At 11:25 AM 11/21/2005 -0500, you wrote: >While cruising the Diesel Duck 462-1 in the Philippines in April of this > > RPM Knots Fuel GPH > > > > 1250 6.6 1.9 > > 1300 6.7 2.0 > > 1350 7.0 2.3 > > 1400 7.1 2.4 > > 1450 7.3 2.8 > > 1500 7.5 3.8 > > 1550 7.7 4.0 > > 1600 7.7 4.1 > > 1650 7.8 4.2 > > 1700 7.9 4.3 > > 1750 8.0 4.7 > > 1800 8.1 5.0 > > 1850 8.4 5.6 > > 1900 8.5 5.8 A few observations. The engine in that boat as I recall is a Cummins 155 B (or similar) rated at about 150 hp at 2800 rpm and 7.6 gals per hour. The numbers provided above can provide additional information. The fuel burn at 2.5 gals per hour provides a speed of 7.1 at 1400 rpm. If the speed is actually 7.7 at 1500(2.5 gph), the difference may be attributable to current. In any event notice that all of this is correct then compensating for current by increasing rpm results in nearly 1.5 gals per hour of increased fuel burn for an increase in speed of only 10 percent (0.6 knots). The fuel burn goes up by about 35 percent but the speed increases by 10%. This diminishing returns problem only gets worse. Notice that an increase of speed of 20 percent to 8.4 results in a fuel burn of 5.6 gph or roughly 220 percent in fuel. The boat's top speed is about 9.0 and at that rate the fuel burn will be 7.6 gph. In other words from 8.4 to 9.0 (0.6 knots) an increase of about 7 percent, the fuel burn goes up by 2 gph or about 35 percent, again. The end result is that instead of getting over 3 miles per gallon at 6.6 knots, at 9 knots the mileage has deteriorated to barely more than 1.1 miles per gallon. As you can see fuel burn rates are dramatically influenced by engine rpm, with small changes in rpm resulting in dramatic decreases in fuel range. One more item worth discussing. Notice that the max fuel burn is about 7.6 gals per hour. This works out to about 20 hp per gal per hour. This is an excellent burn rate as many small diesels are closer to 15 hp per gal per hour. This burn rate per hp is not a flat curve and you can't expect this engine to be that efficient across it's entire rpm range. Ideally one would like to run their engine at that point in it's torque curve where torque is maximum and fuel EFFICIENCY is highest (max hp per gallon of fuel burned). The fuel burn numbers from above can be converted back into rough horsepower numbers by simply multiplying the fuel consumption by 20. In other words, 6.6 knots equals 1.9 gallons or 38 hp and 1250 rpm. 1500 rpm equals 3.8 gph and 7.5 knots and about 76 hp. 1900 rpm, 8.5 knots, 5.8 gph and about 110 hp. Mike Capt. Mike Maurice Tualatin(Portland), Oregon