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 TB 740-97-4
CHAPTER 7
COCOONING INSTRUCTIONS
142. General. The basic requirements for the cocooning of vessels involves the application of three coats of sprayable plastic
coating, one coat of bituminous coating, and one coat of aluminum coating, plus the installation of a dynamic dehumidification
system. The cocoon is bonded to the hull sides and supported by wood framing. The wood framing extends from the main deck
level up to and including the superstructure, and is so constructed as to allow access to the interior of the cocoon for inspection
purposes. Vessels painted with vinyl paints on the hull sides present a perfect bonding surface for the cocoon skin. The hull sides of
vessels coated with conventional paint require a permanent bonding area. This bonding area is obtained by sandblasting an 8 inch
band to "White Metal" and applying an inorganic zinc coating conforming to MIL-P23236.
143. Preparation of the Package. Cushioning material will be applied to all sharp edges and projections of the item and wood
framing. The item and wood framing will be covered with a snug-fitting shroud of osnaburg cloth conforming to FED-CCC-C-429.
The shroud will be fastened to the bonding area with adhesive conforming to FED-MMM-A-189. The fabric will be the base for the
sprayable plastic coating.
144. Sprayable Plastic Coating. The fabric will be sprayed with three coats of sprayable plastic conforming to type I, class 2 of
MIL-C-3254. Each coat will be dyed a different color as visual aid to obtain adequate coverage. The first coat is dyed yellow, the
second red and the third blue. The plastic will be dyed by adding 2 ounces to each 5 gallons of plastic solution, using butter yellow
aniline dye (FSN 6820-285-8458), red aniline dye (FSN 6820-286-5484), and blue aniline dye (FSN 6820-255-8201) respectively for
the first, second and third coats. The recommended pressures are 20 to 30 pounds on the fluid tank and 70 pounds minimum
atomizing pressure at the gun. The fluid pressure will be increased when more than one gun is used. The gun should be held 8
inches from, and perpendicular to. the surface being coated. The surface of the coating should appear wet and glossy. The
thickness of each coat will be approximately .015 inch. When the density of color of the sprayed coat matches that of the material in
the supply tank, it would indicate that the thickness is correct.
145. Bituminous Coating. The coating material will conform to type II of MIL-C-3254. The type I plastic coating must be allowed to
dry thoroughly 24 to 48 hours before the bituminous coating is applied. The coating should be approximately .125 inch thick.
Recommended air pressure at the gun is 60 to 90 pounds.
146. Aluminum Coating. The bituminous coating must be dry (usually 72 hours are needed) before the aluminum coating is
applied. The aluminum coating solution will conform to type III of MILC-3254. The coating should be .002 to .003 inch thick.
Recommended gun pressure is 60 pounds.
147. Fume Exhaust. An exhaust blower, powered by an air motor or by an explosion-proof motor, will be used to exhaust
hazardous fumes generated by spraying of the barrier materials. For convenience the exhaust may be attached to the outer terminus
of one of the air circulation ducts. The exhaust should be operated not only during the spraying operations but also intermittently until
the materials are dry. The fumes must be thoroughly exhausted from the completed package before the dehumidifier is placed in
operation.
148. Installation of Ductwork. The dry air and moist air return ducts will be of 4-inch diameter downspout or flexible tubing. A
suitable or wooden support will be used for securing the ducts at the points of intersection with the barrier. The dry air and moist
return lines will terminate as near opposite ends of the package as practicable. The dry air lines will be carried upward 6 to 8 feet
above the deck. The moist air will be drawn from the bottom of the package, preferably inside engine compartment near the floor
plates
149. Humidistat. A humidistat will be set to maintain a 40 percent relative humidity plus or minus 5 percent within the dehumidified
zone. The humidistat will be installed near the center of the package. Wiring will be attached in accordance with wiring diagram
furnished with the instrument.
150. Dehumidification Machine. A package
7-1
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