Definition of "boat race"
(gambling, slang) A fixed horse race, with a specific horse arranged to win in advance.
Quotations
"Now," Herbie says, dropping his voice away down low, in case old Cap Duhaine may be around somewhere listening, "it is the third race, and the horse is a horse by the name of Never Despair. It is a boat race," Herbie says. "They are going to shoo in Never Despair. Everything else in the race is a cooler," he says.
1944, Damon Runyon, “A Story Goes With It”, in Stories à la Carte