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HOw to test fuel capacity?

Discussion in 'Technical Discussion' started by Danvilletim, Jun 21, 2016.

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  1. Danvilletim, Jun 21, 2016
    #1
    Danvilletim

    Danvilletim Senior Member

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    We are suppose to hold 2300 gallons, but I have my doubts. It's not safe to run them empty and fill up. How do you reasonably check?
  2. P46-Curaçao, Jun 21, 2016
    #2
    P46-Curaçao

    P46-Curaçao Senior Member

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  3. Pascal, Jun 21, 2016
    #3
    Pascal

    Pascal Senior Member

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    Not to many options. First try checking with the builder, they should have records and be able to tell you what they put in the boat. Unless they went belly up ... :(

    Measuring the tank dimensions is an option if you can. Tanks are often partially buried..

    If the tank as sight tubes or a top access port so you can use a dipstick, you can bring it down to the minimum safe level you d be confortable with and then fill it up. It will not give you the actual capacity but the safe / usable capacity

    Last option would be to hook up a transfer pump and empty the tank into another one before filling

    Or maybe somebody here owns or runs a sister ship and can confirm tankage

    The last thing I d use is a broker or YW listing :)
  4. Capt Fred, Jun 22, 2016
    #4
    Capt Fred

    Capt Fred Senior Member

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    Just a reminder that there is an air gap at the top and often the tanks cannot be sucked completely dry which amounts to about a 20 percent difference between measured volume and usable capacity. My tanks are stated to be 300 gallons but I begin to suck air at with 222 used.
  5. Pascal, Jun 22, 2016
    #5
    Pascal

    Pascal Senior Member

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    20% is a lot, far more than I ve seen on any boat i ve owed or run. Sounds like the pick up doesn't extend far enough.
  6. Norseman, Jun 22, 2016
    #6
    Norseman

    Norseman Senior Member

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    Agree, 20% is a lot to haul around.
    (Long shot maybe, but did you look for a reserve valve or switch that will let you suck up the rest? On one of my boats I had a similar un-usable capacity but it was to protect the system from sucking up dirt and dead algaes from the bottom of the tank. If all the fuel was needed for an emergency or whatever, the pick-up tube could be pushed all the way down to the bottom of the tank)

    Never had to use the feature, but I would also take the tank apart and clean the insides every 5 years. Windex and paper towels worked great, although not very "Nautical". I am sure West Marine will sell something really expensive to do the same job..:rolleyes:
  7. Capt J, Jun 23, 2016
    #7
    Capt J

    Capt J Senior Member

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    If you can get good access to the tank and it's square or rectangular you can calculate it or many tanks have a tag on the top of them with the certification,tank builder, and size. If not, fill the tank completely, then get some 55 gallon drums and a pump (might as well fit a 2 micron racor or other filter on the suction line of your pump while you're at it, fill the tank and pump it into 55 gallon drums and measure it that way. Then pump it back. Usually 10% is not usable.
  8. Pascal, Jun 23, 2016
    #8
    Pascal

    Pascal Senior Member

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    Well I am a bit lazy so I d rather use a much fuel as possible then empty the rest in one or two drum to check amount then top off the tank.

    Much less work than lining up 40 drums to measure a 2300 gal tank :)
  9. Capt J, Jun 23, 2016
    #9
    Capt J

    Capt J Senior Member

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    Yeah, that is true and easier......But then you don't have the opportunity to polish it all and give your marina neighbors something to look at.
  10. Pascal, Jun 24, 2016
    #10
    Pascal

    Pascal Senior Member

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    Having just finished pumping 40 gals of oil in and out of the boat I can't imagine doing 2000 USg :) and yes the dock neighbors were watching ...
  11. Capt J, Jun 24, 2016
    #11
    Capt J

    Capt J Senior Member

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    Diesel pumps a heck of a lot faster than oil, like 10x faster. I literally topped off a surface drive boat, and it wouldn't get on plane, so we then pumped and gave away 300 gallons of fuel to one of the owners buddies.....it went 45 minutes to pump that with an oberdorfer gear pump.....
  12. Pascal, Jun 25, 2016
    #12
    Pascal

    Pascal Senior Member

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    Yeah, we have a gear pump to transfer fuel from the stern tank to the main and its 15 minutes to move 400 USG.

    I still don't want to line up all those drums :)