How the problems are made
Each target is given a true course and speed, then observed every 6 minutes. Bearings are printed to the whole degree and ranges to 0.1 nm, and the middle plots sit within 0.04 nm of the line through the first and last, so the plot is straight when you draw it. Every answer in the key is worked from those printed numbers, the same way you plot them. CPAs are either nil (a steady bearing) or at least 0.5 nm, and no answer sits on a rounding edge. Answers count as right within 0.2 nm, 2° for directions, 3° for a target’s course and aspect, 1 knot and 1 minute; the avoiding action allows 5° for a new course, 1.5 knots for a new speed, 0.3 nm for the bow crossing range and other targets’ new CPAs, and 2 minutes for times after the alteration. Avoiding action is always a turn to starboard or a cut in speed for a vessel forward of the beam, on every level. It never turns toward another target abeam or abaft the beam, every other target is more than 2 nm off when own ship alters, and none ends up both closer than it would have come and inside the CPA asked for. Printed sheets are true to scale: 1 nm is 6 mm, with a bar to check against.
An example
In set SEA226 (intro, north-up), own ship steers 342° at 15 knots. The target is at 039°, 10.0 nm at 0906 and 042°, 6.6 nm at 0918. M1 to M3 is 3.43 nm in 12 minutes, so the relative speed is 17.1 knots along 213°. The perpendicular from own ship meets the RML at 123°, 1.0 nm, at 0941. Own ship’s 12-minute run is 3.0 nm along 342°, ending at M1; from its start to M3 gives the target’s true course, 270° at 14.0 knots. At 0924 a turn to starboard to 050° opens the CPA to 2 nm. Open set SEA226
What each level asks
| Level | Plot | Questions |
|---|---|---|
| Intro | One target, three plots; sometimes a fixed object or a steady bearing | DRM, SRM, CPA, TCPA, bow crossing, true course and speed, aspect, a new course or speed |
| Radar observer (STCW / USCG) | Two or three targets, three or four plots, north-up or head-up | All of the above for each target, which comes closest, and the other targets’ CPAs after the alteration |
| Maneuvering board | Own ship at the center of a 10-ring board, with 1:1 to 4:1 scales | CPA in yards with the speed triangle, a course to pass at a set distance, changing station, true and relative wind |
Questions
How do you find CPA and TCPA on a radar plot?
Plot the target's ranges and bearings, draw the relative movement line (RML) from the first plot through the last and extend it past own ship. A perpendicular from the center to the RML gives the CPA: its bearing and range. Divide the distance from the last plot to the CPA by the relative speed to get the time.
How do you find a target's true course and speed?
Use the vector triangle. Draw own ship's run for the plotting interval (er) in the direction of own course so it ends at the first plot (r, or O). Its start is e (W). The line from e to the last plot (m, or A) is the target's true vector: its direction is the course, its length per interval is the speed.
What is the 6-minute rule?
Six minutes is a tenth of an hour, so the distance run in 6 minutes is the speed divided by 10: 15 knots is 1.5 nm. Plotting every 6 minutes makes every vector easy to scale. For 12 minutes, divide by 5.
What does aspect mean here?
Aspect is the relative bearing of own ship as seen from the target, measured from the target's bow: up to 180 degrees, Red when own ship is on the target's port side and Green on its starboard side. Here it is given at the time of the last plot.
Which way should you alter course in restricted visibility?
Rule 19(d): a vessel that detects another by radar alone, and finds a risk of collision or a close-quarters situation developing, shall act in ample time. A course change shall so far as possible avoid a turn to port for a vessel forward of the beam (other than one being overtaken) and a turn toward a vessel abeam or abaft the beam. The exercises follow this as geometry practice only.
What is the difference between head-up and north-up plotting?
On a north-up display the bearings are true and the picture stays still when own ship turns. On a head-up display the ship's head is at the top and echoes show at relative bearings, so you add own course to get true bearings. Choose Head-up to practise that conversion; the answers are still asked in degrees true.
Sources, read October 25, 2026: NGA Pub. 1310, Radar Navigation and Maneuvering Board Manual, 7th edition, 2001 (PDF copy): chapter 3 rapid radar plotting and examples 1 to 5, chapter 6 maneuvering board examples 1 to 10, appendix C problems; U.S. Coast Guard Navigation Rules, amalgamated (updated September 2020), Rules 7, 8 and 19; IMO Resolution A.483(XII), Training in radar observation and plotting (1981, PDF); 46 CFR 11.480, Radar Observer; Massachusetts Maritime Academy radar observer assessment OICNW-3-1F (CPA within 0.5 nm, TCPA within 3 minutes).