sheathed on this system, and when she was taken in hand in 1891 for refit and repair, the outer thickness of planking was removed, the inner thickness refastened with naval brass bolts, and the outer thickness refastened.

The system adopted since 1887, for sheathed vessels in the Royal Navy, is by a single thickness of teak.1 The principal features of this system are as follows:

1. The adoption of such a thickness of wood sheathing as will admit of thorough caulking. The mean finished thickness of teak accepted is 4 in. for large ships, and 33 in. for the smaller classes.

2. The use of naval brass bolts and nuts with their points screwed through the bottom plating, and with plate washers underneath the nuts.

3 The thorough water-testing of the skin plating before the planking is worked.

4. The most careful fitting, fairing, and fastening of the planks; the coating of all faying surfaces with suitable compositions before the planks are fitted in place, and the subsequent injection of composition in order to fill any spaces left between the planking and the plating.

5. The use of hempen grummets steeped in red-lead, under the bolt heads and under the plate washers to secure watertightness in the bolt holes. The use of a plug of cement over the bolt head to prevent the sheathing nails coming into contact with the bolts and destroying the insulation.

Fig. 111 shows the method of fastening above described.

For any vessel sheathed with copper it is impossible to use iron or steel for stem, sternpost, etc., in consequence of the galvanic action referred to above. For these vessels these portions are made of the copper alloy phosphor bronze, a material which 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 1 Sec paper by Sir W. H. White (I.N.A., 1896).

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.

Every three years (annually in the case of destroyers and ships whose plating does not exceed in.) a complete survey is made by the dockyard officers.

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. 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. The use of liquid fuel is still in the experimental stage; if it could be adopted, the getting on board and the storage would be 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