fuel tank install

Discussion in 'Boat Design' started by maritimebilly, Apr 27, 2011.

  1. maritimebilly
    Joined: Jul 2010
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    Location: Ma

    maritimebilly Junior Member

    Ok guys I have done a lot of reading but still not clear on what to do in this situation.. I have a 18ft center console.. I am replacing the stringers right now with the prisma composite deals from jamestowndistributors.. the stringer height is 6" and I luckily found a aluminum tank that is 5" high..now I can configure the stringers in any which way to make this tank sit right.. due to the 1" clearance between the top of the tank and the deck I dont have much room to work with..

    my question to you guys..do I encapsulate the tank with stringers on all sides of it and foam it in with no limber holes and hope for the best? or use the neoprene stuff or what? if you would use something other than 4lb density foam such as the rubber stuff etc.. please send a link as to where to get it.. look at the pics and let me know what you think.. thanks a lot..and dont worry about the fill connections and coating the tank etc i have that figured out.. just want to know best way to hold this in there and get say 10-15 years out of it.
     

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  2. El Sea
    Joined: Aug 2006
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    Location: St Petersburg, Florida

    El Sea Junior Member

    That tank needs to be secured in all direction, fwd, aft, port, stb'd, up & down. I would place limber holes on all stringers so as to drain to bildge area.

    If the tank is to sit on the bottom as shown in the photos, I would place 1/4" rubber strips on the bottom. This will allow air to circulate and water to drain.

    I would also look into coating the tank to reduce corrosion over the next twenty years.

    Finally, I would make absolutely sure the tank is properly grounded so as not to fail in the first five years.

    Good Luck
     
  3. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    Absolutely do not foam in the tank. This is a sure death sentence for a tank. The thing that kills metal tanks is moisture, constantly in contact with the tank, so you want the air to freely circulate around all sides, and the bottom of the tank.

    A quote from one of my web pages

    Do not paint aluminum (See Aluminum Boats and Tanks: To paint or not to paint; http://newboatbuilders.com/docs/aluminum.pdf. It can be done but is hardly worth all the effort. Bare aluminum tanks will last 10 to 20 years if you keep them dry. I have seen 20 year old aluminum tanks that look as good as the day they went into the boat.

    What you need are mounts for the tank that keep it secure so it won't move, but also keep it off the floor out of bilge water. I would fabricate hangers that hang the tank from the stringers. Weld the hangers to the tank and bolt them to the stringers.

    Do put in those limber holes. That will help keep water out of the compartment.
     
  4. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Ike's well meant advice is "Absolutely do not foam in the tank" and "Do not paint aluminum".

    I didn't know that 20 years ago, so when my 90 gallon got a leak, I had a new bottom welded in and painted it brown just like it was done by the manufacturer in 1980. Then I emptied two cans of polyurethane foam in the compartment and pushed the tank down until the foam rose to half the tank height. I clamped some timber on top to prevent the tank from being lifted by the curing foam and left it there for a few days. Then I cut away the excess foam, reconnected the plumbing, installed the fuel gauge element and screwed the plywood cover in place.

    As I said, that was 20 years ago. In the meanwhile I changed from gasoline to diesel engines, refurbished the cabin upholstery, spray painted the dull gelcoat, replaced all windows, the instruments, wiring, steering, anchor winch, fridge and even the stainless kitchen top. But the foamed-in tank I never looked at again....
     
  5. Ike
    Joined: Apr 2006
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    Ike Senior Member

    CDK, I am sure you had that experience, and you were darned lucky. Your was one of a few that do survive well when foamed in.

    I spent 25 years working in the USCG Office of Boating Safety and one of my areas was fuel systems. I spent many years on the ABYC Fuel systems committee. In that time I have looked at hundreds of aluminum tanks that failed. Almost every one that was foamed in had pinholes in the bottom. I have seen a few over the years, maybe half a dozen that did very well and had never leaked although foamed in.

    In the 1980's I was project officer for the USCG on a study conducted by Underwriters Laboratories. The UL Engineer heading the research was Robert Loeser who is a bit of a legend in the boating industry. We examined hundreds of aluminum tanks. Somewhere buried in my archives is a copy of the study and I would post it here but it is still copyrighted and owned by the government, and sold through the NTIS so I would probably hear nasty things from them. But I have found a pretty good synopsis of it at Lake St Clair Network http://www.lakestclair.net/captcorner/sc_fuel_tanks.htm A Study on Problems With Aluminum Fuel Tanks in Recreational Boats is available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161 (Tel: (703) 487-4650). The price is $21.50 and the document accession number is PB95191664.

    I also wrote an article in Pacific Yachting January 2009 in which I mention the study http://newboatbuilders.com/docs/PY_JAN09_51-54_FUEL_TANKS.pdf (by the way, the publisher left out a very important word in the article which changes the meaning of the sentence, and making it wrong? Can you find it? If you do you win. What? I don't know, but....)

    Anyway, This is one of the reasons that when the USCG proposed the Fuel systems regulations (borrowed almost word for word from ABYC standards) they made the requirements for foaming in tanks extremely rigorous.

    This is just part of it. There are also requirements for the foam that is to be used.

    To make this long story shorter, yes some foamed in tanks do survive well if installed correctly. But most do not. Most develop pinhole leaks (that you can't even see but will be revealed by a 3 psi pressure test). That is why I always recommend never foaming in tanks.
     
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  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    It cannot hurt to warn people for the possible issues with foamed in tanks, but the fact that the ABYC text exists means that it can be done.

    My tank developed a number of pinholes from the inside, probably from waves slapping against the vent, allowing a few drops of seawater in. There were "snail trails" all over the bottom, with a meeting place in the lowest corner where the pinholes were. Because there was a lot of pitting along the trails as well I had a whole new bottom welded in.
     
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  7. Ike
    Joined: Apr 2006
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    Ike Senior Member

    the ABYC standard for foaming in tanks is very rigid and I have seen a lot of foamed in tanks that don't meet it. I have rarely (maybe one or two) seen any that did. But it is still used by some of the industry, mainly because they don't want to build a mounting system for the tank. They feel it is easier and cheaper to foam it in. They think this cushions the tank and prevents moisture from collecting.

    Obviously we disagree on that.
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    With legal plastic tanks available, it solves the problem of corrosion. Foaming a plastic tank in should be less critical.
     

  9. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    As usual Gonzo, you are right. If the question had been what type of tank?, I would have said plastic.
     
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