Determining Fuel Tank Size

[Arch]

At some point, likely about 10 years ago, the fuel tanks in my 36' Marine Trader were replaced with aluminum saddle tanks. The tanks are odd shaped and so far I have not been able to get accurate measurements to determine volume.

There are no drains or valves on the bottom of the tanks, and no sight glasses. One of the two fuel gauges works but I have no way to determine its accuracy. The fill tubes are curved and dropping a line through them would not reach the lowest point in the tanks.

A note in the ships log indicates the tank placard shows 172 gallon volume but the placard is no longer readable.

I am hesitant to run a tank dry. I do not have a transfer pump but will install one if I can't come up with a better answer.

Your thoughts and wisdom are requested ?
Thanks,
Arch

 

[O C Diver]

Can you stick the tank? This is like using a dip stick to determine fuel level and then have a graph to show what the remaining gallonage is. If you wish to determine the capacity of a tank, measue the outside in inches, length, width, and height. Multiple the 3 and divide by 231to get gallon capcapacity.

Ted

 

[Martin J]

HI
Had the same problem when I bought my yacht. Measured the 4 sides of the tank at every inch of depth. Did a simple spreadsheet showing fuel at every inch and then cumlative as the tank level increases. the outside of my tanks are curved to the hull. Found perfectly accurate results.Now I just read the sight glass's inch of depth and viola! One thing I invested in was a bosch laser measurer. . Made the job far easier than a tape ruler etc.