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DESIGN OF THE SUBMARINE TORPEDO BOAT 105
Where P = collapsing pressure,
C = 826.845 constant derived from experiment,
R = required section modulus.
Hence assuming 200 pounds as a safe allowable collaps-
ing pressure and 12 feet as the diameter of the boat, sub-
stituting the values, the formula reads,
200X 12 .
R = ---------= 2.03 the required section.
826.845
Neglecting the extra thickness due to the shell plating
this modulus calls for a section 5X 3X 12.8 pounds angle
and will resist collapse against a head of 454 feet.
From the same tests it was determined that the elastic
limit of the metal was the limiting stress of the plating
against permanent set, and that the thickness should be
increased directly as the diameter of the boat. For the
thickness of shell plating the following formula has been
deduced:
PR diameter in inches
T = ------------------------ ----—
2X E
Where P = collapsing pressure,
T = thickness of the plate,
E = elastic limit = 30,000.
Substituting values as before we have
200X 12X 12
T = -----------------------= .48 inches, thickness of plate.
2X 30,000
Safety in surface navigation may still be materially
increased by altering the form of the superstructure for-
ward so as to give greater free-board and by effecting some-