Vincent T5AM 500cc Marine Engine
Object ID1113111
Date1944-01-01
Works No44
Accession NoIF:2016:64
StatusOn display
Category Engine
Collection IDInternal Fire Core Collection
Made ByVincent Engineers (Stevenage) Ltd
Made InEngland
Description

500cc opposed piston lifeboat engine.

(Text by Kim Siddorn whoi donated).

The Vincent Marine Engine 

A classic example of being conceived in good time but born too late, the Vincent marine engine was originally made for an air/sea rescue role and fitted to airborne lifeboats, a complete aluminium shell which could be dropped to men in the water from an aircraft. Vincents gave up motorcycle production during the war, concentrating on making specialist components at their Stevenage factory, one of which - for instance - was rocket fuses. Phil Vincent's agile mind was never far from a novel solution to a perceived problem and he found an Air Ministry brief for an engine in which which frugality of fuel consumption was vital - and the other parameters were tough too.

It had to be capable of being started by hand, fully radio screened, waterproof, light in weight and smooth running and able to run for long periods with little maintenance. The construction had to be compact so that the hull of the lifeboat would fit cleanly against the fuselage of the aircraft that carried it and be able to withstand a 5G deceleration as it hit the water. The specification called for 15 bhp at 3000 rpm from an engine that had to be able to run satisfactorily on any petrol, from 70 octane "pool" to highly leaded 120 octane aviation spirit. 

Worked up from an original concept by Phil Irving in 1942, the 500cc Lifeboat Engine (as it became known) was produced with Pacific rescue missions in mond. For a fuel consumption of 50 gallons, the boat seemed to be capable of a total mileage of over 1000 sea miles at an average speed of 5 knots compared to an Austin marine engine's best performance of 500 miles at 4 knots on the same quantity of petrol and the prototype passed its AID inspection out of the box. However, development of a reverse gear, electric start etc, and a vacillating Air Ministry kept Vincents busy until 1949 and that was too late, only fifty being made. Of this single batch, there are around a dozen left, this example having the s/n 44. 

For the technically minded, the device weighs just 256 lbs (116 kilos) and has a watercooled inlet manifold and exhaust. It is a two-stroke cycle, twin crankshaft opposed six, the pistons moving inwards to form a common combustion space, thus this six has three bores. The centre bore of the three provides compressed mixture for the outer two cylinders, the mixture not being compressed in the crankcase as in normal two-strokes. The pumping cylinders have cross heads like a steam engine, allowing straight, round section connecting rods to be sealed from the crankcase with gland seals. The mixture is circulated both "above" and "below" the pumping pistons, transfering to one set of power pistons on the inward stroke and to the other set on the outward stroke thus making best use of the capacity available.

Location
ConditionFair
Images
  
History
2016-07-29

23rd August, 1945.

REPORT ON SEA TRIALS OF VINCENT H.R.D. MARINE ENGINE NO. T5AM/X/2.

Following the acceptance test carried out on 26/7/45, engine No. T5AM/X/2 was installed in the Air Sea Rescue Lifeboat No. CE.9 at the yards of Messrs. Uffa Fox, Cowes, I.O.W. Preliminary trials were run under A.I.D. observation and measurement on 3/8/45, with a 12" diameter x 8 3/4" pitch propeller over a half-mile course in the Medina River. Times for the distance were recorded by stop-watch and fuel consumption measured by time taken to consume 1/2 pint of M.T.72 petrol from a gravity tank. Engine r.p.m. were determined primarily by "Hasler" counter, secondarily by "Smith" tachometer which was found to compare accurately with the Hasler readings. Propeller r.p.m. equals 5/7 of the engine speed with the particular reduction-gear ratio employed.

At full throttle, the engine could turn the propeller at 1520 r.p.m. with a heavy increase in fuel consumption but no increase in speed over that given at 1430 r.p.m. and a stop was fitted to the throttle lever, limiting the r.p.m. to the lower figure.

Further tests were conducted over the same course on 4/8/45 and 7/8/45, on each day conditions were similar, weather being sunny and warm and water smooth although tide conditions were not precisely identical.

At the end of trials, the engine-hatch was filled with water, up to deck level and the engine was started up and run for approximately 1/4 hour, the bilge pump removing approx. 1 gal. per minute during that period.

The results are summarized in the table below, each speed being the mean of two runs opposite directions. The boat was then taken to the open sea off St. Catherine's Point to test its behaviour under rougher conditions. With a fresh breeze and a moderate sea on 9/8/45, propeller speed reached 1415 r.p.m. with the throttle setting which had previously given 1430 r.p.m. this being to some extent due to the engine running cooler than before owing to the absence of a hatch cover. At the reduced speed of 5.3 knots, the engine ran so cool that intermittent misfiring occurred, which was cured by re-setting the water-temperature control valve. Fuel consumption at this speed was measured with the engine below its correct temperature; the results recorded (not under A.I.D. observation) are given below.

The boat was then taken through a heavy swell which appeared to have no adverse effect on the running. When coasting down the slopes of long waves, the r.p.m. rose at times from 1430 to 1500 r.p.m. On 11/8/45 the boat was used to pick up a rubber dinghy and parachutes, thus simulating conditions when rescuing a ditched crew, and on all occasions the engine was restarted with ease.

Table 1
Date Engine
r.p.m.
Propeller
r.p.m.
Speed
(knots>
Time to use
1/2 pint fuel
Range with
50 gals fuel
3.8.4512148684.317m20s924
7.8.4513509655.07113m47s932
4.8.45140010005.22814m57s1019
7.8.45141510105.30214m31s1026
3.8.45174012456.0008m11s655
7.8.45174012456.2107m49s649
4.8.45201014306.8714m40s427
7.8.45201014306.9124m37s425


Table 2
Engine
r.p.m.
Propeller
r.p.m.
Estimated
speed knots
Time to use
1/2 pint fuel
Range with
50 gals fuel
198014156.025m17s480
142510185.3313m27s955

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