Number One man in the world of motorboating is this skillful, sea-wise skipper whose career covers more than half a century of power boats. In tribute to his standing, his certificate in the United States Power Squadron and his government license both read "No. 1." And as a longtime national chief commander of the U.S.P.S., as author of most of the rules that govern its procedure, and as a referee, arbiter and judge of practically every power regatta of consequence, Charles Chapman has had an influence on all who go down to the sea in motorboats. In fact, members of the 232 branch units of the Power Squadron learn their lessons from his Piloting, Seamanship and Small Boat Handling, the standard text on the matter, bible of the sport. Chap's knowledge comes from experience. Among other things, as holder of a degree in marine engineering from Cornell, he rode as navigator with the great Gar Wood when they raced a train from Miami to New York in 1921 and when, four years later, the same pair beat the Twentieth Century Limited from Albany to New York. Now, at 77, retired from that kind of splash, Chapman is editor of Motor Boating and cuts his wakes with an open 22-footer out of Essex, Conn.