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 TB 740-97-4
They can be obtained through normal publications requisitioning procedures.
d. Preparation for dynamic dehumidification for Method B.
(1) Dehumidified area. The entire interior of the tug, including the anchor windlass and towing motor room, will be prepared
for dynamic dehumidification. The vessel will be divided into zones, and each zone dehumidified individually.
(2) Establishment of zones. The number of zones and the arrangement of zones will be based on the following criteria:
(a) Availability of ingress thru top side openings into the cabin and quarters area and main deck openings into the
interior of vessel without cutting openings into bulkhead or main deck.
(b) Arrangement of zones that will provide maximum air circulation with the minimum of ductwork, which will deliver
dry air to essential compartments of vessel within the D/H zone.
(c) Air path to duct should be direct and short. This reduces ductwork and friction loss and saves time, labor, and
material at time of deprocessing and activation.
(3) Provisions for air circulation. Within the boundary of each zone being dehumidified, all interior doors, hatch and scuttle
covers, manhole covers, and handhole covers will be secured in the open position. Galley ranges, refrigerator doors, cabinet doors,
and similar items will be left open. Enclosed switchboard's distribution panels and other electrical assemblies will be secured in open
position and exposed to dry air. All dampers in the ventilation system will be turned to the open position. All tanks located in zones
being dehumidified will be opened for circulation of air by removal of covers and drain plugs. Drain cocks, where present, will be
opened.
(4) Sealing for dehumidification . Methods and materials used in sealing for dehumidification will be in accordance with this
bulletin. Detailed sealing requirements will be the same as that specified for Method A-, with the following exceptions:
(a) All doors, vents, windows and portlights, except those used for introduction of dry-air and moist-air return ducts,
humidistat cables and sensing elements will be sealed with strippable boating and bituminous coating.
(b) The access door, designated for inspection purposes under Method A, will be sealed as specified for other exterior
doors. Sensing elements will be installed in the dehumidified area(s) for inspection purposes.
(5) Dynamic dehumidification. installation. A minimum of eight package dehumidifiers, single desiccant bed, absorbent
type, 10,000 cubic foot capacity, 110-volt, alternating-current will be installed. The machine, with covers and stands fabricated as
shown in this bulletin, will be located on the outside of the tug, adjacent to the zone which they service. The machines will be
positioned to require the minimum of ductwork.
(6) Duct Installation. Four-inch-diameter, No 26 gauge, galvanized tubing, with necessary ells, tees, reducing fittings and
connections, will be installed as required. Ductwork, when necessary, will be supported on 2-x4-inch wood or metal stanchions. The
ductwork will be secured to the stanchions with galvanized strapping. Flexible ductwork used within the dehumidified zones will be
supported by wire, rope, or other suitable means.
(7) Humidistats. The operation of each dehumidifier will be controlled by a humidistat set to maintain a relative humidity of
40 percent, plus or minus 5 percent, within the dehumidified zone. Humidistats will be installed for each machine. Humidistats will
be installed within the dehumidified area, approximately three feet above the deck. They will be located well away from the incoming
dry air. Locate humidistats near the return air supply to the dehumidifier. Wiring will be in accordance with wiring diagrams
furnished with the instrument.
(8) 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 dehumidified zones. Sensing elements will be located near the points from which the moist air is withdrawn. In no case
will they be in the path of incoming air.
(9) Machine connections. In zones where two or more dehumidification machines are used, they specified. Where multiple
machine use is required, and space is limited, they may be stacked, as shown in figure 71, and connected with the necessary elbows
and tees as required. Connection of the ducts to the dehumidification machine will be made with union or slip joint connections to
permit easy removal of machines for servicing.
(10)
Air tightness test. The air test outlined in chapter 5 of this bulletin will be performed to assure economical
operation of machines and that vessel is reasonably water and air tight.
U-4
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