strain on the forward hook. No difficulty occurred in the releasing operation.

5. The boat, when floating and engaged with the falls, was unhooked by hand, while the gear remained locked. Blocks were again engaged by hand with the lifting hooks, to demonstrate

that the whole operation could be performed by two men in a very few seconds.

6. With the boat fully loaded with over thirty men, and a number of the occupants standing on the fore-and-aft hollow shaft or pipe, the gear easily released the hooks.

7. The final test was a severe one for the davits. The fully loaded boat was raised until the keel became well clear of the water; under this condition the operating lever was raised, and

the boat released without difficulty. The photograph shown in Fig. 190 illustrates the position of the boat immediately after release.

There are several other gears on the market which appear to fulfil the requirements of the British Board of Trade, but it is considered that sufficient reference has been made in this section to actual gears now in operation, and also to the tests carried out, to give the reader a general idea of the requirements which enable a boat to successfully take the water after being released from the lower blocks attached to the davit falls.

SECTION C.-CONSTRUCTION OF BUOYANCY AIR-CASES ALL lifeboats must be in possession of a certain amount of reserve buoyancy. The open lifeboats are fitted with buoyancy aircases along their sides, and the pontoon lifeboats are dependent on a number of watertight compartments, which are an integral part of the hull.

The internal buoyancy tanks of Class IA and IB lifeboats are usually constructed of the best quality copper or yellow metal of not less than 18 oz. to the superficial foot. These are placed along the sides of the boat under the side benches.

It is admissible to fit buoyancy air-tanks at the ends of a boat, but never in the bottom. Although it is an inconvenience to fit a buoyancy-tank at the forward or after ends, as it interferes with the stowage of equipment and the fitting of the lifting hooks, yet an air-case in the fore end has the advantage of giving lifting power to the boat should the latter become flooded with water.

When cases are fitted in the ends, they should be separated into two distinct portions on each side of the lifting hooks, to prevent the latter being unshipped when it becomes necessary to remove the buoyancy air-cases for inspection.

The method of construction of buoyancy air-cases is briefly described as follows:

The size of a copper or Muntz metal sheet supplied to the tankmaker is usually 4 ft. by 3 ft., and weighs about 25.2 ozs., which conforms to the requirements of the Board of Trade, viz. 18 ozs. to the superficial foot.

From the information supplied to him by the boat-builder, the tank-maker knows the internal capacity of the boat. In this connection it is well to remember that all open lifeboats of Class IA should be constructed with a coefficient of not less than 64, which means that the internal capacity divided by the

apparent unit of capacity exceeds the actual number of persons which can be comfortably seated in a boat. As an example, take an open lifeboat 28-0' x 8'5' x 3'5', which will give a capacity of about 540 cub. ft. The number of persons which can be appropriated is about fifty. The number of cubic feet of buoyancy-tanks must therefore be fifty-four and not fifty.

The amount of buoyancy-tank capacity depends on the boat capacity, and not on the number of persons carried.

The tank-maker usually has standard moulds to suit the shape of the bilge of ordinary pulling boats, but in the case of motor boats, open boats of Class II., and nested boats, it is necessary to make special moulds to suit the form of boat.

The end sections of the metal air-cases are cut to the shape given by the moulds, with the addition of a margin of about 2 in. to allow for the single hook joint. A gauge mark is then made round the three edges, and the corners cut as shown in Fig. 191 A.

The sectional pieces are then placed in an edging or flanging machine, which flattens and stiffens the material. The gauge marks on the straight edges are set to the grips of the machine, and by the aid of the lever brought up to the horizontal position, the straight edges are turned up to a right angle. The curved edge has to be treated separately by hand at the bench, until the section takes the form as illustrated in Fig. 191 B.

The edges of the end sections are turned over by hand in hook fashion as shown in Fig. 191 c, ready for the reception of the sides of the air-cases.

The sides of the metal air-cases usually require two longitudinal joining seams, which are brought together with double hook joints. The material is placed in the edging-machine and the hook formed in the one movement by the operation of the lever brought to the vertical position. The edges of the two separate sheets of metal are thus made to hook into one another as shown in Fig. 191 D. The completion of the double hook joint is made with a stamping-tool, which brings the hooks into close joint, and the sides into line as shown in Fig. 191 E.

In the final treatment a wooden mallet is used, followed by a steel hammer which makes a tight joint.

Similar procedure is followed in making the connections of the sides and end sections, except that the joints are only of the single hook type.

All the joints and corners are carefully soldered. Great care should be taken with the closing of the corners, for it is here where leakage is usually discovered.

When the tank-makers understand that every buoyancy aircase has to be water-tested, it naturally makes them careful as to the quality of the joints.

The width of the hook joints should not be less than in.

FIG. 191.-Method of constructing metal buoyancy air-cases.

Tanks must not exceed 4 ft. in length, and where they are more than 3 ft. 6 in. in length a divisional bulkhead should be fitted at the half-length for stiffening purposes. This is sometimes done by inserting a skeleton bulkhead made of hardwood battens, properly secured by fore-and-aft stays to prevent

movement. An improved method is to fit a metal divisional bulkhead secured by small angle lugs and soldered to the sides of the air-case. (See Figs. 191 F and G.) An alternative method is to corrugate the sides, which appears to satisfy the requirements of the water test, provided the depth of the tank is within reasonable limits.

The writer's experience has proved that 4 ft. is far too great a length for buoyancy-tanks. They cannot be inserted between the thwarts under the side benches, without making portable the solid support under the thwart fitted in line with the tank cleading, which is considered very undesirable. The tanks have to be periodically inspected, and it is, therefore, necessary to make them easily removable; three feet is considered to be the maximum length for general utility purposes.

The material from which the buoyancy-tanks are made should be periodically inspected for surface defects, and strips cut and tested for ductility.

The manufacturer's stamp must always be inserted on the yellow-metal sheets, and the latter should occasionally be weighed to ascertain if they fulfil the requirements as to weight and thickness, viz. not less than 18 ozs. to the square foot.

There is more in this question of surface inspection than one would imagine. The boatbuilder or tank-maker has no guarantee from the metal merchant as to the quality of the material beyond the insertion of the trade stamp. It is the opinion of many builders that it would be preferable for the sheets to be inspected. and samples tested before the whole of the material is delivered. Defective tanks are a source of great danger to the boat. Zinc and galvanised iron are considered unsuitable for the purpose of air-cases or buoyant apparatus.

Instances have occurred during the survey of old boats when taking out the buoyancy air-cases for inspection, when it has been found that some of the tanks have become defective and leaky.

The boat during the voyage has probably been flooded to keep the planking tight, with the result that the buoyancy tanks have become full of water. In course of time the defective joint has rusted up, retaining the water inside the tank, destroying the purpose of the air-case, and endangering the stability of the boat. The necessity for water-testing each individual tank before delivery to the boatbuilder is, therefore, obvious.

Metals which have been cold-worked are sometimes liable to what is termed "season-cracking," which only makes an