Here you go, Bill.....
On my 25.5 I have a Perko standard masthead light (front & Rear) and it takes a FESTOON bulb (double ended) about 10 watts. There is a short bulb and a long bulb...I think you will want the long bulb. You can get the bulbs in the auto lamp dept at Wal-Mart, but the bulbs at a boat store (Aqua Signal, Perko, Sea-Dog, etc) will have stainless steel for the metal part, which will last longer in the weather. The part # at Sailnet is ABI840805. Dave