STRESS OJW SPANS

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of the water and the shape of the hull are two factors also operating
on the boat, and the object of yacht designers is to build a boat that
will respond fully to the forward component AC and resist the side
component AD.

Cargo Spans.—The tension on the pendants of a span between two
masts can be readily arrived at by constructing an appropriate parallelo-
gram of forces The illustration shows the usual school apparatus for
demonstrating the principle. The arrangement of pulleys and 'weights

Fig 12 —Balanced Forces.
is obvious. . A bight of cord has been led over two pulleys and a weight
slung in the centre of it. The weight happens to be 2i Ibs,, and it is
balanced in equilibrium by a 2-lb. weight at the end of the cord leading
over the left hand pulley and a 1-lb. weight at the end of the cord
over the right hand pulley, thus indicating that the tension on the
left hand cord is 2 Ibs. and on the right hand cord 1 lb.5 the respective
pendants making angles of 22 degrees and 53 degrees with the vertical.
By increasing or decreasing the weights relatively to each other the