2008 REED’s East Coast Edition - Navigation
SAMPLE RADAR PLOT
Range Scale Six Miles
Data: Conclusions:
1030 Echo 322° (Rel.) 1036 Echo 321° (Rel.) O➔A indicates collision
Boathead 240° Boathead 239° in 12 mins.
Bearing 202° Bearing 202° W➔A indicates other vessel
Range 4.4M (O) Range 3.0M (A) course 348°, speed 9k
In this example, the navigator has plotted an approaching target at 10:30 and 6 minutes later.
By extending the track, he or she can immediately see that a collision is probable. By plotting
his own six-minute track, W➔O, the navigator can deduce the other vessel’s course and speed
vector, W➔A. The navigator has then predicted the target’s position at 10:42. The two dotted
lines extending from the 10:42 mark represent relative motion tracks that would keep the tar-
get vessel at a one mile Closest Point of Approach. The navigator determines the new course
required by vector analysis — the easiest way is to take a parallel of the dotted line back so it
runs through the original A, then swing the W➔O vector around W until it touches the new
line. The course change to 325° is definitely preferable, in case the target decides to change
course (probably to starboard). This type of plotting sheet, known as a manuevering board, is
also useful for other relative motion problems like current drift and set, determing true wind
speed and direction, and hurricane avoidance.
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