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 TB 740-97-4
(c) Machine connections. Connections of ducts to dehumidification machine will be made with unions or slip joints
connections to permit easy removal of machine for servicing.
(d) Ductwork supports. Flexible ductwork used within the D/H zones will be supported by wire, rope or other suitable
means. Ductwork on deck will be supported on metal or wood stanchions. The duct will be secured to the stanchions by galvanized
steel strapping.
(e) Humidistat. The humidistat will be set to maintain a 40-percent relative humidity, plus or minus 5 percent, within
the dehumidified zones. The humidistat will be located about 5 feet above the deck near the return air supply to the dehumidification
machine.
(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.
(g) Surveillance.
1. Drying Period. During the initial drydown period, the dehumidifier should be adjusted to the manufacturer's
specifications for maximum efficiency in that period. The distribution of D/H air in the D/H supply system is adjusted in this period.
For the first estimate, the required percentage of air in various D/H outlets are set by feeling the flow of the air by hand. A good
sense of judgment is needed In this requirement. However, sling psychrometer readings will be taken at sensing stations in the vital
air return paths. The D/H outlets are adjusted to increase or decrease air flow with the recorded relative humidity. If the readings in
the zone should differ less than 40, plus or minus 5 percent, or read lower than the R/H prescribed, the air flow in that area outlet
should be decreased. If the reading is higher than that prescribed, the air flow to that area should be increased.
2. Normal D/H period. After the initial drydown period has been attained (approximately 3 or 4 weeks*), the
residual moisture in the air and in materials aboard the vessel are in balancing state. The moisture load is reduced as indicated by
the lapsed running time indicators on the humidifier. Quarterly inspections will be made within the vessel from four predetermined
stations; fore, aft, engineroom, and above deck quarters and cabins. Relative humidity readings will be recorded at each station. If
variance from the prescribed R/H 40, plus or minus 5 percent, is noted between stations, air flow adjustments, as previously
described, will be made to achieve proper air flow balance.
d. Preparation for dynamic dehumidification for Method B.
(1) Dehumidified Area. The entire interior of the vessel, except the liquid cargo tanks and dry cargo hold, will be prepared
for dynamic dehumidification. The vessel will be divided into four zones and each zone dehumidified individually.
(a) Zone 1. The anchor windlass on main deck of forecastle.
(c) Zone 3. Pump room on main deck of vessel.
(d) Zone 4. Engineroom, crew's quarters, pilot house, radio and chart room, sanitary facilities, passageways, and all
other areas to which there is access from one or more of the above mentioned areas will be included In zone 4.
(2) Provisions for air circulation. Within each zone being dehumidified, all interior doors, hatch and scuttle covers, manhole
covers, and handhole covers will be secured in the open position, or removed and secured as applicable. Galley range and
refrigerator doors will be secured In open position. Enclosed switchboards, distribution panels, and other electrical assemblies will be
secured open and exposed to the air. All dampers in ventilation system will be turned to open position. All tanks located in areas
being dehumidified will be opened for circulation of air by removal of covers and drain plugs. Drain cocks, where present, will be
opened. Covers and plugs will be tagged and secured adjacent to their places of use. The escape hatch from the engineroom and
passageways to the main deck will be left open. all doors to the officer's mess, crew's mess, meat and vegetable lockers, mate's and
crew's lavatory, and seaman's and gunner's quarters will be secured in an open position.
*This is the minimum period of time. In some instances, the drydown period could last from two to three months, based on the amount of moisture in the
air and the materials aboard the vessel.
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