Smoke on the Water [1994]

Diagram of hydroplane

Like a hybrid of Indy ram cars and jet airplanes, unlimited hydroplanes, also called thunderboats, have several unique features and components:

1. Cockpit: A fully enclosed safety capsule, complete with onboard oxygen system, protects the driver.

2. Ram wing: Center section of the hull acts as an airfoil or wing and provides aerodynamic lift.

3. Airscoop: Intake in cowling provides air to engine. Often extended or modified for saltwater courses to prevent salt buildup on turbine blades.

4. Engine: Usually a Lycoming turbine but can also be a WWII vintage aircraft engine or a combination of various piston engines.

5. Cowling: Covers the engine and improves aerodynamics.

6. Deck: Upper surface of the hull.

7. Tall fin assembly: Two vertical stabilizers with a horizontal wing between them provide directional stability.

8. Turbine exhaust tube: Large metal pipe dissipates engine exhaust. Provides no thrust,

9. Transom: Vertical surface across rear of boat.

10. Tiplets: Small wing-shaped extensions on the rear of the hull help lift the transom and stabilize the boat if the bow pitches up.

11. Rudder: Blade mounted on the transom that is controlled by the steering wheel to turn the boat.

12. Propeller: The only force that moves the boat. Limited to two or three blades.

13. Strut: Holds the prop shaft's rear bearing mount.

14. Prop shaft: Transmits power from the engine to the prop.

15. Skid fin: Blade mounted underneath and to the rear on the left sponson. It helps prevent the boat from sliding right as it turns left.

16. Runner:
The bottom surface of the sponson that touches the water at the bottom. Changing its shape, angle of attack, or dihedral changes the hull's ride.

17. Nontrip chine: Vertical surfaces of the hull; they are inclined to help in cornering,

18. Sponson: The two pontoonlike structures at the front of the hull provide buoyancy. When there is no deck between the sponsons, as in this example, the design is called a "picklefork."

19. Canard: An airfoil-shaped spar mounted between the sponsons. Flaps or ailerons are often mounted on the trailing edge of the canard and are controlled by the driver to stabilize the boat; they provide bowup or bow-down aerodynamic force.

20. Airtrap: An extension of the inside wall that forms the boat's tunnel. Modifying its length changes the hull's ride.

21. Tunnel: The space beneath the hull and between the sponsons and airtrap. It holds a cushion of air on which the boat travels.

Whether you class them as ground-effect vehicles or flying boats, unlimited hydroplane racers are chockfull of high speed and high tech. To Bill Doner, the new commissioner of American Power Boat Assn.'s (APBA) unlimited hydroplane racing, it doesn't matter how you see them just as long as you see them. Around since the 1920s, the sport lags far behind car racing in popularity, but it's not for lack of speed and excitement, he maintains.

One of Doner's top priorities is increasing the number of teams currently on the circuit so they can stage competitive racing weekends. "We'll have 15 to 20 teams, but they don't all compete in every race. And attrition eats up a lot of boats as well," he says.

One method he is willing to try is limiting the technology, thus keeping costs down. "It's very difficult to get new competitors to enter this sport," he notes. "There's no other form of boat racing that prepares you for the unlimiteds and it's a big jump in expenses and capabilities." Still, designers and drivers are taking advantage of every rule and pushing speeds higher year after year.

Power and props

The heart of a successful hydroplane is a small powerplant capable of consistently generating tons of horsepower. For three decades, the engines of choice were WWII fighter aircraft engines, 12-cylinder Rolls-Royce Griffons, Merlins, and Allisons capable of 2,500 hp. In the late 1970s, however, as these engines became scarce, boat designers sought alternatives.

"At that time, it was obvious the sport needed to move on to a modern, more reliable and powerful engine, and one more readily available," says Jim Lucero, crew chief for R. J. Reynolds' Smokin' Joe Racing Team and the sport's winningest crew chief

In the late 1970s, racing teams struck gold with Lycoming's turbine jet engines developed for the Army's CH-47 Chinook helicopter. After being rebuilt and tightened to the manufacturer's original specs, these powerful, lightweight aviation engines crank out about 3,200 hp.

Because these engines are no longer in production, teams acquire them from a Defense Dept. engine-overhaul facility in Corpus Christi, Tex. "We bid on engines coming up for sale by the lot," says Lucero. "And by the time the smoke clears and we have an engine mounted in a hydroplane, we'll have about $60,000 invested in it."

These engines require considerable maintenance, about an hour of down time for every 15 minutes of run time, according to Jay Leckrone, crew chief for the Miss Exide team. "We usually have two of our crew people dedicated to the engine program, and that's all they do."

Adding to the maintenance woes is that racing drivers run the engines too fast and too hot in their chase for the checkered flag. "There's an old rule with turbine engines," says Leckrone. "You can overspeed or overtemp them, but you can't do both. But that's exactly what we're doing constantly with them."

The engines were designed to operate at 98 to 102% of full power, and to have a peak engine temperature of 710°C for no more then 10 sec. Drivers race them at 106 to 108%, and temperatures shoot as high as 840°C for about 15 sec during every turn on the race course.

"Because we're overloading these engines, the rotors and all the rotating parts inside are 'growing' because they're heated and spun so hard," says Leckrone. "They all grow about .0015 in. each race weekend. We end up changing a lot of turbine blades, and they're becoming scarce now. But it's like any other kind of racing: the cost of winning is that you have to hurt equipment."

To help save the engines and minimize the cost of sponsoring an unlimited hydroplane team, the APBA's ruling body for hydroplanes has mandated that this year all racers begin using a fuel restrictor limiting fuel consumption to 4.7 gal/min. Prior to the restrictor, Leckrone's team burned in excess of 5 gal/min. According to several crew chiefs, however, teams can weasel around this regulation by renozzling the engine to get the same rpm and temperature they had without the restrictor.

"The restrictor is a step in the right direction, "says Leckrone, "but it doesn't solve all the problems. My preference is for an rpm governor. Then it wouldn't matter what nozzle you put in, or how much fuel you threw into the engine. A magnetic sensor could read engine rpm and once a boat hit 102%, a valve would open and start dumping fuel rather than feeding it into the engine. Officials worry this might lead some folks to putting different gearing in their gearboxes to make the sensor think the engine is at 102% when it is really at 108%. They think it would lead to too much cheating and be difficult to inspect. The restrictor, on the other hand, is very easy to inspect."

Hydroplanes do use gearboxes, but they cannot have driver-changeable gear ratios. These V-drive gearboxes take power from the drive shaft coming out the front, or inlet end of the engine, at 15,000 to 17,500 rpm, and transfer it to the propeller shaft at about 9,000 to 11,000 rpm.

Teams are just beginning to look at replacements for the Lycoming turbines. They realize that the engines have been out of production, racing chews them up, and eventually they will be unavailable. Current rules allow using any engine, but turbines must be run in stock condition while piston engines may be modified in any way.

Automotive or Indy engines would be an expensive alternative. "You would need 10 automotive engines, running two at a time in the boat, to get you through a race weekend notes Leckrone. "The engines would have to be replaced and rebuilt after every heat."

Another possibility is a British Marine Product 12-liter V-12 engine. It is rated at 1,000 hp at 3,200 rpm, and guaranteed to provide that horsepower for 300 hours. Leckrone and his crew raced a smaller Gran Prix boat with it and it easily powered the boat to 170 mph.

Still another alternative is a commercially available Russian turbine engine. Although it is not approved for racing, Leckrone got permission to test it to see if it is a viable option. Unfortunately, the engine costs about $100,000, considerably more than a Lycoming. It is also slightly longer than current engines, and the power shaft comes out of the exhaust end of the engine. This change from Lycoming's configuration would require modifications to the boat.

Prop specs
Prop specs

Hydroplanes are pushed across the water by a propeller; the jet engines provide no thrust. Limited by the rules to two- or three-bladed props in order to keep production and development costs down, racing teams spend about $10,000 per prop. And they can't get much more than 45 min. of run time from each one.

These propellers are cut so thin for efficiency; all of their fatigue lifecycle is used up after 45 min. The prop then becomes brittle, "like a hand grenade waiting to go off," says Leckrone. "If you lose a blade when running at full speed, the best thing that will happen is you lose your propeller shaft bearings and more than likely rip out the bottom of the boat. If you lose the prop altogether, the boat will probably flip over. The prop creates so much lift at 200 mph that when you take it away, the tail end settles into the water very fast and all the air coming in under the boat from the front end just pushes it over."

"We custom-build props, starting with a forged billet, and then use a CNC machine to cut the blades," says Lucero. Most teams use a 15-in. diameter, three-bladed prop with 26 in. of pitch, (the distance a blade travels forward through the water in one revolution), between 10 and 17° of rake (the angle between prop hub and outer edge of the blade), and between 5 and 7° of shaft angle (the angle between the shaft and bottom of the hull).

Changing any of those prop variables affects ride and handling. Reducing the rake, for example, causes a boat's front end to lift; adding rake pins it down.

Racing teams design their props, as well as many of their boats' other components, in secrecy. Leckrone's team, for example, is working on a prop that pushed one of their boats to 238 mph, 15 mph faster than the current unlimited speed record. His team aims to use that prop to set a new record, possibly in October.


Because all unlimited hydroplane boats are designed for the same purpose and race under identical restrictions, their performance specifications aren't far from one another. But drivers differ, and, according to Jay Leckrone, crew chief for the Miss Exide team of Detroit, "The driver contributes the most to the win, by far."

A perfect example of this, cites Leckrone, is Chip Hanauer, driver of the Miss Budweiser. Last year, he won seven of 10 races, raising his total career wins to 50. This makes him second only to Bill Muncey, who racked up 62 victories between 1950 and 1979. Although the Budweiser team is well-financed and well-crewed, two crucial factors in a winning team, Leckrone gives Hanauer the lion's share of credit for Miss Budweiser taking the checkered flag so often. "Chip probably gives the Bud boat a 7mph advantage," he says.

Becoming an unlimited hydroplane driver is an involved process. First, they must be members of the American Power Boat Assn. and pass a physical exam. They must also be qualified scuba divers and pass an oral test on the racing rules.

For drivers just starting in the unlimited class, they must have 10 heats of competition during the last calendar year in one of the smaller boat classes — 2.5, 4, 5, or 6-liter boats. They must have placed fourth or better in at least half of those heats. Prospective drivers then must run 15 laps at 130 mph or faster for referees and do a timed lap in which the boat completes a lap in a minute, plus or minus three seconds, (the timed lap isn't as hard as it sounds since that's the way drivers start each race in smaller classes.)

Next, the driver races in two competitive unlimited heats, starting in lane six, the outermost lane. A referee then decides if the driver shows enough skill and awareness to qualify. Other drivers may complain if they feel a new driver is unsafe, but they don't hold veto power over qualifications.

Even these qualification procedures aren't strict enough for Leckrone. "I can take a person who has never raced before and set them up in four different class boats over a weekend. They race three heats per class, and boom, they've get all the required driving experience in one weekend," he says. "Some drivers come from boats with a top speed of 80 mph, and suddenly they're going 200 mph. That's not safe. I think you should have to race Gran Prix boats that go about 170 mph, and have 10 heats in those boats before you move up to unlimited."

Flying and left turns

A three-point hull is the most common hull design on the race circuit. It touches the water in three places: the two sponsons, or pontoon-like parts in front, and the prop in the rear. The sponsons provide buoyancy, and their shape helps the front end of the boat clear the water once it is going fast enough. This reduces drag and leads to speeds of over 200 mph on straightaways.

To control how high the boat's nose lifts, drivers manipulate a few aerodynamic surfaces. On boats like Lucero's, the ram wing, or hull section between the sponsons and cockpit, has canards on its leading edge. Other boats have flaps on the rear of the ram wing. In the cockpit, the driver's right foot controls the throttle while the left controls the flaps or canards.

"We once used power-assisted flaps that were controlled from a button on the steering wheel, but we got away from that to keep down costs," Lucero says. "It was getting to the point where well-financed teams were using computer-controlled devices to stabilize the boat, almost fly-by-wire. Now all the surfaces have to be manually operated."

Among three-point hulls, there are two distinct boat designs. The conventional single-wing boat packs air underneath and rides on that cushion of air. The newer two-wing design, such as Lucero's boat, has a wing up front, or ram wing, and another in the rear. "It's hard to tell that a boat has a two-wing design when it's just sitting in the water," notes Leckrone. "But when it's running, the hull is literally a-foot-and-a-half out of the water. It's more like piloting an aircraft than a boat."

Unlike airplanes, however, hydroplanes cannot have movable surfaces above water for steering. Steering is accomplished with just a 90-in.2 rudder; the prop shaft does not pivot for steering. Designers do, however, take advantage of the fact that races consist solely of straightaways and left turns.

A visible example of this is that the right sponson is larger than the left. This lets the right sponson support the full weight of the boat in turns. The cockpit and engine are offset slightly left to make the center of gravity better suited for left turns. The rear vertical stabilizers are also offset, or canted to facilitate left turns. To help the rudder steer, a skid fin, a triangular blade 3-ft across and 2.5-ft deep, extends down from the bottom of the left sponson. When the boat turns, it kicks sideways about 20°, leaning against the skid fin and raising a wall of water.

Five years ago, teams experimented with offsetting the prop shaft to help in turns, says Leckrone. Instead of going straight back from the engine to the prop, the shaft angled right. But when boats without this feature set most records and won most races, the other teams abandoned this trick.

All this attention to improving turn performance is paying off, according to Morley Smith, who owned a boat design company for 25 years. "The straightaway record was set in 1962 with a piston engine, and it hasn't been broken yet. But lap speeds back then were around 110 mph, which means they slowed tremendously when they cornered," he points out. "Today, straightaway speeds aren't essentially much higher, but record lap speeds are up around 170 mph, which means they're not slowing down that much in the turns."

Turns are also hard on the engine. Not only do they strain them by rapidly changing torque requirements, they also limit cooling. Airscoops on unlimited hydroplanes have about four ft2 of inlet area, and 70% of intake air goes to cooling the turbine engine. In turns, as the boat yaws, a much smaller cross-section of the airscoop is turned into the wind. This reduces the amount of cooling air available and raises engine temperatures by 100°C.

Airscoops are one of the few parts teams modify when shifting from freshwater to saltwater courses. While drivers prefer saltwater because it is denser, giving the boat more buoyancy and the prop more to bite into, salt wreaks havoc on engines. Salt buildup on the turbine blades and corrosion ruin them. To avoid this, teams either extend the airscoop to prevent salt from reaching the engine, or add baffles to filter it out.

Material and safety

Most hydroplanes are of a honeycomb composite construction with aluminum skins and core panels, says Lucero. Where the engine and gearbox are mounted to the hull, extra material reinforces the structure. This construction has enough inherent buoyancy to make the boats virtually unsinkable.

A few boats, like one of Leckrone's, are totally graphite and Kevlar. His team has learned how to design and fabricate with composites from various sources including Cyanamid in California, and Boeing. (Many unlimited hydroplane teams have located in Seattle partly because they use much of the same technology and many of the same suppliers as Boeing, which is headquartered there.)

All-composite hulls are the wave of the future, according to Leckrone. "Where most boats come out of the box weighing around 5,000 lb, ours weighs 4,200 lb. And although all boats have to weigh 6,000 lb when they race, it sure is nice being able to put that weight exactly where we want it."

A tubular roll cage surrounds the cockpit, protecting the driver. The area around the driver is also reinforced and enclosed. Most boats use an F-16 aircraft canopy as a windshield or roof for the cockpit. Leckrone's team, for example, takes what would be the windshield portion of the canopy, surrounds and tops it with Kevlar and carbon fiber, and adds side windows made of bulletproof Lexan.

Because boats often flip over and end bottom-up in accidents, there is an escape hatch in the floor of the driver compartment. And although the cockpits are largely waterproof, drivers are always on a closed-air system with each boat carrying a 25-min supply.

A rule of thumb used to be that in an accident, the driver would jump from the boat while it was airborne. Now, with much higher speeds and enclosed cockpits, drivers stay with the boat and wait until it stops. They then exit on their own or wait for a rescue team to open the escape hatch and free them.

"Since this system was put in practice, the sport has had about 25 to 30 serious accidents, with no major fatalities and only a couple serious injuries," says Lucero.

In one of last year's most spectacular accidents, Mark Tate, driving the Winston Eagle, flipped the boat while at full speed on a straightaway, and it flew 400 ft. down the track. Fortunately, his only injuries were two fingers broken when his hands hit the dashboard. He didn't even miss a race.

(Reprinted from Machine Design, Vol. 66 no. 14, July 25, 1994, pp. 34-40. ©Penton Media, Inc. Used by permission)