Optimal Cruise Speed for Fuel Efficiency? 1998 272

[GradyChris]

Curious where folks are running their 272 Sailfish (or similar Sailfish/Marlin) to achieve the right blend of fuel efficiency and speed. Speed and/or RPM's
Twin 225 OX66 Yamaha

I know this boat/motor combo is very thirsty on fuel so any little help making sure I'm running at the ideal range is helpful.

 

[Doc Stressor]

Determining the best rpm for fuel efficiency on any boat is actually very simple. It is the lowest rpm/speed that will keep the boat solidly on plane in any given sea condition. While an engine's peak efficiency, in theory, is at the peak of its torque curve, the effect of air and water resistance, which increase according to the square of velocity, has a far greater effect.

Then there's always the factor of how fast you want to get to where you are going which is often an even greater factor.

 

[trapper]

Now we know why they call you Doc! I have always questioned optimum cruise. It seems for example, if 3800 rpm was your most efficient engine speed and it took 30 minutes to get to your destination. How do you know how much more fuel you would use if you cruised at 4000 rpm and got to your destination in 25 minutes. Save time on the water by going faster, less engine running time, or going slower and taking more running engine time. Have I just said what Doc did,, only a lot more confusing??? Anyway conditions allowing, I run my Yam f 200i4 at around 4000 rpm. Like the sound... appears to get good milage... and no chance of "lugging" the motor. Yes I use both my trim tabs and my engine trim tilt to reach what FEELS like best ride for conditions. If I have muddied the water, I apologize but I have learned to be a slow learner in this life, and it just maybe too late to make changes. Cheers, trapper

 

[GradyChris]

Thanks both....last yr when I brought the boat up from CT to NH 205 miles all water route I ran about 3400 RPM's when conditions allowed it.
That felt like a comfortable/safe cruise speed for the boat but will be getting more time in it this season so will experiment at different RPM's and see what the fuel mpg gauges read.

 

[Jitrag]

Gradychris,

I picked up a 98 272 Sailfish in May of 2018. I also was wondering what the sweet spot is or should be for the boat. Anyway, there are many variables but I am wondering if the previous owner had the correct props on the 225 OX66s.

I have attached a picture from our ride a few weekends ago for your review. The boat was making just under 26kts at 4300 rpm, no trim tabs deployed, engines trimmed to 2, 7 people, 3/4 fuel main tank and full aux tank.

Let me know what you all think as I would assume a higher speed at 4300 rpm?

 

[Jitrag]

Thanks both....last yr when I brought the boat up from CT to NH 205 miles all water route I ran about 3400 RPM's when conditions allowed it.
That felt like a comfortable/safe cruise speed for the boat but will be getting more time in it this season so will experiment at different RPM's and see what the fuel mpg gauges read.

Do you recall what your speed was at 3400 rpm?

 

[Jitrag]

Do you recall what your speed was at 3400 rpms?

 

[DennisG01]

Conditions and load will cause large variances in RPM, speed and efficiency. It makes hard to compare from one rig - even if they are identical - to another. Since you have gauges that tell you efficiency, just use that. But generally speaking, the upper 3K range is pretty good sweet spot for OX's. Once you get comfortably into the 4K range, the fuel usage usually jumps faster than the speed.

FYI... 26kts is 30mph. A pretty good speed for cruising. But with 7 people on board, that's why RPM's were higher. Try it again with just you - it'll be a noticeable difference. Also do a WOT run with just you to see if you can get the RPM's into the proper range for your engine - ideally at the top end of the range, or even slightly over with a light load. That's how you'll know if you have the right props on there.

 

[Jitrag]

Thanks and I appreciate the feedback!

 

[Jitrag]

Conditions and load will cause large variances in RPM, speed and efficiency. It makes hard to compare from one rig - even if they are identical - to another. Since you have gauges that tell you efficiency, just use that. But generally speaking, the upper 3K range is pretty good sweet spot for OX's. Once you get comfortably into the 4K range, the fuel usage usually jumps faster than the speed.

FYI... 26kts is 30mph. A pretty good speed for cruising. But with 7 people on board, that's why RPM's were higher. Try it again with just you - it'll be a noticeable difference. Also do a WOT run with just you to see if you can get the RPM's into the proper range for your engine - ideally at the top end of the range, or even slightly over with a light load. That's how you'll know if you have the right props on there.

Thanks

 

[glacierbaze]

Optimal fuel efficiency is miles per gallon period. And I don't believe that it is the slowest planing speed for every set up. A good boat cover is your best investment for your boat and an accurate real time fuel read out on your GPS is the best investment for your wallet.

 

[Toothpick 10]

You really need the performance information for your boat and motor combination. If you have a fuel flow gauge, you could develop your own information. I actually emailed GW and they provided me the performance information for my boat and motor combination. It turns out that for my combination, 4,500 rpm provides the highest MPGs.

For every 500 rpm increment, they check the MPH and the Gallons of Fuel used per hour. They then divide the MPH by the GPH and get the MPG