of either radar would not cause the supply of electrical energy to the other radar to be interrupted or adversely affected Table of Contents APPENDIX B GLOSSARY AND ABBREVIATIONS acrossthescope A radar contact Whose direction of relative motion is perpendicular to the direction of the heading ash indicator of the radar Also called LIMBO CONTACT advance The distance a vessel moves in its original direction after the helm is put over Automatic frequency control aerial Antenna afterglow The slowly decaying luminescence of the screen of the cathoderay tube after excitation by an electron beam has ceased See PERSISTENCE amplify To increase the strength of a radar signal or echo antenna A conductor or system of conductors consisting of horn and re ector used for radiating or receiving radar waves Also called AERIAL anticlutter control means for reducing or eliminating interferences from sea return and weather apparent wind See RELATIVE WIND A Automatic radar plotting aid attenuation The decrease in the strength of a radar wave resulting from absorption scattering and re ection by the medium through which it passes waveguide atmosphere and by obstructions in its path Also attenuation of the wave may be the result of arti cial means such as the inclusion of an attenuator in the circuitry or by placing an absorbing device in the path of the wave automatic frequency control AFC An electronic means for preventing drift in radio frequency or maintaining the frequency within speci ed limits The AFC maintains the local oscillator of the radar on the frequency necessary to obtain a constant or near constant difference in the frequency of the radar echo magnetron frequency and the local oscillator frequency azimuth While this term is frequently used for bearing in radar applications the term azimuth is usually restricted to the direction of celestial bodies among marine navigators azimuthstabilized PPI See STABILIZED PPI beam width The angular Width of a radar beam between halfpower points See LOBE bearin The direction of the line of sight from the radar antenna to the contact Sometimes called AZIMJTH although in marine usage the latter term is usually restricted to the directions of celestial bodies bearing cursor The radial line inscribed on a transparent disk which can be rotated manually about an axis coincident with the center of the PPI It is used for bearing determination Other lines inscribed parallel to the radial line have many useful purposes in radar plotting blind sector A sector on the radarscope in which radar echoes cannot be received because of an obstruction near the antenna See SHADOW SECTOR cathoderay tube CRT The radarscope picture tube Within which a stream of electrons is directed against a uorescent screen PPI On the face of the tube or screen PPI light is emitted at the points Where the electrons strike 373 Table of Contents challenger See TNTERROGATOR circle spacing The distance in yards between successive whole numbered circles Unless otherwise designated it is always 1000 yards clutter Unwanted radar echoes re ected from heavy rain snow waves etc which may obscure relatively large areas on the radarscope cone of courses Mathematically calculated limits relative to datum within which a submarine must be in order to intercept the torpedo danger zone contact Any echo detected on the radarscope not evaluated as clutter or as a false echo contrast The difference in intensity of illumination of the radarscope between radar images and the background of the screen corner re ector See RADAR REFLECTOR CPA Closest point of approach course Direction of actual movement relative to true north crossband racon A racon which transmits at a frequency not within the marine radar frequency band To be able to use this type of racon the ship39s radar receiver must be capable of being tuned to the frequency of the cross band racon or special accessory equipment is required In either case the radarscope will be blank except for the racon signal See TNBAND RACON RT Cathode ray tube crystal A crystalline substance which allows electric current to pass in only one direction datum In Antisubmarine Warfare ASW the last known position of an enemy submarine at a speci ed time Lacking other knowledge this is the position and time of torpedoing de nition The clarity and delity of the detail of radar images on the radarscope A combination of good resolution and focus adjustment is required for good de nition distance circles Circles concentric to the formation center with radii of speci ed distances used in the designation of main body stations in a circular formation Circles are designated by means of their radii in thousands of yards from the formation center double stabilization The stabilization of a HeadingUpward PPI display to North The cathoderay tube with the PPI display stabilized to North is rotated to keep ship s heading upward downthescope A radar contact whose direction of relative motion is generally in the opposite direction of the heading ash indicator of the radar DRM Direction of relative movement The direction of movement of the maneuvering ship relative to the reference ship always in the direction of M1 gt M2 gt M3 gt duct A layer within the atmosphere where refraction and re ection results in the trapping of radar waves and consequently their propagation over abnormally long distances Ducts are associated with temperature inversions in the atmosphere EBL Electronic bearing line echo The radar signal re ected back to the antenna by an object39 the image of the re ected signal on the radarscope Also called RETURN echo box A cavity resonant at the transmitted frequency which produces an arti cial radar target signal for tuning or testing the overall performance of a radar set The oscillations developed in the resonant cavity will be greater at higher power outputs of the transmitter Table of Contents echo box performance monitor An accessory which is used for tuning the radar receiver and checking overall performance by visual inspection An arti cial echo as received from the echo box will appear as a narrow plume from the center of the PPI The length of this plume as compared with its length when the radar is known to be operating at a high performance level is indicative of the current performance level face The viewing surface PPI of a cathoderay tube The inner surface of the face is coated with a uorescent layer which emits light under the impact of a stream of electrons Also called SCREEN fast time constant FTC circuit An electronic circuit designed to reduce the undesirable effects of clutter With the FTC circuit in operation only the nearer edge of an echo having a long time duration is displayed on the radarscope The use of this circuit tends to reduce saturation of the scope which could be caused by clutter ctitious ship An imaginary ship presumed to maintain constant course and speed substituted for a maneuvering ship which alters course and speed uorescence Emission of light or other radiant energy as a result of and only during absorption of radiation from some other source An example is the glowing of the screen of a cathoderay tube during bombardment by a stream of electrons The continued emission of light after absorption of radiation is called PHOSPHORESCENCE formation axis An arbitrarily selected direction from which all bearings used in the designation of main body stations in a circular formation are measured The formation axis is always indicated as a true direction from the formation center formation center The arbitrarily selected point of origin for the polar coordinate system around which a circular formation is formed It is designated station Zero formation guide A ship designated by the OTC as guide and with reference to which all ships in the formation maintain position The guide may or may not be at the formation center FTC Fast time constant gain RCVR control A control used to increase or decrease the sensitivity of the receiver RCVR This control analogous to the volume control of a broadcast receiver regulates the intensity of the echoes displayed on the radarscope geographical plot A plot of the actual movements of objects ships with respect to the earth Also called NAVIGATIONAL PLOT heading ash An illuminated radial line on the PPI for indicating own ship s heading on the bearing dial Also called HEADTNG MARKER headingupward display See UNSTABILIZED DISPLAY inband racon A racon which transmits in the marine radar frequency band e g the 3 centimeter band The transmitter sweeps through a range of frequencies within the band to insure that a radar receiver tuned to a particular frequency within the band will be able to detect the signal See CROSS BAND RACON intensity control A control for regulating the intensity of background illumination on the radarscope Also called BRILLIANCE CONTROL interference Unwanted and confusing signals or patterns produced on the radarscope by another radar or transmitter on the same frequency and more rarely by the effects of nearby electrical equipment or machinery or by atmospheric phenomena interrogator A radar transmitter which sends out a pulse that triggers a transponder An interrogator is usually combined in a single unit with a responsor which receives the reply from a transponder and produces an output suitable for feeding a display system the combined unit is called an TNTERROGATOR RESPONSOR lm age retaining panel kilohertz kHz A frequency of one thousand cycles per second See MEGAHERTZ 375 Table of Contents limbo contacts See ACROSSTHESCOPE limited lines of approach Mathematically calculated limits relative to the force within which an attacking submarine must be in order that it can reach the torpedo danger zone lobe Of the threedim ensional radiation pattern transmitted by a directional antenna one of the portions within which the eld strength or power is everywhere greater than a selected value The halfpower level is used frequently as this reference value The direction of the axis of the major lobe of the radiation pattern is the direction of maximum radiation See SIDE LOBES maneuvering ship M moving unit except the reference ship MCPA Minutes to closest point of approach megacycle per second Mc A frequency of one million cycles per second The equivalent term MEGAHERTZ MHz is now coming into more frequent use megahertz A frequency of one million cycles per second See KILOHERTZ microsecond One millionth of 1 second microwaves Commonly very short radio waves having wavelengths of l millimeter to 30 centimeters While the limits of the microwave region are not clearly de ned they are generally considered to be the region in which radar operates minor lobes Side lobes missile danger zone An area which the submarine must enter in order to be within maximum effective missile firing range MRM Miles of relative movement The distance along the relative movement line between any two speci ed points or times Also called RELATIVE DISTANCE nanosecond One billionth of 1 second northupward display See STABILIZED DISPLAY L New relative movement line paint The bright area on the PPI resulting from the brightening of the sweep by the echoes Also the act of forming the bright area on the PPI by the sweep persistence A measure of the time of decay of the luminescence of the face of the cathoderay tube after excitation by the stream of electrons has ceased Relatively slow decay is indicative of high persistence Persistence is the length of time during which phosphorescence takes place phosphorescence Emission of light without sensible heat particularly as a result of but continuing after absorption of radiation from some other source An example is the glowing of the screen of a cathoderay tube after the beam of electrons has moved to another part of the screen It is this property that results in the chartlike picture which gives the PPI its principal value PERSISTENCE is the length of time during which phosphorescence takes place The emission of light or other radiant energy as a result of and only during absorption of radiation from some other source is called FLUORESCENCE plan position indicator PPI The face or screen of a cathoderay tube on which radar images appear in correct relation to each other so that the scope face presents a chartlike representation of the area about the antenna the direction of a contact or target being represented by the direction of its echo from the center and its range by its distance from the center plotting head Re ection plotter polarization The orientation in space of the electric axis of a radar wave This electric axis which is at right angles to the magnetic axis may be either horizontal vertical or circular With circular polarization the axis rotate resulting in a spiral transmission of the radar wave Circular polarization is used for reducing rain clutter Table of Contents PPI Plan position indicator pulse An extremely short burst of radar wave transmission followed by a relatively long period of no transmission pulse duration Pulse length pulse length The time duration measured in microseconds of a single radar pulse Also called PULSE DURATION pulse recurrence rate PRR Pulse repetition rate pulse repetition rate PRR The number of pulses transmitted per second racon A radar beacon which when triggered by a ship s radar signal transmits a reply which provides the range and bearing to the beacon on the PPI display of the ship The reply may be coded for identi cation purposes in which case it will consist of a series of concentric arcs on the PPI The range is the measurement on the PPI to the arc nearest its center the bearing is the middle of the racon arcs If the reply is not coded the racon signal will appear as a radial line extending from just beyond the re ected echo of the racon installation or from just beyond the point where the echo would be painted if detected See IN BAND RACON CROSSBAND RACON RAMARK radar indicator A unit of a radar set which provides a visual indication of radar echoes received using a cathoderay tube for such indication Besides the cathoderay tube the radar indicator is comprised of sweep and calibration circuits and associated power supplies radar receiver A unit of a radar set which demodulates received radar echoes ampli es the echoes and delivers them to the radar indicator The radar receiver differs from the usual superheterodyne communications receiver in that its sensitivity is much greater it has a better signal to noise ratio and it is designed to pass a pulse type signal radar re ector A metal device designed for re ecting strong echoes of impinging radar signals towards their source The corner re ector consists of three mutually perpendicular metal plates Corner re ectors are sometimes assembled in clusters to insure good echo returns from all directions radar repeater A unit which duplicates the PPI display at a location remote from the main radar indicator installation Also called PPI REPEATER REMOTE PPI radar transmitter unit of a radar set in which the radiofrequency power is generated and the pulse is modulated The modulator of the transmitter provides the timing trigger for the radar indicator ramark A radar beacon which continuously transmits a signal appearing as a radial line on the PPI indicating the direction of the beacon from the ship For identi cation purposes the radial line may be formed by a series of dots or dashes The radial line appears even if the beacon is outside the range for which the radar is set as long as the radar receiver is within the power range of the beacon Unlike the RACON the ram ark does not provide the range to the beacon range markers Equally spaced concentric rings of light on the PPI which permit the radar observer to determine the range to a contact in accordance with the range setting or the range of the outer rings See VARIABLE RANGE MARKER range selector A control for selecting the range setting for the radar indicator VR Short for RECEIVER reference ship R The ship to which the movement of others is referred re ection plotter An attachment tted to a PPI which provides a plotting surface permitting radar plotting without parallax errors Any mark made on the plotting surface will be re ected on the radarscope directly below Also called PLOTTING HEAD 377 Table of Contents refraction The bending of the radar beam in passing obliquely through regions of the atmosphere of different densities relative motion display A type of radarscope display in which the position of own ship is xed at the center of the PPI and all detected objects or contacts move relative to own ship See TRUE MOTION DISPLAY relative movement line The locus of positions occupied by the maneuvering ship relative to the reference ship relative plot The plot of the positions occupied by the maneuvering ship relative to the reference ship relative vector A velocity vector which depicts the relative movement of an object ship in motion with respect to another object ship usually in motion relative wind The speed and relative direction from which the wind appears to blow 39 T WIND with reference to a mov1ng point See APPAREN remote PPI Radar repeater resolution The degree of ability of a radar set to indicate separately the echoes of two contacts in range bearing and elevation With respect to range the minimum range difference between separate contacts at the same bearing which will allow both to appear as separate distinct echoes on the PPI bearing the minimum angular separation between two contacts at the same range which will allow both to appear as separate distinct echoes on the PPI elevation the minimum angular separation in a vertical plane between two contacts at the same range and bearing which will allow both to appear as separate distinct echoes on the PPI responder beacon Transponder beacon RML Relative m ovem ent line scan To investigate an area or space by varying the direction of the radar antenna and thus the radar beam Normally scanning is done by continuous rotation of the antenna scanner A unit of a radar set consisting of the antenna and drive assembly for rotating the antenna cope Short for RADARSCOPE screen The face of a cathoderay tube on which radar images are displayed screen axis An arbitrarily selected direction from which all bearings used in the designation of screen stations in a circular formation are measured The screen axis is always indicated as a true direction from the screen center screen center The selected point of origin for the polar coordinate system around which a screen is formed The screen center usually coincides with the formation center but may be a speci ed true bearing and distance from screen station numbering Screening stations are designated by means of a station number consisting of four or more digits The last three digits are the bearing of the screening station relative to the screen axis while the pre xed digits indicate the radius of the distance circle in thousands of yards from the screen center sea return Clutter on the radarscope which is the result of the radar signal being re ected from the sea especially near the ship sensitivity time control STC An electronic circuit designed to reduce automatically the sensitivity of the receiver to nearby targets Also called SWEPT GAIN CONTROL shadow sector A sector on the radarscope in which the appearance of radar echoes is improbable because of an obstruction near the antenna While both blind and shadow sectors have the same basic cause blind sectors Table of Contents generally occur at the larger angles subtended by the obstruction See BLIND SECTOR side lobes Unwanted lobes of a radiation pattern ie lobes other than major lobes Also called MINOR LOBES speed triangle The usual designation of the VECTOR DIAGRAM when scaled in ts o SRM Speed of relative movement The speed of the maneuvering ship relative to the reference ship stabilized display NorthUpward display in which the orientation of the relative motion presentation is xed to an unchanging reference North This display is NorthUpward norm ally In an UNSTABILIZED DISPLAY the orientation of the relative motion presentation changes with changes in ship s heading See DOUBLE STABILIZATION stabilized PPI See STABILIZED DISPLAY station numbering ositions in a circular formation other than the formation center are designated by means of a station number consisting of four or more digits The last three digits are the bearing of the station relative to the formation axis while the pre xed digits indicate the radius of the distance circle in thousands of yards Thus station 4090 indicates a position bearing 90 degrees relative to the formation axis on a distance circle with a radius of 4000 yards from the formation center Sensitivity time control strobe Variable range marker sweep As determined by the time base or range calibration the radial movement of the stream of electrons impinging on the face of the cathoderay tube The origin of the sweep is the center of the face of the cathoderay tube or PPI Because of the very high speed of movement of the point of impingement the successive points of impingement appear as a continuously luminous line The line rotates in synchronism with the radar antenna If an echo is received during the time of radial travel of the electron stream from the center to the outer edge of the face of the tube the sweep will be increased in brightness at the point of travel of the electron stream corresponding to the range of the contact from which the echo is received Since the sweep rotates in synchronism with the radar antenna this increased brightness will occur on the bearing from which the echo is received With this increased brightness and the persistence of the tube face paint corresponding to the object being illuminated by the radar beam appears on the PPI swept gain control Sensitivity time control Time to closest point of approach time line A line joining the heads of two vectors which represent successive courses and speeds of a speci c unit in passing from an initial to a nal position in known time via a speci ed intermediate point This line also touches the head of a constructive unit which proceeds directly from the initial to the nal position in the same time By general usage this constructive unit is called the ctitious ship The head of its vector divides the time line into segments inversely proportional to the times spent by the unit on the rst and second legs The time line is used in twocourse problems torpedo danger zone An area which the submarine must enter in order to be within maximum effective torpedo firing range trace The luminous line resulting from the movement of the points of impingement of the electron stream on the face of the cathoderay tube See SWEEP transfer The distance a vessel moves perpendicular to its initial direction in making a turn transponderA transmitterreceiver capable of accepting the challenge radar signal of an interrogator and automatically transmitting an appropriate reply See RACON transponder beacon A beacon having a transponder Also called RESPONDER BEACON trigger A sharp voltage pulse usually of from 01 to 04 microseconds duration which is applied to the modulator tubes to re the transmitter and which 379 Table of Contents is applied simultaneously to the sweep generator to start the electron beam moving radially from the sweep origin to the edge of the face of the cathoderay tube true motion display ype of radarscope display in which own ship and other moving contacts move on the PPI in accordance with their true courses and speed This display is similar to a navigational geographical plot See RELATIVE MOTION DISPLAY true vector A velocity vector which depicts actual movement with respect to the earth true wind True direction and force of wind relative to a xed point on the earth unstabilized display HeadingUpward A PPI display in which the orientation of the relative motion presentation is set to ship s heading and thus changes with changes in ship s heading In this Heading Upward display radar echoes are shown at their relative bearings A true bearing dial which is continuously set to ship s course at the 000 degrees relative bearing is normally used with this display for determining true bearings This true bearing dial may be either manually or automatically set to ship s course When set automatically by a course input from the gyrocompass the true bearing dial is sometimes called a STABILIZED AZIlIUTH SCALE The latter term which appears in manufacturer39s instruction books and operating manuals is more in conformity with air navigation rather than marine navigation usage See DOUBLE STABILIZATION upthescope A radar contact whose direction of relative motion is generally in the same direction as the heading ash indicator of the radar variable range marker A luminous range circle or ring on the PPI the radius of which is continuously adjustable The range setting of this marker is read on the range counter of the radar indicator vector A directed line segment representing direction and magnitude vector diagram A graphical means of adding and subtracting vectors When the vector magnitude is scaled in knots this diagram is usually called SPEED TRIANGLE velocity vector A vector the magnitude of which represents rate of movem em a velocity vector may be either true or relative depending upon whether it depicts actual movement with respect to the earth or the relative movement of an object ship in motion with respect to another object ship Variable range marker TS Vessel traf c system MTR Short for TRANSMITTER Table of Contents APPENDIX C RELATIVE MOTION PROBLEMS RAPE RADAR PLOTTIN G PROBLEMS 1 Own ship on course 311 speed 17 knots obtains the following radar bearings and ranges at the times indicated using a radar setting of 24 miles Time Bearing Range mi 1136 280 160 1142 274 136 1148 265 114 Required 1 Range at CPA 2 Time at CPA 3 Direction of relative movement CDRNI Solution 1R 82 mi 2 T 12045 3 DRM 131 2 Own ship on course 000 speed 12 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0410 035 111 0416 031 92 0422 025 73 Required 1 Distance at which the contact will cross dead ahead 2 Direction of relative movement DRlI 3 Speed of relative movement SRNI relative speed 4 Range at CPA 5 Bearing of contact at CPA 6 Relative distance MRNI from 0422 position of contact to the CPA 7 Time at CPA 8 Distance own ship travels from the time of the rst plot 0410 to the time of the last plot 0422 of the contact 9 True course of the contact 10 Actual distance traveled by the contact between 0410 and 0422 l 1 True speed of the contact Solution Assuming that the contact maintains course and speed 1 D 43 mi 2 DRM 234 3 SRM 20 kn 4 R 35 mi 5 B 324 6 MRM 65 mi 7 T 0441 8 D 24 mi 9 C 270 10 D 32 mi 11 S 16 kn 381 Table of Contents 3 Own ship on course 030 speed 23 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 1020 081 108 1023 082 92 1026 083 77 Required 1 Range at CPA 2 Bearing of contact at CPA 3 Speed of relative movement SR1l39 relative speed Time at CPA 5 Distance own ship travels from the time of the rst plot 1020 to the time of the last plot 1026 of the contact distance own ship travels in 6 minutes 4 V 6 True course of the contact 7 Actual distance traveled by the contact between 1020 and 1026 8 True speed of the contact 9 Assuming that the contact has turned on its running lights during daylight hours because of inclement weather what side lights might be seen at CPA Solution Assuming that the contact maintains course and speed 1 R 10 mi 2 B 167 3 SRM 32 kn 4 T 1041 5 D 23 mi 6 C 304 7 D 22 mi 8 S 22 kn 9 starboard green side light 4 Own ship on course 000 speed 11 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 1100 080 120 1106 080 108 1112 080 96 Required 1 Range at CPA 2 Speed of relative movement SR1l39 relative speed Time at CPA 4 True course of contact L Decision When the range to the contact decreases to 6 miles own ship will change course so that the contact will pass safely ahead with a CPA of 20 miles Required 5 New course for own ship 6 New SRM after course change Solution Assuming that the contact maintains course and speed 1 Nil39 risk of collision exists 2 SRM 12 kn 3 T 1200 4 307 5 063 6 New RM 22 kn Table of Contents 5 Own ship on course 220 speed 12 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0300 297 117 0306 296 100 0312 295 85 Required 1 Range at CPA 2 Speed of relative movement SR1l39 relative speed Time at CPA 4 True course of contact L Decision When the range to the contact decreases to 6 miles own ship will change course so that the contact will clear ahead in minimum time with a CPA of 30 miles Required 5 New course for own ship 6 New SRM after course change Solution Assuming that the contact maintains course and speed 1 R 12 mi 2 SRM 165 kn 3 T 0343 4 C 161 5 Come right to 290 6 New SRM 28 kn 6 Own ship on course 316 speed 21 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 1206 357 118 1212 358 102 1218 359 87 Required 1 Range at CPA 2 Speed of relative movement SR1l39 relative speed 3 True course of contact 4 True speed of contact Decision When the range to the contact decreases to 6 miles own ship will change course so that the contact will clear ahead in minimum time with a CPA of 3 miles Required 5 New course for own ship Solution Assuming that the contact maintains course and speed1 R 11 mi 2 SRM 155 kn 3 C 269 4 S 125 kn 5 C 002 383 Table of Contents 7 Own ship on course 000 speed 10 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0400 010 111 0406 010 90 0412 010 71 Required 1 Range at CPA 2 Speed of relative movement SR1l39 relative speed 3 Time at CPA 4 True course of contact 5 True speed of contact Decision Own ship will change course at 0418 so that the contact will clear ahead on own ship39s port side with a CPA of 2 miles Required 6 New course for own ship Solution Assuming that the contact maintains course and speed 1 Nil 2 SRM 20 kn 3 T 0433 4 C 200 5 S 10 kn 6 C 046 8 Own ship on course 052 speed 15 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 24 miles Time Bearing Range mi 0340 052 149 0346 052 116 0352 052 83 Required 1 Range at CPA 2 True course of contact 3 Assuming that there are no other vessels in the area and that the contact is a large passenger ship clearly visible at 0352 is this a crossing meeting or overtaking situation 4 True speed of contact Decision A decision is made to change course when the range to the contact decreases to 6 miles 5 New course of own ship to clear the contact port to port with a CPA of 3 miles Solution Assuming that the contact maintains course and speed 1 Nil39 risk of collision exists 2 C 232 3 Meeting 4 S 18 kn 5 C 119 Table of Contents 9 Own ship on course 070 speed 16 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0306 015 108 0312 016 83 0318 017 59 Required 1 Range at CPA 2 Time at CPA 3 True course of the contact 4 True speed of the contact Decision When the range to the contact decreases to 5 miles own ship will change speed only so that contact will clear ahead at a distance of 3 miles Required 5 New speed of own ship Solution Assuming that the contact maintains course and speed 1 R 05 mi 2 T 0333 3 C 152 4 S 21 kn 5 S 314 kn 10 Own ship on course 093 speed 18 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0452 112 59 0458 120 42 0504 137 27 Required 1 Range at CPA 2 Relative distance MRNI from 0452 to 0504 position of contact 3 Speed of relative movement SR1l39 relative speed 4 Direction of relative movement DR1l 5 Distance own ship travels from the time of the rst plot 0452 to the time of the last plot 0504 of the contact 6 True course and speed of the contact Solution Assuming that the contact maintains course and speed 1 R 19 mi 2 MRM 36 mi 3 SRM 18 kn 4 DRM 273 5 D 36 mi 6 The contact is either a stationary object or a vessel underway but with no way on 385 Table of Contents 11 Own ship on course 315 speed 11 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 24 miles Time Bearing Range mi 0405 319 17 8 0417 320 15 6 0429 321 13 4 Required 1 Range at CPA 2 True course and speed of the contact Decision When the range to the contact decreases to 8 miles own ship will change course so that the contact will pass safely to starboard with a CPA of 3 miles Required 3 New course for own ship Solution Assuming that the contact maintains course and speed 1 R 16 mi 2 The contact is either stationary or a vessel with little or no way on 3 C 303 12 Own ship on course 342 speed 11 knots half speed obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0906 287 120 0912 287 102 0918 288 84 Required 1 Range at CPA 2 True course of the contact 3 True speed of the contact 4 Is this a crossing meeting or overtaking situation Decision Own ship is accelerating to full speed of 18 knots and will change course at 0924 when the speed is 15 knots so that the contact will clear astern with a CPA of 2 miles Required 5 New course for own ship Solution Assuming that the contact maintains course and speed 1 R 05 mi 2 C 067 3 S 15 kn 4 Crossing 5 C 006 Table of Contents 13 Own ship on course 350 speed 18 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0200 030 100 0203 029 87 0206 028 74 Required 1 Range at CPA 2 True course of the contact 3 True speed of the contact Decision When the range to the contact decreases to 6 miles own ship changes course to 039 Required 4 New range at CPA 5 Describe how the new time at CPA would be computed 6 New time at CPA 7 At what bearing and range to the contact can own ship safely resume the original course of 350 and obtain a CPA of 3 miles 8 What would be the bene t if any of bringing own ship slowly back to the original course of 350 once the point referred to in 7 above is reached Solution Assuming that the contact maintains course and speed 1 R 10 mi 2 C 252 3 S 185 kn 4 R 30 mi 5 Determine the original relative speed SR1l39 then using it determine the time at MX Next determine the new SRM39 then using it determine how long it will take for the contact to move in relative motion down the new RML from MX to the new CPA 6 T 0219 7 When the contact bears 318 range 30 miles 8 The slow return to the original course will serve to insure that the contact will remain outside the 3mile danger or buffer zone after own ship is steady on 350 14 Own ship on course 330 speed 20 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0608 300 120 0614 300 100 0620 300 80 Required 1 Range at CPA 2 Time at CPA 3 True course of the contact 4 True speed of the contact 5 What danger if any would be present if own ship maintained course and speed and contact changed course to 120 at 0620 Decision Assume that the contact maintains its original course and speed and that own ship39s speed has been reduced to 115 knots when the range to the contact has decreased to 6 miles Required 6 New range at CPA 7 Will the contact pass ahead or astern of own ship Solution 1 Nil39 risk of collision exists 2 T 0644 3 C 045 4 S 105 kn 5 None 6 R 20 mi 7 Ahead 387 Table of Contents 15 Own ship on course 022 speed 32 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 24 miles Time Contact1 ContacIB Cantatch 0423 070 232 mi 170 238 mi 025 226 mi 0426 070 211 mi 170 238 mi 023 212 mi 0429 070 191 mi 170 238 mi 020 190 mi The observations are made on a warm summer morning The weather is calm the sea state is 0 From sea water temperature measurements and weather reports it is determined that the temperature of the air immediately above the sea is 12 F cooler than the air 300 feet above the ship Also the relative humidity immediately above the sea is 30 greater than at 300 feet above the ship Required 1 Since the contacts are detected at ranges longer than normal to what do you attribute the radar s increased detection capability 2 Ranges at CPA for the three contacts 3 True courses of the contacts 4 True speeds of the contacts 5 Which contact presents the greatest threat 6 1f own ship has adequate sea room should own ship come left or right of contact A Decision When the range to contact A decreases to 12 miles own ship will change course so that no contact will pass within 4 miles Required 7 New course for own ship Solution Assuming that the contacts maintain course and speed 1 Super refraction 2 Contact Anil Contact BR 238 mi Contact CR 92 mi 3 Contact AC 299 Contact BC 022 Contact CC 282 4 Contact AS 30 kn Contact B S 32 kn Contact CS 19 kn 5 Contact A it is on collision course 6 Come right 7 C 063 16 Own ship on course 120 speed 12 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Contact1 ContacIB Contact C 0300 095 87 mi 128 100 mi 160 77 mi 0306 093 78 mi 128 83 mi 164 70 mi 0312 090 70 mi 128 66 mi 170 63 mi Required 1 Ranges at CPA for the three contacts 2 True courses of the contacts 3 Which contact presents the greatest danger 4 Which contact if any might be a lightship at anchor Decision When the range to contact B decreases to 6 miles own ship will change course to 190 Required 5 At what time will the range to contact B be 6 miles 6 New CPA of contact C after course change to 190 Solution Assuming the contacts maintain course and speed 1 Contact AR 30 mi contact Bnil contact CR 43 mi 2 contact AC 138 contact BC 329 contact CC 101 3 Contact B it is on collision course 4 None 5 T 0314 6 R 32 mi Table of Contents MANEUVERIN G BOARD PROBLEMS 17 Own ship on course 298 speed 13 knots obtains the following radar 18 Own ship on course 073 speed 195 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 bearings and ranges at the times indicated using a radar range setting of 20 miles miles Time Bearing Range mil Time Bearing Range mi 0639 267 190 1530 343 162 0651 2665 160 1540 343 147 0709 265 115 1546 343 138 0729 261 65 1558 343 120 0735 2555 49 1606 3425 109 0737 252 43 1612 3415 101 0741 2425 33 1624 3395 84 16325 336 73 Required 1644 3285 60 1 Range at CPA as determined at 0729 1657 315 4397 2 Time at CPA as determined at 0729 Required 3 Course of other ship as determined at 0729 1 Range at CPA aS determined at 1558 4 Speed of other ship as determined at 0729 2 Time at CPA as determined at 1558 5 Range at CPA as determined at 0741 3 Course of other ship as determined at 1558 6 Time at CPA as determined at 0741 4 Speed of other ship as determined at 1558 7 Course of other ship as determined at 0741 5 Range at CPA as determined at 1624 8 Speed of other ship as determined at 0741 6 Time at CPA aS determined at 1624 S01 tion 7 Course of other ship as determined at 1624 1 R 10 mi 2 T 0755 3 c 030 4 s 70 kn 5 R 20 mi 6 T 8 Speed other Ship as determined at 162439 07495 D C 064 8 S 70 kn 9 Range at CPA as determined at 1657 10 Time at CPA as determined at 1657 l 1 Course of other ship as determined at 1657 12 Speed of other ship as determined at 1657 Solution 1 R 00 mi 2 T 1718 3 C 098 4 S 215 kn 5 R 20 mi 6 T 1721 n c 098 8 s 200 kn 9 R 37 mi 10 T 1718 11 c 098 12 s 180 kn Table of Contents 389 19 Own ship on course 140 speed 5 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 miles Time Bearing Range mi 0257 142 105 0303 141 5 8 0308 141 6 0312 135 45 0314 1265 4 0317 1105 32 Required 1 Range at CPA as determined at 0308 2 Time at CPA as determined at 0308 3 Course of other ship as determined at 0308 4 Speed of other ship as determined at 0308 5 Range at CPA as determined at 0317 6 Time at CPA as determined at 0317 7 Course of other ship as determined at 0317 8 Speed of other ship as determined at 0317 Solution 1 R 02 mi 2 T 0322 3 c 325 4 s 200 kn 5 R 30 mi 6 T 0320 7 c 006 8 s 200 kn 20 Own ship on course 001 speed 15 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 15 miles Time Bearing Range mi 2243 138 140 2255 1375 126 2318 136 99 2332 140 80 2351 1665 55 00025 1915 50 0008 204 51 0014 214 51 0020 222 495 0026 230 485 Required 1 Range at CPA as determined at 2318 2 Time at CPA as determined at 2318 3 Course of other ship as determined at 2318 4 Speed of other ship as determined at 2318 5 Predicted range of other vessel as it crosses dead ahead of own ship as determined at 2318 6 Predicted time of crossing ahead as determined at 2318 7 Course of other ship as determined at 2351 8 Speed of other ship as determined at 2351 9 Predicted range of other vessel as it crosses dead astern of own ship as determined at 2351 10 Predicted time of crossing astern as determined at 2351 11 Direction of relative movement between 00025 and 0008 12 Relative speed between 00025 and 0008 13 Course of other ship as determined at 0026 14 Speed of other ship as determined at 0026 Solution 1 R 12 mi 2 T 0042 3 C 349 4 S 210 kn 5 R 20 mi 6 T 0056 7 C 326 8 S 210 kn 9 R 51 mi 10 T 2358 11 DRM 2815 12 SRM 120 kn 13 C 349 14 S 210 kn Table of Contents 21 Own ship on course 196 speed 8 knots obtains the following radar 22 Own ship on course 092 speed 12 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 12 bearings and ranges at the times indicated using a radar range setting of 16 miles miles Time Bearing Range mi Time Bearing Range mi 2303 016 110 1720 335 150 2309 016 100 1750 3345 117 2318 016 85 1830 333 72 2330 016 65 1854 3255 45 2340 0115 49 1858 3155 40 2350 3595 34 1902 3035 36 2400 3335 22 1906 2895 34 00105 286 20 1914 2635 33 0020 2475 25 1930 2125 38 0026 2335 32 1950 1845 68 Required Required 1 Range at CPA as determined at 2318 1 Range at CPA as determined at 1830 2 Time at CPA as determined at 2318 2 Time at CPA as determined at 1830 3 Course of other ship as determined at 2318 3 Course of other ship as determined at 1830 4 Speed of other ship as determined at 2318 4 Speed of other ship as determined at 1830 5 Range at CPA as determined at 2400 5 Course of other ship as determined at 1906 6 Time at CPA as determined at 2400 6 Speed of other ship as determined at 1906 7 Course of other ship as determined at 2400 7 Course of other ship as determined at 1950 8 Speed of other ship as determined at 2400 8 Speed of other ship as determined at 1950 9 Course of other ship as determined at 0026 Solution 1 R 05 mi 2 T 19355 3 c 114 4 s 160 kn 5 c 147 6 s 160 kn 7 c 124 8 s 200 kn 10 Speed of other ship as determined at 0026 Solution 1 R 00 mi 2 T 0009 3 c 196 4 s 180 kn 5 R 20 mi 6 T 0006 7 c 207 8 s 180 kn 9 c 196 10 s 180 kn Table of Contents 391 23 Own ship on course 080 speed 125 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 16 miles Time Bearing Range mi 0035 038 14 5 0044 0385 132 0106 040 100 Required 1 Range at CPA 2 Time at CPA 3 Course of other ship 4 Speed of other ship Decision When the range decreases to 80 miles own ship will turn to the left to increase the CPA distance to 30 miles Required 5 6 Predicted bearing of other ship when own ship changes course V Predicted time of change of course 7 New course for own ship 8 Time at new CPA 9 Time at which own ship is dead astern of other ship Solution 1 R 10 mi 2 T 0215 3 c 124 4 s 90 kn 5 T 0120 6 B 0415 7 c 064 8 T 0200 9 T 0204 Table of Contents 24 Own ship on course 251 speed 185 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 miles Time Bearing Range mi 0327 314 162 0337 3145 147 0351 315 126 0401 3155 111 04135 315 91 0422 305 67 Required As determined at 0401 1 Range at CPA 2 Time at CPA 3 Course of other ship 4 Speed of other ship Decision Own ship will pass astern of other vessel with a CPA of 40 miles and new direction of relative movement perpendicular to own ship39s original course maintaining a speed of 185 knots The original course will be resumed when the other ship is dead ahead of this course Required 5 New direction of relative movement 6 Predicted time of change of course 7 Predicted bearing of other ship when own ship changes course 8 Predicted range of other ship when own ship changes course 9 New course for own ship 10 Predicted new relative speed 11 Predicted time at which other ship is dead ahead of own ship 12 Predicted range of other ship when it is dead ahead of own ship 13 Predicted time at CPA as determined at 0422 14 Bearing of other ship when it is dead ahead of own ship39s original course 15 Predicted time of resuming original course Solution 1 R 10 mi 2 T 0515 3 C 222 4 S 160 kn 5 DRM 161 6 T 0411 7 B 3165 8 R 96 mi 9 C 292 10 SRM 198 kn 11 T 0428 12 R53 mi 13 T 04385 14 B 251 15 T 04385 393 Table of Contents 25 Own ship on course 035 speed 20 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 15 miles Time Bearing Range mi 1900 035 144 1906 035 128 1915 035 104 1924 035 80 1933 035 56 1941 030 35 1947 015 19 Required As determined at 1915 1 Range at CPA 2 Time at CPA 3 Course of other ship 4 Speed of other ship Decision When the range decreases to 50 miles own ship will change course to the right maintaining a speed of 20 knots to pass the other ship with a CPA of 10 mile Original course of 035 will be resumed when the other ship is broad on the port quarter Required 5 6 New course for own ship Bearing of CPA as determined at 1935 8 Predicted time at 10 mile CPA as determined at 1935 V Predicted time of change of course to the right I 9 Bearing of other ship when own ship commences turn to original course 10 Predicted time of resuming original course Solution 1 R 00 mi 2 T 1954 3 c 035 4 s 40 kn 5 T 1935 6 c 044 7 B 314 8 T 1952 913 269 10 T 1957 Table of Contents 26 Own ship on course 173 speed 165 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 miles Time Bearing Range mi 2125 5 221 16 0 2130 2205 15 0 2137 5 219 13 2 2142 218 12 2 21515 2155 10 0 2158 2055 83 2206 185 67 Required As determined at 2142 1 Range at CPA 2 Time at CPA 3 Predicted range other ship will be dead ahead 4 Predicted time of crossing ahead 5 Course of other ship 6 Speed of other ship Decision When range decreases to 10 miles own ship will change course to the right to bearing of stern of other vessel assume 05 right of radar contact Required 7 Range at new CPA 8 Time at new CPA 9 Direction of new relative movement line 10 New relative speed 11 New course of own ship Decision Own ship will resume original course when bearing of other vessel is the same as the original course of own ship Required 12 Predicted time of resuming original course 13 Distance displaced to right of original course line 14 Additional distance steamed in avoiding other vessel 15 Time lost in avoiding other vessel Solution 1 R 25 mi 2 T 2233 3 R 30 mi 4 T 22255 5 C 120 6 S 147 kn 7 R 63 mi 8 T 22115 9 DRM 075 10 SRM 232 kn 11 C 216 12 T 22095 13 D 34 mi 14 D 13 mi 15 t less than 5 min 395 Table of Contents 27 Own ship on course 274 speed 155 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 miles Time Bearing Range mi 0815 008 144 0839 006 101 0853 004 76 Required 1 Range at CPA 2 Time at CPA 3 Course of other ship 4 Speed of other ship Decision When the range decreases to 60 miles own ship will commence action to obtain a CPA distance of 40 miles with own ship crossing astern of other vessel Required 5 Predicted bearing of other ship when at a range of 60 miles 6 Predicted time when other ship is at 60 mile range and own ship must commence action to obtain the desired CPA of 40 miles Decision Own ship may 1 alter course to right and maintain speed of 155 knots or 2 reduce speed and maintain course of 274 Required 7 New course if own ship maintains speed of 155 knots 8 Predicted time when other vessel bears 274 and own ship s original course can be resumed 9 New speed if own ship maintains course of 274 10 Predicted time when other vessel crosses ahead of own ship and original speed of 155 knots can be resumed Solution 1 R 11 mi 2 T 0935 3 c 242 4 s 200 kn 513 002 6 T 0902 7 c 019 8 T 0916 9 s 82 kn 10 T 0936 Table of Contents 28 Own ship on course 052 speed 85 knots obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 miles Time Bearing Range mi 0542 052 18 5 0544 052 17 5 0549 052 15 0 0550 052 14 5 Required 1 Range at CPA 2 Time at CPA 3 Course of other ship 4 Speed of other ship Decision At 0555 own ship is to alter course to right to provide a CPA distance of 20 miles on own ship s port side Required 5 Predicted bearing of other ship when own ship changes course 6 Predicted range of other ship when own ship changes course 7 New course for own ship Own ship continues to track other ship and obtains the following radar bearings and ranges at the times indicated using a radar range setting of 20 miles Time Bearing Range mi 0559 050 100 06045 0435 74 06065 040 65 0609 034 55 Required 8 Course of other ship as determined at 0609 9 Speed of other ship as determined at 0609 10 Range at CPA as determined at 0609 Solution 1 R 00 mi 2 T 0619 3 c 232 4 s 215 kn 513 052 6 R 120 mi 7 c 086 8 c 241 9 s 215 kn 10 R 30 mi 397 Table of Contents APPENDIX D BIBLIOGRAPHY Boulding RSH Principles and Practice of Radar Seventh Edition London George Newnes Limited 1963 851 pages illus Brown Ernest B Simpli ed Radar Plotting NAVIGATION Journal of the Institute ofNavigation Vol 16 No 2 pp 157167 Washington DC Summer 1969 Budinger Thomas F LTJG United States Coast Guard Iceberg Detection By Radar Proceedings of the MerchantMarine Council Vol 17 No 9 pp 152156 September 1960 Burger W Radar Observer s Hanc mok for Merchant Navy O icers Sixth Edition Glasgow Brown Son amp Ferguson 1978 350p illus Carpenter Max H and Captain Wayne M Waldo Real Time Method of Radar Planing Centreville Maryland Cornell Maritime Press 1975 75 p illus Carpenter Max H and Captain Wayne M Waldo Automated Collision Avoidance A 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