A-504 is preserved at Chatham
Class overview
Name	McLachlan class
Builders	William Osborne, Littlehampton
Operators	Royal National Lifeboat Institution
Preceded by	Hatch
Succeeded by	Atlantic 21
Built	1967–1973
In service	1967–1988
Completed	10
Retired	10
General characteristics
Length	18 ft 6 in (5.64 m)
Beam	8 ft (2.4 m)
Propulsion	2 x 60 hp inboard engines with sterndrives
Speed	22 knots (25 mph; 41 km/h)
Complement	2-3

The McLachlan-class lifeboat was an A-class lifeboat operated by the Royal National Lifeboat Institution (RNLI) of the United Kingdom and Ireland from 1967 to 1988. It was replaced by the B-class (Atlantic 21).^[1]

The McLachlan-class lifeboat was the second type of the 1960s fast Inshore lifeboat in service with the RNLI. It was designed by J. Allen McLachlan MRINA, a naval architect, former RNLI chief draughtsman and partner at longtime yacht and lifeboat designers G. L. Watson & Co. of Glasgow.^[2]

The first trial boat, numbered 18-02 by the RNLI, was built by W. A. Souter of Cowes. The boat was constructed from 3 layers of mahogony with foam-filled watertight compartments, and was noted by its use of a 'ragged chine hull', with nine chines that cushioned the hull and reduced pounding. The helm was in a standing position, in a sunken bridge deck, with a weathershield in front of the controls. A 90 hp. Evinrude engine gave a speed of 20.9 knots.^[3]

in September 1969, following successful trials, the RNLI placed an order for 4 boats with boat-builder William Osbourne of Littlehampton, to be constructed with GRP hulls, fitted with twin sterndrive Ford 60 hp marinised petrol engines, and each costing £3,400. 18-02 would later be fitted with twin 47 hp Perkins diesel engines. William Osborne built a further five McLachlan lifeboats in the 1970s. Most remained afloat, but two were kept on carriages. The one at Weston-super-Mare being launched down a long slipway and that at Peel IOM was launched with the aid of a tractor.^[3][4][5]

In the early 1970s, it was decided to reclassify the 17 and 18-foot boats as A-class lifeboats, and their numbers were changed according; 18-004 becoming A-504, 18-007 becoming A-507 etc.^[6]

Although not classed as lifeboats, two further McLachlan designed boats were constructed for use as Boarding boats at Humber Lifeboat Station, (BB-239) and (BB-240).^[6]

A-504 (formerly 18-004) at Weston-super-Mare, was launched at 10:30pm on the 13 September 1975 into an easterly gale, to a motor-boat stranded on the rocks. In difficult conditions, 5 people were rescued. Julian Morris was awarded the RNLI Bronze Medal, and crew members Bernard Watts and Ian Watts both received the Thanks of the Institution inscribed on Vellum. The boat is now on display in the RNLI Historic Lifeboat Collection at Chatham Historic Dockyard.^[6][7]

All the McLachlan lifeboats had been retired by the late 1980s, with the exception of the prototype boat, which went on to be a boarding boat at Humber until 1994.^[6]

• RNLI Fleet