An engine mounted inside the watercraft (as opposed to the one mounted on the transom) with a propeller shaft protruding through the bottom of the boat.
Test boat power: Single 230-bhp Yanmar 4LHDTE in-line-4 diesel inboard with 210.86 cid, 3.94“bore x 4.33” stroke, swinging a 18“x 16” four-bladed bronze prop through a 1.59:1 reduction.