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remember this easily if you think of something that is
TRUE as being CORRECT or already corrected.
Another handy memory aid, CAN DEAD MEN
VOTE TWICE, gives the key to the problem of
changing from one to the other. Each word in our
memory aid represents a word in our problem, as
follows:
CAN
COMPASS
DEAD
DEVIATION
MEN
MAGNETIC
VOTE
VARIATION
TWICE
TRUE
Variation and deviation are always given as
EASTERLY or WESTERLY errors, and when
CORRECTING (converting from compass to true),
ADD easterly errors, and SUBTRACT westerly errors.
When UNCORRECTING (converting from true to
compass), SUBTRACT easterly errors, and ADD
westerly errors.
Suppose the true course, taken from a chart, is 095°;
variation, taken from the same chart, is 2° westerly; and
deviation, taken from the deviation table, is 3° westerly.
Now work the problem. Put down the things you know
as follows:
C
D
M
V
T
3°W
2°W°
095°
Do not forget the W (for westerly) or E (for easterly);
otherwise you will not know whether to add or subtract
the error. Now, true course was given, and we want to
find compass course. We are uncorrecting; therefore, we
add westerly errors and subtract easterly errors. Both
errors are westerly, so we add them both.
C
D
M
V
T
100°
3°W
097°
2°W°
095°
Compass course is 100°.
Let us now set up a problem converting compass
course to true course. We have given compass 193°,
variation 7° easterly, and deviation 2° westerly.
This time we are correcting; therefore, we add
easterly and subtract westerly errors.
C
D
M
V
T
193°
2°W
191°
7°E°
198°
After a little practice, you can work these problems
in your head. Because it is compass course or true course
you are interested in, find the algebraic sum of the two
errors. An algebraic sum is obtained by adding the two
errors if they are in the same direction, or subtracting
the smaller error from the larger error if they are in
opposite directions. The total error then is added to, or
subtracted from, whichever course is given.
In many boats, deviation is very small or
nonexistent; and when this is true, merely apply
variation and you have your answer. In some boats,
however, the motor and the other metal objects do cause
deviation. These boats must be swung, deviation tables
made out, and the date used when correcting the
compasses.
RULES OF THE ROAD
LEARNING OBJECTIVES: List and explain
the basic Rules of the Road. Identify and list
sound signals.
International Rules of the Road are specific rules for
all vessels while on the high seas and in connecting
waters that are navigable by seagoing vessels. The
Inland Rules apply to all vessels operating on the inland
waters of the United States, and to vessels of the United
States operating on the Canadian waters of the Great
Lakes (to the extent that there is no conflict with
Canadian law).
As a Seaman, you will need a basic knowledge of
the Rules of the Road for boat operation.
The International Rules were formalized at the
convention on the International Regulations for
Preventing Collisions at Sea, 1972. These rules are
commonly called 72 COLREGS.
The Inland Rules discussed in this chapter replace
the old Inland Rules, Western River Rules, Great Lakes
Rules, their respective pilot rules, and parts of the
Motorboat Act of 1940. Many of the old navigation rules
were enacted in the last century. Occasionally,
provisions were added to cope with the increasing
complexities of water transportation. Eventually, the
navigation rules for the United States inland waterways
became such a confusing patchwork of requirements
that in the 1960s several unsuccessful attempts were
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