Re: How much fuel can I expect to burn?
Fuel consumption is a very elusive number to obtain unless you have a flow meter or make some test runs at specific rpm and actually measure the fuel consumption. However, at wide open throttle, your engine will burn roughly 10% of its rated horsepower or in your case 11.5 gallons/hour. Since you may then ask well -- what does that mean in miles/gallon, you can't tell that unless you measure consumption at the end of a trip run at a specific speed.
If you boat runs 30 MPH at wide open throttle and you burn 10 g/hr a 30 mile trip would cost you 10 gallons of fuel which comes to 3 mpg. Most boats in the 20 foot range will have 30 gallon or larger fuel tanks. At a slower cruise speed of say 2/3 throttle consumption might be in the 7 - 8 g/hr range. Fuel economy is very dependent on load, speed, hull design and conditioin, water conditions, wind, and engine mechanical condition. Having engine installation and prop optimized for those conditions helps greatly.
