IN THE PAST FEW YEARS, the RNLI has been exploring the possibilities of introducing intermediate lifeboats into its fleet: fast boats of about 35 feet in length, essentially simple but with outstanding seakeeping qualities, which would bridge the operational gap between present offshore and inshore lifeboats, thus giving greater flexibility in the provision of effective cover to all parts of the coast. It was thought that, at a few stations, such an intermediate boat might well be able to replace a small offshore lifeboat at a lower capital cost and still do the job effectively with the added advantage of greater speed. Equally it was thought that such a boat could be stationed at places where, because of the necessary range of operation or the severity of wind and sea which could be expected, a bigger boat is needed than the Atlantic 21, the largest of the inshore lifeboats.

Two intermediate lifeboats are at present being developed, one of which has been designed by the Institution's own staff. She is the RNLI Medina 35 and the prototype of this experimental boat was launched at Cowes on the Isle of Wight last autumn. To be named Mountbatten of Burma, she was on show at the London Boat Show in early January.

Throughout its history the Institution has been noted for its pioneering work in lifeboat design and also for the contribution which its work has made, over the years, to the general develop-ment of small boats. The RNLI Medina is adding yet another chapter to that history. Here is an advanced idea which offers great and challenging promise; or perhaps it would be truer to say that here is an already proven idea, taken a large step forward; in fact the rigid inflatable concept, so successful in the outboard-engined Atlantic 21, has now been applied to a 35ft boat with inboard engines.

The prototype RNLI Medina 35 has been developed by the Institution's Cowes Base design team under the leadership of David Stogdon, MBE; she has been built by W. A. Souter and Son Ltd. The Cowes Base is on the east bank of the River Medina, opposite Souter's Yard on the west.

Design and construction In essence, the RNLI Medina 35 is an extension of the ideas embodied in the Atlantic 21, the Institution's outstandingly successful rigid inflatableinshore lifeboat which was also developed at the Cowes Base. Whereas, however, the Atlantic 21 is driven by twin outboard engines, the Medina's power comes from twin inboard diesel engines. The design problems are not, therefore, the same and so she must be regarded as a different member of the same family rather than as a larger version of the same boat.

The Medina's hull is sharply veed forward for easy riding and good seakeeping and includes a bold sheer, while the after body has a 29in flat for the last 9 feet. This feature, besides assisting planing, provides directional stability and allows the boat to stay upright when beaching. Cold moulded of four layers of 5mm mahogany with a '/2in marine ply deck, the hull is divided into watertight compartments by five longitudinal wooden box girders and seven transverse watertight bulkheads between which are additional intercostals.

The skin is slightly curved throughout for greater strength.

This rigid hull is the 'boat' on which the Medina runs and which carries her up the back of waves, her sheer giving her considerable reserve buoyancy forward. The sponson, mounted like a vast inflatable gunwale, is designed to be clear of the water under way.

An important function of the sponson is to give the Medina her stability, particularly when she is at rest and when she is heavily loaded. In fact, the more people there are on board, that is, the more the 31 in diameter sponson is pushed down on to the water, the greater will be the stability.

The sponson is made by Avon of lloz hypalon/neoprene fabric, a very strong air-retaining material. The 31 indiameter tubes (which taper down to 25in in the bow so that they do not obstruct forward vision) are supported inboard by glass fibre box seatings and are glued to the hull by laminated reinforcing strips. The tubes are divided into compartments by inner baffles, those in the forward part being so designed that, should the outer skin of the sponson be damaged, these baffles will move to take up the shape of either the bow or the shoulder sections.

The present aluminium superstructure provides the steering position for the helmsman and also a basic shelter big enough to take a stretcher and survivors.

The helmsman has an uninterrupted vision all round and can see almost the entire deck. His position has been so designed that the height of the floor and the fore and aft position of the padded backrest can both be adjusted to suit his height and reach. It should be emphasized that this is a prototype console from which an improved version will be developed after evaluation trials.

A gantry at the after end of the superstructure carries a radar scanner, navigation and blue flashing lights and the VHP aerial. These can be swung down aft to reduce overall height when the boat is housed. The boat is fitted with a Pye Beaver VHP radio, a Seafarer III echo sounder and a Decca 060 radar. The radome of the radar, which was donated to the RNLI by Decca Radar Ltd, has been specially strengthened to withstand damage, should the boat be capsized.

A roll bar in the stern of the boat carries a deflated buoyancy bag. In the unlikely event of the boat being capsized the crew can inflate the bag by pulling a handle on the transom to activate compressed air cylinders and the boat will right. If inverted, the boat will float high enough on her sponson to leave a good air space between the deck and the sea and room for her crew to carry out any work necessary to the boat's righting and the safe recovery of survivors and the crew themselves.

This is a feature unique to rigid inflatables.

All these arrangements have been proved in a controlled capsize and righting trial.

Deck arrangements and the accommodation in the shelter are at present in a skeleton stage and there is still much work to be done taking into account experience now being gained on sea trials. However, there are already indications of the kind of analytical thought which will characteristise the whole deck layout when it is complete: such as the anchor chain made up on flexible bollards so that, once the anchor is dropped over the sponson, the chain can follow freely; the neoprene quick release 'channels' to hold the anchor warp where it crosses the sponson and the deck so that, on a rough, dark night, there is no dangerous loose rope lying on deck; the tubular sampson posts fore and aft standing so high thatit would be possible to make fast alongside a vessel with high freeboard without chafing on the inflatable sponsons; the generous scuppers in the transom; the provision of continuous handholds.

The Medina will be manned by a helmsman and three crew members all of whom will be provided with secure positions which can be occupied when the boat is at full speed.

Engines The RNLI Medina 35 is fitted with twin Sabre 212hp diesel engines, their power being transmitted through twin Sternpowr outdrive units type 83. On initial trials the boat has shown that she runs well with very good, smooth acceleration and little change of trim. A speed of more than 26 knots at 2, oO rpm has been reached on measured mile trials; this means that the Medina should have at her command that extra burst of power which can be used to get her out of trouble in breaking seas.

The engines, housed in a watertight aluminium casing, are modified as are Continued on page 21.