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 TM 55-1905-223-SDC
b. Basis of assignment. The factors responsible for the assignment of the above limits on drafts and
displacement are as follows:
(1) Reserve buoyancy.
(2) Structural strength.
CAUTION
Operating at displacements over the limiting value is detrimental to the safety
and performance of the ship in several ways which are briefly summarized
below:
c. Dangers of overloading:
(1) Adverse effects on the survival power and safety of the ship:
(a) Reserve buoyancy and floodable length. If the drafts before damage exceed the limiting
values, one compartment flooding would probably result in flooding water coming over the main
deck aft.
(b) Structural strength. Longitudinal strength is ample for all approved conditions of loading and is
not a factor in beaching. Uniform loading of cargo, diesel oil and ballast throughout the length of the ship will
result in decreased bending moments and stresses in the hull and decks. The longitudinal bending moment
varies as the displacement for a given local distribution and therefore hull stresses will increase in the same
ratio. Extreme overloading may raise stresses to a point where structural cracks or even failures will occur,
especially in heavy weather. Moreover, if the limiting displacement is exceeded, the reserve of strength
available to withstand the effects of damage is reduced.
(c) Transverse stability. If excess cargo is carried high in the ship, safety is impaired by the rise in
center of gravity which detracts from every element of stability, namely metacentric height, righting arms,
range of stability and reserve of dynamical stability.
(2) Adverse effects on other characteristics:
(a) Speed. Increased resistance at large displacements cuts down the speed obtainable from a
given horsepower. If a given speed must be made good, substantial increases in power are sometimes
necessary.
(b) Cruising radius. Increased fuel consumption for a given mileage, due to excessive
displacement, will reduce the effective cruising radius.
(c) Dryness. Overloading will reduce freeboard to the weather deck, and thus give a wetter and
less efficient ship in rough weather. The possibility of superstructure damage and damage to topside cargo
from heavy water coming on board must be considered.
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