non-cored fibreglass panels instead of ply

Discussion in 'Materials' started by Richard Atkin, Jul 13, 2009.

  1. Richard Atkin
    Joined: Jul 2007
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    Richard Atkin atn_atkin@hotmail.com

    Would it be insane to consider using prelaminated fibreglass panels (maybe g10 epoxy glass panels) for the shell of a 33 ft hard chined monohull, using plywood construction technique?

    I want it to be an easy build (I have no boatbuilding experience) and don't want cored hull below the waterline.
    Extra frames and stringers can be added for stiffness. I don't mind if the boat ends up weighing about 1.5 times more than foam core FRP.

    Could I expect off-the-shelf prelaminated panels to be stronger than hand-layed solid FRP?
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Actually weight is a prime consideration in regard to the abilities of the yacht.

    Adding 50% more to the build just isn't reasonable frankly and quite dangerous.

    If you're looking to use 'glass panel construction, in replacement of the plywood on a hard chine design, you'll have to engineer the replacement 'glass panels to have similar physical properties as the plywood or re-engineer the structure for the new panel material.

    In answer to you question about G-10, yes, it's nuts. In general reply to the concept, it's feasible, but unless you have specific plans arranged around developed 'glass panel (or what ever) construction, you'll have hire out a conversion. This of course is based on the nature of the original question.

    You certainly don't have to use cored construction in the hull if you don't want to and there are many plans available that offer just this.
     
  3. apex1

    apex1 Guest

    I would´nt call it insane, but it is a bit senseless. A top quality marine ply is stronger than every prefab. Poly panel! Much stronger.

    Regards
    Richard
     
  4. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    Thanks Par and Richard.

    The boat is my own amateur design (with a lot of help from Gary Baigent and other experts). It's a trailerable twin masted coastal daysailer. No furniture/luxuries - just a couple of mattresses in the cabins. My design process is a bit unusual. I have designed the boat to be slightly 'underweight' with a transom that sits well above the waterline. The hull can afford to sink to some extent depending on the final choice of materials and construction, and will be 'good enough' as long as the boat stays within about 1.7 tonnes (including crew weight and equipment). The two freestanding masts will be professionally designed and built AFTER the hull materials and weight have been decided. The final boat performance is not actually important to me, as long as it stays within reasonable safety parameters - and it will.

    I want to steer away from ply or any kind of water absorbant materials that could be exposed to water from any imperfections in the hull. I know that recent foam core hulls are more reliable than the older ones that suffer from delamination of the core, but they still require a lot of time and expertise to get it right. Even so, I don't believe in claims that a sandwich skin construction has better resistance to point impact than a thicker single skin. That just doesn't make sense. I like the idea of compromising with extra bracing to support a not-so-thick single skin. This method is lighter than the old thick single skin boats, and any water leaks are easily spotted and repaired with no concern about rot.

    Plywood is strong and easy to work with - but my lazy attitude towards boat care and maintenance means I would probably end up with rot in the years to come.

    I haven't ruled out the possibilty of buying about 500 kg of G-10 wholesale, but perhaps I should do some strength testing before I do anything stupid :)
     
  5. PAR
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    PAR Yacht Designer/Builder

    What's wrong with one of the few different single skin one off methods? G-10 would be ridiculously heavy.
     
  6. gonzo
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    gonzo Senior Member

    If you have experts help you design, what did they say about the skin calculations? If the claims about cored construction don't make sense to you , maybe the best thing would be for you to spend some time looking at testing results. Also, look at stiffness differences between plywood and solid fiberglass. The design is obviously for flat panels which is a poor use of fiberglass
     
  7. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    The boat is never going to be left in the water for long periods. It'll be on the trailer most of the time. Maybe I should be less paranoid about rot and just build the damn thing out of ply.
    I owned a tiny ply boat when I was a kid and could never keep the water out of the ply - I think it was due to tiny cracks from thermal changes. I became hooked on the idea of plastic fantastic, but I guess a ply boat can last if you take care of it.
    It would be way easier to build. My boat design is still in the early stages. It could be rounded or flat chine.
    I really hate the idea of spending hours in the garage working with chemicals. I will study ply construction in more detail.

    Thanks guys for the comments.
     
  8. apex1

    apex1 Guest

    Well, a wise decision imho!
    If you manage to encapsulate the ply properly in Epoxy (not too hard to achieve), and give it the same attention you would invest in a GRP boat you have a better one at possibly lower cost.
    Look our cold moulded boats are nothing but ply done with EP and have proven thousand times to stand the test of time better than most of the GRP competitors. And on top, they are lighter and therefore perform better.

    Regards
    Richard
     
  9. shugabear
    Joined: Jul 2009
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    shugabear jr member

    ply is good and if it wont sit in the water than go with that yet if it does stay wet then the epoxy may work better but its your boat i dont think its so crazy
     
  10. PAR
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    PAR Yacht Designer/Builder

    Build it in 'glass if you want, though you will not escape the chemicals thing as this is worse then coating plywood.

    Again, there are several single skin, one off 'glass building methods, which don't have cored construction. Why not one of these?
     
  11. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    I havent ruled out the possibility of solid fibreglass.

    Would a thoroughly encapsulated birch plywood last as well as solid fibreglass?

    If ply is encapsulated with epoxy, it can't dry out on the trailer can it??

    Solid fibreglass can become less stiff with age, but the boat will still be good enough to go sailing, even if it is a little 'soft'.

    Rotten ply can leave you with a boat that is too costly to repair.

    But....I would enjoy building with ply. DAMN!! I need to think about this
     
  12. apex1

    apex1 Guest

    >>>Would a thoroughly encapsulated birch plywood last as well as solid fibreglass? <<< longer, much longer....

    I would´nt recommend Birch ply as material of choice, use a hardwood marine ply (just marine ply).

    >>>If ply is encapsulated with epoxy, it can't dry out on the trailer can it?<<<


    No, it does´nt. But you have to make sure that no freshwater finds it´s way into the hull. (same is valid for ALL other materials too)

    >>>Solid fibreglass can become less stiff with age, but the boat will still be good enough to go sailing, even if it is a little 'soft'.<<<

    EVERY boatbuilding material has a fatigue related weakness after some years. GRP has the worst rate!

    >>>Rotten ply can leave you with a boat that is too costly to repair.<<<

    Rotten GRP can be much more of a prob. (and it does "rot" if there is water ingress)

    Think about it, it is worth to keep a eye on plywood construction! Or go a even easier and sometimes cheaper way, make a strip planked, cold moulded combination. Very common, easier than sheet ply, probably stronger than sheet ply (if designed to that method i.e. round bilge).

    Regards
    Richard
     
  13. otseg
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    otseg Junior Member

    80% of my fiberglass repair in my repair side of my buisness was somehow core related, and that experience comes from running 80,000 man hours a year for 10 years.

    Go for the single skin. Think of all the Roberts and Colvin chine steel or aluminum amateur built sailboats built, and a high quality laminate is a great substitute.

    A good cad guy can turn your lines into developable panels that can be laid up full size, full length, Then just "stich and glue" them together.

    Coincidentally I have a 20 x 80' heated flat vacuum molding table that all of the panels could be infused with glass/epoxy in a week. This is shameless self promotion and I resemble that remark.
     
  14. rwatson
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    rwatson Senior Member

    Hi Otseg and Richard.

    This technique is of great interest to me, as I am considering a similar build in a 28' trailer sailer. I have asked my NA to do a developable version, with sort of constant radius bilge turn.

    In my case, I am planning to to flat sheet FG with the 'inside' having a foam layer.
    Then the one sided glassed foam gets placed stitch and glue style in a 'basket', and the inside gets laid up by hand.

    I was re-assured by the web site Manie placed on the 'board'
    http://www.voile.org/trimaran/progre...ber11_2005.htm

    I did discuss this technique without using foam (just straight FG layup inside), but my NA assured me it would be way overweight, and not very stiff without the foam.

    I have read all the talk about foam being problematic, but so is every other material, so I have opted for problematic and light.

    Whats the saying - "you can sail a fast boat slowly, but you cant sail a slow boat fast"
     

  15. otseg
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    otseg Junior Member

    I have built a dozen Harry Schoell designed powerboats from 16' to 85' over 25 years in exactly the way you describe. Concurrently Derek Kelsal has been doing the same thing. Google him, and surf his site. It is an excellent method. Its all about good secondary bonds, prep the surface to be bonded with grinding just before lamination.
     

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