RedactedNarrative: Owner had just got his vessel back from the shop for minor repairs when it would not turn over. He asked his friend a mechanic to look at it. It was on a lifted dock the mechanic went to borrow a diagnostic scanner to hook up on the engine.He returned and removed a few of the spark plugs and the cylinders had gas in them and he was cranking the engine to remove the gas when the boat exploded. Cause of explosion was due to gas vapor building up in the boat and a spark ignited them.