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 TB 55-1900-201-45/1
advised of the circumstances and proposed corrective measures. 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 in-
stance 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 banks 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. Consequently, plating replacement may be called for even though the deterioration may be less than 25 per-
cent. In such case it is usually sufficient to replace less than a full plate.
d. In the case of riveted construction, bands of stress corrosion may be observed, mostly immediately adjacent
to the riveted lapped butts, even where the plating surface is generally quite fair. Experience has shown that cracking
develops in these areas. Since such cracks are in primary hull girder material, their occurrence must be regarded as a
very serious matter. Where zones of serious corrosion are noted, appropriate preventive action in the form of plating
replacement should be taken before any actual cracking develops. In making such replacements, as in the case of
welded construction, renewal of less than a complete plate is acceptable if the condition of the balance of the plate is
satisfactory. The butts of such renewal inserts should be flush welded, care being taken to insure 100 percent penetra-
tion. Originally riveted seams should be riveted, with sufficient existing riveting adjacent to welds released and re-driven
to insure 100 percent sound riveting.
e. Tank tops are considered in the computation of scantlings for load line assignment both by ABS and the
Coast Guard and must of necessity be maintained in reasonable condition consistent with their inclusion in the section
modulus. Apart from the function of the tank top and the double bottom internals in contribution directly to the section
modulus, there are two other structural functions which are equally important. First, without support by the bottom trans-
verses and longitudinals, the bottom plating has insufficient rigidity to carry compressive loading and tends to buckle
when the vessel is subjected to a hogging bending moment. Secondly, 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 loaded. It must be main-
tained in efficient condition to safely perform these functions.
f. A moderate amount of buckling of tank tops as acceptable provided buckling is confined to the plating be-
tween transverse and longitudinal girders. Fairness of transverses and girders may be checked by sighting or use of a
taut line along the frame and girders lines. If floors or girders are found to be appreciably deformed or cracked they
should be repaired or replaced. In doing such work, obvious defects such as sharp cornered or raggedly cut lightening
holes or other cut-outs should be made fair. Buckling of floors or girders not associated with grounding or other external
damage may
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