Volkswagen also makes marine versions of their TDI engines... from a 40 HP 4 cylinder to a 150 HP 5 cylinder, NA or Turbo.

http://www.volkswagen-marine.com/index_e.htm

http://www.autoshoppingcenter.com/VW/VW_marine.html

I told my uncle several years ago that he should put a Mercedes-Benz 617 Turbo in his boat. It had a dead Mercury 150 HP 4 banger that was just begging to be junked.