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Thread: Aluminum Deck lid thickness- Need advice

  1. #1

    Default Aluminum Deck lid thickness- Need advice

    For those who have aluminum boats, I'm looking for advice. I'm wanting to have a few deck lids (built like the top of a shoe box) built to cover the holds on my boat. They will be a piece of aluminum sheet metal with the edges bent at 90 degrees to form a small 1.5" lip around the permiteter of the hatch. The lids will be 38" wide by 60" long, so I'm thinking 3/16" aluminum plate would be adequate, but kind of doubt 1/8" would be strong enough to be constantly walked on. A little bit of flex is acceptable, but not to where it feels "weak". Any advice or suggestions would be appreciated. I was looking at Seawolf boat's website, and they use 3/16" aluminum on their decks.

  2. #2
    Member Xerophobic's Avatar
    Join Date
    Nov 2007
    Calgary Alberta


    You will probably find it tough to get crisp 90 degree bends in 3/16" material. Check with your fabricator first on the ability to make these bends. More than likely 0.160" may be as much as can be formed this way

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  3. #3
    Moderator AKmud's Avatar
    Join Date
    Oct 2005
    Wasilla, Alaska, United States


    The lid can always be strengthened with 1" angle welded to the under side.

    Call Gary at Greatland Welding (Palmer/Wasilla Hwy - 745-2383) and ask him, he will answer any of your fab questions as well as do the work for you. Great people out there.

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  4. #4
    Member akrstabout's Avatar
    Join Date
    Dec 2006

    Default Greer tank

    made boxes for me for the boat. Never installed them. came the boat I had built. My boat builder in now a member on the forums, Rick Cheverton. The boxes are 1/8" think. Only have an 1/2'' lip formed at 90*. Cool boxes. even painted them to match the boat. Just never needed them.

    You will need angle or channel welded underneath for support. Diamond plate is a tougher aluminum. Use the .100 and channel underneath and u will be good to go.

  5. #5
    Member JOAT's Avatar
    Join Date
    Aug 2007
    Soldotna, ALASKA since '78


    If you don't require an absolutely flat surface, then consider Method 2- When forming the lid, put in an "X" crease from corner to corner. This will greatly strengthen the lid, but welding in a matching spine to the inside will make it bulletproof. You'll have a slightly raised pyramid shape to the whole structure, but no so much that you can't walk on them. For the size of the lids (3'x5'), you'll want to go as thick as you have the ability to fab. With 1/8" material, the only way it will be solid enough for this size is with the "X" bends and/or internal bracing.

    You won't be able to get 90 bends with a 1.5" lip in 3/16 without some serious hydraulics, but you can cut them to size and weld on the lips all around or you can make a kerf cut at the bend on the inside for about half the thickness, then do the bend, and finish it with by welding around the inside (over the cuts). The exterior of the edges will give the appearance of a sharp break.
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  6. #6

    Default Thanks

    Thanks for the advice. The two fab shops I spoke with didn't mention having a problem with bending 3/16th's plate, but if 1/8" plate will be sufficient strength if they weld in some angle bracing, then I'll stay with the 1/8". That way will be lighter and cheaper.

  7. #7

    Default Pre-Fabricated Lids supplies pre-fabricated aluminum hatches.

    I imagine there are other off-the shelf vendors also.

    No idea what they cost..........................

  8. #8
    Join Date
    Apr 2006


    A hatch cover of that size will feel springy regardless of thickness, unless you do some bracing underneath. 1/8" thick with bracing on 12" centers should get you in the ballpark (not that I'm doing any structural calcs to back that up - it's just my gut talking). Bracing can consist of structural shapes or shapes made from bent plate.

  9. #9


    Vek- You're right about the spongy feeling. That's why I'm going with 1/8" plate (cheapest and lightest), and welding 1.5" angle underneath to firm it up. Thanks.

  10. #10
    Member Mel Roe's Avatar
    Join Date
    Apr 2006

    Default hatch covers

    I had the local fabricating shop bend me two hatch covers that were roughly 40"x60" and they were able to put the 90 degree bend but had a minimum lip heighth of 1 5/8" and I went with 1/4" aluminum with 3/8" thick by 1 1/2" flat bar welded in a cross patern on the underneath side for support. The hatches are solid and I have had 600Ibs on them with no problems. I may have gone overkill but I wanted to do it once and not have to worry about a hatch lid collapsing and having to redo them only to cost me more in the long run. Good luck



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