The experimental prototype of a new design of 38ft lifeboat which is fast, yet capable of launching from a carriage, is now under construction and will begin trials in the spring. Edward Wake-Walker examines her development.THE RNLI HAS A PROUD RECORD of innovation in boat design; it is a record born of the unique demands on an organisation which is required to provide lifeboats capable of enduring the worst conditions, of performing tasks at sea asked of no other vessel and of being ready and able to launch at all states of tide and weather from stations on every stretch of the United Kingdom and Ireland's varied coastline.

Where a lifeboat can be moored afloat in a harbour which does not dry out at low tide or where a slipway allows a launch at any time, the RNLI does not need recourse to the time-honoured method of launching the lifeboat from a carriage. But on many parts of the coast this will always be the only way to guarantee a 24-hour service and thereare 23 stations today where a lifeboat, larger than the inflatable D and C class and rigid inflatable Atlantic 21, is towed by tractor to the water's edge and launched from a carriage. All these stations are served faithfully by the wooden hulled 37ft Oakley or the more recent 37ft 6in Rother class lifeboats.

The last of the Rothers was built in 1982 and with its completion came the end of the building of conventional wooden-hulled, 9 knot lifeboats. Since the 1960's the RNLI has been intent upon the development of faster lifeboats, built either from glass reinforced plastic or steel. First came the successful introduction of the 'fast afloat boats', in the shape of the 44ft Waveney followed by the 50ft Thames and 52ft Arun class, capable of 18 knots and, most recently, the 20 knot, 33ft Brede. Further research and development has produced the slipway launched, 47ft Tyne class lifeboat whose maximum speed of 18 knots effectively halves the time taken by a conventional slipway launched lifeboat to reach a casualty.

Naturally enough, the technical department of the RNLI has also turned its attention towards the development of a fast lifeboat that can be launched from a carriage. The development of the Medina class with her diesel driven waterjet propulsion has been a major project in recent years and she is at present undergoing launching trials on different parts of the coast. However, there are many places where the Medina will not be a suitable replacement for an Oakley or Rother. The RNLI is therefore working on a brand new design for an all-weather lifeboat known for the moment simply as the 'fast carriage boat'.

In drawing up the plans for such a boat there were a number of pre-requisites to bear in mind. First of all, the RNLI wanted a lifeboat capable of 18 knots, which meant a hull design very different from her predecessors. Self-righting was to be achieved by the inherent buoyancy of a watertight wheelhouse rather than by the self-flooding water ballast tanks of the Oakleys, and this wheelhouse would also need to give full protection to the crew and sufficient space for all the most up-to-date communication and navigational equipment. Incorporating these aims, the design had also to take into account the existing boathouses and launching carriages with which the new lifeboats would need to be compatible. All these requirements led to the eventual determination of the fast carriage boat's dimensions.

One important aspect of any new design is the derivation of the required engine power. It is now common practice to have made scale models of the boat's hull, and to tow these models in a testing tank. The results of these tests not only indicate the way the boat will react when at sea, but also provide essential data on the required engine power and propellers. Such tests were carried out for the fast carriage boat.In the past, when the RNLI has developed a new hull, such as that of the Arun and the Tyne, a larger scale model has also been built to study the boat's sea-keeping qualities. However, the development of the fast carriage boat has been different because here the larger scale model is being built full size.

Had past practice been followed, to achieve effective sea-keeping trials, a model of some 10 to 15 feet would have been necessary—getting on for half the size. Because full scale testing is much more reliable than model testing, as suitable engines were available and, moreover, because the cost of model testing would end up almost equivalent to building a full-size aluminium alloy hull, the decision to go straight into building an experimental prototype was made. This will of course mean a considerable saving in time and cost if the trials on the prototype prove successful.

Once the boat has been proven in full size, production of a new class of lifeboat can go ahead without further delay.

This is the first time the RNLI has built a boat with an aluminium hull. It does not automatically follow that all boats of the new class of lifeboat will be built of this material. Aluminium does, however, have possible advantages that make the experiment well worth while.

The design team are interested to see whether a lighter aluminium boat (10 to 11 tons) is more or less seaworthy than other lifeboats and whether she is more or less manageable on the beach than the existing 13 ton Oakleys and Rothers. Also, making her initially lighter, the trials officers will be able to ballast the boat down to the displacement of a steel-hulled boat (an alternative building material) to make valuable performance comparisons.

The diagrams and photographs show how the fast carriage boat looks. Her length, 38ft (11.57 metres), reflects the 37ft Oakley and 37ft 6in Rother dimensions.

Her beam, 12ft 6in (3.81 metres) is such to ensure the ready installation of her twin engines and also gives due regard to the standard beam/length ratios for this size and type of vessel.

Her depth (not draft), 6ft (1.82 metres) is designed to give good access to machinery and a reasonably low freeboard for recovering survivors while keeping enough height in the bow for good seakeeping and to prevent too much spray from covering the lifeboat in rough weather. She is of round bilge, semi-displacement form with a soft nose stem and a tunnel stern to give protection to the propellers. The hull is sub-divided by four watertight bulkheads into five compartments which comprise a forepeak cable locker, a survivors' cabin with seating for ten people, machinery space, tank space and an aft peak steering gear compartment.

The wheelhouse is to contain permanent seating for a crew of six, with an additional jump seat provided for a doctor. Space inside is very restricted, and to enable the design and operations staff to produce the most practical arrangement of seats and equipment, a full scale mock up of the wheelhouse has been produced. The console is to house engine controls, the hydraulic steering unit and wheel, tachometers, alarms, compass, helm indicator and controls for VHP direction finder units, navigation lights, wipers, horn and thesearchlight. At the navigator's position is to be fitted the radar display, a chart justify table and a Decca Navigator display. The mechanic's position will have, as well as the main switchboard, a radio table with MF radio transmitter and receiver, VHP radio telephone and MF direction finder.

The boat will be powered by twin Caterpillar 3208T engines, turbo-charged to develop a maximum continuous rating of 250 shaft horsepower at 2800 revolutions per minute. Her maximum speed will be 18 knots with a continuous running speed of 16 knots. A fuel capacity of 1266 litres will give her a duration of 15 hours at cruising speed.

The experimental fast carriage boat is nearing completion; the hull is being fitted out by William Osborne's of Littlehampton, the builders of many lifeboats through the years, including many of the 37ft Oakleys and Rothers.

The hull was built under sub-contract at Cunningham and Sons at Ford in Sussex.

The new boat will enter the water for the first time in spring 1986 when she will carry out self-righting trials prior to other technical trials. Operational evaluation trials will follow and these will only be concluded when the RNLI's staff are fully satisfied that the boat is in practice a lifeboat worthy of the RNLI..