Firefloat 80 was the smaller of two prototype firefloats built by Vosper Ltd of Portsmouth for the RAF and designed primarily for combating fires in seaplanes or ships. The craft also has a subsidiary role of provding salvage pumping facilities to seaplanes or ships in emergency.
The craft was constructed of mild steel and the hull galvanised. Unlike the larger 60ft prototype, the main maachinery fitted was used for both propulsion and pumping. The main machinery consisted of four Perkins S6M diesels each rated at 100 bhp at 2,000 rpm and drove two Rotol variable pitch propellers. The main gearboxes gave a reduction ratio of 1.97:1. The two engines on each shaft drove through special toothed clutches and were disposed one forward and one aft of the main gearboxes. This arrangement allowed one or two engines to be used for propulsion and / or pumping. The Rotol was a hydraulically operated three bladed propellor. The blade angle range was 110 degrees, ie from 20 degrees astern through 90 degrees ahead. The aforementioned arrangement allowed control to suit the conditions under which the craft was operating. Twin rudders were arranged in line with the shafts. The propulsion system not only ensured that the craft had the utmost of ease to manooeuvre, but compensated for the powerful reaction force produced by the foam and water jets - estimated at some 1,100lb when all four monitors were in action. As an additional means of counteracting the force, Firefloat 80 also had two reaction jets fitted forward, to port and starboard, giving equal and opposite thrust to the force of the monitors.
The fire fighting equipment, which was the same as fitted to the larger 60ft prototype, comprised four monitors. The two main monitors, specially designed by the Pyrene Company were each capable of delivering 350 gallons per minute of water or 1,800 gallons per minute of foam, at a pressure of 130psi. They were mounted on the main deck, one amidships and one aft. Two small monitors, of the standard RAF pattern, each delivered 150 gallons per minute of water or 900 gallons per minute of foam at a pressure of 130psi, were mounted on the forward raised deck, one each side immediately forward of the wheelhouse. All four monitors operated through 360 degrees in the horizontal plane and 180 degrees in the vertical plane.
Two foam pourers were fitted, one to port and one to startboard, slightly forward of midships and approximately 1 inch above the waterline. They enabled a blanket of foam to be spread on the surface of the water, thus extinguishing burning oil or debris. Two 2.5 inch instantaneous double outlet type breeching connections were fitted on deck to provide a coupling for hose when firemen had to board a vessel. The monitors, pourers, breeching connections and reaction jets were served from a firemain fed by two Drysdale 5 fire pumps, fitted in the after end of the engine room. Specially designed, the pumps were of the water ring primer type, and each was capable of delivering 500 gpm against a head of 300 ft when running at a speed of 1,800 rpm.
Two four-jet foam inductors were mounted on the wheelhouse of the craft. Controlled by firemen, they drew foam compound from the foam tank in the forward compartment by means of water undr pressure. The mixture of water and compound was delivered to the forcing unit with which all monitors and pourers were fitted.
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