STSfiSSES ON A SHIP

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longitudinals have evidently been thrown out of line due to severe racking
strains, and fractures would be looked for at all the top and bottom
corner connections.

Fig 7.—Racking

Collapsing Stresses.—The water presses inwards on every submerged
part of the ship in a direction perpendicular to the skin surface with a
force which increases at a uniform rate of 64 Ibs. per square foot for
every foot depth of water. The function of the skeleton framework
of the ship is to keep the shell plating to its designed shape. The
plating is comparatively thin and flexible and it might readily yield
inwards to the pressure of the water were it not for the frames and
other stifieners. When the ship is under way the plating has to push the

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Fig 8.—Collapsing Forces.
water away at the bows, and in doing so has a tendency to vibrate, or to
move out and in, these pulsations being called ' 'panting. * * When the ship
is pitching" into a head sea excessive pounding is set up forward and aft
when she rises and falls, the local stresses at the stern being aggravated
by the racing of the propeller. Evidence of this is made obvious on
occasions by strained plating and slack rivets. The ship girder is,
therefore, specially strengthened at the ends by means of "panting"
beams, thickened plating, "breasthooks/V'erutches," closer spacing of