Fuel tank inspection port

Discussion in 'Materials' started by gtflash, Oct 6, 2016.

  1. gtflash
    Joined: Jun 2006
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    Location: uk

    gtflash Senior Member

    I have a powerboat with a built in vinyl ester fuel tank. The boat has been laid up during repairs. Today I fired it up after filling some petrol into tank and I quite quickly hit water in the fuel.

    I have cleaned and scrubbed tank and flushed with water about 6 months ago, it's possible I didn't get all the water out. However my concern is the inspection port. It is a large grp plate about 8" dia. Mounted on it is the pickup, and sender. I re sealed this when I closed the tank, -and I used nitrile gasket I made. I made it over sized and bedded everything down with fuel safe blue sealer. Although I can not confirm water came through inspection port, I am suspicious of it as the builder has made it so the inspection port is actually slightly recessed. It is the lowest part of the tank roof, maybe 1/4" lower and 9" dia recess in tank roof, and water pools there. Possibly water passed through my gasket or the screw holes. I have also noticed the blue sealant gasket has broken down where it has been in contact with water.

    So my question is. Is there any way I can raise the recess and make the inspection area the highest point (petrol fuel safe). Effectively filling around fuel inspection hole and raising it? Or could I build some sort of crude fence around the recess area?

    I have found how water was getting onto top of tank, some cable holes were not sealed and I left the deck plate off while working on it, but I think I need to install some insurance into tank roof. Any ideas appreciated. I will try to get a picture
     
  2. gtflash
    Joined: Jun 2006
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    Location: uk

    gtflash Senior Member

    Picture from before I took it apart
     

    Attached Files:

  3. Capt Drake
    Joined: May 2015
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    Location: Florida

    Capt Drake Junior Member

    A good fuel rated gasket or sealer should have done the job, if you see that the the sealer has broken or has cracks/gaps after being there for a while you may have not used the proper sealer. You can use gasket and a sealer, however in my experience one sealer, gasket or sealer, is better than combining both as they may not be compatible together.

    As for raising the port, you can build one that pretty much an extension that you would bold in same place where the port is, which will leave you with the same problem. Or you can build one and attach it with same material of the tank.

    IMO i wold get the best rated petrol sealer, clean area properly and seat it well, polish the fuel you have in tank and add, if you don't already have, a good fuel water separator.
     
  4. gtflash
    Joined: Jun 2006
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    Location: uk

    gtflash Senior Member

    Thank you capt. I have a fuel water separator. Today I found a slightly thicker fuel safe sealer. I Bought a generic one before from local car shop last time. I have found he source of the pooling water. A blocked weap hole :(

    I am curious if I could polish my own fuel. I read about fuel polish today but don't know anything about it. . I only have about 60ltr max in tank.
     
  5. Capt Drake
    Joined: May 2015
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    Location: Florida

    Capt Drake Junior Member

    There is a company here in Ft. Myers Florida thats called Algae-X they make fuel treatments and polishing systems for engine while running, however, the do make a stand alone unit that they either install on boats or companies that provide the service buys for their use.
    You can see their website and see their polishing system its just a very small micron filter element and water separator a pump which is used to recirculate the fuel.
    The system is expensive but I'm sure you can put a similar together.
     
  6. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    The reason the plate is recessed is to create a ullage, a space to allow fuel to expand into as it warms up. Most tanks both diesel and gas (or petrol) have a built in 5% ullage. Without the ullage it goes up the vent line and spits out into the water (a definite no no)
     
  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    How does a depressed draw line, and sender location create ullage?

    I do not recall ever seeing a metal tank with a recessed spot for any reason. In fact ABYC specifically states that the top of any metal tank cannot trap any water on the upper surface.
     

  8. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    Barry you are absolutely right. Don't know what I was thinking. Too much wine and not enough sleep, results in a senior moment. Actually with Gas tanks on recreational boats it's a Federal Regulation. Water is not allowed to accumulate on the top of a tank. ABYC extends that to diesel as well. So. Mia Culpa.
     
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