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 TB 55-1900-201-45/1
construction, special attention should be paid to the riveting of butts. Discovery of working or loose riveted butts calls for
prompt corrective action. This may be evidence of cracking at the rivet holes not yet sufficiently extensive to extend be-
yond the rivet head. Cracking of the plate will, in general, call for replacement of that portion of the plating. Buckling of
deck plating is uncommon; however, the use of thinner high strength plating increases the likelihood. Any such buckling
can seriously impair the strength of the vessel and calls for corrective action.
E-17. Deck Longitudinals. In tank vessels the corrosive deterioration of deck longitudinals may be much more rapid
than that of deck plating. These longitudinals are necessary to support the deck plating so that it can carry local hydro-
static loading, to provide panel stiffness to the deck plating so that, as a part of the hull girder, it can carry compressive
loading without buckling, and also to directly contribute to the hull girder stiffness and strength. Because the relative im-
portance of these factors may be different when dealing with different designs, it is very difficult to lay down any gener-
ally applicable wastage limits. However, for the usual proportions of longitudinals to plating and usual spans of a tanker
of about T2 size, deterioration of some deck longitudinals up to a maximum of about 40 percent or about .18" wastage,
whichever is the lesser, may be accepted provided the average deterioration is not more than about 30 percent or about
14" wastage, whichever is the lesser. For a single voyage, maximum deterioration of some longitudinals as high as
about 50 percent or about .22" wastage has been accepted. The above applies to longitudinals fabricated from structural
shapes such as inverted angles or T bars. In the case of flat bar longitudinals, the strength of the combined deck plate
and longitudinal is critical in compression. Consequently, not more than about a 20 percent corrosion allowance should
be permitted. Additionally, flat bar longitudinals should be faired or replaced if they are distorted or buckled to any de-
gree. In the case of river tank barges not carrying any deck cargo, general deterioration of deck longitudinals up to about
40 percent may be accepted. Since the obvious necessity for maintaining oil tightness does not apply to the rake ends,
they tend to be neglected. This should not be permitted since the rake ends provide the major buoyancy of the vessel
and are, therefore, vital to seaworthiness.
E-18. Keel Plating. In recongnition of local strength factors and also the additional corrosion to which keel plates are
subject as a result of being unavailable for painting when sitting on keel blocks in drydock, keel plating is normally of
greater thickness than the balance of the bottom plating. Taking account of the fact that a large part of this extra thick-
ness may be regarded as an additional corrosion allowance, it is generally satisfactory to defer the replacement of keel
plating until the wastage is somewhat more than would otherwise be considered acceptable. In determining the amount
of such extension, consideration should be given to the condition of adjacent "A" strake(s). If the adjacent plating is in
good condition and does not require replacement, the keel plating may be accepted
E-10
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