Roostertails Unlimited:
[1973]
Chapter 5 - The Powerplant
The most important element in the operation of the hydro is, of course, the
engine. Many models have been used but only two have had any element of success
-- the Allison and the Rolls-Royce Merlin. Most arrived as surplus at the end of
the Second World War and became the basis of powerplants before long.
The Allison engine was built by General Motors and had powered the Curtis
P-40 "Warhawk", the Lockheed P-38 and the North American P-51
"Mustang". This engine was the first one used in Slo-Mo-Shun IV
and actually was the main power of the majority of hydroplanes in the early days
after the war. It is slightly larger than the Rolls Merlin in displacement and
has a higher stock horsepower.
The Rolls-Royce Merlin was built by Packard and served as the powerplant for
most of the British fighter planes, including the "Spitfire" and the
Hawker "Hurricane". This engine now serves as the power for the vast
majority of the hydroplanes of today mainly because of their superior
supercharger, a unit which compresses the air-fuel mixture before it is sent to
the cylinder to be ignited, thus giving the engine about 500 extra horsepower.
On the Allison the supercharger has a single-stage, one-speed
"blower". The Merlin has a two-stage, two-speed supercharger besides
having an inner and after cooler in its intake system, which means the
supercharger is surrounded and cooled by a water jacket. Between the engine and
the ‘charger’ the air-fuel mixture is compressed to 44 pounds per square
inch pressure, goes through the inner cooler which stabilizes the mixture
temperature and prevents the expansion of the intake gases too son. This gives
it more power. The infamous "quill shaft", that has eliminated so many
boats through the years, is a thin rod that connects the supercharger to the
power unit.
Inside the supercharger are impeller blades that whirl around at above 35,000
r.p.m. — near supersonic speed. These razor sharp fans get white hot instantly
and can "grow" enough to fuse to the side of the chamber and cause a
supercharger malfunction. If the boat should leap from the water there results
an instant overspeeding of the engine with an accompanying increase in
supercharger speed; this is when the "growth" occurs.
To further compare the two types of engines, we find the Allison has a higher
low-speed torque, in fact, at 100 m.p.h. it has more power but has a slower rate
of acceleration. The Rolls Merlin, on the other hand, has increasing power with
rising speed, which will not slack off. The Merlin is also 250 pounds heavier
and must, therefore, be mounted several inches behind the location of an
Allison.
Both engines are V-12s and have about the same outside dimensions. Each
cylinder of both models has two exhaust and two intake valves and are ignited by
a couple of spark plugs which are fired independently by a pair of magnetos.
They have either fuel-injection or a standard two or three barrel carburetor,
have seven main bearings and are liquid cooled. The water is fed to the engines
through water intakes that hang from the back of each sponson. Most engines are
designed for a constant water pressure of 25 pounds per square inch. At high
speeds, when the pick-up pressure is greater, a spring-loaded relief valve opens
to keep the pressure at a constant. The engines had cost about $45,000 apiece
for their respective governments to produce. They now sell for less than
$10,000.
To transform the engine from airplane use to hydroplane use it must be
inserted backwards, the supercharger is turned upside-down so that the
carburetor sits atop the engine instead of on the bottom, as it was in the
airplane, and the propeller gears are replaced by a special gear box
manufactured especially for the sport.
Other engines have been tried through the years. The Rolls-Royce Griffon,
which powered Canadian aircraft and is still used in some British craft, is
larger and more powerful than its sister the Rolls Merlin. It was used in the Supertest
entries and was very fast, then later in Harrah's Club and Budweiser Malt
Liquor. They are now mostly controlled by the Budweiser organization. Austin
Snell tried to drop a Daimler-Benz Mercedes engine, from the ME-109
Messerschmitt, into his Coral Reef. More than one problem was encountered
in this venture, not the least of which was the necessity to mount it
upside-down.
In addition to the most popular Allison models: the G-6, the-113 and the
-111, the old Scooter Too had a special model W-24 Allison which had 24
cylinders, the first $ Bill had a rare -1710 model and Wildroot
Charlie ran on a -117. The Gale VII used a V-16 Packard but it never
panned out.
A couple owners have actively tested turbine engines for the Unlimiteds, none
successful enough to compete with the rest of the field. Westinghouse and
General Electric turbines were used in these tests. Early in 1973 the plans for
another turbine powered hydroplane were introduced. The craft uses twin Lycoming
T-53 "Huey" helicopter engines, which put out 1700 horsepower and
weigh only 465 pounds.
The automobile engine has been tried on numerous occasions. In 1956, a boat
named Miss Skyway was powered by two Chevy V-8s with a V-belt drive to
the prop shaft ...she never went faster than 45 m.p.h. Miss U, the
"one-point" boat, was powered by a six cylinder Ranger. Chrysler
Crew appeared in 1966 with twin Chrysler Hemis as its powerplant, she was
more successful than most but an Allison eventually replaced them because of a
strike at Chrysler Motors in 1968. The idea caught on and in 1967 The
Dutchman was powered by a pair of Fords, she failed to qualify. Ron Jones
built a boat in 1969 that had twin Chevrolet Mercrusers, but it never raced,
then in 1970 two boats appeared that were auto powered: the Pride of Pay 'n
Pak and Atlas Van Lines, U-29. Both were powered by Chrysler Hemis
and both had them replaced by conventional power when the season ended.
There is presently a revolution brewing in the engine development of
Unlimiteds...the turbocharger. Tested a great deal at Indianapolis this concept
was first introduced in a manner especially made for Unlimiteds by Bob Fendler
on his Allison powered Lincoln Thrift in 1972, the same hull mentioned
above as Atlas, U-29. A different version was used on Harrah's Club
in 1965 but its particular set-up never evolved and was replaced. The
turbocharger takes the place of a supercharger and can be adjusted to
accommodate the situation, be it qualifying or racing, and is much quieter than
its supercharger cousin.
Instead of compressing the air-fuel mixture with the mechanical power of its
own engine's revolutions through the quill shaft, as does the supercharger, the
turbocharger compresses the mix with power supplied by the exhaust. When the
engine with a supercharger is throttled back, the power continues to be produced
at the same rate but with no r.p.m’s to take it up. With the turbocharger,
this excess power is vented off through a special valve which can be closed when
all the power is again needed. To date the turbocharger idea has worked very
well and is becoming more popular.
There have been many configurations of engine placement in the hull also. In
1953, the Gale III had a single engine but two contra-rotating propellers
from one gear box. Later, in 1954, a boat named Miss Wayne had a pair of
Allisons placed side-by-side with contra-rotating props. There have been many
famous attempts at tandem mountings, few successful. Jack Schafer insisted on
this design in most of his Such Crusts and it was also used in both Gale
VI’s. Both applications were always being plagued with mechanical troubles
- especially in the gear box. The notable exception is Miss Pepsi which
was quite competitive with its twin engines.
Let's look at the performance of a typical engine used in a hydroplane. In
racing trim the Rolls-Royce Merlin displaces 1650 cubic inches, has a bore and
stroke of 5.5" x 6.0" and a supercharger ratio of 5.80:1. The engine
can turn at 4200 revolutions per minute, though it was designed for about half
that amount in airplane use, and coupled with a gear box ratio of approximately
3:1, the shaft rotates at over 12,000 revolutions per minute. As it races the
Unlimited powerplant produces about 2500 horsepower.
The engines are made for the most part of lightweight metals such as aluminum
and magnesium, and with certain internal modifications the performance is much
higher than for what they were designed. As a result they must be overhauled
completely after operation for only an hour, sometimes less, compared to every
300-400 hours while in their original role.
To feed this monster is gasoline that fills two 40-50 gallon tanks on either
side of the cockpit and engine compartment. The fuel tanks are made of welded
aluminum wrapped with reinforced fiberglass so that if a crack should appear it
can be repaired with a little resin and cloth between heats. As the boat goes
through the turns at high speeds the fuel is thrown high against the wall of the
tank. This leaves a void and fills the fuel lines with air which causes a
backfire with slowdown or can even blow a part of the engine off. To help
eliminate this problem, there is a partition that traps some fuel over the fuel
line intake within the tank.
The fuel type is categorized according to a system which refers to its
comparison with the highest known anti-knock product at the same the scale was
created ... iso-octane. An octane number of 100 was considered the equivalent of
pure iso-octane. Fuels have surpassed that scale and a high test aviation fuel
with a performance rating of 115-145 is used as the base in most hydros. The
"115" refers to the lean figure while the "145" is the
performance possible with a rich mixture setting. Your car probably uses a fuel
rated at nearly 100 but some cheap gas can be as low as 80.
Added to this fuel are many things, including alcohol. Some crews add a
couple cc's of tetra-ethyl lead to help govern the rate of burn in the engine
and boost performance. The Hawaii Kai III used a "super"
mixture which blended two select and pure hydrocarbons in a 60/40 ratio, this
combination gave it a performance rating of 176-196. The engine loves the fuel
and consumes almost five gallons per mile ...it would never win in a good
mileage contest.
To give the boat an extra boost as it exits the turn a squirt of
"laughing gas" is given the powerplant. Also known as Nitrous Oxide,
this substance causes a large explosion in the engine and a quick spurt of extra
power. It cannot be injected for more than five seconds at any one time,
however, because it would blow the engine apart with the higher manifold
pressure created. This idea was first used in Miss Exide in 1963.
An Unlimited Hydroplane engine holds 15 gallons of oil to keep it well
lubricated and to start the thing is an electric starter motor somewhat like the
one in your car. The difference is that it takes two 24-volt batteries to do the
trick - these are hidden beneath the driver's seat.
(Reprinted from Roostertails Unlimited by Andy Muntz, 1973)
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