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 TB 55-1900-201-45/1
and gaging is subject to the approval of the OCMI. See (h) below for remarks specifically pertaining to ultrasonic meas-
urement.
c. There are two approaches to gaging. In the first, gaging is used to provide a quantitative basis for evaluating
a questionable local condition. Even though this involves only limited gaging, it should not be undertaken unless there is
sufficient cause. Deep pitting over an area, holes, fractures, excessively thin edges on structural shapes, bands or belts
of corrosion across bottom plating which may indicate heavy working, are all justifiable bases for requiring gaging in the
affected area. However, care must be exercised not to extend the gaging so as to have it become a "fishing expedition."
The ship owner should be forewarned that requirements bases on a local survey of this kind may have to be extended
when the plate eages in way of the renewals are examined by the inspector.
d. Belt gaging goes far beyond the investigating of a local condition as described in the previous paragraph. It
involves taking readings around several complete transverse sections of the hull including deck, sides and bottom. It is
intended to furnish information which may be used to assess the average wastage of the hull envelope and its conse-
quent effect on the longitudinal strength of the vessel. Belt gaging is a major undertaking, costly to the ship in both time
and money. It should be required only for good and sufficient cause; as for example, in the following cases:
(1)
A vessel coming under Coast Guard certification for the first time.
(2)
A vessel upgrading her service to a more exposed route.
(3)
A vessel undergoing a major conversion.
(4)
A vessel which has had a structural failure which could be attributable to age or general deterio-
ration.
(5)
A vessel in which the general condition, as evidenced by the parameters described in paragraph
(c) above, is such that there is a serious question concerning her seaworthiness.
e. In addition to the above, it should be noted that Section 43 of the American Bureau of Shipping Rules for
Building and Classing Steel Vessels also provides guidance in the matter of gaging. At the special survey occurring ap-
proximately 8 years after build, and thereafter, surveyors may require gaging where considered necessary. At the spe-
cial survey occurring approximately 12-15 years after build for tankers and 16-20 years after build for ordinary vessels,
general gaging to determine the thickness of shell, deck, and other main scantlings is required. The results of these
gagings are submitted
E-4
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