THE STEEL HULL of the fast slipway lifeboat is built upside down, so that the welder can look down on his work, both making the work easier and also making it possible for him to achieve the best results: the integrity and strength of the whole structure is dependent on the high quality of the welder's skill. Once all the exterior work is completed, however, the hull is released from its deck jig and, with a crane at each end, turned through 180 degrees until it is right way up. In Fig. 4 the fully plated hull of the first of the two prototypes being built at Fairey Marine (Cowes) can be seen turned right way up, while, in the background, the skeleton of the second prototype, still at the earlier stage, is inverted, awaiting plating.

Now the detail of the hull has taken shape: for instance, Fig. 1 shows the fine entry of the forefoot of the stem, and Fig. 2 the protective curve of the propeller tunnels; deep bilge keels will eventually give further protection.

Once the hull is turned upright, it is water tested. All compartments and tanks which must be watertight are filled with water and a check made to see that there are no seepages whatsoever through the welded joints. Once the watertightness has been proved of the water and fuel tanks, down in the bilges, their tops are fitted and a final compressed air test made to establish their complete tightness. All void spaces in the structure of the hull will eventually be enclosed and filled with foam to provide buoyancy and to prevent the entry of water should the hull at any time be damaged.

Meanwhile work goes ahead on welding into place all deck structure seatings and hull skin fittings. When this stage is complete, the next operation for a steel boat is shot blasting: the cleansing under pressure of the whole of the outside of the hull, the internal bulkheads, the tank tops and all the deck structure. A shower of grit forced at high velocity through a hose is directed at every inch of surface, removing all mill scale and rust from the steel and leaving a shining clean surface ready for protective coats of primer and undercoats of paint. All the steel surfaces to which the aluminium deck and superstructure will later be attached are included in the shot blasting; these surfaces will then be sprayed with zinc to prevent corrosion which would otherwise be caused by electrolytic action between the steel and aluminium, metal alloys of differing nobility.

All this basic testing, cleansing and protective work has to be done while the hull is clear, but while it is going on other major components are being prepared ready for fitting. The aluminium superstructure is being built in another part of the yard, and the engines (see Fig. 3), having passed their initial bench tests, have been delivered to Cowes.

The engines are twin General Motors 8V-71 turbocharged intercooled marine diesel engines developing 425 shp at 2,300 rpm continuous rating, and they are fitted with Allison type M20 reverse reduction gear boxes with a reduction ration of 2.04:1. Soon, they will be lifted into their places, to port and starboard in the engine room.

(to be continued).