1973 APBA Gold Cup
Columbia River, Tri-Cities WA, July 22, 1973

Unlimited Hydroplanes ‘73: A Period of Experimentation

Will It Revolutionize Unlimited Hydroplane Racing?
The Unlimiteds
Unlimited Hydroplanes ‘73: A Period of Experimentation
Chenoweth Pilots Bud to Victory in Tri-Cities

Bud ‘Rides’ Pak’s Broken Prop


Turbines, turbo-charging, space-age materials, wing stabilizers — it’s an interesting year for the unlimited hydroplanes.

For the past 20 years, no one has been able to find a better power plant for unlimited hydroplanes than World War II aircraft engines. Perhaps this will be changing?

The supply of the big 12-cylinder V-type aircraft engines which gave the free world air superiority in World War II is still surprisingly good. One of the major problems is finding enough mechanics and crew members who are skilled at working on the engines. After all, there aren’t too many other calls these days for people to work on World War II aircraft engines!

Even putting an aircraft engine into a hydro isn’t simple; major changes are necessary to adapt an engine to water usage. First, the engine as it was set up for airplane use, is reversed. The front becomes the rear, and vice versa. Second, the supercharger is turned upside down, so that carburetor sits on top of the engine instead of on the bottom. (Fighter planes had air intakes on the bottom of the fuselage and the carburetor was mounted upside down). Third, the propeller gears are removed and a special gear box manufactured especially for racing is installed. This gearbox delivers three times the speed of the engine to the propeller—when the engine is turning 4,000 RPM’s the propeller is turning over 12,000 RPM’s.

The mortality rate among engines is fearsome. In fighter aircraft, these engines were overhauled every 300-400 hours. In hydroplanes, an engine cannot be operated for more than one hour without being completely disassembled. Many engines last less than one 15-mile heat due to the terrific strain.

Turbo-charging akin to that of the Indianapolis 500 cars is an innovation in the Lincoln Thrift and Miss U.S. boats.

Most boats use a gear-driven fan to compress air for faster engine operation. Since the fans operate at supersonic speeds above 35,000 RPM’s they can be a source of constant problems.

In turbo-charging, exhaust gases are pumped back through the engine to turn the fan. The exhaust is recycled with new fuel and the result is greater acceleration off the turns.

The two Schoenith-owned boats, Atlas and Gales’s Roostertail, are using a new fuel injection system that "sprays" fuel directly into the cylinder in a search of greater fuel efficiency and better acceleration.

The exotic metals and materials of today are being utilized in at least two of the unlimited hydros to keep the weight down.

George Simon’s new Miss U.S. tips the scales at just under 5,000 in racing trim compared to 6,500 to over 7,000 pounds for some boats. Miss U.S., utilizing lightweight titanium and magnesium in hull construction to keep the weight down, is probably the lightest boat in the ‘73 fleet.

The new Pay ‘N Pak weighs in at about 6,000 pounds, also considerably lighter than most boats. The new Pak utilizes honeycombed aluminum that is actually two sheets of aluminum bonded and separated by a honeycombed aluminum core.

Boat owners seemed to be satisfied that they are reaching maximum safe speeds on the straightaways. Their challenge now is to develop a boat design and power source that can make better time around the corners.

Hydroplane hulls are designed so that air pressure on the top of the curved front deck keeps the boat down, while air pressure in a tunnel between the sponsons lifts it up. One compensates for the other in a properly balanced boat.

As the boat rises on a column of air, it "walks" on its two sponsons, spilling out air, keeping the boat from becoming airborne, but just barely touching the water. Obviously, the delicate balance is a hard thing to achieve.

The "wing" or horizontal stabilizer on the tail fin of Pay ‘N Pak is adjustable. If the boat is not riding quite right because of water conditions, the pitch of the stabilizer can be adjusted to improve the riding characteristics of the boat.

The Pay ‘N Pak crew uses a video tape machine to record the performance of their boat for "playback at a more convenient time" for study. The driver also has a radio receiver in his helmet to pick up information relayed from the beach.

Somehow, the use of automotive power for the unlimiteds is not being mentioned very much during the ‘73 season. For one thing, the hydro people have been reluctant to drop the length and weight restrictions that would be necessary for auto engines to be competitive. Now a boat must be at least 28 feet long and weigh over 4,000 pounds—and most designers say that’s too long and too heavy for efficient use of automotive power.

And now, the biggest news is a turbine-powered boat that hopefully will make its first racing appearance in the Gold Cup.

Lighter boats? New power plants? What changes will be forthcoming in the 1974 unlimited fleet?

(Reprinted from the 1973 Tri-Cities Gold Cup programme)

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