The Severn class is the largest of the current RNLI fleet being 17 metres (c. 56 feet) long overall and just under 6 metres (c. 18 feet) wide at the widest point. The hull, decks and superstructure are built from fibre reinforced composite (an epoxy resin matrix reinforced with glass and Kevlar fibres) combining strength with light weight. The combination of buoyancy and weight distribution provided by the design make her inherently self-righting. As the boat is subdivided into seven watertight compartments she can maintain her self-righting capability even if water enters through hull damage. Weighing just under 45 tonnes the Severn is given a top speed of 25 knots by her two massive V12 Caterpillar diesel engines. (For the technically minded they are CAT 3412A twin turbocharged, aftercooled diesels each producing approximately 1,200 bhp @ 2,300 rpm). Our fuel capacity is 5,500 litres (1,200 gallons) giving a maximum range of 250 nautical miles at full speed.

The wheelhouse provides permanent seating for 6 crew plus a medic as well as two stretcher positions. It also houses the sophisticated electronics including autopilot, daylight-viewing radar, laser chart plotter, satellite navigator and even a closed circuit television system. Furthest forward are the Helmsman's, Coxswain's and Navigator's positions mounted side by side. The Helmsman's console pictured below is fitted with compass, helm position indicator, steering, engine and bow thruster controls. There are also tachometers, the indicators and controls for the trimplanes, and autopilot together with intercom as well as an array of switches. Between the Helmsman and Navigator, the Coxswain's position has been designed to allow him to obtain and pass on maximum information whilst on the way to a casualty or during a search. This position allows view and use of the radar and laser plotter as well as a console displaying compass, echo sounder, speed log and wind speed and direction. There is also an independent VHF radio and multi-channel voice recorder to monitor radio and intercom conversations.The radar and laser chart plotter are mounted side by side at the Navigator's position and both are electronically interfaced with the GPS satellite navigator so that they all effectively share information.

Behind the Navigator's position on the starboard side is the Mechanic's position. Since the CCTV system gives views of the engine room from two separate angles and the console shows readings from the engines' computer control systems, giving detailed diagnostics of the operation of each engine, the Mechanic can remotely monitor the situation in the engine room backed up by occasional physical checks. The Mechanic normally acts as our radio operator and the communications equipment includes not only MF and VHF radios and DSC (Digital Selective Calling) sets on both frequency ranges but also a VHF direction finder to assist in the location of casualties in adverse conditions. Mounted on the port side opposite the Mechanic and behind the Helmsman are two further crew positions. All seats in the main wheelhouse are fitted with full harness seat-belts and are pneumatically damped to reduce jarring when the boat is travelling at high speed in heavy weather.

Down below in the forward cabin there is stowage for a wide variety of gear including crash helmets, protective clothing, stretchers, fire hoses, veering lines and mechanical spares as well as rocket powered line throwing equipment capable of passing a light line up to 250m. An escape hatch onto the foredeck provides an alternative exit if the main path is blocked by fire or water. The lower survivors' cabin provides seating for 12 persons. The backs of the central seats can be folded down to form a bench for stretcher stowage for which special webbing securing straps are provided. Alongside the seating below is a small galley comprising sink, water boiler and microwave oven enabling us to prepare simple drinks and soups if at sea for long periods. Moving aft of the lower survivors' cabin is the tank space containing the diesel tanks together with the complex pipes and valves which enable the engines to be run from both tanks or either specific tank in case of fuel contamination. Further aft again is the engine room housing the main engines, gearboxes and associated pipework, electronics and hydraulics. Just consider that the cubic capacity of each of these giant engines is 27 litres and compare that to the nearer 2 litre capacity of an average road going diesel powered car and you will get some idea of their phenomenal power ! Furthest aft beyond the engine room is a compartment known as the "tiller flat". This contains not only the mechanical linkages connecting the hydraulic power to the rudders but also houses an independently run generator that can provide electrical power to back up or substitute for the batteries or alternators if necessary.

Out on deck there are lockers and stowages for a variety of ropes, fire hoses and hand tools. On each side of the wheelhouse A-frames with lifting block and tackles are provided alongside the lowered well decks to assist with the recovery of persons from the water. A self contained diesel salvage pump is stowed in a watertight container that can be passed or floated over to a casualty. This pump can be used for pumping out water when a vessel's own pumps cannot cope or alternatively can be used for fire fighting. Our inflatable "Y-boat" is carried on top of the wheelhouse, from where it can be launched using a hydraulic crane mounted on the after deck. The Y-boat is used in appropriate weather conditions mostly for entering shallow water where it is not possible to take the Severn such as in the recovery of persons from beaches and from under the cliffs. The inflatable can where weather conditions allow be used for the transfer of persons between vessels in deeper water to avoid unnecessary damage. Three fire fighting hydrants are located on deck, one forward and one on either side of the wheelhouse. All of the principal controls to operate the boat are duplicated on the flybridge on top of the wheelhouse allowing the boat to be controlled from here for close manoeuvring with better all round visibility than below in the Helmsman's position. Intercom and an independent VHF radio allow those on the flybridge to remain in contact with others whilst a repeater showing radar and chart plotter information allows access to the same information as the Navigator below.