Fuel tank estimate

[ProMaritime]

Drain the tank and then fill it with a pre-measured amount of water and note how much it takes to top off. Obviously drain out all the water and then have your tank or tanks cleaned. Experimenting with real fuel could get expensive, dangerous and messy.

 

[OldDan1943]

Drain the tank and then fill it with a pre-measured amount of water and note how much it takes to top off. Obviously drain out all the water and then have your tank or tanks cleaned. Experimenting with real fuel could get expensive, dangerous and messy.

Put water in my fuel tanks on purpose? I dont think so. LOL

 

[Comodave]

I don’t think I would go with the water either. Too much possibility of not getting all the water out if the tank isn’t easily accessible, mine aren’t.

 

[Bkay]

Do you have access through a clean out? My tanks are asymmetric - they are slightly wider at the top so I didn't trust simple measurements and math. I was able to transfer out all fuel till they were dry and we added 150 measured gallons. I could then measure the free space above the fuel line and took the 4 inches x width x length to calculate room for another 21 gallons. So now I call them 170 gallon tanks.

 

[Rufus]

As DennisB1 and AUSCAN before him stated, if you can get external measurements (including angles if possible), it's a simple matter of applying some trigonometry. If you lost your sine-cosine tables, hire a small high school kid or two to crawl around, take measurements, and solve the problem.

 

[MYTraveler]

one gallon us = 232 cubic inches.

231?

 

[ProMaritime]

Well then how would your calculate your tanks exact volume? By wasting hundreds of gallons of fuel? Or hiring an engineering firm to calculate it? What a jerk.

 

[Rufus]

Well then how would your calculate your tanks exact volume? By wasting hundreds of gallons of fuel? Or hiring an engineering firm to calculate it? What a jerk.

The calculations are simple high school math..... (Post #35)

 

[DennisB1]

Correct 1 gal = 231inches cubed

 

[DennisB1]

If you know the internal dimensions accurately the math works. If you have odd shapes break in down in the rectangles and angular sections and calculate the volumes. It becomes a book keeping exercise if the tank has a complex shape. Done it lots of times and when you fill your tank you verify your calculations. If you work your way up in 1 inch heights you get an accurate tank volume at a give depth of fuel. You can either stick it with a measuring rod or with a sight gauge measurement.

 

[OldDan1943]

There is a difference between theory and real.
All we really need to know is "getting close".
Like your car, you get down to a quarter tank, you are desperately searching for a gas station.
On a boat, if we get down to 1/3 of a tank, we are searching for and planning our next fill up.
The exact number of gallons is immaterial. We should be thinking about 'usable" gallons. Anything else is an exercise in mathematics. Plus we all know, there and reality seldom are seldom are the same.
Reality is getting close enough to get to the next fuel stop.
Think about comfort. Enough fuel and food and water, that is the question.
If you have 50 gallons with a flat seas means nothing if you are rocking and rolling. You theorists can make your plans based upon math etc but the relativists will get to the next port with a bit of fuel, food and water.

 

[psneeld]

Ah, but if you know the exact amount left down to within couple gallons (usable) and can measure it at any time...... and an accurate fuel burn

The 1/3, 1/3, 1/3 rule isn't as critical.

Especially boats that burn 2 gph and carry 400 gallons or so.

 

[OldDan1943]

Ah, but if you know the exact amount left down to within couple gallons (usable) and can measure it at any time...... and an accurate fuel burn

The 1/3, 1/3, 1/3 rule isn't as critical.

Especially boats that burn 2 gph and carry 400 gallons or so.

A Flow Scan sure does help.
According to the sea trial of my boat, 400 gallons, 1000 RPM, 6.5 knots, 1 gph. I think I'd get bored before I ran out of fuel. LOL I wouldn't bet on the distance..... it sure doesn't account for sea state and currents.