Advice needed on bulkhead retabbing to hull

Discussion in 'Boatbuilding' started by isaksp00, Jul 3, 2012.

  1. isaksp00
    Joined: Jul 2012
    Posts: 1
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    Location: Lake Wallenpaupack

    isaksp00 New Member

    I'm a total newbie here, and found conflicting or confusing comments in other threads here, so looking for very basic advice.

    I have a 23 ft Hunter sailboat and stbd bulkhead has disintegrated from dryrot. It was ply, probably marine ply but not sure, 3/4 in thick by 2 ft tall and extended out 9 in at top, tapering down to nothing at bottom. I posted pics on the Hunter forum: http://forums.hunter.sailboatowners.com/showthread.php?p=935991#post935991

    Note that these are not floor-to-ceiling bulkheads, but serve only as support for the chainplates that the port and stbd shrouds attach to. While I did rebed the chainplates, the prior owner must have had leaks for years.

    The shelf fiddle has been removed and I ground out the fiberglass tabs and removed the old wood (the plys fell apart like dry pie crust). I also ground just the surface of the old tabbing against the hull, so the yellow layer (probably glue that held the fuzzy liner in place) is gone and it is basically clean glass (sort of a darkish fleshy color).

    I don't want to use new ply, and in any case finding marine grade ply isn't easy. I bought some poplar hardwood, same 3/4 in thickness and will shape it.

    Questions:
    1. Any reason not to use hardwood like poplar, and should the glass/epoxy tabbing repair adhere well to it?
    2. I have seen a West help post that recommended "738 Biaxial Fabric (with a mat backing)" for the tabbing strips, and have seen posts here saying mat backing isn't needed and wastes epoxy. Any recommendations on type and thickness of glass cloth? Thought I'd repeat what Hunter did - 4 inches along hull and 2 along wood. How many layers?
    3. I have West System epoxy and have used with filler for rudder repair, but have never done any work wetting and applying cloth. Any advice on technique, or a good book or web source to read? E.g., proper surface prep?
    Thanks, Peter
     
  2. tunnels

    tunnels Previous Member

    For chain plates they want throwing away and solid glass plates made and fitting . looks like the tension is pulling so hard the bolts are sliding iand would eventually rip out through the wood . solid glass just 9 mm thick glassed to the hull would be trouble free for ever . leaks no matter . :p
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Solid hardwood wouldn't be a wise choice for these pieces, as they lack cross grain strength and will quickly split with any moisture content changes and less then perfect encapsulation techniques (common for a novice laminator).

    Use G-10, plywood or other dimensionally stable material. G-10 (or other man made product) being inert will offer the best longevity. Plywood is used because it's cheap, dimensionally stable and easy to shape. If well encapsulated and proper bedding, it'll last for decades.

    Combo fabrics (1708, etc.) aren't necessary with epoxy. The mat is just a waste of epoxy and weakens the end result with high resin to fiber ratios. If using epoxy, just use straight 45/45 biax fabric or tape. You'll want to stagger the seams and lots of overlap on both the hull shell and the backing plate. Several inches on each is best. You can't go wrong with too much, but you sure can with too little. 4 layers of biax would be a minimum for a chain plate backer tabbing, on that size boat.
     
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