Lou Whitman, a 49-year-old sailing-canoe expert from Brooklyn, deserves much of the credit for the U.S. victory over Britain early this month in the competition for the little-publicized International Challenge Cup, 69-year-old sailing-canoe trophy originally put up by the N.Y. Canoe Club. The U.S. four-man team, sailing in canoes designed by Team Captain Whitman, edged Britain 2-1 in races at Sea Cliff, N.Y. An apartment-house owner, Whitman's knowledge of naval architecture is self-taught. Sailing canoes are extremely specialized, differing from ordinary canoes in having a full deck over a hull designed for sailing, not paddling. In 1948 Whitman and Adolph Morse of Yonkers, N.Y. (shown at left sitting on the end of the hiking board of a Whitman-designed boat) went to Britain to try to regain the cup which the British had sailed off with in 1933 after almost 50 years of trying. Whitman and Morse did not bring back the cup, but they brought back a lot of knowledge. In 1952 Whitman again went to Britain, this time with Ma√±ana II, a boat of his own design. He was successful and returned with the cup. This year marked the second straight U.S. win.