a s p o t t e r ' s g u i d e Why are there so many different designs of lifeboat when the purpose of every lifeboat is so similar-the saving of life at sea? Surely, one might think, all lifeboats are designed to weather the worst of conditions, be as reliable as humanly possible and bring survivors safely ashore, so their designs should be very similar - perhaps even common across the board? Alas, such an ideal is thwarted by a variety of factors, of which the different conditions around the coast, the type of casualty and the march of technology are but the three greatest.

Coastal conditions The RNLI has undertaken to meet the Government's requirementtoprovide allweather lifeboat cover around the coasts of Britain and Ireland and does so up to 50 miles out to sea. This, in overall terms, determines the general area in which a lifeboat station must be located, and the pattern of casualties within that area may narrow the ideal location still further. The number of sites suitable for keeping and launching a lifeboat in that locality will certainly be limited, and there may not be an easy option at all. The need for a readily-available crew near the station must also be taken into account when a site is considered.

Afloat Boats The ideal location for a lifeboat is on a deep-water mooring in a sheltered harbour, with a nearby community able to provide a crew. The lifeboat can then be of a class designed to lie afloat - a type of design which involves less compromise than other classes as size and weight are determined more by the likely conditions and casualties than any other factor and the propellers do not need to be in tunnels or protected in other ways, although this useful feature is incorporated on the latest generation of 25-knot boats.

Slipway Boats If there is no suitable harbour then a slipway launch is one of two remaining options. The boat can be kept safely out of the water and launched relatively easily in virtually any conditions. The disadvantages include returning to the slipway in bad weather, which may be tricky, and slipway-launched lifeboats sometimes need to wait in a sheltered position until conditions moderate enough to allow rehousing.

Slipway launched boats must have a number of features which make their design even more complex than afloat boats. They must have propellers which are protected from damage on the slipway and they must be small enough and light enough to handle on the slipway yet still be able to function as all-weather lifeboats. The cost of building and maintaining a slipway is high when compared with afloat or carriage-launch facilities.

Carriage Boats Finally, if no harbour or suitable slipway site is available and the coastline consists of flat beaches a lifeboat can be launched and recovered with a special carriage and waterproof tractor. This is very labour intensive, and as the beach may be exposed recovery can be difficult and may have to be postponed in very bad weather.

Again carriage-launch lifeboats are a complex design compromise. They must have propellers protected against damage on the carriage, and when grounded on the beach during recovery, and they must also be light enough to haul across a beach and small enough to fit on a manageable size of carriage.

The Exceptions Lifeboats designed primarily for slipway or carriage launching are multi-purpose boats, and local conditions sometimes dictate the use of a different class of lifeboat to that which might be expected.

Salcombe's lifeboat, for example, lies afloat, but the shallow water over the harbour bar means that protected propellers would be an advantage. As a result Salcombe has a Tyne class lifeboat - a class which is usually slipway launched but which can also lie afloat when needed. A similar situation exists at several other stations. At Barmouth an even shallower draft boat is needed and a Mersey class, primarily designed for carriage launching, lies afloat there.

Similarly the restricted size of boathouse and slipway at Swanage means that a smaller, lighter Mersey class is used instead of the more usual slipwaylaunched Tyne class. Several other Mersey class lifeboats lie afloat or launch from slipways to meet local needs.

Inshore Lifeboats In addition to the overall all-weather lifeboat cover the pattern of casualties can lead to a need for a lifeboat capable of rapid launching and high speeds to pro-vide a quick response time, plus the ability to work close inshore. The need first arose in the 1960s, with increasing leisure use of the sea and coast, and the D, C, and Atlantic classes were developed to provide the lifeboats required.

Some operate from purely ILB stations and others in tandem with an all-weather lifeboat.

The simplest inshore lifeboat (ILB) is the D class inflatable, the 'standard' ILB which is used where day-time cover is required. With its single outboard engine the D class is light enough to man-handle ashore and in shallows and has sufficient sea-keeping ability to meet most ILB needs.

The C class ILB was developed to provide an inflatable with a night-time capability and for slightly more rigorous conditions. Slightly larger than a D class it has twin outboard engines but is inevitably heavier and less easy to manhandle ashore.

The rigid inflatable Atlantic was developed to provide a faster, more seakindly ILB than a pure inflatable, and although still relatively easy to manhandle it is used where the need for high speed and seakindliness outweigh portability ashore.

The new Atlantic 75 is a development of the Atlantic 21 and their roles are interchangeable.

The need to provide the right lifeboat cover leads to situations where the usual ILB-only or ILB-and-all-weather situation does not apply. Southend, for example, has no all-weather lifeboat but operates an Atlantic 21 and two all-year-round D class inflatables.

Technology With an operational life of some 20 years there will often be more than one class of lifeboat designed for a particular purpose in service at any time. The Waveney (1964), Arun (1971), Tyne (1982) and Mersey (1988) gradually replaced classes of traditional 9-knot lifeboats and the new 25-knot boats, the Trent and Severn, will gradually replace earlier afloat lifeboats.

Even now the first ideas for a new slipway boat are being formulated, to produce a lifeboat which will not enter service until at least 2003 but which will take advantage of technological advances in the 20 years since the Tyne was introduced in 1982. Lifeboat development cannot stand still, and by 2003 it will be time to look again at the replacements for the carriage-launched Mersey, introduced less than five years ago...ClaSS 46 built, all in service All-weather lifeboat, designed to lie afloat Length: 52ft and 54ft (15.9m and 16.5m) Beam: 17ft (5.18m) Speed: 18 knots Range: 230 miles First built: 1 971 Last built: 1 990 Displacement: Standard GRP boats 31 tons (wood prototype: 25 tons, steel 32 tons) Engines: Twin Caterpillar diesels, from 460hp to 500hp each depending on age of boat The Institution's most numerous afloat lifeboat. Identifying features include sheerline sweeping down amidships for ease of survivor recovery, prominent wheelhouse and upper steering position. Carries Y class inflatable on wheelhouse roof. 54-footers are identical to the 52- footers except for a rounded instead of a flat transom.

Operational Numbers: 52-footers are 52-01 and 52-02(both wood construction), 52-08 to 52-29 and 52-31 to 52-46 (all GRP) in numerical order of build. The single, steel Arun is 52-030 (initial zero indicates aluminium construction), and the 54-footers are 54-03 to 54-07 (all GRP).

Tyne ClaSS 40 built, all in service All-weather lifeboat, designed to for slipway launch and to lie afloat when required Length: 47ft (14.3m) Speed: 17.5 knots First built: 1982 Displacement: 25 tons approx Beam: 14ft (4,27m) Range: 240 miles Last built: 1990 Engines: Twin GM diesels, 425hp each The Institution's main slipway launched lifeboat, although eleven lie afloat at moorings. Identifying 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.

Propellers are fully protected by substantial bilge keels.Steel construction.

Operational Numbers: 47-001 to 47-040 (the initial zero indicates steel construction) Mersey ClaSS 37 built, all in service All-weather lifeboat, designed primarily for carriage launching but can lie afloat or be slipway launched when required Length: 38ft (11.6m) Beam: 13ft (4m) Speed: 16 knots First built: 1988 Displacement: 14 tons approx Range: 140 miles Last built: 1993 Engines: Twin Caterpillar diesels, 285hp each The Institution's main carriage launched lifeboat, although some lie afloat at moorings or are slipway launched. Identifying features include slightly 'boxy' wheelhouse set well aft and sheerline flattened towards the bow. Propellers are fully protected by partial tunnels in the hull and substantial bilge keels. Aluminium or Fibre Reinforced Composite (FRC) construction.

Operational Numbers: 1 2-001 to 1 2-01 0 (the initial zero indicates aluminium construction) and 12-11 to 12-37 (FRC) ClaSS 32 built, all in service All-weather lifeboat, designed to lie afloat .

Length: 44ft (13.4m) Beam: 12ft (3.66m) Speed: 15.5 knots Range: 190 miles First built: 1 964 Last built: 1 982 Displacement: 18.5 tons approx Engines: Twin Caterpillar or GM diesels, 203hp to 250hp each The Institution's first 'fast' lifeboat, based on US Coastguard cutter (the prototype was built in the USA). Identifying features include 'cut-out' in sheerline from wheelhouse aft, tall almost 'sentry box' wheelhouse and separate cabin set well aft, noticeably rounded transom. Propellers not protected. Steel construction.

Operational Numbers: 44-001 to 44-032 (the initial zero indicates steel construction)Thames ClaSS 2 built, 2. in service All-weather lifeboat, designed to lie afloat Length: 50ft (15.2m) Beam: 14ft 6in (4.42m) Speed: 17.5 knots Range: 210 miles First built: 1973 Last built: 1976 Displacement: 24.75 and 27.2 tons Engines: Twin GM diesels, 290hp eacht In many respects a larger version of the Waveney class for stations requiring a larger afloat lifeboat. Identifying features: similar to Waveney, but larger and with much less obvious 'cut-out' in sheerline and less rounded transom. Wheelhouse looks less tall than Waveney. Steel construction.

Operational Numbers: 50-001 and 50-002 (Initial zero indicates steel construction) ClaSS 12 built, 7 in service Intermediate lifeboat, designed to lie afloat Length: 33ft (1 Om) Beam: 1 1 ft 6in (3.5m) Speed: 18.5 knots Range: 140 miles First built: 1 982 Last built: 1 985 Displacement: 9 tons approx Engines: Twin Caterpillar diesels, 203hp each Designed to lie afloat at moorings at stations not requiring an all-weather lifeboat, although Bredes can operate in virtually any conditions experienced at the stations to which they are allocated. Based on a commercial hull the identifying features include their relatively small size, a 'pilot boat' appearance and a fairly bulky wheelhouse. Shallow, slightly reversed sheerline.

Propellers not protected. GRP construction.

Operational Numbers: 33-06 to 33-12 (earlier boats withdrawn from service) Trent ClaSS prototype only All-weather lifeboat, designed to lie afloat but with protected propellers to take the ground if required Length: 45ft 11 in (14m) Beam: 14ft 10in (4.53m) Speed: 25 knots Range: 250 miles First built: 1992 (prototype) Last built: Current build programme Displacement: 25.5 tons approx Engines: Twin MAN diesels, 808hp each (Prototype currently fitted with two Perkins diesels for evaluation) A new class of 25-knot lifeboat to replace current afloat boats as they reach the end of their service lives. Identifying features include sheerline sweeping down for survivor recovery, Tall wheelhouse with prominent upper steering position - which will be slightly further forward on production boats.

First 'hard chine' hull design for RNLI. Propellers fully protected by substantial bilge keels. Fibre Reinforced Composite (FRC) construction.

Operational Numbers: 14-01 onwards (prototype only built as at August 1993) Severn ClaSS prototype only All-weather lifeboat, designed to lie afloat but with protected propellers to take the ground if required Length: 55ft 9in (17m) Beam: 18ft (5.5m) Speed: 25 knots Range: 250 miles First built: 1992 (prototype) Last built: Current build programme Displacement: 37.5 tons approx Engines:TwinCaterpillardiesels,1,050hpeach A new class of 25-knot lifeboat to replace current afloat boats as they reach the end of their service lives. Shares hull shape with Trent class. Superficial resemblence to Arun class but 'chunkier' feel all round - especially aft and visually greater freeboard. Identifying features include almost full width upper steering position. Wheelhouse will be one window shorter (from the bow) on production boats. Propellers protected by substantial bilge keels. Fibre Reinforced Composite (FRC) construction.

Operational Numbers: 17-01 onwards (prototype only built as at August 1993)D class inflatable Inshore lifeboat Length: 16ft (4.9m) Speed: 20 knots First built: 1963 Last built: current (modified design) The most numerous of the RNLI's Inshore lifeboat classes. Identifying features include single outboard engine and Operational Number on side tube Current Operational Numbers: D-292 to D-451 (changes as early boats are withdrawn and new ones added) C class inflatable Inshore lifeboat Length: 17ft 6in (5.3m) Speed: 27 knots First built: 1979 Last built: 1990 Visually similar to D class but larger and with twin engines to give night capability.

Identifying features include twin outboard engines and Operational Number on side tube Current Operational Numbers: C-509 to C-523 Atlantic 21 class rigid inflatable Inshore lifeboat Length: 22ft 9in (6.9m) Speed: 28 knots First built: 1972 Last built: 1993 Fast rigid inflatable. Identifying features include GRP hull with inflatable sponsons, 'roll bar' aft carrying righting bag and Operational Number on side tube Operational Numbers: B-511 to B595 (changes as early boats are withdrawn and replaced by At/antic 75, below) Atlantic 75 class rigid inflatable Inshore lifeboat Length: 24ft (7.3m) Speed: 32/34 knots First built: 1993 Last built: Current Fast rigid inflatabledeveloped from Atlantic 21. Appearance very similar to Atlantic 21 and additional size difficult to judge. 700- series Operational Number on side tube is best guide! Operational Numbers: B-700 onwards.