can be made to give good castings, and which also possesses good strength.

Copper sheathing.—The surface of the vessel is payed over with pitch, and tarred paper is placed on, and the copper sheets are then fixed on with brass nails.

Ships of the largest size have been built on this system, and for vessels on foreign stations likely to remain undocked for long periods, the prevention of fouling obtained is worth the extra expense involved. The following comparisons show the cost in money and measured mile speed in the case of ships of Edgar and Apollo classes. In these classes a direct comparison is possible, as the vessels were similar in all respects except in the matter of sheathing.

For the outer bottom plating of a steel ship we have to rely on anti-fouling compositions to keep the bottom clean. With vessels running on fixed routes at uniform rates of speed, experience should soon determine the composition which gives the best results. For vessels of the Navy, however, such uniform conditions do not obtain, and compositions which are suited to a vessel at anchor for long periods may be of little use to the same vessel when steaming. Trials are continually being made to determine the most suitable compositions to be used, and to investigate the merits of new paints offered for trial.

The usual basis of these anti-fouling compositions has been copper, but because of the galvanic action between copper and iron or steel, it is held that copper is undesirable. The introduction of poisonous matters as copper or arsenic is said to have an effect on the germs of marine growths that are deposited. An anti-fouling paint should have a certain soapiness, so that by wasting away slowly it may get rid of the marine growths, etc., that attach themselves, and by exposing the poisonous matters kill the germs that are deposited. It is clear, therefore, than an iron or steel

ship requires frequent docking in order to renew the anti-fouling paint. On these occasions the bottom should be carefully examined to see if the surface has become corroded.

Prevention of Corrosion Inside.-We have seen above that no part of a ship's structure must be left bare, or else rusting and corrosion will certainly ensue. Examination is continually necessary to ascertain how far the paint is protecting the steel structure, and it is necessary to provide access to all parts for this purpose. For places of which no use is made, access is usually obtained by manholes, Figs. 48 and 50, the latter being the type fitted on bulkheads, etc., and the former to the double-bottom compartments. The means of access to every compartment of a ship is given in the book of watertight compartments supplied, of which a specimen page is given at the end of Chapter IX.

It is laid down that every accessible part of the outer and inner bottom and framing is to be inspected once a quarter by the engineer officer and the carpenter, and any defects discovered are to be made good. In the event of dampness, the steel must be thoroughly dried and all traces of rust removed before applying the paint. Well-slacked lime is to be used in places from which water cannot be removed.

The survey of the hulls of steel vessels is made by the dockyard officers as follows:-Battleships, first and second class cruisers, every four years. Third class cruisers, scouts, and small vessels with plating over 10 lbs. ( in.), every two years. Torpedoboat destroyers, torpedo. boats, and other small vessels with plating 10 lbs. and under, every year.

Pipes at the lower parts of a ship should preferably be of galvanized iron, and not copper or lead. If, however, copper or lead pipes have to be used, it is necessary that they be well painted, covered with canvas, painted to make quite waterproof. In way of metal valves zinc protectors are fitted to assist in preventing corrosion.

The inner bottom plating under engines and boilers is specially liable to corrosion, especially the upper surface, due apparently to the fretting action of the ashes and hot water. These parts should be frequently examined, and where rust is found to be forming, or where the paint is abraded, the surface should be thoroughly scaled, cleaned, and dried, and coated with three coats of red-lead paint.

Cement. The cementing carried out in recent ships is of far less extent than that formerly adopted. The double bottom, which

under ordinary circumstances will not contain water, is not cemented at all except in those spaces used for reserve feed water, where the bottom is coated with hard cement 1 to 2 in. thick. This cement, however, is being dispensed with in the most recent ships. Before and abaft double bottom, just sufficient cement is used so that water will not obtain a lodgment anywhere, but will readily flow to the pump suctions. In parts, as at the extreme ends of the ship, where a considerable amount of cement is necessary, the cement is mixed with coke to keep the weight as small as possible. Cement may even be detrimental, supposing it to get cracked through any cause, as then water will get down to the plating, and corrosion may go on unnoticed.

The insides of fresh-water tanks are coated with "Rosbonite." In living spaces, etc., corrosion and discomfort is caused by the sweating of steel work, owing to the condensation of moisture from the air. In such spaces the under side of decks, bulkheads, etc., are painted with one coat of red-lead and then covered with fine cork and painted white. The cork does not cool so quickly as the steel, and so condensation does not take place so readily. This application is termed cork cementing.

(A very complete discussion of rusting, corrosion, and fouling in given in Professor Lewes's "Service Chemistry." See also a paper by Mr. Holzapfel, I.N.A., 1904.)

CHAPTER XII.

COALING,

THE rapid coaling of war vessels is a matter of considerable importance, and the present chapter is devoted to a brief consideration of the methods adopted for coaling in some recent large ships of the British Navy. Liquid fuel is coming largely into use, and the getting on board and the storage is a matter quite simple in comparison with what is necessary in the case of coal.

The subject of coaling divides naturally into three parts, viz.

1. coaling ship, i.e. getting the coal on board from lighters, etc.; 2. getting the coal down into the several bunkers; and 3. getting coal from the bunkers to stokeholds. The two latter are specially difficult in war-ships, because of the large number of bunkers caused by the extensive system of watertight subdivision (see Figs. 52 and 53), and also by the presence of the armoured decks, which it is undesirable to pierce more than is absolutely necessary.

1. Coaling Ship.-Figs. 112 and 112A show the general

arrangements adopted in a large cruiser. These arrangements would, of course, be supplemented when coaling from a ship in which derricks, transporters, etc., are fitted for dealing with the coal.

BOAT

DERRICK.

TO WINCH

HATCH

There are two steam coal winches, one on each side of the upper deck, each having a central barrel and two side warping barrels. The coal is got on board by a Temperley transporter (two in some ships), which can be suspended either from the derrick on the foremast or from the main derrick on the mainmast. This transporter is 55 ft. long, and is fixed in position by means of guys. It has to be used in a slanting direction, so that the carrier will travel down by gravity when the coal-bags are empty. The transporter consists of an I beam, with a sheave on the upper end plumbing the upper deck; the lower end can be arranged to plumb the hold of the lighter.

WATER LINE.

FIG. 112A.

The beam is provided with stops about 5 ft. apart, any one of which may be used to fix the load when it is desired to raise or lower. The lower end of the beam is fitted with a stop. The carrier itself runs on four rollers on the lower flange of the beam, and is composed of two side plates containing a number of cams. The purchase passes over a sheave on the carrier, and at its lower end has a heavy ball attached. Take the instant when the load is being lifted as Fig. 113. The double cam at the top is caught in the stop and the carrier is fixed. A further lift of the load, however, lifts up the pawl lever and catches the ball in the suspender hook as Fig. 114, and the weight is taken by the carrier. This movement of the levers, however, releases the double cam at the top away from the stop, and the whole carrier is then free to be hauled up the beam by hauling on the purchase. In order to fix the carrier to lower the load, it is hauled just past the desired stop as Figs. 115 and 116. The rope is then slightly slackened, and the toggle catches and turns the cam into the stop as Fig. 117. In this movement of the cam the carrier gets locked, and the ball gets released from the suspender hook and the weight