Ideas for a hatch liner... using stringers/ribs to support liner?

Discussion in 'Boat Design' started by dlpanadero, Apr 11, 2016.

  1. dlpanadero
    Joined: Mar 2016
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    dlpanadero Junior Member

    I am rebuilding (or have rebuilt) the stringers/ribs up in the bow area of my 15' Pathfinder, under the front deck. There was an OEM thick plastic hatch liner up under there that was all warped and had to be ripped out in order to access the hull and replace the stringers. Now that the new stringers are (almost) done and rebuilt, I have to think about replacing the hatch liner, and am considering a couple ideas. I am either thinking of resting the liner directly on top of the stringers, or 'hanging' it off the hull wall so it 'floats' up above the stringers. (This is how it was originally). It seems resting the liner directly on top of the stringers would be a fair bit easier, but I don't know how concerned I should be with the amount of extra weight/force directly impacting the top of the stringers. (The gas tank will be up there jostling around, as well as an anchor and whatever odds and ends).

    I'll attach some pics of the rebuilt stringers to try and give an idea of what im talking about. (In the pics there's no laminate over the stringers, but they will have 2 layers of 1708 biaxial over them). Thanks so much for your time and any advice

    [​IMG]
     
  2. hoytedow
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    hoytedow Wood Butcher

    If it will be holding anything heavy I would want support under the hatch liner floor.
     
  3. PAR
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    PAR Yacht Designer/Builder

    I prefer to "hang" things like lockers, cockpit liners, etc. It isolates loads from the hull shell and other structural elements, offers storage options under them and won't impart or transmit any damage to or from the hull shell.

    If the locker was previously hung from the deck cap or liner, you'd be wise to do the same again.
     
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  4. hoytedow
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    hoytedow Wood Butcher

    Now that you say it that way, I changed my mind about it.

    I would want the liner to have a strong floor though. I am reminded of the fiberglass bathtub that someone cracked the floor by stepping on because it was too thin.
     
  5. dlpanadero
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    dlpanadero Junior Member

    Thanks for the responses. I was a bit skeptical too about placing them right on top of the stringers, even though I don't anticipate a lot of weight being up there. I'll find a way to hang it from the deck, or possibly tab in a 'ledge' onto the hull wall, then just cut out a 'floor' that spans the width of the compartment and sits on top of the ledge. that way it will be suspended up off the stringer system. thanks again.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Agreed, the laminate need to be stout enough, though how much you can fit in a locker can be a good guide to how hefty it really needs to be, unless of course it's going to be used to store lead ingots or a pile of sharp fluted anchors. If it's a typical cockpit locker, the worst it'll see is a rusting pair of vice grips, under a handful of stained PFD's, a few dock lines and couple of fenders.
     
  7. dlpanadero
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    dlpanadero Junior Member

    Haha yeah PAR that's probably pretty accurate as far as what the contents of the locker will include, I don't anticipate hauling any lead ingots up there LOL. However the gas tank does sit up there, but its a small 6 gallon. I'm thinking 2 layers of biaxial over a core material will be more than sufficient. With possibly a reinforcing rib on the underside for good measure. What do you think about tabbing in a ledge on either side of the hull, then just spanning a 'floor' across that sits on top of the ledges? Would putting this strain on the hull sides be a bad idea?
     
  8. PAR
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    PAR Yacht Designer/Builder

    The reason I like the "hanging" locker is so no loads in it or from the hull shell can intermingle. Let's say you're sailing hard, in a really rough patch, the boat is pitching, yawing and slamming down. Each and all of these movements will strain the hull shell and some natural deflection will occur. If the locker is tied to the hull shell, it will transmit these loads into the liner or deck cap. The reverse is also true, so you have a hefty load in the locker, in the same obnoxious seaway and this load (locker contents) starts slamming around in there, transmitting these loads to the hull shell.

    Can they be built to take this additional loading, well sure, but why bother if you don't need to. Again, if you need some seriously reinforced locker for something special, then consider tying the hull shell to the locker (and in turn the liner/deck cap). But if on the other hand, it just a locker hiding all the things you've forgotten you've stowed in there, consider the isolation approuch. You'll eliminate stress cracking from load transfers and the locker can just be a locker, not part of the hull shells structural elements. I'm not concerned about a simple shelf on cleats thing straining the hull, so much as what will happen to a hull shell mounted set of cleats and it's shelf, when the hull flexes it's much heavier laminate around the relatively flimsy shelf/cleat arrangement. In other words, something's going to give and this will be the comparatively scrawny shelf/cleat deal, unless you make this shelf/cleat setup as tough as the hull shell it's attached to.

    Your build ideas sound like how I'd do it. I'd make the core incorporate the reinforcement ribs, say a raised perimeter and a couple of "ribs" standing proud on the bottom, maybe the sides too. a couple of layers of biax over everything and probably all laminated at once to the locker sides and upper flange (where it ties to the liner/deck cap).
     

  9. dlpanadero
    Joined: Mar 2016
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    dlpanadero Junior Member

    Awesome. Thanks again for the replies and advice/insight. Much appreciated.. I'll try and post some "after" pics when I'm done
     
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