RedactedNarrative: Owner/operator advised that at approximately 2:44 pm he pulled up to another boater who waved him over.  While talking to them he shifted the boat into gear and heard a boom.  The operator and passengers saw flames coming up from the engine compartment.  All on board got off the boat and into the water and then into other boats who came to assist.  The fire quickly spread and the boat became fully engulfed.  The fire department towed the boat to the boat launch.  I assisted in putting out the fire utilizing a jetski to spray it off.  It appeared to have been a mechanical issue and no operator error involved.