In this article we'll describe what it takes with regards to equipment ranging from the hull to the motor to the propeller, for the very popular mid-level 2.5 Litre Stock class. Qualifying as a racer is pretty basic, we'll describe that too.

Overview | The Hull | Engine | Fuel | Drivetrain | Propellers | Qualifying as a racer

Overview:

The APBA 2.5L Stock class is a relatively low cost, technically simple class of limited inboard hydroplane racing. Historically, this class offers good competition at high performance speeds, with reasonable expense and reasonable equipment durability through restrictions on engine size, engine modifications, and hull size / weight.

The "2.5L" part of the name indicates the maximum engine displacement limit of 2.5 Liters (2500 cc) or 153 cubic inches. The "Stock" portion indicates keeping the engine components to automotive factory-built configuration to limit horsepower with the goal of containing costs

While offering dependable performance these boats approach 100 mph on the oval race course straights (70-75 mph average lap speed), with the current record for a straightaway kilo being 110 mph ... these speeds are plenty fast and plenty thrilling! At the regatta, the USA boats use the class designation S preceding the number (as in S1), while Canadian boats (they have them too, eh!) are noted by CS preceding the number (CS15 for example).

The 2.5L Stock class is one of the most popular hydroplane racing classes, often having the largest number of competing boats at most any regatta. If there are inboard hydroplanes on the regatta schedule, the 2.5L Stocks are racing. The class is popular with the novice driver / owner as well as the more experienced. The Ford 2300 engine is easily assembled and maintained by both the novice and experienced racer. The large number of boats ensures good competition; the speeds are high enough to ensure a good challenge to driver skill; the simplicity of equipment helps durability (to finish first one must first finish); costs are manageable, especially for those on a limited budget. The relatively small size of an S boat lends to easy towing and storage; it is also easy to manage at the races, while waiting in the water for a race or unloading from / loading onto the trailer, not requiring a large pit crew.

The Hull:

The hull is at least 13.5 feet in length, with 15.5 feet being pretty average. A dry hull weight minimum of 975 pounds is specified, with the weight including the driver and driver's gear (any water left in the hull after a race is drained out before weighing). Today's hulls are three point hydro style, constructed either of wood, composites (fiberglass-like materials such as kevlar, carbon fiber, with nomex honeycomb, balsacore, and foamcore paneling), or a combination of both type materials. A safety cell cockpit or a welded steel tubing roll cage surrounds the driver who is restrained by a racing safety harness (seat belt, crotch strap, and shoulder harness). In all of the active S boats today (USA and Canada), the driver sits ahead of the engine, in a so-called "cab-forward" fashion. The end result is a pretty racy looking machine, which resembles a jet fighter more than a traditional boat!

Engine:

The APBA class rules have defined the engine as either a 2000 cc Ford four cylinder or a 2300 cc Ford four cylinder engine, both commonly known as Pinto engines, as their original use was in the Ford Pinto from the 1970's. The 2300 engine has been produced as late as 1995 in Ford Ranger pickup trucks, so it is not a rare motor and is a highly developed, dependable powerplant offering good performance with simplicity of design. Simplicity of design and dependability is especially important, as this class thrives with an engine delivering competitive speed and power, while being easy to tune by even the novice motorhead. The single brand engine allowed enables easy inspection ensuring a level playing field, easy to find parts, easy installation into the hydroplane, and easy technology sharing (facts, parts, secrets, techniques, the "hot setup") among racers, all enabling close competition on the water.

The 2300cc motor has become the mainstay in the class, the 2000 cc engine does not produce quite enough power to easily compete in the 2.5L Stock class, so this discussion will focus on the 2300. This inline four cylinder, cast iron block and head, single overhead camshaft engine displaces 140 cubic inches, with 3.780 inch bore and 3.126 inch stroke . The engines use a specified camshaft, which was used by Ford for marine versions. The crossflow cylinder head (intake on one side, exhaust on the other, separating the ports and manifolds, helps airflow and performance) remains stock, as designed and manufactured by Ford. Machining is only allowed to "blueprint" the component (to bring it to optimum dimensions within the original blueprint specs), to make repairs, or to correct normal wear and tear. The other components in the head (hydraulic lash adjusters, rocker arms, valve spring caps) remain stock, keeping this system dependable with minimal attention required. Valve springs can be changed to aftermarket brands, but there is little advantage in doing so, as the stock marine components developed and designed for the motor function very well. The camshaft can be advanced or retarded by adjusting the cam drive sprocket to help tune the engine power curve to fit the performance needs of the racer. The camshaft drive belt and sprockets are external to the engine, allowing easy adjustments and maintenance. Engine rpm between 6200 and 6500 rpm is typical for the race course straights.

A Rochester 2-barrel marine carburetor set on a cast iron marine (OMC marine) inlet manifold allows this engine to produce around 140 horsepower in race trim. An optional carburetor is the Holley 500 cfm two barrel (model 4412), and an aftermarket aluminum manifold (Esslinger) can also be utilized.

Exhaust headers are allowed, with three popular types: "zoomies" or short individual pipes; "4 into 1" tube headers; and "Tri-Y" 4 into 2 into 1 tube headers. Stainless steel is sometimes used, but plain steel tube is equally effective and more cost efficient. All three types of headers win races, fitting right in with the simplicity theme.

Ignition can be the stock, points type marine; or as an option, electronic ignitions are acceptable for those who do not like to set points. The restriction here is that whatever distributor is used, it must fit into the stock position and be driven in the stock manner by the intermediate shaft. Spark plugs used are generally the OMC marine specified heat range, with all manufacturers accepted. A popular spark plug in use is the Champion RS9YC; other ignition components are easily available from the local auto parts store. Automotive type electrical starter motors are used, and the boat hull clearance usually defines exactly the configuration used. 12 volt electrical systems are universal; most racers do not use a charging system (alternator, generator), so a battery charger hooked up to the battery is a common sight in the pits. Usually oil pressure and coolant temperature gages are employed to allow the driver to monitor engine condition.

Some special parts needed for racing are an aluminum flywheel for quick throttle response, and usually a specially fabricated oil pan is needed to fit the engine properly in the boat hull (clearances can get pretty tight!). The fabricated oil pan also keeps the oil where the oil pump can pump it, aiding in the longevity of the engine.

The cooling system is typical hydroplane - the stock water pump and thermostat housing is discarded, and no radiator is carried onboard. Instead, cooling lake water is picked up by a tube on the rudder, piped directly into the engine block; the pressure provided by the boat moving forward forces the water throughout the engine block and head, with the water exiting from the top of the head and block to be piped overboard, back into the lake. Thus, the hydroplane avails itself of the world's largest radiator: lakes, streams, rivers, and even the ocean; the user can forget about radiator hoses, thermostats, and all that stuff, making for simple maintenance and virtually no expense. Where the stock water pump and thermostat housing each resided, a plate is installed to provide sealing. The plate sometimes is part of the engine mount, doubling up in function!

Fuel:

Fuel used is pump gasoline with no additives. Most boats can carry three or four gallons of fuel; a 5-mile race and 5-minute warm-up period will consume maybe two gallons of fuel. Any grade of gasoline is allowed, as long as it is gasoline and free of additives. Types used range from whatever pump was available at the local gas station to racing gas (Sunoco, Union 76, VP, TurboBlue, etc.), all at the option of the user.

Drivetrain:

Engine mounts are commonly fabricated out of aluminum plates, with a plate attached to the front of the engine and a plate attached to the bellhousing flange (aka, flywheel housing or clutch housing) at the engine rear. These plates, mounted across the motor, are bolted to aluminum angle material, which is fastened to the longitudinal stringers of the boat hull. The engine is carefully aligned with the prop shaft to allow smooth transfer of power from the engine to the prop. For this stock engine class, no gearbox is allowed. To get the correct propeller rotation for the left hand turns, the propeller shaft is coupled to the crankshaft nose (front of the engine, but it faces rearward in the boat!) rather than from the flywheel in every other application of these engines. This unique drive system works well, as the 2.3L Ford engine has a strong enough crankshaft nose to transfer the power to the prop shaft and propeller. The coupling is commonly accomplished by using a tight link double row roller chain wrapped around two sprockets, which are attached to the crankshaft nose and propeller shaft end respectively. Another coupling design provides for a male and female splined joint, which slide together and are locked into position by split bushings. With no transmissions or clutches, either coupling method means the prop is connected directly to the engine. To maintain safety, engines are never started on land / trailer with the devices coupled. The couplers are only hooked up just prior to the boats being placed in the water. The system is simple, very durable, and easy to maintain, fitting right in with the philosophy of the class.

Propellers:

Speaking of propellers, these boats can only use one at a time. The prop is generally stainless steel, with the three or four blades tuned by size and shape for the racecourse. Typically, these are around 10-10.25 inch overall outside blade diameter, with a 17 to 18.5 inch pitch. The props are usually 1 inch spline, although 7/8 inch spline props were popular awhile ago. Suppliers include Mercury Racing, Dewald, Titus. Prop selection goes like this: big course, big prop; small course, small prop. The fine tuning is entirely up to the user, and is more art than science!

Qualifying as a Racer:

Qualifying as a racer is pretty basic. First of all you must be a member of the American Power Boat Association, and one of it's racing member clubs such as the Marine Prop Riders. The certifications are basic ... you'll need a good general physical report from your doctor and to successfully complete the "dunk-test". The dunk-test is performed by certified divers, they give instruction and then strap you into a simulated hydroplane cockpit at the pools edge, and flip you upside-down. You must remove the steering wheel, unlock your safety harness, get out of the cockpit and rise to the surface. You will have a scuba air system and it's not a time-trial ... the point is to teach you not to panic and to follow the steps exactly. At this point you are ready to climb into an inboard hydroplane at an APBA event! Initially you will run under special instructions per the referee at the event ... they may have you do some solo test laps, then for your first few heats you will run behind the race to get a feel for things. When the referee feels you are ready, he signs your form and you are a fully qualified racer!

Thanks to D. W. "Eli" Whitney for the majority of this text