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Purpose of fuel tank coffin?

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  • Purpose of fuel tank coffin?

    I was hoping that some of you seasoned boaters could answer this.

    Im just trying to learn from people smarter than me.

    What is the purpose of a coffin for the below deck fuel tank?

    Most of the threads I have read and photos indicate that the coffin has holes bored through the walls for a variety of reasons. Therefore, since foam is not fuel proof it is not liquid tight so it cant be to contain fuel if it leaks. If the coffin is to be installed and surrounded by foam, and the tank will be surrounded by foam, what role does the coffin provide? Why cant the tank be installed with foam between it and the bottom of the boat?

    Along those lines, why are most coffins built by making a form, glassing, removing, and only keeping the fiberglass? If its something that isnt going to be seen, and the dimension tolerances are several inches of foam on both sides, then why are they made with forms? Maybe the answer to the question above will answer this too.
    Capt Mud Flat[br]\'73 Mako 232[br]Mandeville, LA

  • #2
    Conventional wisdom says the coffin was added to help support the deck around the fuel tank cover.

    The earlier boats did not have them

    the coffins don't have cores to keep them light(er)
    76 25 \"Aenigma\"[br]73 17[br]Richland/Long Beach, MS[br][br][br]17 project[br]


    • #3
      With the foam supporting it, the coffin definitely adds to the structural rigidity of the deck and the hull beneath.
      ROGUE I[br]1978 235 CC[br]Newburyport, MA[br]ROGUE II[br]1987 17\' Montauk[br]Camden, ME[br]


      • #4
        It's called a coffin because that's where aluminum tanks goe to corrode and die, sitting in a non-ventilated, moisture collecting coffin...

        In addition to structural integrity, it elevates the tank off the hull so water can pass under it in the bilge. My 22's had tubing encased in the foam so water could pass.