I have a 2002 Carver Mariner 350 with twin 6.2 MPI MercCruisers. Has anyone tests for fuel consumption at different RPM? I am try to determine the best cruising speed for a long trip I'm about to do. Thanks!
Generally the most efficient cruise speed is about 80%. From there down to where your bow first starts to rise you're plowing. Many manufacturers are recommending that you run at 90% these days, but I generally don't agree, especially with gas.
Although NYCAP is correct, I'd like for you to define "a long trip" from where to where? And what is your fuel capacity? How many people are going to be aboard?
The general rule of thumb is that there is no in-between; you should go at hull speed which is about 6-8 knots coming up from idle, or cruise by getting up on plane first, then backing rpm's down to just over what is needed to stay on plane. Push it more than that and your fuel efficiency drops off a cliff. We just got back from a trip 3 hours each way and kept the rpm's at 3400 to get between 16-17 knots most of the time, fully loaded, although we have 350's , 5.7 ltr.
Test Power: 2 x 375-hp Crusader 6.0 HO MPI Range RPM MPH Knots Total GPH MPG NMPG Stat. Mile NM KM KPH LPH KPL dBA 650 4.6 4.0 1.5 3.0 2.6 683 593 1099 7.40 5.68 1.29 63 1000 5.8 5.0 2.0 2.9 2.5 653 567 1051 9.30 7.57 1.23 70 1500 7.9 6.8 4.0 2.0 1.7 442 384 711 12.70 15.14 0.83 75 2000 9.8 8.5 7.0 1.4 1.2 315 274 507 15.80 26.50 0.60 74 2500 11.3 9.8 11.6 1.0 0.8 218 190 351 18.20 43.91 0.41 75 3000 16.9 14.7 19.9 0.9 0.7 191 166 307 27.20 75.33 0.36 77 3500 22.0 19.1 27.9 0.8 0.7 177 154 285 35.40 105.61 0.34 79 4000 25.9 22.5 33.7 0.8 0.7 173 150 278 41.70 127.57 0.33 86 4500 29.6 25.7 46.7 0.6 0.6 142 124 229 47.60 176.78 0.27 86 5000 31.7 27.6 50.9 0.6 0.5 140 122 225 51.00 192.68 0.26 87