SINCE HER INTRODUCTION to the RNLI fleet in 1971, the Atlantic 21 inshore lifeboat has not only proved her worth on service, but has also shown herself to be a thoroughbred among boats.

With her speed, range, manoeuvrability and seaworthiness she has opened up a whole new line of thought on small boat design.

Being a thoroughbred, she must be handled like one. Crew training is essential if the Atlantic 21 is to give of her best, and one of the first things the crew have to learn is that whereas the natural reaction in the face of danger is to slow down, which indeed may be the seamanlike action to take, in the Atlantic 21 there are occasions when a better answer is to use the boat's power and manoeuvrability to get out of trouble. For one thing, the Atlantic 21's stability is, to a certain extent, increased with increased speed.

In bad weather the Atlantic 21 is extremely safe running, because she has enough speed (30 knots) to get away from unstable seas in shallow water. Similarly, going to windward, she has the speed to be steered round breaking crests; or, when necessary, getting off the beach, she can turn her bow directly into the breaking wave and use her power to drive through.

The boat can continue at a good speed in a beam sea; if in danger from a breaking top, she can turn her quarter to the sea and run clear.

However, although unlikely, a capsize could happen. In that event the crew, in the water, would attach themselves to the boat, which cannot blow away while upside-down; the sea anchor streams automatically when she goes over. When everyone is accounted for, the crew pull the activating cord which releases gas to fill the buoyancy bag housed on the roll bar aft, and within seconds the boat rights herself. But there is far more to it than just righting the boat if the objective—the completion of the service, not the creation of a second casualty—is to be achieved. The boat must right and the crew re-board her; the engines must start; and she must be able to complete the rescue with all equipment, including the radio, in working order.

Quite a challenge to the RNLI technical departments.

First and foremost, the engines must be in good shape to re-start on righting; so they must have remained watertight Positions of the three gravity valves designed at the RNLI depot, East Cowes; when the engine is inverted, they will keep it watertight.

Lower-motor cover N.R. Valve Drain.

Exhaust Capsize Valve.

Photograph above was taken during capsize and righting exercise. The crew, clear of the Atlantic 21 but attached to her by lifeline, have pulled the activating cord, gas has been released into buoyancy bag and the boat is righting. Note motor cover non-return valves and also the hooded scoops of air intake valves (swung through 180°) on after end of outboard engines.watertight during the time the boat was capsized.

Watertighting, when the engines are inverted, has been achieved by the introduction of three gravity valves, with minimum mechanical movement, designed at the RNLI depot, Cowes (patents have been applied for), used in conjunction with flexible sealants.

1. Air intake valve: Housed in a casing on top of the motor cover is a horizontal tubular valve attached to a hooded air intake scoop in such a way that both are free to pivot together through 360°. The scoop slopes down aft to the motor cover and acts as a pendulum. In normal running, air is sucked up through the scoop into the end of the tubular valve and out again through a port in its top, to make its way to the engine. Should the boat capsize, the pendulum hoods swings through 180°, turning the valve so that its port is closed and water cannot penetrate.

A secondary function of the valve, but still important, is the protection of the air intake from spray, should the boat come upright stern to breaking seas.

If excessive swing of the air intake scoop were to build up while the boat is underway, the valve might, intermittently, be partially closed, thus interrupting the normal, and necessary, flow of air to the engine. To prevent this happening, a second pendulum has been added inside the scoop. It is rather like a bell clapper (though neoprene bushes on the scoop sides prevent it from sounding like one!), and its weight and independent movement dampen down swing and discourage any over-liveliness.

2. Exhaust capsize valve: Normally exhaust gases are discharged through the propeller, but when the motor isidling the exhaust gases cannot overcome the water pressure and so idling holes are drilled at the top of the exhaust housing by the motor manufacturer.

The exhaust then leaves the exhaust housing through these holes and escapes through two slots in the motor casing.

In the event of a capsize, water would reach the cylinders via these holes. This problem has been overcome by blanking off the normal holes and replacing them with holes of equal area leading into a horizontal manifold on the side of the exhaust housing inside the casing. The exhaust then goes into an exhaust valve: a perpendicular tube round the top of which are five outlet holes.

Resting at the base of the tube, beneath these holes, is a ball valve. As the engine is inverted in a capsize, the ball immediately falls into the seat, thus preventing water inside the casing from entering the cylinders, while a weighted sleeve on a spindle falls down outside the tube to complete the seal.

3. Motor cover non-return valve drain: The motor cover drain at the after end of the engine has been modified with the addition of a simple gravity ball valve which falls to close the apertures when the engine is inverted.

An extension contains a buoyant ball valve: if the water builds up when going astern, this ball will float up and close the valve.

All joints in the engine casing are meticulously sealed with flexible sealants and vibration reduced to the minimum by stiffening resilient mountings. To complete the picture, there are nonreturn valves in fuel vents; engines are cut out on capsize by a mercury switch in the control panel; batteries are nonspill.

All motor instruments and wiring must, of course, be 100 per cent watertight.

After coming upright from capsize, it is only a matter of minutes before the engines will be running again—J.D..