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 TB 55-1900-201-45/1
original scantlings are below requirements, the maximum acceptable deterioration is reduced. As an example, for con-
verted LST's, originally built to less than commercial scantlings, 1/4" deck planting, 3/8" stringer and sheer strakes, and
3/8" bottom plating including the bilge strakes should generally be replaced when wasted more than 15 percent. In deal-
ing with ex-LCI's and other lightly built vessels converted to merchant service similar reduced corrosion allowances
are in order. Also, individual members may sometimes be made oversize to compensate for some other feature of the
overall design. In such a case, an extra corrosion allowance would not be justified. Because of these ramifications, it
may not be practical for inspectors to determine whether a vessel's original scantlings are under or over requirements.
When it is believed that the original scantlings may have been light, the matter should be referred to the field (mmt) of-
fice or to the Commandant (MMT) before a full corrosion allowance is permitted. On the other hand, if the owner re-
quests an increased corrosion allowance because of oversized scantlings, he should offer suitable verification. Proper
notation on the original plans of the vessel or documentary evidence from the classification society would be acceptable
for this purpose.
E-13. Special Coatings. Recent advances in protective coating technology have given promise that corrosion in ship
steel may be virtually eliminated. Based on this, ships constructed since 1965 have had the option of building the scant-
lings which are, in general, 10% below the scantlings tabulated in the American Bureau of Shipping "Rules for Building
and Classing Steel Vessels", provided acceptable special coatings have been applied. In all such cases, the approved
hull structural plans clearly indicate such reduction by showing, for each plate and structural shape, both the required
tabular scantling and the permitted reduced scantling. For example, a structural shape would be indicated on the plan as
follows:
16" x 4' x 20.4# FLG PL
16" x 4" x 17.85# FLG PL
Normally, painting of the hull structure has not been the subject of Coast Guard requirements. However, in the case of
vessels which have been allowed to have reduced scantlings on the basis of special coatings, it is a valid concern of the
Coast Guard inspector to insure that such coatings are maintained. If corrosion has occurred, evaluation of the degree
should be referred to the required tabular scantling and not to the as-built scantling.
E-14. High Strength Steels.
a. The use of high strength steels in some recently built ships introduces new problems which must be carefully
considered when evaluating structural renewals or repairs. These steels offer significant
E-8
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