Rotten stringers, hull warping

Discussion in 'Boat Design' started by oLopez, Nov 2, 2021.

  1. oLopez
    Joined: Nov 2021
    Posts: 8
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    Location: UK

    oLopez Junior Member

    Hi everyone. Hoping you lovely people can help me sort out a little pickle.

    I got a boat that i knew needed some work, an old Horizon Caribbean Broads river cruiser, but i didn't realise quite how much work that is until i started ripping floorboards out and digging in the innards.

    Boat has a solid GRP hull but wood encapsulated stringers, plus other type of stringer which seem to be to hold the sole but also offer structural support (sorry don't know the actual name). These are made of timber and are attached at the ends with some strap tabbing.

    Anyway, anything that is (was?) wood is rotten right through, stringers, those sole supports, bottom of the bulkheads, roof... basically anything that gives structural support by means of having wood inside, and the hull is warping with a bunch of the stringers already collapsed. (The GRP in them is barely over 1 mm thick in the centre 2/3rds).

    I opened up one of the good stringers yesterday to re-core it (Good as in still didn't show signs of collapsing, but the core was wet mush) and in the time it took me to clean it up and fit the new core the hull had given in about 1/4 inch. Not great.

    I then went to do one of the timber stringers, and similarly, in the time the it took me to cut a new one and slip it in the strap the hull had shifted a few mm. Enough that i couldn't slip it back in correctly.

    So to the point, any suggestions on what could be the best way to re-core/reinforce the stringers to stop the warping without causing any further deformation?

    Just wrapping a load of extra glass without bothering to clean the goo sounds like the safest, but some of them are that deformed that it would not be a proper perpendicular 'beam'. Cutting top and bottoms open to slip a core and make some relief cuts in the GRP to allow it to lay flat seems it would also allow the hull to deform even if i'm quick.

    Likewise, with the timber ones, the time it takes for the epoxy to set would make for plenty of time for the boat to choose a new shape.

    Any ideas of how i could go about the while thing?

    Little rough drawing of what i'm talking about. Ca take some picture if it helps or someone is curious.

    Thanks
     

    Attached Files:

  2. Tops
    Joined: Aug 2021
    Posts: 61
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    Location: Minnesota

    Tops Junior Member

    Hello oLopez,
    Pictures of your boat as-is would help the discussion.
    If you have a link to a sister boat that is whole or have basic drawings of the boat to share that would be good too.
    I am looking at a similar repair to a small sailboat and was considering some temporary bracing and only removing one piece at a time. Since the annotated picture the entire v-berth is redone and tied in (beams across and glassed to hull) so the front of the boat is well braced.
    Tops_s21_replace_floors.jpg
    Tops_s21_vb_glassed.jpg
     
    Last edited: Nov 2, 2021
  3. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Hi tops. That looks pretty tidy.

    Boat is one like this https://www.broadlandyachtbrokers.co.uk/boats/456 only if you imagine that boat having been in every major conflict since ww2 and kept in the rain forest in between. o_O

    Did think about bracimg but couldn't figure out how other than building temporary stringers and jacking them in to the roof, but the roof is also in bad state so can't see that working out well.

    Here's is some photos to get an idea of how.much trouble ingot myself into. Got into demolition mode last night when finding some dry rot to go along the wet rot, but should be visible ok. And yes, those are inch wide holes in the stringers someone drilled to run central heating pipes and didn't bother sealing...
     

    Attached Files:

  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum oLopez.
    How is the boat currently supported on the outside?
    Is it possible to add some additional supports in an effort to stop the hull from distorting / warping?
    Perhaps some transverse frames on the outside?
    It sounds like you will end up with a bare hull and deck by the time you finish stripping out rotten wood.
    I presume that the deck and cabin are GRP as well?
    What type of engine do you have, and what condition is it in?
    Be aware that the cost of re-building this boat will probably exceed the cost of buying a boat in good second hand condition that is 'ready to go'.
     
  5. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Hi bajansailor.

    Boat is currently in the water as the process of taking it out would cause additional stress. For transversal support I considered doing from the inside with chain blocks, but yet again I don't want to introduce new stresses which might make it warp in other ways.

    Hull and cabin is solid GRP yes, and the engine is ok(ish). Haha.

    Yes, looks like I'll have to redo all of it but I'm hoping to do it as I go, starting from the bow and doing them in sequence.

    Edit: It's 'only' 4 stringers plus the one I started and a bunch of those timber ones, so once I work out the best way of doing it should not take too long. ("Too long" being relative...)
     
  6. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Reading again that didn't sound as intended. I was already expecting/planning to do the full fitout and refurb. Is the structural bit that caught me out
     
  7. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Re terminology, stringers are usually the longitudinal members - your photos show some transverse frames.

    Maybe you will just have to replace them one by one, and not worry about if you get a bit of deflection / distortion?
    I don't envy you - I can see a lot of fibreglass grinding in your life ahead......

    You mention that the roof is also in a bad state - I presume that it is cored, probably with balsa (?)
    Is it flexing? If the core in the roof is mushy as well, then that is another big job to re-do.
     
  8. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Yes I'm not worried about a bit of distortion. Thus boat leaves in canals and it's top speed is 7 knots. Haha

    Its just that by the time I take a template and cut the new core the shape has changed ever so slightly so doessn't fit anymore plus that distortion likely causes extra stress farther along so would like to avoid as much as possible.

    As for the roof, yes, it used to be balsa before it turned to mud and it's sagging all over. Once done with the deck I'm hoping to jack it up using thick plywood in between to shape it back to original, then open it at the top in grid sections, recore with foam and stick bond back the too skin sections, but that's a tale for another day...
     
  9. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Think I worked out a way to do some of the timber stringers.

    Use the sagging roof to my advantage and have the bulkheads pressing down on them with the waterlogged roof's weight behind it. That should keep everything down till the epoxy sets.

    So jack up and support bulkheads, screw stringer to bulkheads, drop them, then glass. Should work?
     

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  10. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    To have a successful adhesion, the hull must be dry and clean. You need to grind all the gelcoat and degrease the area. Otherwise, the repair will fail.
     
    Tops likes this.
  11. Tops
    Joined: Aug 2021
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    Location: Minnesota

    Tops Junior Member

    The bottle jack might be too much at this point. I am thinking temporary transverse supports glassed to the hull curve above the bilge and then go after each frame/saddle/floor one at a time. Then new bulkheads and then fix ceiling and then fit out the insides. I would also consider marking out the plane of the cabin sole on the hull so you know where it needs to be when all is finished. My projects have been less extensive, if someone else tells you differently they may have good reasons that escape me at this point.
     
  12. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Roger that. The crustiness visible in the pics is just that i decided to start at one end and slowly moving along rather than moving up and down the boat all day moving the sole boards along every time. Thanks
     

  13. oLopez
    Joined: Nov 2021
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    Location: UK

    oLopez Junior Member

    Jack is only now to bring the bulkhead/stringer back to level as it had sagged due to the rot everywhere. I don't trust jacks to hold... Was gonna put studs but i like the idea of making a temporary base lower down with one-off stringers. Was thinking about putting the battery bank under the sole so might even do something a bit more permanent to house them and/or other sundries

    Thanks Tops
     
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