MARBLEHEAD – Eleven 19th Century firefighters’ handtubs will compete Saturday in what fans claim is the oldest organized sport in the United States – a fireman’s muster – and supporters are predicting large crowds. With summer returning to the North Shore after the heavy rain, supporters are predicting a turnout of 3,000 for the event."The weather makes a difference," said Harold Hansen, president of the OKOs Handtub Association, one of three area handtub clubs that will compete in the 11-tub field.The tubs will compete in two classes, A (10-inch pistons) and B (pistons that are 7 inches or less). Crews will try to pump the longest stream of water from each handtub in turn and the winner in each class will get a prize.According to Hansen, a 40-year handtub veteran who is also a member of Marblehead’s Gerry 5 Handtub Association, the best either Marblehead pump has done so far this summer is third place, so both teams are thirsty for victory.And the Atlantic One Handtub Association from Swampscott, the third area club in this competition, always threatens to be the spoiler. One problem with out-of-town competitions is getting a pumping crew together."In Marblehead we should do OK," Hansen said.The event will feature a parade at 10 a.m. and a competition at 1 p.m. The parade will begin in front of the Marblehead Veterans Middle School, proceed downtown on Pleasant Street, then follow Mugford Street to the Reynolds Playground.The pumping competition begins at noon at Reynolds Field, which is off Green Street, and is scheduled to run through 3:30 p.m. Prizes will be awarded for the longest streams of water pumped.This year’s Fireman’s Muster is dedicated to the late Wayne D. Martin, brother of David Martin of the Gerry 5. Wayne Martin is credited with restoring the Gerry 5. David Martin, 66, has been pumping since he was 13. In those days as many as 30 handtubs would compete in a muster, but those numbers have shrunk with time.