in large ships 6 inches in diameter in wake of the double bottom, and tapers slightly from this part to the ends of the vessel. This pipe has branches, each with a separate stop valve, leading into each double bottom and watertight flat compartment, and also to pockets in the bilges above the double bottoms in the machinery spaces, for the purpose of pumping them out. Sluice-valves are fitted on the watertight flats beyond the double bottom proper for draining water above the flats to the suction pipes. The ship's large hand pumps are also connected to this suction pipe, and are arranged so that either pump can draw from any compartment.

The main suction pipe can also be utilised for filling the double bottom compartments when required, by connecting the valve-box with the sea suction, but to guard against the accidental introduction of salt water into the tanks appropriated for storage of reserve feed-water, portable connections are used between these tanks and the valve-boxes.

Main drain pipe and general drainage arrangements. To further facilitate the pumping out of the hold of a ship divided into several compartments, large galvanised steel drain pipes are fitted. Fig. 3426 shows the arrangement of drain pipes, main suction pipe, and general drainage arrangements for the machinery compartments and adjacent spaces in a modern battleship. In this case the main drain pipes D D D are 15 inches diameter throughout the length of the machinery spaces, and are continued beyond these spaces, as far as the double bottom and watertight flats extend, but are gradually reduced in diameter, and the extreme ends are carried up so as to drain water from the forward and after parts of the protective deck.

The drains, E E E, from the wing spaces and bunkers adjacent to the machinery spaces lead directly into the bilges of these compartments, and the main drain receives the water by means of sluice valves F FF. Outside the machinery spaces, where not convenient to flood the bilges, the drains lead direct to the main drain pipes.

Sluice-valves are fitted to the main drain pipes at each watertight bulkhead, and where the main drain is fitted in duplicate, or where it has branch connections leading into another watertight compartment, non-return valves, G GG, are fitted to provide against the drainage from one compartment flowing into another, in case the sluice-valves are unintentionally open. The main drain pipes terminate in large sluice-valves at the forward and after bulkheads of the engine rooms; these valves regulate the flow of water to the engine room compartments, the two engine room compartments being connected by a large sluice-valve at the middle line bulkhead. The main drain pipe is intended to deal with considerable quantities of water, which flow into the engine-room bilges, and if so large in amount that the ordinary steam bilge pumps are unable to deal with it, it can be pumped out by the circulating pump through its bilge suction, waterways being provided in the engine bearers for free access to these suctions.

For convenience the main drain pipe was, in the older ships, carried through the double bottom, but it was not in connection with it, and was fitted only for the drainage of compartments in the hold of the ship. In modern ships the drain pipes are not run through the double bottom, various accidents to the outer skin of the vessel and consequent fracture of the drain pipe having shown the danger of such a lead.

They are now always placed above the inner bottom. Arrangements are made for flushing the main drain pipes near the ends direct from the sea, and chains are sometimes fitted for clearing them when choked. Drainage of small amount can be dealt with as follows:

(1) In double bottoms and under watertight flats beyond the double bottoms:-By ship's hand pumps direct or by the main suction.

(2) Machinery spaces over double bottoms:-By the ship's hand pumps direct; through the main suction pipe by the ship's hand pumps or steam bilge pumps; or by the ordinary steam pump bilge suction. Other spaces over double bottoms and over the watertight flats at ends of double bottoms:-By draining into the main drain, or to the compartments under the watertight flats by means of sluice-valves. (3) From bunker compartments at sides of engine and boiler rooms:-By sluice-valves to engine and boiler rooms, the water being then dealt with as at (2).

(4) From wing compartments adjacent to the machinery spaces :By running to bilges of machinery compartment by pipes with sluicevalves at the bulkhead. From wing compartments beyond the machinery spaces and at the ends above the protective deck :-By running direct to the main drain and thus to the engine room bilges.

Drain cisterns. In the older warships the main drain pipes are connected to large drain cisterns, and the small pump suctions are led to these, arrangements being made so that the cisterns overflow into the engine room bilges when the circulating pumps are required.

Flooding cocks.-To the most dangerous parts of the ship, such as the magazines, shell- and spirit-rooms, &c., flooding pipes are led, connected with the sea by Kingston or other valves and sea-cocks in the ordinary manner, so that in case of fire the compartment may be flooded with water from the sea. Special precautions have to be taken to prevent these cocks being tampered with; and, as a rule, there is between the ordinary sea-cock and the compartment an additiona) cock or valve, which is locked, and can only be opened by the officer entrusted with the key.

Arrangements are also made in warships so that when they are in dry dock these parts may then be flooded from the shore water pipes, by means of branches on the flooding system, fitted for this purpose.

Fire-main.-All the fire and bilge and latrine steam pumps, except any worked off the main engines, also the ship's hand pumps, are fitted with sea suctions, and are arranged to deliver the water into a pipe called the fire-main, which is carried fore-and-aft in the ship, with branches leading to different parts as required. At various points in the fire-main, delivery valves with suitable screwed nozzles are fitted, to which hoses may be connected to direct water on any required spot. Non-return valves should be fitted at the junctions of delivery pipes from pumping engines with the fire-main, and the pumps should have sufficient power to produce the necessary pressure in the main.

For dealing with small fires, small bib-valves are fitted to enable water to be quickly drawn off in buckets, to avoid the delay which might be caused by rigging a hose.

Besides the branches on the fire-main for the sanitary arrange ments, others are fitted for washing-out boilers and guns, for running through hawse-pipes when working cables, and for capstan water service.

CHAPTER XXVIII.

AUXILIARY MACHINERY AND FITTINGS.

IN modern steamships, especially in those of the Royal Navy, the auxiliary machinery and fittings are of great importance. In H.M.S. 'Powerful,' for example, there are ninety-nine different auxiliary steamengines for various purposes in addition to the main engines of the ship. In the battleships of the Majestic' class there are 72 auxiliary steam-engines and 32 hydraulic turning engines, lifts, bollards, &c. Those vessels are really huge floating war machines, where all the principal operations for working, steering, and fighting are performed by steam or hydraulic power with little manual labour, so that the vessel's efficiency will depend largely on the condition of the machinery department.

The enumeration of the various kinds of work on board ships that are now done by steam power would be sufficient to show the importance of this part of the duty of the engineer. In addition to the

main propelling engines, steam power is used for ventilating the ship and supplying air to the boilers; weighing the anchor; steering; pumping; working turrets, and loading, training, and working the guns; compressing air for charging and launching torpedoes; putting torpedo and other boats into and lifting them out of the water; distilling fresh water; producing electricity for lighting the vessel and for search lights; for refrigerating purposes; for actuating the machines supplied in the workshop; lifting coal into the vessel, &c.

The development of electrical science has now rendered possible the transmission in a very efficient and economical manner of the power generated in the dynamo to electric motors for various purposes in different parts of the ship, and this is taken advantage of to work ventilating fans, &c., in confined spaces, where the heat of steam pipes would be objectionable. It also reduces the complication, as the necessary wire leads can be run along in places where steam and exhaust pipes would be most difficult. Such motors will probably be much more extensively used on board ship in the future than they are at present.

Steering engine. Figs. 343 and 344 show an arrangement of steam steering engine which has been largely fitted and found efficient. The shaft A, leading to the tiller, is driven by the engine through a system of toothed gearing, which reduces the speed of revolution to a sufficient extent to obtain the necessary turning moment to work the rudder readily, when the ship is moving at full speed.

The speciality in this engine is the fitting by which it is stopped when the helm is moved to the required angle, the rudder being held