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 (d) Stud and doubler plate to be continuous filet welded.
(e) Drill and countersink, 1/4 inch deep, the doubler plates to allow for flush welding of the studs.
(7) The following is an accepted rule to follow in determining the quantity of zinc required under
velocity conditions of active service. Two zincs of type ZHC protect 400 square feet (37.25 square
meters) of freshly painted steel, 200 square feet (18.6 square meters) of steel coated with paint one year
old, or 100 square feet (9.3 square meters) of bare steel. This rule also applies to aluminum hulls. No less
than two zinc anodes equivalent to the ZHC type shall be provided for the protection of steel hull boats.
(a) Midships Area. Two-thirds of the calculated quantity or zinc anodes that's needed to give
complete protection shall be equally divided into two rows on both port and starboard sides of the hull.
Half the anodes for each side shall be installed butted end-to-end, long axis fore and aft on the forward
end of each bilge keel and half on the aft end of each bilge keel. As an alternate method, the anodes may
be installed port and starboard just beneath the turn of the bilge, butted end-to-end and long axis fore and
aft. Half the anodes for each side shall be installed forward of midships and the other, aft of midships.
Where practical the rows shall be positioned to avoid passing over fuel tanks even though the rows
become discontinuous. This precaution is taken to avoid "gas-freeing" the fuel tanks, in case welding is
necessary to attach studs or straps for mounting the anodes.
(b) Stern Area The entire stern system, or 1/3 the anodes necessary for the complete hull system,
shall be butted end-to-end with the axis fore and aft. They shall be located along the centerline keel or
just beneath the turn of the bilge and divided equally between the port and starboard sides of the hull. If a
large number of zincs are required for stern protection, it may be practical to increase the number of rows.
However, in no case should the spacing between rows be less than four feet. Begin all rows at least five
feet forward of the propeller plate and extend forward. Zincs shall be positioned so that the anodes are
always 100% immersed under light load.
(c) Sea Chests. Zinc anode protectors conforming to shape and size as necessary will be attached
to the interior of sea chests. No less than one 6-inch by 6-inch anode shall be provided for each sea
chest. If nonferrous sea valves are fitted in conjunction with steel sea chests, a medium steel protection
sleeve, to serve as a waster piece, should be fitted inside the sea chest at the junction of the sea chest
and the valve. The sleeve should project down into the sea chest and be long enough so that it can be
removed for replacement through the valve opening once the valve has been removed. As an alternative,
the sleeve may be fitted in sections, which can be removed from the exterior of the ship through the sea
chest.
(d) Internal Bilge Areas. Each compartment where water is held shall be considered for cathodic
protection. Zinc anodes should be installed in all bilge spaces, which are subjected to water more than 50
percent of the time, and in those areas, which are susceptible to excess corrosion. One zinc anode (ZHC
type) should be installed for every 250 square feet of steel surface. Bolt-on anodes should be used for
this installation so that depleted anodes can readily be replaced by crewmembers. Anodes should
normally be located on the garboard strake close to the centerline keel. Care should be taken to mask
anodes when painting bilge spaces so as not to coat the zincs. Optimum functioning of the anodes
depends upon the zinc being completely immersed in water and the surface being free of paint and
excessive grease and oil.
(e) Salt Water Pumps. Zinc anodes should be located as close to the base of the pump as possible to
protect against excessive corrosion due to salt-water leakage.
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