NANCE : Naval), the steering gear, the watertight hatches and doors, the arrangements for pumping, flooding, draining and fresh and salt water supply, the anchor and cable arrangements, the ventilation and many others. It is impossible in the space available to give even a brief description of these fittings or of the installa tions of which they form part, but the principles underlying the ventilation system of a modern warship will be outlined. In the living spaces of the ship, and in the ordinary storerooms, maga zines, etc., it is of the greatest importance that a definite supply of fresh air should be available.
On the other hand, in compartments such as washplaces, latrines, stores where food is kept, and auxiliary machinery com partments—in short in any spaces where foul or overheated air is generated—the first consideration is to remove this air directly overboard and not allow it to penetrate into other parts of the ship. This is effected by fans which exhaust from the spaces in question and deliver the exhausted air into the open. The air required to replace that exhausted is allowed to enter as it will through hatches or doors ; although not usually fresh it is suffi ciently pure for supply to the spaces for which this "exhaust" system of ventilation is adopted.
In the main engine rooms a combination of both systems is employed ; the heated air is removed by large exhaust fans and the fresh air supplied by smaller fans and also allowed to enter naturally through hatches. In the boiler rooms the supply of fresh air to the furnaces ventilates also the compartments them selves. Tn order to obviate the passage of air trunking as far as
possible through watertight bulkheads a large number of small fans are required; in a modern cruiser about 7o fans are fitted for the ventilation of the ship (i.e., in addition to those for the main machinery spaces), and they are capable in the aggregate of supplying and about i oo,000 cubic feet of air per minute.
As regards the arrangements in the spaces themselves, experi ence has shown that the most successful method is to fit both supply and exhaust high up in the compartments. The fresh air, owing to its greater density, sinks soon after entry, flows over the floor of the space and finally drives out the lighter foul air which has risen. A vigorous movement of air is required under tropical conditions, whereas in cold climates the contrary is the case. This difficulty is overcome by controlling the speed of the fans, so as to vary the quantity of air they supply, and by providing means for altering the direction and amount of the supply at any point. Steam heaters are also fitted near some of the fans, so that, when necessary, the air supplied may be warmed to a comfortable tem perature before it is distributed in the ship. Natural ventilation by cowls, windsails, etc., although used extensively in mercantile vessels is only used in warships for small spaces situated near the open and when required under tropical conditions as an auxiliary to the ordinary ventilation. (W. J. B.)