• Through the end of the run draw a line T. If the current was estimated to be nil dur-
parallel to the first position line. This ing the interval between the bearings, what
line is the first position line advanced was the ship’s position at 2330 hours?
and it should be marked by its direction, • Plot the two position lines as described.
the time of its observation, and the time • From any convenient point A on the first
(of the second bearing) to which it’s ad- LOP, lay off the run (AB) 270°, 4 1/2 miles.
vanced. • Through B draw the advanced LOP par-
• The point where the advanced line cross- allel to PA; the point where it cuts the
es the second LOP is the running fix. second bearing is the running fix.
The accuracy of these fixes depends not Figure 4 presents an example of a running
only on the accuracy of the bearings and fix in current and making leeway.
their angle of crossing, but also on your accu-
racy in estimating the leeway and current that
affect the “run” between the bearings. As with
a simultaneous fix, you can better assess the
reliability of a running fix when you transfer
two bearings up to the time of a third. You
can generally treat this small triangle with
greater confidence than a running fix from
only two bearings. Also, the principle of the
running fix applies when you obtain the posi-
Figure 4
tion lines from different objects. A bearing of In this example a vessel steering 270° T
one object may be advanced to cross with a is moving through the water at 9 knots
bearing of another object that was not sight- through the water and making 5° leeway due
ed until after the first one was lost to view. to a northerly wind. At 2300 hours a light-
Figure 3 presents an example of a running house, P, bore 315° T. At 2330 hours the same
fix with no current or leeway. light bore 040° T. The current was estimated
to be setting 010° at 2 knots. Find the vessel’s
ass
position at 2330.
• Plot the two position lines as described
omp
above. C
• From any convenient point A on the
first position line, lay off AB (4 1/2 miles
along the wake course adjusted for leeway
– 265°).
ion
Figure 3
• From point B lay off BC, the current effect
at
for 30 minutes (1 mile in the direction of ig
In this example a vessel steering 270° T is 010°). The estimated run, then, is AC.
a
v
moving through the water at 9 knots and Through point C draw the transferred LOP
N
making no leeway. At 2300 a lighthouse, P, parallel to PA. The point where it cuts the
bore 315° T. At 2330 the same light bore 040° second bearing is the fix
The Compass
closed bowl. Magnets attached to the card’s
Magnetic Compasses
underside align it to the earth’s magnetic
Most yachtsmen rely on magnetic com- axis. “Variation” is the difference between
passes, which can be quite accurate and don’t “magnetic” and “true” north, the result of
need electrical power. They are, however, the earth’s magnetic poles not being located
influenced by metal objects on the boat, at the geographic poles.
thereby requiring you to convert compass To offset the disturbance caused by mag-
readings to magnetic directions. This is mag- netic material near the compass, you can
netic deviation. adjust the positions of the compensating
Traditional magnetic compasses consist of magnets under the card on a conventional
a circular card floating in a fluid-filled en- compass or adjust the resistors on a fluxgate
839