Yanmar Pleasure Boat Marine Engine Help

To estimate fuel consumption

This example is the 6CX-ETE, 420hp @ 2700 rpm, engine

To work out an approximate fuel consumption: select the rpm from along the bottom of the chart and go up to the propeller power curve, go to the right and select the horsepower (hp).
Write it down.
Back to the vertical rpm line, go up to where it intersects the specific fuel consumption curve. Go to the right and select the specific fuel consumption (sfc) in grams per horsepower per hour, write it down.
Multiply your hp figure by your sfc figure and divide by *850, this is the fuel consumption in litres per hour.
U.S. operators may multiply the hp x sfc and divide by *3220 for fuel consumption in U.S. gallons per hour.
The example shows that at 2300rpm, the propeller absorbs 250hp x 165sfc divided by 850 = 48.5litres per hour.
or:
2300rpm, 250hp x 165sfc divided by 3220 = 12.8 U.S. gallons per hour.
* (The specific gravity of diesel is given as 850 grams per litre and 3220 grams per U.S. gallon. The S.G. can vary but the figure given is commonly used.)
Also, for a more accurate figure multiply the answer by 1.03-1.05 to account for drive train losses. In this example 48.5 x 1.03 = 50 litres/hour.

The new ENGINE BROCHURES have the fuel consumption in litres and US gallons per hour, you dont have to work it out. ( That's if you can read them !! )
Fuel consumption is effected by many factors. The specific gravity and cetane value of the diesel being used, the drag on the boat...wetted area, weight, dirty hull, etc. A prop must absorb 420hp from the 6CX-ETE at 2700rpm, if it doesn't match the power curve, your fuel consumption calculation will not be in the ballpark. For best engine life match the prop to the applicable engine power curve with a fully laden vessel, see the SEA TRIAL page.