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 TB 55-1900-201-45/1
2-24. Inspection of Aluminum Hulls.
a. Inspection of aluminum boats for corrosion usually is con- fined to two main areas. The first area is in the inte-
rior structure, particularly the bilge area, and the second area is in the underwater, outside surface of the hull. The bilge
areas must be properly protected and maintained by good house keeping techniques. If not, the area may be subject to
pitting-type corrosion where bilge water and sediment remain in longtime contact with the aluminum.
b. In order to assure continued protection by the anodes, the condition of galvanic anodes, used to suppress bilge
area corrosion, should be checked. Anodes that have been consumed should be replaced with new material and those
unconsumed should be cleaned by stainless steel wire brushing at periodic intervals. The exterior surfaces of the hull
shall be examined to evaluate the condition of the anti- fouling paint system. Look for localized corrosion resulting from
galvanic attack between aluminum and non-aluminum components, such as those found in the through hull fittings, the
bearing housing, and struts for the shaft and propellers. An examination shall also be made for pitting corrosion on the
transom in the vicinity of the exhaust. Inspect all structural welds, especially in the aft bottom area. This should be ex-
amined to confirm that there has been no cracking within the welds as the result of vibration or fatigue or in the plate ad-
jacent to the welds.
2-25. Cavitation Corrosion. The most common areas where cavitation corrosion may be found is in the vicinity of the
shaft, propellers or any other protruding underwater components. Where such damage is found, corrective actions con-
sist of restoring the damaged metal by welding and grinding, or by replacement of the damaged part and installation of
zincs type ZHC or ZHS. As an interim measure, the dam- aged metal may be replaced with an aluminum pigmented
epoxy cement, with a positive requirement that the epoxy be replaced by welding at the first opportunity.
2-26. Deck Fittings and Machinery.
a. Usually, vessels constructed of aluminum will be fitted with aluminum mooring and towing fittings. These are
welded directly to an aluminum doubler pad or insert plate. The fittings and weld areas shall be inspected for signs of
incipient cracking or other failures due to overload conditions.
b. Deck equipment and machinery and other miscellaneous gear will normally be attached to the aluminum hull
by bolting. Faying surfaces between these dissimilar metals must be insulated in accordance with the vessel's drawings.
Under no circumstances should red lead, canvas or other wicking type material be used as an insulation gasket. Syn-
thetic rubber is acceptable; however, the material selected should not be subject to cold flow, cracking or creeping.
2-19
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