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 TB 740-97-4
3. Ducts to zone 3. To permit introduction of air ducts to the interior of zone 3, the hatch on the starboard side of
the pump room will be removed and stowed in the pump room. The hatch opening will be covered with a blank constructed of No. 18
gauge galvanized sheet metal with flanged holes for attaching the air ducts. The blanks will be secured to the bulkhead with clips
riveted to the blank, by tack welding at the corners, or by other suitable means. The dry-air lines will be introduced through the top
opening in the blank, and the moist-air return line will be attached to the bottom opening in the blank.
4. Ducts to Zone 4. To permit introduction of air ducts to the interior of zone 4, the skylights will be removed and
stored in the pilothouse. The skylight opening will be covered with a blank constructed of No. 18 gauge galvanized sheet metal with
four flanged openings (2 on starboard side and 2 on port side) for attaching the air ducts. The blanks will be secured to the bulkhead
with clips riveted to the blank, by tack welding at corners, or by other suitable means. Attach dry-air and moist-air return lines to the
openings in the blank. Attach flexible tubing to the two dry-air lines, and run one line forward of engine room and one line aft of
engine room.
(c) Humidistats. The operation of each dehumidification machine will be controlled by a humidistat set to maintain a
40-percent relative humidity, plus or minus 5 percent, within the dehumidified zones. Humidistats will be installed for each machine.
Humidistats will be installed within the dehumidified area, approximately three feet above the compartment deck. They will be located
well away from the incoming dry air. Locate humidistats near the return air supply to the dehumidification machine. Wiring will be
attached in accordance with wiring diagram furnished with the instruments.
(d) Sensing elements. Humidity sensing elements of an approved type will be installed in the dehumidified area for
inspection purposes. The number of elements used will be limited to the number required for a reasonable check on vapor diffusion
within the zones. Sensing elements will be located near the points from which moist air is withdrawn. In no case will they be in the
path of incoming air.
(e) Machine connections. In zones where two or more machines are used, they may be connected in multiples of two
or more. This can be accomplished by stacking the machines and connecting them together by use of piping, elbows, and tees as
required (see fig. 71). Connection of the ducts to the dehumidification machines will be made with unions or slip joint connections to
permit easy removal of machines for servicing.
(f) Air tightness test. The air test outlined in this bulletin will be performed to assure economical operation of the D/H
machine. Air leaks can be detected by its noise or by means of smoke bomb, soap and water, or fine powder such as flour.
3. Liquid Cargo Tanks. Liquid cargo tanks will be coated with preservative oil conforming to MILL-21260, type I or II, grade 30.
4. Venting of Cargo Tanks. Manhole access covers of liquid cargo tanks will be removed and stowed in the dry cargo hold. Vents
fabricated from No. 18 sheet metal will be placed over the manhole access holes. The vents shall be fabricated in two parts. One
part will be a metal coaming with at least four openings of equal distance, fitted with wire mesh to permit breathing. The top of the
coaming will be fitted with a cap. The cap will be a cone type or have a taper to allow water runoff. The cap will be fabricated to
permit ease of removal for inspection of cargo tanks without disturbing the coaming. The cap may be a snug fitting slip type, or it
may be fastened to the coaming with sheet metal screws. The aperture between the coaming and the manhole cover opening will be
filled with bituminous coating and strippable compound to effect a watertight seal.
5. Venting of Dry Cargo Hold. Dry cargo hold will be vented to prevent condensation within the hold. Ventilator cowls will be
installed over dry cargo hold hatches. The ventilators will be installed in a manner that will prevent the entry of water.
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