fuel mileage

[RobertThoreson]

I have a fastwin 18 behind a 14 foot crestliner commodore. When I bought the boat, it came with 2 tanks. I was just wondering the theoretical distance/time I could run with 12 gal of fuel. I'm not planning on doing it but just a thought. I haven't even heard my motor run yet so I have no idea what my perticular motor will get mileage wise. Any thoughts?

 

[Sea Rider]

Is that a 2 strokes OB ? If so about 12% of it's HP per hour at full hammer down, provided that OB reaches it's max wot rpm range. All OB's have their own best cruising speed range to maintain good plane with least fuel comsumption. More speed more fuel. Will depend on how in a hurry you are to reach your final destination.

Happy Boating

 

[RobertThoreson]

Yes it's a 2 stroke. And by that equation, I'd be empty in about 5.5 hours. Even just using rough numbers, that's a lot sooner than I thought. I thought it would run for days lol

 

[RobertThoreson]

And that gives me a 50 mile radius from my home port

 

[jimmbo]

The consumption rate sounds reasonable. Our 63 40hp had about a 28 mile radius for the same amount of fuel @ WOT. Our 65 90hp was about 17 mile radius.

 

[robert graham]

Google: Yamaha Outboard Performance Bulletins and try to find a similar boat and motor(2 strokes) to yours for lots of statistics on GPH, MPG, etc.....may prove helpful in establishing your range. I expect your boat/ motor will run most efficiently just past minimum plane speed at around 3500 RPM's....

 

[Sea Rider]

If wanting good mileage what you can do is install an induction tach, gor for a wot spin as usually loaded and depending on the wot reading dial a prop, usually a less pitch one to pull wot revs around or at max wot rpm range factory stated for that OB. Once there can throttle at the speed you like best throughout the throttle range. Mileage wise is maintaining combo on perfect plane while OB runs smoothly at a X given rpm.

Mine loves revving at 4700 rpm which gives the best mileage. OTOH, nobody if' it's not a shareholder of a Petrol Company would dare to boat at full throttle start to finish. 2 strokes OB's guzzle gasoline at an amazing rate when at full throttle, better enyoy your outing at a less speed.

Happy Boating

 

[phillnjack2]

to get the best fuel economy get to max revs and max speed then back off 500 to 700 rpm and youl be amazed at how much you can save, and not
lose too much top end.

 

[Sea Rider]

What if max wot revs are way down the min revs or OB lugging ? The best fuel eonomy is achived if OB runs at least middle to max wot rpm as currently loaded, once there can throttle way less to maintain a perfect plane at a given X rpm/speed.

Happy Boating

 

[gm280]

The real only true way you can accurately figure out MPG is to install a fuel flow unit to measure the amount of fuel used at any given RPM. Then with a GPS reading you can calculate the absolute best RPM/Speed/Fuel Consumption. But that all cost money to install. So just run and figure out how much fuel you used for the distance you traveled. But don't wait until you are out of fuel to figure that out either. :facepalm: It takes a while but everybody eventually figures out their boat's capabilities and fuel consumption without doing all those things. JMHO

 

[David Young]

Fill both tanks and find a good speed you like to go. Start a timer to see how long it will take to run out of gas. I did this with my 15 foot 1977 70 horse power tri hull, just for fun. I top out at 35 mph (GPS), I went on a cruse at 27 to 29 mph and it took 2 1/2 hours to burn 6 gallons of gas. A lot better than I was expecting

 

[Sea Rider]

2 strokes stated 10% fuel consumption per hour per HP while running full hammer down at near or max wot range and load is very conservative. When planing fuel consumption on your next far away outing plan it at a bit higher rate, it's better to count with more fuel on tank than with less.

Would you say that an older heavier OB will consume less ? if so, how come new lighter Tohatsu 2 strokes OB's and their rebadged brands are factory rated to consume 12% on all their 2 strokes 2 clinder OB's and between 11-11.5 % depending on HP on therir 3-4 cylinder models.

Road fuel comsumption transporting same weight is near 4 :1 if comparing same distance traveled with a boat, that's due to excessive water drag on hull.

Happy Boating

 

[jerryjerry05]

The older outboards were really hard on gas.
​My dad had a 68 65hp4cyl. Johnson.
Used on a whaler.
​It had 2 12 gal tanks under the console.
He used to say the 65 was gas cooled as it used SO much fuel.

​In 88 he bought a 70/75 Johnson.
His usage went down about 50%

My boat twin 88/85hp gets about 2.3 MPG.
​A common trip is 50 +/- using about 20-24 gal.

Like the others suggest don't run at wide open.
​I run at 42-4500 depending on conditions.