I did quite a bit of research on this. What I found is that the majority of boats get their best "miles per gallon" at right around 3000 rpm. Some are a little different, but you can see performance charts on the boattest.com web site. According to them, the newer H200 gets just under 4mpg at about 2700 rpm at a speed of about 25 mph.
http://www.boattest.com/boats/boat_vide ... est-Result. You have a different motor and different boat, but it should give you some idea. Looking at other performance ratings of other boats in this size category, 3.5 to 4 mpg at around 3000 rpm is average.
If you hold 44 gallons, you can expect 160 miles or so from a tank at 2700 rpm. That equates to 5.5 to 7 gallons per hour, so you get about 6 to 7 hours of mid-speed cruising time on that tank. At WOT, it ran 2.6 mpg, 17 gph, and 45 mph. So, you get 2.5 hours at WOT, and cruise about 120 miles.
So, do you want to cover distance, or cruise all day? It's up to you, but hopefully that helps you figure out your consumption.
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2008 Four Winns F224
5.0 Volvo Penta
Towing with Audi Q7 4.2 V8
