Have you been wondering why the hydroplanes carry a letter AND a number with their names? What a good question! The owner of the boat chooses the number that the boat carries. The APBA uses letter prefixes to differentiate between each class of hydroplanes. Each class has its own specific rules mostly with regard to the length of the boat, size of the engine, and whether the engine may be modified or is required to be stock. These rules often changed with the development of new engines, so the letter classifications did not always designate the same size of boat through the years.

North American Inboard Hydroplane class 1950 – 1975
letter motor size motor description
Y 48ci – 850cc modified
T 44ci – 72ci stock
L 91ci – 98ci modified
S 136ci – 145ci stock
A 135ci – 150ci – 2.5 litre modified
N 225ci Div. II & regular 225ci (thru-’75) modified (slightly)
F 225ci Div. l – 266ci – 305ci modified
E 280ci stock
J 7-Litre Div. II stock
H 7-Litre, 7-Litre Div. I modified
GP started officially in U.S. as a class in 1974 modified
U always been unlimited modified
CM 3-litre (Canadian)
CQ 6-litre (Canadian)