How to find your boat sweet spot for best range

[ShoestringMariner]

Is there a general rule of thumb regarding cruising speeds maximum fuel efficiency?

For instance, does a boat generally consume less fuel once it is just up on plane or do faster speeds generally equate to better fuel efficiency? Do certain RPMs seem to work better than others? I realize that all boats are different. But I’m trying to figure out how to get the best out of my boat in terms of range. (16 foot StarCraft aluminum)

 

[tpenfield]

About 3500 rpm tends to be the range where there is the best efficiency. Maybe a big higher with an outboard.

 

[alldodge]

Without using a fuel meter and logging distance and speed this is my opinion, others will vary:

Get the boat to planing speed and note rpm and speed. Speed is best with GPS because the water pressure driven ones are not that sensitive, but no issue if you don't have one available

Just throwing numbers out here
Increase rpm a little and adjust trim as needed noting amount of speed increase for a given rpm. If you can increase rpm by 100 and gain 2 or 3 mph, then the next 100 rpm you get 1 to 2 mph, you have just passed the sweet spot. Just note what changes in speed for each 100 rpm change

After you know this you can do some prop slip calculations to see how efficient your prop is doing

 

[Scott Danforth]

as stated, need a fuel meter to find the sweet spot for your boat/motor/load at that moment in time as it varies with load such as stuff in the boat, current, wind, etc.

your best fuel economy will be at idle....however it will take all day to get anywhere. the nest best cruise speed will be about 3-5mph over planing speed (varies with motor, hull, etc). the worst will be just at or below planing speed as this is basically still in the hole and burning about 3x the fuel if your above planing speed.

for new boats, I usually head over to boattest.com as they actually install fuel meters and test boats. for example, on my searay it was 3400 RPM with a 19 pitch prop when loaded with 2 people and gear.

 

[robert graham]

You may refer to the Yamaha Outboard Performance Bulletins for charts showing various boats and motors MPH, GPH, MPG, etc.....mine is an 1870 MV Jon with C90 Yamaha motor and best overall range and efficiency is about 3500 RPM's.....which is about 22 MPH. Faster ain't better and slower ain't better....just above plane speed trimmed up for best RPM's. And the way these old 2 strokes drink gas, it can be important on a long haul between fuel docks!

 

[Sea Rider]

For best fuel consumption and mileage need to prop engine right to run at least middle to max wot rpm range as usually loaded. Once there cruise at a reduced throttle for engine to rev smoothly while maintaining excellent plane. If lightly loaded much better compared to medium or fully loaded as will need to throttle much more.

Happy Boating

 

[ajgraz]

Of course you use less gallons per hour (gph) at slow, displacement speeds...but as you surmise, you get far better miles per gallon (mpg) once on plane. As previous posters said, once going faster than "just on plane," mpg tends to start dropping gradually with increased rpm.

Every small boat with outboard I've ever owned--once propped right as mentioned by Sea Rider--got best fuel economy (mpg) at 3500-4000rpm, usually closer to 3500.

 

[444]

Really tough for me to tell accurately. Mine seems to do best in the 3000-3500 range but it's tough to stay out of the throttle.

 

[dingbat]

Been running fuel flow monitoring for 5-6 years now.

The difference in fuel consumption between 4000 and 5500 rpm is pale compared to the effect conditions have on my fuel usage.

On the same 70 mile round trip I’ve averaged 1.9 mpg and I’ve averaged 0.9 mpg. Nothing changed but the conditions.

The 1.9 average was at a higher average speed

Cruise = 4300 rpm @ 27 kts-1.9 mpg
WOT = 5500 rpm @ 34.5 kts= 1.7 mpg