Inboard Stirling engines are becoming popular on the River Thames in England. They are novel and can be very quiet. The first I knew of this it was fitted in a boat called Robert. Mine is the first in Australia, so I called my boat Bob.
Bob was built to test Stirling engines and to take my wife fishing. The design objective was a flat bottomed boat that my wife (who has balance problems) could get in and out of. The hull is extended behind the transom either side of the outboard to increase the buoyancy and to provide a step for entry when the stern is on the beach. Extended bollards (“molgogers” British tugs) can be placed in vertical rod holders to help balance when entering or moving around in the boat. They can also carry bunting.
My granddaughter painted the sea gulls on the bow. I love watching seagulls fly.
Our web master with the Stirling Engine Society in England has described my Stirling outboard as “The only known Stirling outboard”. All the others are inboard engines mainly because of their weight. “Stirling Engine Boats.com/ home page”. The engine has been a 20 year development project.