New Record: Speed Boat Sets 178 Mile Mark Famed racing boat Slo-mo-shun fourth (Slo-mo-shun IV) roars across Lake Washington to set a new all-time speed record. More honors for the world's fastest boat. CU pilot Stanley Sayres. He and one of the designers climb aboard. Speedboat does its thing, paced by a seaplane (!) flying right near it, just off the water. It makes another run without the seaplane.