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because of the necessity of providing complete watertight subdivision, and this renders the operation of getting coal into the bunkers, and from the bunkers to the stokeholds, correspondingly more difficult. In large merchant ships it is usual to have large cross bunkers, but this is not usually desirable in war-ships, because of the extra length thus entailed, and because a large proportion of the coal can be more economically arranged for
above the armour deck. There is also the fact that the coal thus stowed affords a valuable element of protection to the ship, this being of special importance in the case of deck-protected cruisers (Figs. 21 and 22) (see also Chapter XVII., in which the influence of coal on stability is dealt with). The lower bunkers are restricted in volume by the shape of the ship, and it is found that a large proportion of the total coal capacity is obtained above the pro
tective deck. The wings in a battle-ship (Fig. 12) are arranged for coal stowage when necessary, but these spaces are very much broken up by the deep framing, etc., there, and this renders the operation of getting the coal in and out of these spaces very difficult.
The ship selected to illustrate this part of the subject is the cruiser whose system of watertight subdivision is given in Figs. 52 and 53. There are in this ship two series of upper bunkers, separated by a fore-and-aft watertight bulkhead, and one series of lower bunkers. The upper bunkers extend over the length of engine- and boiler-rooms; those over the engine-room have no fore-and-aft bulkhead, and the coal there may be looked upon as a reserve. The lower bunkers only extend over the length of boiler-rooms.
To coal the upper bunkers (Fig. 120) 20-in. scuttles are provided, as shown, in the main deck, one to each outer bunker and two to each inner bunker. Directly above these, on the upper deck, 18-in. scuttles are fitted. These pairs of scuttles are connected by coaling shoots, usually portable, in halves as shown; in some cases fixed shoots are provided. There is thus direct access from the upper deck to each of these upper bunkers. Escape scuttles are placed to each bunker in the main deck, close to a bulkhead underneath, with chains and footholds on the bulkhead. To coal the lower bunkers there is a 33-in. coaling scuttle, as Fig. 139, in the middle deck. Above this, to the main deck, a rectangular trunk is fitted. Above this, in the main deck, a 20-in. scuttle is fitted, with an 18-in. scuttle, immediately over, in the upper deck. These latter are connected by a portable shoot in the ordinary way. There is thus direct access for coal from the upper deck to the lower bunkers. Escape doors are provided in the side of the ammunition passage, with ladders and hand chains as necessary for getting out
3. Getting Coal from the Bunkers to the Stokeholds.— Doors are provided from each stokehold into the lower bunkers. It is necessary, therefore, to get the coal from the upper to the lower bunkers when the latter are getting empty. The rectangular trunks are provided with doors on each side as shown. The outer side, which is a watertight bulkhead, has a sliding watertight door. The other doors are not watertight They are made in two pieces, so that the lower half hinges up and is secured to the latter, and then both are hinged up clear of the opening and made fast. With these doors all open, and the 33-in. scuttle open, coal can be trimmed from either of the upper bunkers to the lower bunkers. An additional scuttle is provided at the side of each upper outer bunker, and a shoot is taken down as shown, so that coal may be passed into the lower bunkers through the watertight door on the wing bulkhead.
A set of rails is fitted throughout the upper bunkers in order to
enable a coal-bucket to be run along to bring the coal from any upper bunker to any desired lower bunker. The coal-bucket is shown in Fig. 120, and has one side hinged and a sloping bottom. The bucket would be brought up to the trunk and the catch released, and the contents dropped into the lower bunkers. The rail has to be made portable in way of the watertight bulkheads to allow the door to close. Most of these are horizontal sliding doors worked from the main deck, but in the after bunkers they are ordinary hinged doors.
In recent cruisers the wing bulkhead and the divisional bulkhead in the upper bunkers has been dispensed with (see Fig. 23). This considerably increases the coal capacity, and makes the operations of coaling very much simpler.
Care is taken in all coal-bunkers to screen the watertight doors from the pressure of the coal, so that the doors may close and open even if the bunker is full of coal. A specimen screen is shown in Fig. 120. Two side plates support a sloping top plate, and these keep the coal from the door. When the door is free from coal the side plates can be hinged back, and the top plate hinged up out of the way. Screens are also provided, as shown, to the doors in the upper bunkers.
We have seen in Chapter X. the necessity for the efficient ventilation of coal-bunkers and the provision made for the same. It is also necessary to provide means for ascertaining what the temperature is in the body of the coal. For this purpose temperature tubes are placed as shown. For the lower bunkers the temperature tubes are approached from the ammunition passage, for the upper bunkers from deck plates on the main deck. The temperature has to be noted at frequent intervals.
ARMOUR AND DECK PROTECTION.
The three methods of attack which a war-ship may have to withstand are ramming, torpedo- or mine-attack, and gun-fire. The two former would cause damage principally at and below the waterline, and the only protection that can be afforded is the extensive watertight subdivision. For protection against gun-fire, armour plates are provided over as large a portion of the ship as possible. These armour plates are, in most cases, backed up by coal and thick decks. The parts not protected by armour are minutely subdivided in the neighbourhood of the waterline in order to localize damage as far as possible. Thick decks, both above and below water, are also largely employed for purposes of protection.
A large proportion of the weight set aside for protection in modern ships is necessary for the protection of the armament. Thus in a recent battle-ship the total weight provided for protection was 4335 tons, and this is divided as follows:—
Armour and deck protection to hull for the preservation of buoyancy and stability, 2875 tons.
Protection to armament, as barbettes and casemates (not including gun shields), 1460 tons.
This shows that, in this case, about one-third the available weight was devoted to the protection of the armament and twothirds to the ship.
It is proposed to trace briefly the history of the subject from the Warrior until the present time, taking typical ships. The dates given refer to the year in which the ships were laid down.
"Warrior."—The first large vessel provided with armour protection in this country was the Warrior (1859). This ship was built of iron, and was 380 ft: long, and 9200 tons displacement. The armour was 4£ in. thick, and extended, as shown in Fig 121, for a length of 218 ft. and a depth of 22 ft. This 4£-in.