Wrong question... The question is: How fast can you afford to go?
I averaged 6.1 mpg on Levitation over the past 74 hours of running time... That is exactly how fast I can afford to go (1390 rpm / 6 knots / ~1 gph)
I asked a fella on a big yacht with a pair of 1300hp MAN what his fuel burn was... His answer was that at 30 knots it would melt his credit card in exactly 47 minutes...
That is the most exciting post I have seen, its a dream of mine to head over there and cruise around the islands. What were the seas running on your trip and how long did it take you to cross? Was customs an issue on either side?