270

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

apparatus will illustrate very clearly the corresponding changes in the
angles formed by the pendants and the tensions on the spans. It will
be recognised that the greater tension will be on the span which is
nearer to the vertical and that the tension on each will be at its maximum

when the span is taut, as seamen say
when the pendants form nearly a straight
line between the pulleys.

The same results may be arrived at
by construction as follows:—

Example —Two pendants form a span
slung between two masts making angles
with the vertical of 22 and 53 degrees.
Find the tension on each arm, or pendant,
of the span when supporting a weight of
2J tons.

Construction — Draw two parallel
vertical lines to represent the masts;
make angles K and Y equal to 22 and
53 degrees respectively. Points X and Y
are placed anywhere on the masts and

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Fig. 13

represent the positions where the ends of the pendants are made fast
The lines of the angles intersect at A. Now draw AB vertically up-
wards and equal in length to 2£-ton units from a scale of equal parts.
Draw EC parallel to one span and BD
parallel to the other. The length of AD
represents the tension (1 ton) on the arm
from 7, and AC the tension (2 tons)
on the arm from X.

Another Method is to give the lengths
of the pendants and the heights of their
standing ends above the deck as measured
from the rigging plan of the ship, then
draw out the facts to scale and construct
the parallelogram.

Example. — The horizontal distance
between two vertical masts is 80 feet.
The end of one pendant, 60 feet long, is

80 ft

Flg. 14.

made fast 100 feet up one mast and the end of another pendant, 50 feet
long, is made fast 70 feet up the other mast. It is intended to lift a
10-ton boiler by using the pendants as span. Find the tension on eack