Automotive-Powered Inboard Hydroplanes - Engine Builder Magazine

Automotive-Powered Inboard Hydroplanes

They’re fast, have power aplenty, can turn on a dime, and throw a huge column of water behind them. They’re called Inboard Hydroplanes and are one of the most exciting motorsports shows on water with their automotive powerplants.

The Inboard Hydroplane

The looks of these boats spell speed with fighter aircraft aerodynamics on both the center hull and the sponsons. The design allows the boats to ride on a tunnel of air and use the propeller for forward propulsion.

Most of the time at speed, only the rudder, fixed skid fin and the propeller are in the water.

The boats compete on closed courses with a flying start. The races are always five miles in length. Straightaway speeds are as high as 160+mph with the more-powerful boats.

Starting in 1995, safety cockpits were required by insurance companies. The faster classes use closed-canopies. Also, many inboard hydroplanes have engine rev limiters to prohibit over-reving when the prop leaves the water due to rough racecourse conditions.     

Hydroplanes World-Wide

The hot spots in the world of inboard hydroplane racing are North America (US and Canada), and down under (New Zealand and Australia). There is also some activity in Europe, mainly Germany. And there is considerable rule commonality between Canada and the US. Australia and NZ use both American and Asian engines, but mostly from Japan.

In the US, the hotbeds are in the Pacific Northwest, the Midwest, and upper east coast. The US rules are governed by the American Power Boat Association (APBA). Most of the activity in Canada is within 400 miles of Montreal, with US and Canadian drivers often participating against each other in the same events.

US Hydroplane Engine Rules and Regulations

With the exception of the smallest class, all the inboard hydroplanes are automotive powered. They are classified as either Stock or Modified classes. Stock classes use high-test gas and carburetion. Alcohol with fuel injection is used in some of the modified classes.

Automotive engines were introduced to this sport in the early 1930s with the advent of the Ford V8-60 engine. Later, larger flatheads, including the 239 and 255 V8 versions along with some inline flatheads, would find their way into the boats.

But in 1955, motorsports was infatuated with the light and powerful 265cid Chevy V8. It was used in two hydro classes, the Stock 280 cid class (blueprinted, two-barrel carb, no gearbox) and the 266 cid Modified class, which could use alcohol and fuel injection. No nitro or supercharging, but internal engine parts could be replaced with aftermarket pieces.

In 1970, the 280 class became the 5.0L Stock class with mostly Chevy 305 cid engines, along with more limited use of Ford 302 engines. It remains that way today with a  two-barrel carb still required.

The National Modified class of today allows two equal-power engine variations: (1) a 305 with fuel injection and alcohol or (2) a 360 on gasoline with a two-barrel carburetor.

The biggest auto-powered classes are the Grand Prix (GP) and GNH classes. The GPs use a 468 cid supercharged big block Chevy on alcohol, while the GNH class uses a 511 cid engine with gasoline and a single four-barrel carb.  

Hydroplane Engine Tech

There are no generators or air cleaners on these engines due to the short running time of the races. Water pumps are unnecessary since cooling water is provided to the engine by an underwater pick-up. Also, modern high-performance starters are the choice with these engines. Many times, a custom-made velocity stack is used with the carbureted stock classes. For the more-powerful modified engines, modification is required for the fuel injection and alcohol fuel.

In building a modified engine, it is sometimes necessary to purchase aftermarket camshafts, springs, valves, lifters, pistons, rings or rods for performance and reliability. Engine builders find there are actually fewer rules in the modified classes as are only the displacement and fuel are checked during technical inspections.

There are several nationally known engine builders working with automotive hydroplanes (discussed next), but across the nation there are also a number of one-man operations that build hydro engines on their own. Some of these engines have proved very successful and are proof that independents can compete with the big boys.


Gaerte Engines (

For the smaller hydros, Gaerte concentrates on the 165 cid powerplant which is compatible with the 2.5L class. Gaerte 305 racing engines are also a product with US interest. One of those engines is used by many-time national champion Larry Lauterbach.  The shop also builds 350 hydro engines, many of which are provided to Aussie racers.

But with the company’s competence with 400+cid sprint car engines, it’s not surprising that the big block Gaerte technology has found hydro applications. One example is the 468cid big block for the GP class.

Gaerte’s Shawn Hoff explained that the hydro application is harder on the engines than on dirt or paved tracks.

Esslinger Engineering (

A long time provider of engines for open wheel midget racecars, this company provides basically the same engine to the hydroplane racing community.

Brian Exup of Esslinger explained that there are three displacement engines for the hydro application. “They are 155, 161 and 166 cid engines. They all have the same bore with changes to the stroke.”

Exup explained that there are differences in the way this all-aluminum engine is employed in midgets and boats. “With the midgets, the engine is laid over 45 degrees while it’s normally straight up in the hydro. In the boats, the engines don’t run as hot as they do in the midget because of better cooling.”

Wolfe Engines (    

Owner Marty Wolf explained that he has been in the boat racing engine building for 15 years. His concentration is on the 2.5L, 302 and 350 engines, but he also builds the 468 engine.

“With the 468 engine, I like to use Holley Carbs, which I modify to accept fuel curves. The cam can also be changed, putting more gear into it for torque in the mid-range,” he explained. Wolfe indicated that a customer could purchase either a complete engine, or a long or short block.

Roush Industries (

Roush spokesman Kyle Carrothers explained that in the 1990s, the company got into the hydroplane game with its Trans Am small block Ford engines in the National Modified class. Their use continues today.

“Within the past three-four years, we reconfigured our GM Ecotec drag racing engine package for the 2.5L Modified class with good results. We have also prepared both Ford and Chrysler four-cylinder engines for the 2.5L Modified class,” Carrothers said.

Keen’s Performance Engines (757-365-4481)

This Smithfield, VA, hydro engine builder has been in business since the 1960 and has built over a 100+ engines through the years. During the first two decades, according to JR Keen, the company concentrated on the 1.5, 2.5 and 5.0L Stock classes, along with engines for the National Modified and GNH classes.

In recent years, JR has slowed down, but still produces engines that have powered hydroplanes to two world championships along with a 5.0L High Point Champion.


Blue Collar Performance (

This Westland, MI, engine operation reaches back through three generations and has long been recognized as the racing expert on the Ford Flathead engine. Father and son Rich and Ron Willim are still involved in vintage racecars/hydroplanes that use this powerplant.

But they are also involved in engines for modern hydros, namely the 2.5L Stock and Modified classes and the 5.0L class. In that latter class, one of their engines provided the power for the World Championship hydroplane.

Rich explained that many in the industry don’t realize the shock an engine receives when the prop jumps out of the water. “It’s not like a racecar where the load is pretty equal all the time. As that’s the case, we try to use stronger internal components to keep the engine together,” the elder Willim indicated.

Ron indicated that the operation does much more than just build hydro engines, “We also repair them from the wear and tear of competition, and more often than not we try to right the mistakes made by the customer in his attempts to repair it himself!”

Paul Pfaff Racing Engines (

Gordon Jennings of Pfaff Engines explained that the 7.0L engines are the company’s prime product for both the GP and GNH classes. The tracks are different here on the west coast being only a mile in length with very sharp turns.

He indicated that the big hydro engines are a lot different than their land drag racing counterparts. “Our drag engines run at higher rpms, about 9,000 rpm, while the hydro engines are about a thousand less.

With the boat engines jumping out of the water, we install 8,500 rpm rev limiters to prevent internal engine damage.” Jennings continued, “But we have also built a number of the smaller class engines. We will build any of the hydroplane engines, just give us the specs and will build it,” he said.
GNH-A group of GNH boats showing their high speeds and close competition.A very common Grand Prix Class engine is this 468 cubic inch supercharged alcohol-burning Chevy.The other National Modified set-up is typified by this Roush 360 Ford on gas and a single four-barrel carburetor. This Hemi 468 cid engine type is seldom used in the GP Class.The old reliable 2000/2300cc Pinto engines have been the mainstay of the 2.5 Liter Stock Class for many years.

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