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 TB 55-1900-201-45/1
that a local deterioration does not result in a radical change in section or general weakening which could act as a notch.
On the other hand, there may be instances where either general or localized wastages of less than 25 percent would call
for replacement of material. These exceptions are dealt with in paragraphs (E-12) through (E-15) and in the discussions
of the individual major hull components.
E-11. Ship surveyors/personnel engaged in inspection of hulls to determine percentage of waste will observe many and
various over tolerances of hull plate thickness when compared to builders' plans and considering only the nominally
stated plate weight and thickness, e.g., a builder's plan may state certain hull plate is 7.7 # Plate which is 3/16 or .1875
in. in thickness. Actual drilling and gaging of this plate (with no waste) may reveal an actual thickness of .205 in. These
over tolerances are normal and due in part to processes and allowable over tolerances associated with the state of the art
in rolled plate manufacture. Conversely under tolerance is nil, e.g., new 7.7 # Plate = 3/16 or .1875 in. will be no less
generally than .1865 in. The significant thing for inspection personnel to remember is that over tolerances do exist and
should be considered when gaging hull plate. Since source data for rolled hull plate tolerances is not normally published,
the following information is provided as general guidance and/or as a factor that should be considered when gaging hull
plate:
a. ABS Rule 43.1.8, Plate Thickness Tolerances, indicates that new plate from .200 thru .590 in. thick will not
be more than .016 under the stated nominal size. However, the rule does not address over tolerance.
b. 7.7 # Plate (3/16") in widths up to 72" can range up to 8.5% over the stated nominal size.
c. 7.7# Plate (3/16") in widths of 108" to 120" can range up to 14% over the stated nominal size (.1875 + 14% =
actual size of .213).
This information was provided by Bethlehem Steel Corp.
d. The general allowable wastage factor is 25% of the nominal size depicted by the builder's plan, e.g., 7.7 #
Plate which is 3/16 or .1875 in. thick stated nominally can suffer a maximum waste of 25% which equates to .1875 -
25% = .1406 before replacement is required. Do not use over tolerances in computations of wastage.
E-12. Oversize or Undersize Scantlings. There are some vessels in existence which were built to scantlings differing
from those required by the current American Bureau of Shipping Rules. In evaluating the necessity for replacing deterio-
rated structure in such vessels, allowance needs to be made for the fact that the vessel was built to scantlings differing
from the current requirements. Where the original scantlings are known to be in excess of requirements, a corresponding
increased corrosion allowance is acceptable. Conversely, where
E-7
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