A federal judge has sentenced to prison four of the six crewmen of a fishing boat that was seized in San Francisco Bay with about 48,000 pounds of Thai marijuana. U.S. District Judge Charles Legge Friday dealt 10-year sentences to Steven Larsen, 34, of Watsonville; Olen Collum, 36, of Fairfax, and Michael Houlahan, 35, of Mendocino County, and an eight-year term to Tyrone Swader, 44, of Santa Barbara. Awaiting sentencing are the boat’s captain, Miles Ragland, 23, of Bodega Bay, and crewman Ronald Potts, 36, of Woodacre. The 76-foot Oregon Beaver, based in Bodega Bay, was stopped by the Coast Guard when it entered San Francisco Bay. Authorities said it was one of the largest marijuana seizures in West Coast history.