Introduction

The first Stations to be equipped with inflatable lifeboats driven by outboard motors were established by the Royal National Lifeboat Institution in 1963 after the successful outcome of trials carried out through the two preceding years. These boats became known as "Inshore Rescue Boats". Since 1963 various other types of small, fast boats using various forms of construction including wood, glass, reinforced plastics (GRP) and composite wood / inflatable (known as rigid inflatable), have been produced. The sizes range up to 7.35 meters (24.1ft) and all known as "Inshore Lifeboats" (ILB, s).

Outline History of "B" Class Atlantic

Early 1960,s-the starting point of this brief outline history of the development of the Atlantic 21 is Atlantic College in the early 1960,s.
The "United World College of the Atlantic" at St. Donat`s Castle, Llanwit Major, South Glamorgan, was Britain `s first sixth form college.
The first Headmaster of the college was Rear Admiral Desmond Hoare, C.B., M.I.Mech .E., M.R.I.N.A., Royal Navy, (later to become a member of the R.N.L.I. Committee of Management).
The students spend much of their leisure time in sailing and canoeing in the Bristol Channel off the unprotected and rugged beach of stones at the foot of the castle. This activity is carried on virtually all year round. There is a very large rise and fall of tide in the area and the Rear Admiral Hoare considered that such waters demanded a fast beach-launched rescue boat.
The first rescue boat employed was a 4.1 meter (13ft.6ins). R.F.D. inflatable boat with a 20 hp Evinrude outboard motor. This boat was soon followed by a 4.9 meter (16ft) Zodiac with a 40hp motor.
At this time the R.N.L.I. had already gained 3 years experience of operating inflatable rubber boats as Inshore Lifeboats and loaned 3 of them to Rear Admiral Hoare for development purposes.
At Atlantic College the three I.L.B.,s were worked hard. With constant launching and recovery in all weather conditions and at all states of the tide, from a bouldered beach, often through surf, the maintenance required to the fabric of the buoyancy tubes and floor was a never-ending task. In an attempt to reduce this damage, strips of marine ply were bonded to the bottom of the tubes to act as beaching skids; folding internal floors were replaced by one-piece marine ply internal floors (to prevent "folding" of the boat), but fabric repair problems remained.
1963- the first flat, hollow rigid wooden hull was glued directly to the bottom of the buoyancy tube, and to provide better directional stability, small wooden fins were added (and duly broken off) but experience with this hull combination indicated that the developments were heading in the right direction.
1964- A new deep-vee hull design influenced Rear Admiral Hoare`s thinking about this time, and the next step was to use a deep-vee hull form combined with an inflatable buoyancy tube or sponson bonded to it. Boat X1, 4.9 meter (16ft.) in length, was constructed in wood by staff and students in 1960.The floor was vee sectioned with about 20 degree constant dead rise, (0.23 meter)(9 inches) deep on a 1.2 meter (4 foot) wide floor, the floor was installed with it`s upper surface 2.5 cm (1 inch) above the bottom of the buoyancy tube. The floor was strengthened internally at the after end and the transom secured to it with oak angle pieces. The buoyancy tube was bonded to the hull by adhesives and fabric hinge straps. This boat was accepted by the R.N.L.I. for trials at Gorleston, and Lieutenant David Stogden, then Divisional Inspector with the R.N.L.I., and another name linked with Rigid Inflatable Boat History, was very much involved.
1972-The first Atlantic 21 entered R.N.L.I. service in 1972 and was stationed at Hartlepool. With this boat the B500 series came into being and a number of wooden-hulled boats were introduced.
Work began on the provision of a righting capability in 1972. The preliminary experiments to establish the height of the roll bar and the necessary volume of buoyancy were completed at the R.N.L.I. Depot, Cowes
The first full-scale righting trials were held at Littlehampton in May 1973. In a "dry run" CO2 equipment had inflated the bag in 12 seconds, but the actuating mechanism was not tested afloat until further trials the following October. All subsequent trials were held at Cowes and these highlighted many problems. Also in May 1973 the first MK II G.R.P. hull was made for the New Brighton lifeboat.
That good solutions have been found to the "righting problem" was proved when, in 1975, an Atlantic 21 capsized at sea. Everything went according to plan. After righting the lifeboat, the crew were able to re-board and restart the motors. It was found that the VHF radio was still in good working order.
Halmatics of Havant prepared a structural design for building in G.R.P. in consultation with the R.N.L.I., and the first Mark III hull laid up in the summer of 1976. This model was not continued, the external changes to the hull were retained but the internal molding was discarded in favor of the original plywood longitudinal's.
Development work continues on the "B" class Atlantic. It has seen changes in layout, additions to equipment and as a result has consequently grown in weight over the years. Which has inevitably reduced it`s original operating speed and single engine performance. In 1991 it was decided that a survey should be carried out of all available commercial craft which most closely fitted the R.N.L.I. requirement for a lifeboat to replace the Atlantic 21. The requirement was stated as:
- "A 35-40 knot inshore lifeboat capable of being launched from a slipway, davit or off an open beach. The vessel to have better sea keeping qualities then here-to-fore, whist maintaining the characteristics of an I.L.B."
- A number of boats were selected for trials
An in- house development project to design a replacement for the Atlantic 21 was already in progress and was beginning to look an attractive proposition giving higher speed, better single speed performance, softer ride and, with its aerodynamic console, improved crew protection. During wind tunnel trials in speeds of 60 knots the crew protection afforded close to the console on either side, gave a minimal anemometer reading and clear indication of how to improve the crew protection by diverting the wind further around and well over the console using fairings. The width of the console was increased by 5.15 cm (2 inches) at he after end to provide more leg room for the crew within the well. Engines were trialed for performance and investigated for of inversion proofing.
The major differences between the Atlantic 75 and the Atlantic 21 are that the rigid length has been increased by 0.305 meters (12 ins) and the beam by 1.85 cm (1/2 ins). The flat has been reduced and the bow section re-designed to give a finer entry at the strike area and extending further aft than the Atlantic 21. The dead rise remains at 27 degrees.
- The prime objective of the modified design was to provide a softer and easier ride whilst still preventing the boat`s transom and engines from being submerged on landing in heavy weather conditions and thus tending to swamp the boat via the exhaust. The sponson diameter has been increased by 5.1 cm (2 ins) thus increasing the lifeboat`s overall beam by 15 cm (6 ins), compared with the Atlantic 21 and a towing post has been fitted directly behind the console, improving towing action
Apart from the outboard motor support bracket there is no raised transom thus ensuring a free draining deck. The internal design of the hull is similar to that of the Atlantic 21 in that there are six longitude compartments each watertight in its own right. There is also a small bow compartment, which is designed as a free draining sump for those lifeboats which are stored bow down in the boathouse or on the slipway. Additionally the bulkhead to this compartment provides a watertight barrier or "crash bulkhead" should the bow of the lifeboat incur damage. The instrument panels have been designed and re-positioned to give improved and accessibility. The main advantage being that the tachometers and echo sounder are now positioned almost at eye level. As with the Atlantic 21 the engines are inversion proofed (as apposed immersion proofed).
A second prototype Atlantic 75 was then built in order to speed up the evaluation of the new design and the research and development of the various items of equipment, together with the lifeboat,s handling and sea keeping qualities in the various sea conditions likely to be encountered around our shores. To this end the lifeboat was taken to a number of Atlantic 21 Stations around the coast which would provide a variety of operating conditions and after receiving instruction the crew were left to operate the lifeboat for a period of time in order to compare it with their own Atlantic 21 - on each occasion, the staff officer debriefing the crews on completion of the trials had great difficulty in retrieving the new lifeboat from the enthusiastic station personnel concerned. Analysis of the reports received from lifeboat stations and from staff, who carried out specific trials, indicated improvements which could be made and these were also incorporated.
Production lifeboats are being built and fitted out using jigs, templates, and tooling to ensure maximum inter-change ability of both major and minor components. The intention being that any console or roll bar for example will fit any Atlantic 75 and any fitting or components on that console can be changed or replaced in the quickest possible time, in certain cases by coast staff at the station.
The construction has been simplified so that when the lifeboat comes into the R.N.L.I. Inshore Lifeboat Center, Cowes for maintenance, the outboard motors can be removed and taken to the engine shop; the console, complete with all the electrical and motor controls, can be unbolted and removed to the clean area benches, and the hull wheeled into the main boat shed. All parts can be worked in parallel in dedicated workshops. It follows that the time of the original construction has been significantly reduced too. The main intention has been to achieve an interchangeability of units, thus reducing the necessity to withdraw a lifeboat from service for other than major repairs
Motors -the first outboard motors fitted to the Atlantic 21 were twin 40 HP, giving 26 knots, but it was found that more power was required. Moreover, the 40 HP would not idle reliably without stopping and this was not acceptable when effecting a rescue.
In 1973 twin 50 HP outboard motors were fitted. They gave the Atlantic 21 a top speed of 29 knots and also saw the introduction of electrical starting facilities.
In 1976 all Atlantic 21 were fitted with twin 55 HP outboard motors and speeds of 30 knots plus have been reached. In the early 1980`s 60 HP outboard motors were used then these were superseded by twin 50 HP motors of an improved design that developed the same power at the propeller as the 60 HP types.
In 1992 trials were undertaken with a slightly larger Rigid Inflatable (now the Atlantic 75) fitted with 70 HP motors, the opportunity was taken to fit the same 70 HP motors to the existing Atlantic 21 lifeboats as a standard during Surveys
Early in 1991 motors from three manufacturers were chosen for the comparison Atlantic 75 trials. These were all three cylinder motors in the 70-75 HP range. Prior to sea trials one motor from each manufacturer was stripped down to determine the suitability for inversion proofing. There were advantages of each model such that this was not an over-riding factor in the final decision, in terms of performance and fuel consumption very little difference was seen during trials. The choice was therefore dictated by other factors such as reliability, alternator output, manufactures back up, etc., and ease of inversion proofing. The comprehensive trials produced evidence that the best engine for our requirements was the Evinrude 70 HP. This engine also had the added advantage of sharing components and similarities with the twin engine 50 HP in use on the Atlantic 21 at that time.
Carburation -considerable design and development work was required to ensure that an adequate and uniform air supply to each of the three carburetors was possible. A prototype fabricated in aluminum alloy was manufactured after the final design was agreed at ILC Cowes following extensive test tank dynamo meter and sea trials.
Exhaust -The exhaust by-pass system is based on the successful 50 HP design
Electrics

-The electrics of the 70 HP motor were modified in a similar manner to the 50 HP.

Survivor capacity trials -The lifeboat becomes more stable with the additional weight of the survivors and is capable of proceeding at 9 knots with a full survivor capacity (maximum of 22) and crew.

The new Atlantic 75 will gradually replace the 21. Developed at the R.N.L.I.,s Inshore Lifeboat Center at Cowes in 1992, the 75 has it,s name derived from her length of nearly 7.5 meter s.

A modified sponson has been developed to increase the buoyancy at the stern thus giving greater protection to the motors from stalling by swamping as a result of falling back into the sea; being overtaken by a sea; or an over enthusiastic helmsman using too much power when in astern gear. The sponson extension has a designed 10 degrees uplift to reduce the possibility of the extension influencing the dynamic trim in normal conditions.

Source-Handbook for "B" Class Atlantic 21 and 75 Stations