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 TB 55-1900-201-45/1
provided the effective remaining thickness is not less than approximately 75 percent of the original thickness of the adja-
cent strakes and provided it is not buckled or otherwise damaged. If the adjacent plating is wasted so as to, itself, require
replacement, it is generally wise to replace the keel plating even though it may be wasted no more than about 25 percent
of its thickness.
E-19. Bottom Plating, Inner Bottom Plating and Bottom Internals.
a. The bottom plating complements the deck plating as the lower flange of the hull girder. As well as sustaining
a major portion of the hull bending moment, it is subject to increased stress due to water pressure. Its strength may be
reduced either by general or localized corrosion and by buckling. In view of the prime importance of this plating, the
maximum average reduction in thickness to be permitted in about the midships half-length is about 20 percent. If the
wastage exceeds this amount the plating should be renewed. Alternate measures or means of reinforcement can be
considered but since they would constitute a major change in the design of the vessel, plans for same should be submit-
ted for approval to the field (mmt) office or to the Commandant (MMT). If after consideration of the bottom shell plating
with regard to the main longitudinal strength there should remain local areas or plates requiring attention, these may be
dealt with on the basis of a maximum average wastage of about 25 percent from original, provided the plates and sup-
porting structure are otherwise in satisfactory condition. Welded butts which exhibit excessive wastage (grooving) as
compared to the balance of the plate should be rewelded after excavation to sound metal.
b. Joggled lapped seams and butts are particularly prone to excessive local deterioration because of the flexing
which may take place at such joints and because they provide a pocket in which corrosion may develop. Accordingly,
when inspecting plating containing joggled lapped joints, it is important to check the condition of the joint itself and par-
ticularly the plating thickness in way of the joggle. Renewals should be in accordance with Section IV (E-24) of
these notes.
c. Unfair or set-in plating is common forward. A fair degree of deformation of the hull plates in the forward por-
tion of a vessel ordinarily may be accepted without resulting in serious impairment of structural strength. However, for
transversely framed ships, severe buckling or set-in condition of bottom plating within approximately the amidships half
length can seriously impair strength. In general, the greater the athwartship extent of buckling the greater the impairment
in hull strength. Any appreciable buckle of sufficient athwartship extent to cross a center vertical keel or inner bottom
girders is serious. Such a buckle should be corrected 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 loading, or is associated
with excessive wastage, it may be an indication of need for providing additional stiffening. In such instances, the Com-
mandant (MMT) or field (mmt) office should be
E-11
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