non-cored fibreglass panels instead of ply

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

  1. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    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?

    In Australia the process of flat panel constructions is fairly common although mostly in cored construction especially for the making of say- connective bulkheads for catamarans, hull bulkheads, deck panels, sole panels. Variations such as rebates for tabbing(the joining tapes) panels together for neatness & also door jambs & locker recesses easily added onto the table tooling, also upstands for capping returns & the like quite simply added as a few examples. the table will often be simply constructed from melamine faced particle board through to composite gelcoated tables, plate glass & polished aluminium. Melamine sheet is also used in temporary tooling as a form for contact molding of fiberglass components much the same as forms are used in concrete but of coarse detailed to a much greater degree for finish. These techniques could be adapted to your intentions, even curved forms can be skinned with products like 4.5mm poly faced ply for the creation of hulls. The downside is that you get to build everything twice:) once insde out for the form & again to build the part in it, the upside is so long as you work neat on the forms you can get gelcoat finished parts from them. Check out the likes of Kelsal, Sayer yachts for some inspiration, dont be discouraged, some top end builders use techniques such as this, the key is accuracy & neatness as this reflects the finished product. All the best from Jeff.
     
  2. apex1

    apex1 Guest

    It was a challenge, you are right! But the design was taylored to fit that method and the material specifications were exact to the single strip of veneer, so, it was within the abilities. I agree it´s much more effort for a homebuilder than strip / glass but the result is a much stronger and lighter than every glass layup, as you know.
    The method though usually still named strip planking should be better called cold moulded over plank.

    To the maintenance issues. A cold moulded, glass sheathed vessel, professionally executed needs LESS maintenance than a GRPoly one! Of course every dent has to be repaired soon, but the same is valid for every other material. With just steel as a excemption, where there is a larger time window.
    Just look at the problematic gelcoat. Chalking, cracks, water ingress, blister due to hair cracks etc. We do´nt have that with cold moulded.
    The fact that many of the wood epoxy vessels in the US have been poorly constructed, and given the method a bad name, does´nt mean it is a poor method!
    One of my shops does only steel alu btw. and the large yard does GRP (Epoxy/glass/carbon) from 105ft upwards! And we ALL agree that the finest (though most labour intensive) method up to 30 meter is cold moulded (Mahogany) over lightweight strip (Paulownia tomentosa), using a premium formulation and post cure tempering.

    Regards
    Richard
     
  3. apex1

    apex1 Guest

     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There are several different strip plank methods (I can think of at least a dozen). Your technique Richard, the diagonal veneer/strip plank is about the same, from a structural stand point as heavy biax external sheathed/strip plank. These two forms of strip planking are more akin to hand laid GRP construction scantlings, then wooden core. In fact, I use GRP scantling arrangements with these types of builds, in regard to bulkhead placements, etc. This type of building doesn't need a keel, nor a stem or stern post, a true monocoque shell results.

    Again, the above techniques aren't the lightest of the strip planked methods, in fact are "middle of the road" (toward the lighter end) in regard to weight. The lightest is the Lindsay Lord method or my Lord/PAR method, which is just a modernization of the original. These are the lightest of the wooden cored composites, by a fairly substantial margin.

    From a maintenance angle, GRP is well above all other materials. If you parked a 30' single skin GRP hull at a berth next to any other 30' build, then left for 10 years, with nothing done, except the bilge pump kept clear of obstructions. The GRP hull would need to be buffed, cleaned and possibly some bedding renewed, that's it. All the other build materials would have developed issues after a decade of neglect. Of course this assumes the GRP boat didn't use cheap resin and blistered, but those days are long since past anyway. Insurance companies, marina owners and Coast Guards around the world are well aware of this and it's one of the reasons wood is being "taxed" heavily as a boat building material. It's also why you're now seeing the delineation between wood, wood/glass and composite construction on insurance and registration forms. There is a difference and in some cases a huge difference.

    The bottom line for a home builder is they just can't perform some of these methods. It would be very difficult for a novice to build a diagonal veneer/strip with sheathing hull. An especially skilled, perseverant builder might, but the average wouldn't. It would be unlikely an amateur would be able to do a Lord build too. On the other hand a traditional strip plank build with a light sheath is about as easy a method a novice could ask for. In this regard we should probably be talking apples and apples, rather then what a pro shop can do, verses what's practical for a shade tree build, because the two are vastly different in every way we measure (weight, labor, materials, costs, etc.).
     
  5. apex1

    apex1 Guest

    I can agree on that Paul.
     
  6. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    These figures are based on a 40 ft sportfisher. All hand lay up - not prefab panel. 'Panel Span' refers to space between stringers. Not sure if hull is curved or flat panel. The 3 sandwiches represent different core materials.
     

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  7. otseg
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    otseg Junior Member

    One of my all time favorite boats was "Slithy Tove", a Michael Pipe design and build that competed in the 1978 Round Brittain two handed race. Warren Luhrs was his crew incidentally. Slithy was a "panel" boat made of ply that was a pioneer in using "space frames" to transfer loads from rig to keel. Tuesday and Thursday's Child were developements from that. If you can dig up old issues of the Amateur Yacht Reserch Society publications, Slithy was featured. At one time I had every issue and if I can find them will scan a picture. She looked alot like your proposed design.

    From some testing I did 35 years ago, one layer of 10 oz glass on the face of 9 ply 1/2' mahagony plywood will double the failure loading in a three point bending test. Gee, glass can't be that bad after all.

    Nice to finally see some numbers posted.

    The attached data sheets are 2008 tests of a stiched 0-90 32 oz e glass/epoxy flat panel. These were shop made the same as the parts we produced.

    avg 32,000 psi compression and 54,000 psi Tensil strength.
    I can live with that.
     

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  8. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    Thank you for all these very good posts. Everyone is very informative.

    Just a quick note about WEIGHT: Solid frp skin is heavy because it is not porous. Not porous means poor ability to absorb water. The 'weight' in that sense has an advantage.

    Ply has much better strengthh to weight ratio, but nature has designed it to utilise the osmosis effect! Without osmosis the tree will die.

    Provided a single skin EPOXY fibreglass has enough extra ribs betwwen the frames and stringers, it will have the required stiffness, but more importantly for me, it will be more durable to the effects of abrasions and fractures. I will have plenty of time to fix something without the concern of rot. I believe the extra weight required to achieve the same stiffness will be well within my design limits. I am prepared to adjust the design to be suitable for single skin if the engineer decides it should be done.

    I'm glad I recieved such good arguments for using ply. I think ply is a good choice for people who are not so lazy.

    Another point: My design is complete conceptually, but will need a LOT of work done by a NA/NE.

    So now I am sure I will use single skin FRP and I am leaning towards a round bilge hull - but I haven't ruled out the possibilty of using a hard chine shape but with 'bulging' panels (know what I mean?). If frp prefab panels can bend in 2 directions, I can get SOME multi-direction curve, but could keep the sharp angled chines so there will be no tight bends. Just glue and screw to the frame.

    If I decide on hand layup, I will pay someone else to do that part of it.

    I also like the idea of using CAD cutting machines for as many parts as possible.
     
  9. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    Otseg, there doesn't seem to be much on the net about a Slithy Tove. I hope you do manage to find an image. Would love to see it.

    Everyone builds wide sailing monos these days. IMO the quest for more sail area and cabin space can go too far. Nothing wrong with a bit of sea spray coming over the deck as your oversized 'dinghy' skims through the waves on a sunny day. Fun.
     
  10. otseg
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    otseg Junior Member

    I don't believe I have seen my wife's eyes roll back as far as they did tonight when I spread a box of 40 yr old Amateur Yacht research magazines across her kitchen countertop. Slithy is listed in vol 75, 80, and 102. I have 75, bought 80 over the internet tonight and have not found 102. PM me your email and I will send you a scan.

    You can get photo copies from http://www.ayrs.org

    It was a fabulous boat for its day.

    see also the yacht "route 66"

    http://yachtroute66.com/

    and

    http://hiswasymposium.com/pdf/previ...nother new approach to cruising sailboats.pdf
     
  11. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    otseg, the pm thingy wasn't working so please just send it here: atn_atkin@hotmail.com (my public email)

    Thanks very much for going to that effort
     
  12. otseg
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    otseg Junior Member

    Scans
     

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  13. brian eiland
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    brian eiland Senior Member

    I'm also a believer in Kelsall's construction methods,...as I reference here on constructing the Pilgrim 40 superstructure.

    http://www.trawlerforum.com/forums/showpost.php?p=175507&postcount=109


    http://www.trawlerforum.com/forums/showpost.php?p=270901&postcount=300

    If you look thru some of that KSS information and links I just posted, it's hard not to see that this is the ideal manner in which to build the relatively big flat panels of our decks, our cabin sides, and our cabin roof for the new Pilgrim design.

    And these 'pieces' can all be built on a big flat horizontal table that produces parts with a 'finished side' to them, and the glass lay-up can be varied from part to part (main deck different than cabin side, different from cabin roof).

    Set up properly this would all go much faster than traditional hand lay-up, with fewer people, be a much cleaner operation, and produce a superior resin injected piece.

    Derek has worked with PVC foams like this for years, and much prefers them for this process. That said, there are no set rules that the Pilgrim redesign could not utilize the same foam-cored panels for its superstructure. BUT, I also think that the newer resin-injected-ready polypropylene cores could also be utilized in place of his beloved foam ??
     

  14. brian eiland
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    brian eiland Senior Member

    materials for Flat Panel construction

    Here is another subject thread that was looking at these 'polycore materials' for use in flat panel constructions.

    Polycore for flat sheet catamaran
     
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