The Surf-class was a light non-self-righting displacement hull motor lifeboat. Nine were built between 1936 and 1941, and operated by the Royal National Lifeboat Institution (RNLI) between 1936 and 1965.
Designed by RNLI Naval Architect James Rennie Barnett, the Surf-class was the smallest and lightest offshore motor lifeboat produced by the Institution. Intended for stations where launching heavier boats would be difficult, the Surf-class enabled the RNLI to replace traditional 'Pulling and Sailing' (P&S) lifeboats, ones with sails and oars, and plug gaps in motor lifeboat cover. The boats however, were only really suitable for inshore work in moderate conditions and only had long service lives at two stations.
The first two boats were long, with a beam. No shelter was provided on the deck, as this was not considered to be a problem for the kind of services that they were intended for. On service, with crew and gear on board, the boat weighed just tons. Each boat was divided into five water-tight compartments, with approximately ninety air-cases.
Power was provided by two 12-hp 2-cylinder Weyburn F2 horizontal petrol engines, each being water-tight, and capable of operating submerged, although they were also housed in a water-tight engine room.
The first two boats differed in their method of propulsion, the first being fitted with regular twin-screw propellers, whilst the second employed a water-jet propulsion method. The 'Hotchkiss Internal Cones' consisted of a pair of impellers in a conical case, driven by each engine, and working like a centrifugal pump, drawing in water at one end, and forcing it out under pressure at the other. This is a development of the method of hydraulic propulsion used in the early steam-powered life-boats built in 1888. While this was a benefit in shallow waters, the cone powered boat was approximately slower than the screw version.
The first two boats served for less than ten years, before being sold to the Dutch Lifeboat Service KNZHRM in June 1946.
Construction of the next seven boats in the class began in 1938, three years after the first two, all fitted with a shelter ahead of the (tiller) steering position, and built with a slightly wider beam of . Each continued to employ the twin Weyburn F2 engines, and all but one featured Hotchkiss Internal Cone propulsion. Kate Greatorex (ON 816) was fitted with Gill water jets.
These boats served for 10 to 12 years at most of their stations, before being replaced by standard carriage launched boats, but at two locations, and , Surf-class boats continued into the sixties. RNLB John Ryburn (ON 837) was withdrawn from service at at the end of September 1965, after more than twenty-four years on station. During this time, the lifeboat was launched on service only eleven times, but rescued 19 lives. Newburgh lifeboat station was closed when the boat was withdrawn. Norman Nasmyth (ON 836) remained in the Relief fleet until 1966.