Briefly, in the last post we discussed the basic concept of efficiency, particularly that efficiency in trawlers is measured in Gal/Hour. When it comes to boating in general the efficiency of a vessel is measured in Gal/hour, or as stated Gallons per hour. The reason for this is that distance and speed is not an effective measure of engine performance. The pros over at boatingmag.com have this to say:
"You measure fuel efficiency in pounds of fuel used per horsepower developed per hour. The pros call it 'brake-specific fuel consumption.' This makes it important to know that gasoline weighs about 6.1 pounds per gallon and diesel fuel 7.2 pounds per gallon."
As indicated by the equation for gal/per hour this calculation allows you to determine fuel burn for both stopping and while in idol. This model also allows you to measure your efficiency at different speeds/rpm. We are very happy with our diesel Cummins engines.
The Grampstr's Pride operates at 5.9 Gal/Hour at 8 Knots/Hour (approx. 10 MPH), which is our recommended cruising speed. While at full speed of 19 Knots/Hour (22 MPH) the vessel operates at 38 Gal/Hour.
However, we should mention that there are two cruise "sweet spots." The first at 1350 RPM 8Knots (10 MPH), which expends as described above 5.9 Gal/Hr. The second at 2200 RPM when the vessel will travel 15 Knots (17MPH) for 19 Gal/Hour.
Based on this information it is easily determined that although it is fun to go fast the cost of fuel may outweigh the need for speed! But the moral of the story is also to FIND THE SWEET SPOT!