In the beginning it looked as if Bill Muncey's prophecy ("We'll Win the Gold Cup," SI, Aug. 11) might hold water. The two rivals that could best scuttle his chances, the monstrous mahogany Maverick and the pink flash called Hawaii Kai were set against one another in heats 1-A and 2-B. But at the start of heat 2-A luck abandoned both Muncey and his new Miss Thriftway as they boiled into the first turn and broadside into a Coast Guard picket boat. The crash sent two-time winner Muncey (upper right) and four guardsmen to the hospital, Miss Thriftway and the 40-foot boat to the bottom of Lake Washington. After that, there was little doubt among some 500,000 spectators that Jack Regas and Hawaii Kai would be the ultimate winner. Which he was. He won so well, in fact, that he picked up almost all the available points: 1,200 for victories in all three of the 30-mile heats, a bonus of 400 for the fastest heat and 400 more for the best overall (and record) time. As Hawaii Kai howled over the finish line, the tiny Regas almost stood up in his seat, waving a clenched fist in triumph. Then, spirits soaring, he wheeled the hydroplane in a tight turn to give officials, press and spectators a thorough soaking.