Page 337 - Practical Ship Design

294 Chapter IO

Fig. 10.2. An analytical method of calculating the forces and moments in hull and superstructure.

corvette types) is vertical bending of the hull girder. This results in alternating
compressive and tensile stresses in the deck and bottom structure which must be
limited to avoid buckling, fracture or fatigue failure.”
The paper goes on to suggest that longitudinal strength calculations should be
based on bending moments and shear forces which have a 1% probability of
exceedance in the estimated life of the ship taking into account the sea areas in
which the ship is expected to operate.
In warships of frigate or corvette size the strength of the upper deck in
compression is usually the critical factor. The fact that it is compression in the deck
rather than in the bottom that is critical arises from the fact that the bottom structure
has to be of heavier construction than the deck to meet hydrostatic loads.