In 1926, L. Gordon Hammersley averaged what was then considered an outstanding 55.2 miles per hour in winning the first President's Cup Regatta.

This weekend, at least 13 Grand Prix International hydroplanes capable of reaching 160 mph will race for the President's Cup, in the 49th running of the event on the Potomac River off Hains Point.

The Grand Prix limited hydroplanes are the fastest in the nation's eight classes of river boats. They will compete in two heats today and Sunday, with the top six squaring off for the cup at 5 p.m. Sunday. Tom Baker and Henry Knab, both past winners of the event, return.

"We're expecting a full turnout of about 80 or 90 boats," said President's Cup Chairman Tom Hurney, who expects close to 20,000 spectators to view the two-day affair.

The seven other classes of boats that will compete over the 1 2/3-mile course are: 280 cubic inch, 2.5 litre, 145 cubic inch (all hydroplanes), and the flat-bottomed Jersey skiffs, ski-boats and super stocks.

The heats for the Grand Prix hydroplanes will be scored on a graduated point system to determine which six boats advance to the final. Winners in the other categories will be solely determined by points accumulated in heats.