The method of obtaining the correct volume of metal air-cases is dealt with in Section C, Part VI.

Particular care should be given to the arrangements made for the removal of the air-cases to facilitate easy access when the periodical inspections are made to ascertain the condition of the hull.

The tanks must be kept from contact with the steel shell, a simple arrangement being the fitting of two lengths of rope round the tanks to act as a fender.

The lifting-hooks are formed at the head in similar fashion to those approved for wooden lifeboats, and the scantlings are identically the same, as there is very little difference in the weights of the steel boats as compared with those of wood. There is a difference to the keel plate fittings, owing to the formation of the keel. The method of securing the lifting-hook to the hull is shown in Fig. 160.

The whole of the inside and outside of the boat is coated with two good coats of oil-paint.

TYPICAL SPECIFICATION FOR GALVANISED STEEL

LIFEBOAT.

Dimensions: 28′ 0′′ × 8′ 6′′ × 3′ 6′′

=

50 persons.

Shell Plating.-Siemens-Martin mild steel sheets, 14 B.W.G., built on Fawkes' patent embossed steel framing principle, flush plated and flush riveted on outside. Doubling plates in way of chocks. Frames filled with plastic bitumastic composition.

Galvanising. All steel plates galvanised by the hot process after working to shape and punched.

Keel, Stem, and Post. Of bulb tee, 5" x 11" x 11′′ × 1′′. Section of specially rolled steel bar.

Gunwale. Of specially rolled bulb angle section.

Thwarts. Of pitch pine, 8×13".

Side Benches. Of pitch pine, 1 in. thick, continuous over thwarts.

Rudder and Tiller.-Rudder of English elm and tiller of ash or elm.

Buoyancy Tanks.-Constructed of yellow metal of 21 ozs. per sq. ft. To be securely held in place. Rope strops wound round tanks to prevent injury by contact with shell.

Mountings. Galvanised steel thwarts supports, embossed knees, mast step, mast hasp, cleats, 1 set galvanised steel rowlocks, double banked at all thwarts, and steering rowlock

fitted, all attached with galvanised chain. Galvanised shackles at ends.

Lifting-Hooks. To be fitted as per special plan.

Gear Box.-Pine box for stowing details of outfit supplied and fitted.

The Seamless Steel Boat Co., Ltd., of Wakefield, is another well-known firm who have specialised in a particular type of construction, both for ships' boats and motor boats. They have their own patent method of forming the shell plating.

The hull is made of sheets of Siemens-Martin mild steel, pressed into the required shape, welded together at the butts, and riveted to a steel keel bar of the bulb section, which forms the stem, keel, and sternpost. The whole of the shell plating and steel work attached, is thoroughly galvanised.

The inside of the hull is covered with two coats of bitumastic solution, and the outside with two coats of the best white-lead paint.

The top strake is of teak, gunwale of American elm (or formed of special moulded steel), rubbers of American elm, thwarts, side seats, and deck ends, of yellow or red pine.

Canvas soaked with white lead paint is fitted between the plating and keel, stem, and sternpost.

Wood timbers are sometimes fitted, and sprung into position from keel to gunwale, secured in such a way that they can be removed for painting.

A plan which has found favour with the firm is to fit a light steel angle, riveted to the bar keel, and gunwale, so as to be easily removed, with a piece of elm fixed to the bosom of the bar to hold the tanks off the sharp edge of the bar. The idea of the angle is not to stiffen the boat, but merely to hold the tanks away from the hull.

Mr. James Anderson, in a paper read before the Institute of Engineers and Shipbuilders in Scotland, on the 23rd of November, 1915, referred to a new method of forming steel plates for the construction of steel boats, a system which has already been in operation in some of the American yards. The boat appears to be constructed of a number of longitudinal strakes of steel plating, shaped in similar form to the planks of an ordinary clinker-built wooden boat, but the landing edges are secured together by means of a double-hook joint, as shown in Fig. 162. The joints are closed and made watertight with hammers or rollers.

The plating is attached to a V-shaped steel stem, sternpost, and keel. Wood timbers are attached to the shell by means of small lugs, which are closed in with the shell plating. These lugs have two sides in which the timbers lie, and are secured with through fastenings placed in a fore-and-aft direction. By this method it is advocated that no fastenings in the hull will be subjected to corrosion.

An inside and outside gunwale is secured to the plating and timbers.

The interior of the boat is thickly coated with bitumastic solution.

The United States Board of Supervising Inspectors have

issued standard regulations governing the construction of all metallic lifeboats for ocean-going steamers.

The keels, stems, sternposts, gunwales, and nosings, may be of clear grain, sound oak, or other suitable wood, each in one length, except that the gunwale and nosings may be made in two lengths. When made in two lengths, the gunwales must be scarphed with a good long bevel scarph, stiffened on the underside by a piece of gunwale material, at least 2 ft. in length, 11⁄2 in. thick, and the width of the gunwale.

The stem to be of natural or steamed crook, scarphed at least 9 in. in length on the keel, and fastened thereto with two in. through clinch bolts driven through the deadwood.

The sternpost to be stepped over the end of the keel, half the length of the sternpost, and recessed at least 2 in. deep into the keel, the whole to be secured on the inside by a crook or knee of sufficient width to receive the flanges of the shell plates.

Each joint of the stem and sternpost is fitted with two in. stopwaters, under the shell flanges. Bearding of stem and sternpost is not to be less than 1 in.

The flanges of the shell plates on boats not over 20 ft. in length, to lap on the keel, stem, and sternpost, at least 24 in.; in boats over 20 ft., and not over 24 ft. in length, at least 2 in.; and in boats over 24 ft. long, at least 2 in., to be fairly drawn up and nailed over a strip of No. 6 cotton duck, the width of the flange, and secured by three rows of galvanised nails driven zigzag fashion.

No part of the keel, stem, or sternpost, outside of the shell flanges to be covered with sheet steel.

The following particulars give the approved limiting gauge of shell plates, viz. :

All the seams and joints are double riveted. The seams and butt laps are not less than 14 in. The centre of the row of rivets nearest the edge of a sheet are about 3 in. from the edge. Rivets are staggered with not less than 18 rivets to the foot, having countersunk heads. The diameter of shank of rivet is not less than No. 10 B.W.G.

The width or siding of wood keels, stems, and sternposts, vary from 1.8 in. for an 18-ft. boat to 2.8 in. for a 28-ft. boat, while the depth or moulding varies from 4-2 to 5.0 in. respectively.

Steel having one-sixth of the approved sectional area of wood, may be used in lieu of wood for keels, stems, sternposts, and gunwales, of metallic lifeboats.

The keels of all boats over 26 ft. in length are strengthened by the addition of a main keelson extending not more than twothirds the length of the boat, and having one-half the area of the main keel, to which it is through fastened with 3 in. clinch bolts spaced not less than 14 in.

The sizes of wood gunwales vary from 12 in. in depth by 2 in. in width for an 18-ft. boat to 2ğ in. by 2ğ in. for a 30-ft. boat.

The gunwales are attached to the thwarts by steel braces and teed to the thwarts, and secured thereto, and also to the steel plating by bolts, the securing bolts to plating being clinched on the outside.

The sheer strake is brought to within a in. of the top of the gunwale, nailed thereto by 14 in. boat nails, spaced 6 in. apart. Thwarts are made of clear yellow pine or fir, and are of the following scantlings, viz:-

All thwarts over 4 ft. long are supported by stanchions of pine 1 in. by 5 in. Every thwart is secured at each end to the boat side by a double or U flange of No. 16 plate, riveted to the shell with five rivets, the thwarts being fitted between the flanges and secured thereto by five boat nails driven down through the upper flanges, thwarts, and lower flanges, and turned over beneath.

Midship footings are fitted to the inside of the bull over a coat of lead paint, and held in place by straps of No. 18 plate 1 in. wide. The midship footings in boats over 18 ft. and not over 24 ft. long, are not less than 1 in. thick by 12 in. wide, and have three footings on each side, 1 in. thick by 7, 6, and 4 in. respectively in width. Boats over 26 ft. in length, having a keelson, are fitted with three footings on each side, 1 in. thick by 8 in., 6 in., and 5 in. respectively in width. The securing straps pass up through an aperture in the middle of each footing and receive a toggle of gas pipe, § in. in diameter, and of a length not less than two-thirds of the width of the footing. The number of toggles fitted in each footing varies from four to six.

Breasthooks are formed of steel, varying in size from in. thick by 14 in. in width, to in. by 14 in. No breasthooks are less than 9 in. long, and are fastened through the gunwale on each side, with three in. button-headed bolts clinched over the shell

plating.

Rudders are made of clean, straight-grained oak, or fir, stiffened across the bottom edge by a piece of wood of the same character, properly nailed.

Each lifeboat is fitted with an automatic plug. (See Fig. 112.)