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Old 22-04-2009, 02:04   #1
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Question Materials Help - Balsa for reinforcing v-berth

I'm planning to reinforce my v-berth as per these instructions from the designer Bill Shaw:
  1. Sand the inside of the hull to remove any wax, glue, etc.
  2. Apply one layer of 1.5 oz. mat in this area. Catalyze the resin for a slow cure to keep it cool to prevent print through.
  3. Before the mat cures, wet the panel of 3/8" thick balsa with resin that will go against the hull and apply pressure to the balsa for a good bond. Note that you should taper all 4 edges of the balsa over a width of 2".)
  4. After this lay up has cured, apply one layer of 1.5 oz. mat and over this one layer of 1.8 oz. woven roving. This should stiffen the area considerably.
Most of that makes sense to me with the exception of the proper balsa material and the proper tapering.

From what I can see online (Nida-Core, Fiberlay) balsa comes in 24x48 sheets in scrimmed and scored and solid form. The hull in this area is not an even run there is some flare to it and it will as Shaw mentions need to be pressed into place to ensure a good bond with the hull. Can anyone reccomend a proper balsa to use?

As for the tapering the full area to be reinforced is roughly 81"x 24" (it's actually a little smaller and not a rectangle). How much smaller than the total area should the balss be so it can sandwich to the hull is 2 inches (i.e., 79" x 22") good enough? will I also taper the edges as mentioned.

Thanks,
-p
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Old 23-04-2009, 10:29   #2
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thoughts

Couple of thoughts for you.

First, be sure to dewax the area with a solvent before sanding. Second, I would use epoxy rather than polyester for this since it will have a better secondary bond. If you use epoxy, do not use mat--most mat is incompatible due to the binders, plus the adhesion of epoxy is strong enough to forgo using mat as a binder. As far as the balsa, use the kerfed stuff to accomodate the curves.
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Old 23-04-2009, 10:46   #3
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resin

SteveZ,
What are your thoughts on using epoxy versus vinylester resin. I suppose that if one needs later to use a non-epoxy repair later on one should not use epoxy because the other resins will not adhere.

I've used both yet am not and expert on this question.
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Old 23-04-2009, 10:58   #4
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Why not simply use poly laminating resin? It doesn't need to be waterproof per se.

Poly resin $26

Polyesters Resins & Hardener - Fibre Glast Developments

Versus Epoxy $60

Epoxy Resins - Fibre Glast Developments





I would recommend the following between the underside of the shelf and the top of the V-berth:
1. Sand the inside of the hull to remove any wax, glue, etc.
2. Apply one layer of 1.5 oz. mat in this area. Catalyze the resin for a slow cure to keep it cool to prevent print through.
3. Before the mat cures, wet the panel of 3/8" thick balsa with resin that will go against the hull and apply pressure to the balsa for a good bond. Note that you should taper all 4 edges of the balsa over a width of 2".)
4. After this lay up has cured, apply one layer of 1.5 oz. mat and over this one layer of 1.8 oz. woven roving. This should stiffen the area considerably.
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Old 23-04-2009, 22:21   #5
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Why not polyester?

The simple answer SteveZ already gave: epoxy sticks better because it will be a 'mechancial bond' as opposed to a chemical bond.
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Old 23-04-2009, 22:43   #6
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Use epoxy. It's a small amount so cost difference is small and the epoxy bonds so much better with fully cured polyester it's not funny. If you use balsa, you want the precut stuff backed with scrim. Coat the balsa before you use it with a thin coat of resin so the balsa doesn't soak up all the resin from the cloth (like a bloody sponge). 2" lap is just enough. Don't use mat with epoxy, just use the roving. Bed in a layer of thickened epoxy putty, not mat. And 18 oz roving, not 1.8 oz. I'd use 2 layers of roving though.
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Old 24-04-2009, 00:49   #7
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I guess i need to ask the question...Why does a Pearson 424 need this kind of reinforcing???
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Old 24-04-2009, 01:04   #8
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The hull in the bow tends to oil can in heavy seas.
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