Hydroplanes, no matter what size, have one thing in common. When underway they touch the water at three points; the very aft end of the port and starboard sponsons, which all hydroplanes have, and the propeller area. The very first hydroplane was designed and patented by Adolph Apel in 1936. Early hydroplanes had a “shovel nose” or rounded bow. The shovel nose bow gave way over time to the “pickle fork” bow. Beyond that, hydroplanes come in a variety of shapes and sizes from small outboard hydroplanes to the big unlimited hydroplanes. The APBA Vintage and Historic Division provide the rules for classifying the hydroplanes you’ll see at the Antique Raceboat Regatta. Here’s a quick run down of the basics so you can better understand what you will see at the ABM this weekend. You’ll know them by their letter designators.

Inboard Hydroplanes

engine info:
1 cubic inch (CI) = 16.4 cubic centimeters (CC) = 0.164 Liters (L)
135 CI = 2.2 Liter motor
305 CI = 5 Liter motor
426 CI = 7 Liter motor

Y Class – 48 CI to 1L Modified motors, 2 and 4 cycle motors allowed but with rules specific to the motor used; no blowers, superchargers or outdrives permitted; multiple carburetors or fuel injection allowed, same hull rules as T Class. Early Y class boats ran low 70 mph with later Y class speeds to 102 mph.

T Class – 44 CI to 1.5 L Stock motors; minimum weight 750 pounds; maximum length 17’6”. Early T class boats ran low 60 mph with later T class running to low 90 mph.

L Class – 91 – 98 CI (1.6 L) Modified motors; double overhead CAMS allowed; one 2 barrel carburetor running gasoline; minimum length 12’. Early L class boats ran high 50 mph with later L class running to 115 mph.

S Class – 136 CI (2.2 L) Stock motors , one 2 barrel carburetor running gasoline, minimum length 13’6”, minimum weight 975 pounds; fuel injection allowed. Early S class boats ran low 50 mph with later S class running to mid 100 mph.

A Class (CM Class – Canadian equivalent of the A Class) – early class rules limited displacement to 135 ci but was later changed to 153 CI (2.5 L) Modified motors, minimum length 16’; fuel injection allowed; double overhead CAMS, blowers, superchargers are not allowed. Motors were not as modified in the CM class. Early A class boats ran mid 70 mph with later A class running to mid 130 mph.

N Class – 225 CI (3.7 L) Stock motors; one venturi per two cylinders allowed, Early N class boats ran mid 90 mph with later N class running to mid 130 mph.

E Class – Stock 305 CI GM engine with one 2 barrel carburetor (5 liter); minimum length 16’, minimum weight 1450 pounds. No internal motor components allowed. Early E class boats ran low 90 mph with later E class running to mid 120 mph.

National Modified Class (F Class) – engines from 155 to 368 CI (2.5 L to 6 L), minimum lengths 17’ up to 19’ depending on engine, minimum weight is 1600 pounds. Motors are modified and can be 308 CI (5 L) with alcohol or fuel injection, or a 368 CI (6 L) gasoline engine with one 4 barrel carburetor.

Grand National Hydroplane – minimum length 20’, maximum length 26’, minimum weight 2000 pounds, engines must have cast iron blocks and a maximum displacement of 468 CI (7.7 L) with an American made 600 CFM carburetor with specific tolerances running racing gas. Special driver requirements apply. Speeds to 150 mph.

Grand Prix Hydroplane

Grand Prix class started in Canada, in 1974. The class merged with some H class hydroplanes and became a US class. The GP class were governing themselves outside of the APBA until about 1980. This class is the only one that has the same rules outside of the US, and run in Canada, Australia and New Zealand. They currently run a 500 cubic inch blown engine with drive restrictions.

Miss Sapphire N-700
Miss Sapphire (N-700) at speed; note how this hydroplane is barely touching the water other than the propeller shaft and rear of the sponsors.