What RPM to get best MPG
- Thread starter TurboTim
- Start date
Danny Troy
Member
Someone posted a chart recently here, but I can't locate it now. Basically, it showed that the lowest RPM that will keep the boat on plane gave the best mileage. I guess that would vary with each particular boat though. For my boat it's around 3000 - 3200 RPM.
BonBini
New Member
My thoughts are:
1)... Where the hull frees up and moves through the water nicely. ie. my boat feels good at 25mph ish.
2)... Where the engine is turning enough rpms to have the ign timing advanced and have enough air velocity into the cylinders to provide a good air/fuel mix. These two factors will give good fuel efficiency to hp ratio. ie. my 7.4 seems to like 3200 ish.
FWIW... every engine has a peek BSFC (brake specific fuel consumption). This is where the engine produces its highest pumping efficiency (ability to pump air). This sweet spot is also where the engine will produce peek torque.
1)... Where the hull frees up and moves through the water nicely. ie. my boat feels good at 25mph ish.
2)... Where the engine is turning enough rpms to have the ign timing advanced and have enough air velocity into the cylinders to provide a good air/fuel mix. These two factors will give good fuel efficiency to hp ratio. ie. my 7.4 seems to like 3200 ish.
FWIW... every engine has a peek BSFC (brake specific fuel consumption). This is where the engine produces its highest pumping efficiency (ability to pump air). This sweet spot is also where the engine will produce peek torque.
keokie
Well-Known Member
- Dec 27, 2006
- 1,493
- Boat Info
- 2002 310 Sundancer, Westerbeke 4.5 Genset
- Engines
- 496's, Bravo III's, 2.2:1 Gears
Fuel economy in a planing boat is much more about the boat than the motor. You want the best speed per GPH. That will vary from boat to boat.
I have never found a boat that was most effecient at the slowest planing speed. Usually, the most effecient cruising speed is well past the minumum planing speed.
This is one of my complaints about how cruisers tend to be powered. Often times the best efficiencies occur at excessive engine speeds.
Just one example... My 260 with a 350 was most effcient at about 4100 rpm. When I put the 502 in, the best efficiency was at about 3100 rpm. The speed was the same (30-32 mph).
I have never found a boat that was most effecient at the slowest planing speed. Usually, the most effecient cruising speed is well past the minumum planing speed.
This is one of my complaints about how cruisers tend to be powered. Often times the best efficiencies occur at excessive engine speeds.
Just one example... My 260 with a 350 was most effcient at about 4100 rpm. When I put the 502 in, the best efficiency was at about 3100 rpm. The speed was the same (30-32 mph).
berth control
New Member
I agree with keokie, the most efficient will be more specific to your boat than your motor, but I would guess around 25mph, that's what mine is. I get about 1.6 mpg, you will likely get closer to 2.
88dancer300
New Member
- Feb 14, 2010
- 653
- Boat Info
- 1988 Sundancer 300, Heat/AC,gennie,central vac,Ice maker stretched swim platform, monster stereo sys
- Engines
- Twin 5.7 liter 260hp closed cooling system Mercruisers with Alpha one drives.
My 1988 sundancer 300 with a pair of 260s, a gennie, and 1/2 fuel load seems to get the best fuel economy at around 36-3700 RPMs @ about 30 MPH. In some water it is a little fast for the ocean conditions however. It will stay on plane at 3100 RPMs, but the motors are not happy there. They will sing to you when they are happy! It actually sounds real nice at 4300 RPMS, but The fuel consumption is more.