The distinctive colours of orange and blue flash past you as the lifeboat launches on another service - you recognise that she is an RNLI vessel, but what type? The Lifeboat brings you the definitive guide to all operational RNLI lifeboat classes, starting in this issue with the all-weather lifeboats...

Launch types We can all visualise the spectacular launch of the slipway lifeboat, as she crashes into to sea below, but different coastal conditions require different launching methods. Ideally, lifeboats can lay afloat at a mooring in a harbour or estuary but sometimes a lifeboat will need to be launched across a beach from a carriage or a down the slipway.

The Severn and Trent class lifeboats are the latest 'fast afloat' designs which have been developed to replace the Waveney and Arun lifeboats.The Trent class lifeboat is designed to lie afloat either at deep water moorings or at a berth. The sheerline sweeps down for ease of survivor recovery and the hull is of a 'hard chine' design. Propellors are fully protected by substantial bilge keels, enabling her to take ground without damage.

The first production Trent went on station at Ramsgate, Kent in 1994 - the latest to go on station was at Fowey, Cornwall.The Severn is the largest of the fleet and as with the Trent she is designed to lie afloat. She carries a Y class inflatable which can be launched and recovered by a lightweight framework and winch so that rescue can take place closer to the shore. The Severn shares the same hull shape as the Trent class and also has bilge keels to protect the propellers should the lifeboat take ground. At first glance she looks very similar to the Arun class but generally 'chunkier' all round.

The first Severn went on station in Harwich, Essex in October 1996.The Arun class was the RNLI's first UK-designed 'fast' lifeboat. It is the Institution's most numerous all-weather lifeboat which was introduced in 1971. The Arun has a prominent wheelhouse and upper steering position, as with the Trent and Severn, and carries a Y boat on the wheelhouse roof.

The last Arun was built in 1990 - earlier members of the class will be being replaced by Trent and Severn class lifeboats.The Waveney was the first Fast Afloat Boat, introduced in 1967 with a speed of 15.5 knots. Until then the maximum speed of lifeboats was 8-9 knots. It was based on a US Coastguard design and features include a 'cutout' in the sheerline from the wheelhouse aft, tall wheelhouse and separate cabin set well aft and noticeably rounded transom - propellers are not protected as with Trent and Severn classes.

The last of the Waveney lifeboats, which are named after the river at Lowestoft where the first RNLI version was constructed, was built in 1982.The Mersey was the first 'fast' carriage slipway lifeboat, introduced in 1983.

It was designed mainly to be launched from a carriage but can also lie afloat or be slipway launched when required. Features include a slighty 'boxy' wheelhouse set well aft and a sheerline flattened towards the bow.

Propellers are fully protected by partial tunnels and substantial bilge keels.

The last Mersey was built in 1993.The Tyne was the first 'fast' slipway lifeboat and was introduced in 1982. It is the Institution's main slipway lifeboat, but a number lie afloat at moorings for specific operational reasons. At nearly 18 knots it doubled the speed of the earlier slipway boats. Features include low profile appearance of wheelhouse to fit boathouses and separate cabin aft of upper steering position.

Shallow conventional sheerline and flared bow above waterline with propellers protected by substantial bilge keels.

The last Tyne class lifeboat was built in 1990.Introduced in 1973, the Thames is the 'big brother' of the Waveney for stations with a special requirement for a larger afloat lifeboat. Two of this class were built and are still currently in the fleet, stationed at Islay and Dover- both to be replaced by Severns in 1997. Identifying features include a similar appearance to a Waveney, only larger with a less obvious cut-out in the sheerline, less rounded transom and a shorter looking wheelhouse..