Usable Fuel

Does anyone know how much "usable" fuel is actually in the typical tank? The type boat is in my signature and it has a tank with 35 gallon capacity. I have never run it dry and am curious if most modern boat tanks are like airplane tanks and have some unusable fuel? Maxum dealer couldnt answer my question. Again, asking out of curiosity. I track fuel consumption by GPH each fill up. Thanks in advance for any comments.

Re: Usable Fuel

12.3 gallons

That goes along with the rule of thumb...... 1/3d out..... 1/3d back and 1/3d reserve

Re: Usable Fuel

To know for sure, you'd have to run the motor till it stalls out, then refill the tank and compare the gasoline required to refill to the stated tank capacity.
And even that might only be a ballpark, depending on the tank, and how much the gasoline might be sloshing around in the tank, etc....

Re: Usable Fuel

I 'THINK" that it would be gals. per hour, at a given rpm. best to go by the1/3 out, 1/3 play, 1/3 back in. imho!

Re: Usable Fuel

It's going to depend on a number of factors. The tank shape and the pick-up tube are going to make all the difference. If the tube touches the bottom of the tank, then there will be a minimal amount of unusable fuel. Also the longer/wider the tank is, the less usable fuel there will be. A taller/deeper tank where the tube comes to the bottom of the tank will have the least amount of unusable fuel.

If you're a geometry whiz, and have the dimensions of the tank, and can figure out how far the tube is from the bottom of the tank, you can figure it out. Total tank volume (35g), less the volume of the tank that the p/u tube cannot reach, will give you your accessible fuel. Have fun figuring that out.

Or, you can just use the 1/3, 1/3, 1/3 rule as everyone has already said, and not worry about it.

Re: Usable Fuel

Our tank never really gets below half full unless we are fishing, skiing or tubing within sight of the cottage. Then we let it come down to 1/3 full before pulling over to the cottage dock to re-fuel.
Stick with the one third rule in my opinion.