It appears to be powered by the 928 S4 motor, as the intake and air filter assy, along with the cam covers all look identical to the S4. It could be the Cayenne motor, which is built along similar technology, but uses siamese cylinder walls to become more compact. Both use the silicon aluminum cylinder bores, which make them almost totally wear resistant. Great engines! I drive one to work every day.
The boat, however, is an enigma. It's not the first time Porsche strayed outside of what they do best. A designer thinks he/she can design anything, and they certainly can "style" anything. However, boat design is something that should not be "stylized" witout paying the dues for the engineering and functional design too. This boat is highly stylized, an in that regard will he a head turner, but I'd rather have a Donzi, Riva, or Fountain than a poseur any day. While this one will "look good", I seriously doubt if it will run with the Donzi, Fountain, or even a Riva when it comes time to stop looking pretty and get out in the salt and do the deed.