Hi, We just purchased a 94 Carver 350 aft cabin with twin crusader 454xl closed cooled engines on velvet drive 2.57:1 trans. We are trying to find out what the best speed to run this beast at for top fuel economy. As well as what that fuel burn rate would be. If anyone to enlighten us it would be much appreciated. Thank you,
I remember making a run with a 37 ac Carver down to Jersey (ocean run, same motors) and coming in on fumes at about 111nm. Maybe 15 gals per side left. Cruised at about 17 kts. The figures may be a little bit rough, but close, as it was a few years back and it's too late to check my logs.
The most efficient fuel economy is achieved at 'hull speed,' which is about 8 knots. It will take you forever to get anywhere but that is the trade off. The formula is 1.34 x the square root of the hull length in feet at the waterline.
I run a Carver 374 gas boat with twin 7.4L Mercruisers. Depending of speed, wind/weather, and tuning you can expect anywhere from 0.8 MPG to 1.7 MPG. I find that 8-10 MPH is a nice cruising speed, the engines don't load up (1800 RPM) and I get ~1.2 MPG This is a bit longer than I like to post, but it should provide you with some additional information if you're not already familiar with it. Generally, if you're going for best economy (MPG), running at hull speed is best. Hull speed (Knots): Sq. root of waterline length (LWL) multiplied by 1.3. Example, a 28' LOA boat having a waterline length of 25' is sq. root of 25 (5) multiplied by 1.3 = 6.5 Knots. Knots to MPH = Knots X 1.15, in this case, 6.5 X 1.15 = 7.48 MPH. OR: Sq. root of LWL X 1.495 = 7.48 MPH Other than that, running in the "Sweet-spot" (usually 1800 to 2400 RPM) will provide the best compromise between consumption and time. Although you didn't mention the weight of your Carver, more to your point: Therefore, extrapolating from known data and applying it against the unknown/assumed, I suspect your Carver could get around .9 to 1 MPG, which is really about average. Obviously there are other factors like tuning, hull condition, weight-to-power ratios, weather, wind, boat loading, etc. Hope this helps.
You might consider buying a Lowrance LMF400; with this and two fuel sensors you can get the exact fuel burn in gallons per hour. If you have a newer GPS it is likely to be NMEA2000 compatible and that can also be connected to give miles per gallon. This will tell you where the "sweet spot" is, as well as exactly how many gallons to fill each tank (no more spilling) and other useful info. Connecting NMEA2000 items needs some learning, but it's worth it.
