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 TB 55-1900-201-45/1
(3) Set-in plating is common forward. A slight degree of deformation of the hull plates in the forward portion
of a vessel ordinarily may be accepted without resulting in serious impairment of structural strength. However, for trans-
versely framed vessels, severe buckling or set-in condition of bottom plating within approximately the amidships half
length can seriously impair strength. In general, the greater the extent of athwartship buckling the greater the impairment
in hull strength especially those that cross a center vertical keel or inner bottom girder. Such a buckle should be cor-
rected by replacement of plating and the buckled portions of girders. If there is no evidence to indicate the buckle was
caused by grounding or other excessive local load or is associated with excessive wastage, it may be an indication of
need for providing additional stiffening. Buckles of shorter athwartship extent may also require correction, depending
upon the depth or height of buckles, the number of buckles, and their relative locations. For an example, several bottom
buckles within the same frame space are more serious than the same number of the same size buckles distributed in a
random manner. Localized transverse bands of accelerated corrosion or grooving may be found in association with
buckles. These are indicative of localized excessive stress which experience indicates may lead to cracking. Conse-
quently, plating replacement may be called for even though the cracking may be less than 25%.
(4) Tank tops are considered in the computation of scantlings and must be maintained in a fair condition
consistent with their inclusion in the section modulus. Apart from the function of the tank top and the double bottom in-
ternals and in direct contribution to the section modules, there are two other structural functions which are equally im-
portant. First, without support by the bottom transverses and longitudinals, the bottom plating has insufficient rigidity to
carry compressive loading and tend to buckle when the vessel is subjected to a hogging (upward bending) moment. Sec-
ondly, the entire bottom structure has the function of resisting water pressure when the vessel is in ballast and of bearing
the weight of cargo when unloaded. It must be maintained in an efficient condition to safely perform these functions.
(5) A moderate amount of buckling of tank tops is accept- able provided the buckling is confined to the plat-
ing between transverse and longitudinal girders. Fairness of transverse and girders may be checked by line sighting or
the use of a taut line along the frame and girder lines. If floors or girders are found to be appreciably deformed or
cracked, they should be repaired or replaced. Buckling of floors or girders not associated with grounding or other exter-
nal damage may be an indication of structural weakness and need for structural modification or reinforcement, plus re-
pair.
f. Side Plating. In the side plating the strake "between wind and water" is an area which is highly susceptible to
corrosion. The maximum wastage is to be expected in this area. Also, serious localized corrosion may be encountered
in way of overboard discharges and scupper openings.
2-6
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