Stock Outboard Racing

Stock outboard racing is sanctioned by the American Power Boat Association (APBA). It includes seven classes of both hydroplane and runabout hull types. The classes are structured according to the hull type and 2-cycle outboard motor that is used. "Stock" indicates that the motors are not mechanically modified to increase their performance, and limits the type of fuel to standard gasoline (no additives). "Outboard" means that the motors are small self-contained units that are mounted to the boat’s transom. The boats range in length from about 9–13 ft.

Children can start racing at age 9 in the "J" (junior) class. This class runs restrictors on the motor’s intake and a low efficiency propeller to limit the boat’s speed. This gives young racers the confidence they need to become comfortable with their boat. Race events are organized by local clubs (e.g., the Michigan Hydroplane Racing Association [MHRA]), and are conducted all over the United States and Canada. These family oriented, weekend events are open to the public and are often promoted and supported by the local community where they are held. The race event schedule is similar from year to year and can be found on this web site and the APBA web site (www.apba.org). The event that changes from year to year is the Stock, Modified, and J-Class Outboard National Championships. This week-long event is hosted by a different region and club each year.

The primary division of the classes is according to hull type—hydroplane or runabout.

C Stock Hydroplane (CSH)

Hydroplane

A 3-point hydroplane relies on getting lift by channeling air through a tunnel or air trap that runs down the middle and full length of the bottom of the boat. It also gets lift because of its overall airfoil shape. As the boat’s speed increases it gets "on plane"—it lifts up out of the water, thereby decreasing drag and allowing the boat to skip across the top of the water. On either side of the air trap, in the front area of the boat, are sponsons. Sponsons help the boat to plane off, provide stability when turning, and channel air into the air trap at high speeds. When the boat is on plane at high speed, it literally flies across the water. Only the back few inches of the bottom of the boat and the tips of the propeller blades are in the water—the bottom of the sponsons occasionally tap the water. This is where the "3-point" name comes from—2 sponsons and the rear of the transom. The 3-point configuration provides stability. The hydro has a turn fin mounted to the rear of the left sponson. Since all standard racecourses are ovals, and are run in a counter-clockwise direction, the turn fin ensures that the hydro "hangs on" through the turn. When going into a turn the driver shifts their weight to the inside of the turn—this sets the inside sponson and turn fin down and allows the boat to be turned. When coming out of the turn the driver shifts their weight back to the center and back of the cockpit—this balances the boat and allows it to fly again.

C Stock Runabout (CSR)

Runabout

A runabout is a unique high performance design, born from the days when outboard pleasure boats were used for competitive racing on the weekends. The hulls are 10–13 ft long, and have a flat planing surface in the back area of the boat’s bottom. The hulls normally have very pointed noses. Chines (angled surfaces between the bottom and the sides, can be round or flat), sides, front deck, and transom make up the rest of the hull. The hull turns left by "rolling up" on its left chine or by turning flat like a hydroplane by using a pod fin on the left chine. Speeds depend on the motor used, weight, and size of the hull. The hulls are very stable and allow for very competitive racing.

Motors

The motor defines the next level of class division within either the hydroplane or runabout hull types. The classes run increasingly faster, from A to D, with speeds of about 50 mph in the A class to speeds in excess of 80 mph in the D class. The J-class runs at speeds of approximately 35 mph.

The classes are defined according to the type of motor used:

Set Up

Because the boats and motors are so evenly matched, the boat’s "set up" is very important. One part of the set up process is adjusting the height and angle of the motor. If the motor is too deep in the water, too much of the lower unit is in the water causing excessive drag. If the motor is too high, the propeller doesn't get enough "bite" and it’s efficiency is decreased. There are also regulations that determine the minimum allowed propeller shaft distance from the bottom of the boat. The angle of the motor is also important. If the motor is "kicked under" too much, the boat’s nose is pushed down, not enough air can get under the boat and the boat is not allowed to fly. If the motor is "kicked out" too much, the boat’s nose is pushed up and too much air gets under the boat and "blow-overs" can occur. An efficient propeller is one of the most important aspects of the setup. There are several propeller manufacturers that develop propellers for stock outboard racing. Even though you can buy a propeller for a particular boat style and class, finding the best prop can take a lot of testing!