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 TB 740-97-4
The covers will be form fitted over the exterior of hatch covering to permit sealing around the edges. Provisions will be made in the
sheet metal covers for entrance of dehumidification air ducts, cables for humidistats, and sensing elements as required.
(d) Forward and after rake compartments. The covers on the gooseneck vents for the forward and after rake
compartments will be secured in an open position. The exterior terminus of the gooseneck vents will be fitted with standard
galvanized metal insect screens.
(3) Sealing for dehumidification . Methods and materials used in sealing for dehumidification will be in accordance with
this bulletin. Detailed sealing requirements are outlined below:
(a) Exhaust system. Openings in the muffler and the exhaust piping above the machinery house roof will be
closed with blanks, plugs or pressure-sensitive tape and then sealed with strippable coating and bituminous coating.
(b) Louvered door. The door will be secured in closed position and sealed with strippable coating and bituminous
coating. The louvers will be blanked or masked with pressure sensitive tape and sealed with strippable coating and bituminous
coating.
(c) Engine room vents. The engine room vents located on the roof of the machinery house will be closed with
blanks, caps, plugs or pressure-sensitive tape and sealed with strippable coating and bituminous coating.
(d) Cargo tank sheet metal manhole covers. All joints and seams in the covers and apertures between the
coaming and the deck will be sealed with strippable coating and bituminous coating.
(e) After rake and bilge vent. The vent duct from the rake bilge will be disconnected below the machinery house
deck. The opening leading to the engine room will be closed with plugs, caps, blanks, or pressure-sensitive tape and sealed with
strippable coating and bituminous coating.
(f) Dehumidification piping system . The connecting points of all air ducts to areas being dehumidified will be
sealed with strippable coating and bituminous coating. The sealing will be carried over and around flanges, adapters, and other
devices used to attach or introduce the ducts. All joints and seams in the ducts will be similarly sealed.
(4) Installation of dehumidification systems . Three dynamic dehumidification systems (No. 1, 2, and 3) will be installed for
the six cargo tanks. One dynamic dehumidification system (No. 4) will be installed for the engine room.
(a) Dehumidification systems No. 1, 2, and 3. Install three package dehumidifiers, single desiccant bed, absorbent
type, 10,000 cubic foot capacity, 110-volt, alternating current, as shown on figure 25. The machines will be mounted on stands and
protected with covers fabricated in accordance with figure 28. One machine will dehumidify two cargo tanks. The machines will be
installed between the port and starboard manholes and connected to all manholes in accordance with figure 25. Dehumidified air will
be circulated through all manholes by means of 4 inch galvanized metal duct. Connect two lengths of 4 inch flexible hose,
conforming to MIL Spec H-8796, inside each tank to carry air to the lower extremities of the tanks. Install three hair type humidistats,
one in each starboard tank. Each humidistat will be set to maintain a 40 percent relative humidity, plus or minus 5 percent, within
each dehumidified zone accordance with figure 25. Secure the humidistats approximately three feet above the bottom of the tanks.
Connect the humidistats to the dehumidification machines with lengths of No. 18, two-conductor, rubber covered cable with suitable
terminal connectors. Install one sensing element with six foot cable in the metal blank over each manhole in accordance with figure
25. Ductwork run on deck will be supported on wood or metal stanchions. The ducts will be fastened to the stanchions by galvanized
strapping secured to the stanchions.
(b) Dehumidification system No. 4 . A package dehumidifier, similar to and similarly mounted as specified for
systems 1, 2, and 3, will be installed as shown on figure 26 or 27. One machine will be used to dehumidify the engine rooms of from
two to four barges. Four inch diameter, No. 26 gauge, galvanized sheet metal ducts, with necessary ells, reducing fittings, and
connections, will be installed as shown on figure 26 or 27. Suitable penetrations large enough to permit the introduction of air ducts
and the mounting of a sensing element in one blank will be provided in the port and starboard bulkheads of the machinery house of
each barge. The air from the dehumidification machine will enter one side of the machinery house bulkhead and will be removed
from the opposite side. The connecting ducts between the barges will be flexible hose conforming to MIL Spec H-8796. The flexible
hose will be at least four feet longer than the distance between terminal connections.
H-2
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