Vincent lifeboat engine

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The Vincent lifeboat engine was a unique design of two-stroke petrol engine. It was developed during World War II as a highly efficient engine for airborne lifeboats, providing a long range from little fuel.

Requirements

The

air-sea rescue launches.[citation needed
]

Several designs of airborne lifeboat were developed, using both

aviation spirit.[2][3] The best range achieved by the previous Austin marine engine on the same quantity of fuel had been 500 miles at 4 knots.[3] Further requirements were that the engine would be waterproof against submersion of all but its air intake, its ignition system would be radio screened and that it would be reliable enough to not require maintenance during a voyage. As the lifeboat was dropped by parachute, it had to survive a 5 G deceleration as it hit the water.[citation needed
]

Design

The design was developed by

opposed piston engine.[1]

The engine had three horizontal cylinders, the outer two of which were power cylinders and the centre cylinder used as a

transfer ports were angle-drilled to encourage swirl.[5]

The scavenging pistons were even more unusual, being

crosshead form, with a ½" diameter piston rod emerging through a seal to a crosshead formed on the end of the piston rod, where it carried the connecting rod.[6]

The pistons were driven by two separate three-throw crankshafts, coupled by a chain drive. The exhaust crankshaft led the transfer crankshaft by 24°.[note 1] The same chain also drive a reduction sprocket to give a propeller shaft reduction of 2.04:1. Propeller output also passed through a reversing gearbox with two multi-plate oil clutches to select direction.[citation needed]

The main body of the engine was a single aluminium casting, with

dry liners to the cylinders. The crankshafts were also of cast iron.[citation needed
]

Ancillaries were at the ends of the engine. A

electric starter, a dynamo generator and the BTH ignition magneto.[6] The carburettor was an Amal
.

Dimensions[1]
Power pistons 56 mm (bore) × 50.8 mm (stroke)
Capacity 497 cc
Compression ratio 7.0:1
Pump pistons 63.5 mm × 38 mm
Port timing Relative to transfer crank, leads exhaust crankshaft by 24°
Transfer opens 39° bbdc
closes 39° abdc
Exhaust opens 72° bbdc
closes 25° abdc
Weight 264 lb
Performance

Performance of the propeller was limited by cavitation to 15 bhp, so the engine was tuned for maximum economy at just below this power.[1] Fuel consumption was 0.71 pints/bhp/hour at 11 bhp, rising slightly at 14 bhp. This gave the desired range of 1,020 miles at 5.3 knots on 50 gallons of fuel.[citation needed]

Service

Although performing well in its tests, the engine did not enter service.[6] This was due to the unexpectedly rapid end to the war in the Far East, and the lack of urgency that created within the Air Ministry. Although the basic engine was ready on time, much development after this was spent on ancillaries such as electric starting and a reverse gear. The production engines did not appear until 1949.[6]

Survivors

The engine was rare in its period, only fifty being built. Survivors today are few, although a relatively large proportion of around a dozen are claimed to survive.[6]

Developments

Post-war, the lifeboat engine was doubled up into a flat-six (four power cylinders, two pumping) twelve-piston engine for a 10 kVA generator.[7] This engine was unsuccessful owing to problems with the complex crankcase casting warping after machining, preventing a reliable seal.[8]

Other developments

In 1956, Vincent produced the

personal water craft.[9] Although there has frequently been confusion over the "Vincent marine engine", the engine used here was unrelated, a 150 cc air-cooled single-cylinder engine that was also used in the Vincent lawnmower.[10] Owing to quality problems with the fibreglass hull of the craft, rather than any engine problems, these were not a success and the idea was forgotten for over a decade.[citation needed
]

See also

  • Lloyd 650, another two-stroke engine of comparable vintage, with two power cylinders sharing a single double-acting pumping cylinder.

Notes

  1. transfer ports led the exhaust crankshaft by 24°. This is a typical feature of opposed-piston engines, as the longer opening of the exhaust port improves scavenging. The Napier Deltic
    's geometry imposed a convenient lead of 20°.

References

  1. ^ a b c d Irving, P E (1967). "Marine Engines". Vincent Marine Engine. Two Stroke Power Units. London: George Newnes. pp. 246–250.
  2. ^ JK Siddorn. "Vincent marine engines". Archived from the original on 4 November 2012.
  3. ^ a b JK Siddorn (2 February 2010). "Vincent lifeboat engine and double acting pistons". Newsgroup: uk.rec.engines.stationary.
  4. ^ Irving 1967, p. 30
  5. ^ Irving 1967, pp. 35–37
  6. ^ a b c d e f JK Siddorn. "Vincent marine engines". Archived from the original on 4 November 2012.
  7. ^ "Double marine engine genny1". JK Siddorn. Archived from the original on 4 November 2012.
  8. ^ "Vincent Marine Engine". Stationary Engine Magazine (156). February 1987.
  9. ^ "Vincent Amanda Water Scooter".
  10. ^ "Vincent Amanda Jet Ski and Lawn Mower". 2 February 2011.
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