Stadium racing. Very popular with the Nips, betting is the name of the game. Its like greyhound racing but with water & boats. They run with Yamato outboards.
See:-
Tech info on Stadium racing (Google Chrome, if you use it, will translate it)
Stadium racing (in English).
Yamato - Mike Ward
We have two 12' Class B Hal Kelly Jinx utility racers (1950's - early 60's) running Yamato's in the CMBA - they have been clocked at 55mph on GPS!