One day, in my hometown Breda, I came across a speedboat that appeared to be based on a Fiat 850 Spider:
Fiat 850 Speedboat

Now, on Autoblog someone has gone one step further. He converted his Spider into a real vessel. The ultimate "Barchetta.

Fiat 850 Barchetta

Fiat 850 Barchetta

And to prove it's heart is truly a Fiat engine:
850 Barchetta 3

For moving images:
850 Barchetta 4

Fiat 850 Barchetta