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Fuel Coffin Box Question

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  • Fuel Coffin Box Question

    In the middle of the dreaded fuel tank replacement. Old tank is out, coffin is out, foam is out. Has anyone not put the coffin back in? Thinking of glassing in supports between the stingers to support the new tank. Also thinking of not doing any foam. New tank is coated from Sunshine. Anyone else do something similar?

  • #2
    what year/model are you working on? The coffin is structural in most Makos, so if you don't put it back you need to account for that.

    Unless you want to get into some pretty serious modifications I'd recommend glassing the coffin back in and replacing the foam around it to maintain the structural integrity of the liner system.

    As far as foaming around the tank or not, you'll see arguments for both. Definitely not required, but it is an easy way to ensure the tank is uniformly supported. Downside is it can trap water against the tank which leads to corrosion. Without foam you'll need some sort of support under the tank, a lot of guys use strips of neoprene or rubber mats. Supposedly certain types of rubber can accelerate corrosion, so be careful. Less of a concern if it's coated I guess. The real key is preventing standing water against the tank.

    lets see some pics!


    • #3
      1991 211. I was thinking the foam wasnt structural as there was lots of voids in it and of course was completely soaked. One of the previous owners appeared to have taken the tank out before and patched holes in the original tank. There was no foam on top of the tank when I took the panel off. Would love to post pics but still cant figure out how to.....


      • #4
        I eliminated the coffin box when I replaced my tank. Front storage drain was broken, so I dug out alot of foam to repair it. I spaced my tank up 3" off the bottom and poured 4 lb foam under it and on all the sides. Then finished off with 2 lb foam up to the floor for structural support. I built a bulkhead 8" behind my tank to keep bilge water from getting to my new foam. I like all the foam just in case I sink my boat.[]
        1978 Mako 21[br]Schneider [br]Butler, PA