Page 218 - NAVAL SCIENCE 3 TEXTBOOK

224 NAVAL SKILLS

MANEUVERING BOARD

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A maneuvering board nomogram, set up to find the relative speed,
given a distance of relative movement of 4,000 yards and a time of
, six minutes.
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, . , . <. ., ,,' \ put a mark over the elapsed time between 1\1j and 1\J on the upper
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time scale of the nomogram, which is graduated in minutes. Here,
since six minutes elapsed between the range and bearings obtained
for points l\J} and 1\1 , we put a mark at 6 on the time scale. Finally,
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draw a straight line through the two marks using a straight -edge,
Relative motion line for a maneuvering ship, with the CPA to the and extend it down onto the lower speed scale. The point on the
reference ship in the center indicated. speed scale thus defined is the relative speed-20 knots, in this
case (see the illustration),
triangle and the dividers and then move the dividers to the dis-
tance scale in use to determine the distance of CPA. In the exam- MANEUVERING BOARD
ple shown, the 2: 1 scale was used for distance, so the CPA distance
is about 6.000 yards, To determine the bearing at CPA, just extend
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the perpendicular distance line to the outer bearing circle. Here, ,
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the bearing at CPA will be 259 degrees, By convention, CPAs are
normally given in terms of bearing and distance from one's own
vessel to the maneuvering vessel.
Now, to determine the other vessel's true course and speed, we
need to complete the construction of a vector diagram that will
allow us to solve for the other vessel's true course and speed, given
our own vessel's true course and speed vector (which we've already
plotted) and the other vessel's relative course and speed vector.
To determine the other vessel's relative course and speed vec-
tor, we make use of the RML we plotted to find the CPA, The rela-
tive speed is the rate at which the other vessel is proceeding along
its RML; the relative course is the direction of the fu'vIL
To find the relative speed, we use the speed-time-distance
nomogram at the bottom of the maneuvering board, which can "'. . .... ,'
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be thought of as a sort of paper computer. Ib use the nomogram, ~"-<'" --,,-~.~
place a mark on the central distance scale of the nomogranl, cor- ~~~~~2j -~t~~ ~-' -'-.. -~.-~~~" I'll!!!!!! ~-:·~;-::-m-·-·l-:,~-:::::~ ~.:::
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responding with the distance traveled along the R~\'lL betw-een any
two points, say, AJ and 1\1 , Note this scale is graduated in either . ~~ -~ ~~ ~-~- "~,
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yards along the top, or corresponding nautical miles along the bot- Vector diagram on a maneuvering board set up to find the maneu~
vering ship's course and speed (the em vector), given the reference
tom. In our example, the other vessel traveled 4,000 yards between ship's course and speed (the ervector) and the relative course and
AI} and AI , so -we put a mark at 4,000 on the distance scale. Nex"t, speeed (the rm vector),
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