By Stan W Poyser

In 1991-2 design was started for a ‘B’ class flash steam hydro in an effort to increase the existing ‘B’ class flash steam record of about 60 something mph. The ‘B’ class engine embodied several departures from the original ‘A’ class unit in order to be lighter and have improved construction. Every engine/boat builder incorporates their own interpretation of how it should be done, at the same time they should look at the competition and listen to their contemporaries, as they may have tried the proposed changes without success. With this in mind the original concept was maintained i.e. the valve-actuating cam mounted on the crankshaft, but the pump drive transferred to the forward end of the engine and driven by the crankpin, in addition the drive gear would be machined to provide infinite adjustment to the pump stroke as opposed to the time-honoured disc with a series of offset holes to facilitate adjustment.

At this point I feel I should inform the reader of my passion for machining metal, I find it to be satisfying to transform a solid chunk of metal into an operational component. During the design of the engine it was decided that all major screw threads would be screw cut on the lathe to ensure concentricity, accuracy of thread form and correct alignment of components, particularly those associated with the pump ball chambers, glands and rams.

The engine is of conventional construction with a bore of 1 inch and stroke of 5/8 inch, which gives a capacity of a little over 8cc. The crankcase is machined from solid Dural, as are the crankshaft bearing housing, front crankcase cover which also carries the water and fuel pump drive gears and bearings. The crankshaft is machined from a lorry half shaft scrounged from the local garage, the crank pin is 3/9 inch dia. HSS tool-bit pressed into the crank-disc, the con-rod is machined from titanium and fitted with a phosphor bronze little end bush, a 3/8 inch id uncaged INA needle roller bearing is fitted to the big end and runs on the tool steel crankpin.

The cylinder barrel is machined from mild steel and threaded at the lower end where it screws into the crankcase, a mehanite liner with a wall thickness of 1/32 inch is a light press fit into the cylinder barrel. Six exhaust ports 3/8 inch wide x 1/8 inch deep are equi-spaced round the barrel at bottom of the piston stroke to provide the uniflow exhaust.

The cylinder head and valve guide support are machined from tool steel and have a register/spigot to locate this component to the cylinder barrel. The steam inlet valve has 3/8 inch dia. Head and 3/16 inch dia. stem and a lift of .025 thou, the tappet clearance is set to 008-010 thou.

The inlet valve opens 7 degrees before top dead centre and closes 44 degrees after top dead centre, there is no exhaust valve fitted, the uniflow ports open 40 degrees before bottom dead centre and close 40 degrees after bottom centre. Any residual steam in the cylinder after closure being compressed by the ascending piston. The exhaust steam is collected in a steel jacket surrounding the cylinder, then discharged to atmosphere via the silencer, which reduces the noise level to an acceptable level.

The piston is machined from mehanite and fitted with one Dyke ring, having lapped both the cylinder and piston the final running clearance is about three thou.

The water pump ball chamber is fitted with a hand-priming pump for injecting water into the monotube boiler for start up. Water and fuel pumps are mounted on the front crankcase cover and operate at .245 thou stroke via 6-1 reduction spur gears. The water pump bore is .250 inch dia., the fuel pump has a bore of .187 inch dia. Both pumps are of positive displacement design and have 3/16 inch dia. Stainless steel balls for suction and delivery valves, all balls being restricted to a lift of .018 thou and a radial clearance of .005 thou.

Lubrication to the valve and upper cylinder is provided by the hydrostatic system which makes use of the differential in pressure between the feed water and steam pressure at the inlet valve, the water feed to the boiler is fitted with a small tube which supplies water to the bottom of the oil container, this water pressure being higher than steam pressure forces a piston in the oil container to move upwards thus displacing the oil above the piston to be injected into the steam line above the valve via a .015 thou dia. hole thereby lubricating the valve and piston. To date this system has not failed under normal working conditions. Lubrication to the internal crank-case components e.g. Conrod, crank pin, crank shaft bearings, pump drive and cam are catered for by ‘splash’ lubrication from oil within the crankcase.

The monotube boiler and burner arrangement on this model consists of 18ft. of ¼ inch dia. x 20swg stainless steel tube formed into a coil 3 inches in dia at the burner tapering to 2 inches over a length of 14 inches, the burner vaporizing coil is formed from 3/16 inch dia. x 20swg stainless steel tube positioned inside the boiler coil. The whole assembly installed inside a .010 thou stainless steel casing. There are three burner nozzles mounted onto the front end of the boiler wall, the nozzles carry the mounting for the jet block which houses the three burner jets each with an outlet hole .024 thou dia. The outlet end of the casing is formed to an upward swept opening to provide discharge of burnt gases from the burners.

During the running of the A class boats, severe burning and scorching occurred in the boiler area of the hull due to the removal of insulation from the boiler casing to stay within the 16lbs weight limit for the class. With this problem in mind it was decided to construct the hull from 24 swg aluminium, this presented a few difficulties in arriving at a reasonable shape and making the hull watertight, at the same time keeping within the weight limit of 8 lbs for ‘B’ class steamers. All joints were coated with Araldite and riveted, this was a messy undertaking, but the completed hull looked reasonably good. Stress points were reinforced by double plating the areas concerned, and the all up weight came in at 7 lbs 14 ozs.

Phoenix 3 had its first outing at South Cerney in 1993 and recorded a speed of 56mph. Gradually over the following two years this was increased to about 75mph by making adjustments to the engine, pumps, planning angles and burner jets, the greatest problem being to make a propeller to suit this hull-plant combination. During the Phoenix 3 period, the hull suffered from metal fatigue with cracking occurring at the sponson attachment points, and the engine bearers, so in the interests of safety was withdrawn from racing at the end of 1995.

The next hull followed normal construction being built on plywood frames with ¼ sq birch stringers and clad with 1/32 inch marine plywood. In order to reduce the scorching problem an increase in permitted weight to 9 lbs was requested and approved, this change enabled the hull to be ½ inch wider and 3 inches longer improving the airflow around the boiler, which reduced the burning problem. Speeds started to move upwards and on one occasion at Farnborough five consecutive runs were recorded in excess of 85mph. At the St Albans International regatta on August 2^nd 1998 a record for the class was established with a speed of 96.6 mph (from this point onwards things started to go downhill).

The start of the 2001 season prompted me to try a different hull shape, this was to be half round in section on the underside tapering to a pointed nose in an effort to spill air build up under the hull and reduce the possibility of lift at high speed which had been in evidence on the previous hulls. Following a number of poor runs during 2001-2003 it was decided to take this hull out of use and think again about the future. Age and physical constraints were beginning to creep up on me, and it was reluctantly decided to end active power boating.

©copyrightStanPoyser2007