Repairing cracks / splitting in foam cored floors.

Discussion in 'Fiberglass and Composite Boat Building' started by Midday Gun, Jul 13, 2021.

  1. Midday Gun
    Joined: Mar 2019
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    Location: UK

    Midday Gun Junior Member

    It seems unlikely.

    There is no damage at the aftermost end of the keel, I'd expect to see evidence of this being forced into the hull & the floors in that area of the boat are actually in an undamaged condition, no cracking or evidence of previous repairs like the fwd area.

    The crack radiating from the mast support seems to have been caused by the step of the mast sagging due to the core being absolutely sodden with water.
    Contributory factors are that the wooden core of the compression step wasn't a perfect fit & I would guess was installed into the liner before it went into the boat, relying on filler to make up the difference.

    And the splitting on the floors themselves near the keel bolts looks to have all formed in way of the backing plates for the keel bolts. In fact those backing plates look to be sitting slightly on the radius of the glass, which would explain why the cracking is right in the centre on the radius, this boat has had the keel dropped in the past (1992 according to the paperwork I have) and its possible larger backing plates were fitted.
    If the splitting was caused by the structure being stressed or the boat say bouncing on its keel on a road trailer etc then I'd think the damage would be at the outermost ends.
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Are you suggesting there was a core and that core is fully rotten? Or that there was a liner set down and bonded and the open spaces have become water logged?

    if the latter, why did you cut some away?

    As for the furniture, are they traveling perpendicular to the floors? You'll be bonding to the hull mostly and you'd tab a 4" tape 2" to the hull and 2" to the furniture, generally.
     
  3. Midday Gun
    Joined: Mar 2019
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    Location: UK

    Midday Gun Junior Member

    No suggestion of a core as such.
    The hull itself is a solid laminate (the deck is balsa core, but that's normal), the internal molding was laid up separately, and locked into place with a jig before low density expanding foam was injected into the cavities. The internal liner has the all the internal structure like the floors, settees, engine bed, bunks etc. In certain areas the bare hull is exposed (cockpit locker, transom, outboard of settees, above bunk level forepeak, inside various cabinets etc) in all the areas where the liner transitions to bare hull it was glassed in by the builder) All the wooden interior bits, including the main bulkhead fit into slots in the liner & are screwed / bonded in where appropriate.

    I'm sure the expanding foam acted like a core in areas, (albeit not a high density one) but it doesn't appear to have actually made it everywhere, my proposal is to replace the damaged wooden core in the mast compression base, and glass that back into the existing internal liner, the way it was originally fitted.

    Ok in the below picture, the blue area is above the keel & here floors were glassed directly to the bilge.
    In red the areas look cored, you can see the transition of the GRP, but they are completely hollow apart from a few blobs of filler.
    My proposal is to cut out the hollow areas and glass along the yellow line directly to the hull, therefore tying the liner structure in directly.
    20211114_163842 - Copy.jpg
     
  4. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    EC7E8404-8B58-4618-A3F0-2F64C227FBAA.jpeg
    Don't you have concerns about rot in the next floor I marked in blue?

    Will you be removing the tops of the liner I drew in green so the floor can be one piece?

    Are you certain the floors end, or that the very edge of the hull is on each end of the floor?

    I think the plan seems sound, but I'd be a bit concerned of water has migrated to the floor I marked and rotted it.

    If you remove the inner liner and glass to the hull directly, you'll be locking the forward floor in pretty good. But also if it is wet; you'd lose access to it for repair versus opening the side and hogging it out or seeing how wet it is...

    Also, good to understand the void was manufactured tht way; thanks.
     
  5. Midday Gun
    Joined: Mar 2019
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    Location: UK

    Midday Gun Junior Member

    Thanks for the response.
    I'm not concerned about the other floors, they are all foam cored, and as described earlier the foam is a very low density expanding foam, all of their strength comes from the shape and the glasswork. This floor has the oak core because the mast compression post sits on top of it so its carrying the rig compression load.

    The green parts I thought it would be best to leave, that way I can grind a good taper onto them to tie the new glass work into the old liner structure.
    The only way I can make the core in one piece would be if I chopped out the settee bases as it extends past them to where the hull starts to curve up, my plan was to make it in two pieces with a 12:1 scarf joint that I'll bond with thickened epoxy.
    If I cut those green stubs off then I would probably end up having to end up sanding back part of the visible area that's above the cabin sole, I'd rather avoid that & keep it looking original.

    Essentially according to the drawings, in areas where the liner sits against the hull, there should be no gap & it should be bonded in, but I'm finding this not the case, there are bigger gaps & its held in with filler.
    upload_2021-11-19_16-6-40.png

    In the above, the cross hatched areas should be foam core, the red one timber & everything else bonded in.
    All I'm proposing is to replace the areas that are not bonded in with my own glass work, time consuming but its what the factory would have done if they weren't using a liner to save time.
     
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  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Sounds good. I'd say to get the yellow areas cutout sooner than later and let things dry up a week. And not sure if discussed, but I'd use epoxy.
     
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  7. Midday Gun
    Joined: Mar 2019
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    Location: UK

    Midday Gun Junior Member

    The boats out the water on a cradle.
    I'll only cut out sections at a time in order to keep as much structure as possible & work fwd to aft. I have all winter so no mad rush to do it all in one go, I would rather have used vinylester or polyester as they're just nicer to glass with, but epoxy does make more sense in this case I think for as much strength as possible.

    I'll be adding limber holes to allow any water in future to drain out of the inner liner.
     
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