Thorney mishap
What strikes me is the barnacles / growth on the close-up example shown.
Queepee,
That still looks like an air-cooled radial to me.
From experience ( my boat very near there has 2 coats of 'antifouling' paint, but since regulations came in we're not allowed to have effective paint * )
I'd reckon that had been in the water for roughly 6 months at the very least-coud in fact be a matter of years.
*
I used to consider myself quite a 'green' type -but since I've lived with my girlfriend with her large garden in the country, when visiting garden centres I disregard anything which doesn't have warning lables all over it, ideally nuclear.