Hull skin cost per square meter

Discussion in 'Multihulls' started by guzzis3, Dec 20, 2016.

  1. guzzis3
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    guzzis3 Senior Member

    Hi all,

    I'm doing some costings for hull skins to compare the $ cost of various methods. I'm somewhat surprised at the outcome so I'm wondering if my assumptions on resin is wrong. Although to be honest it won't change things that much, unless I'm out by a lot.

    The example is 8 mm divinycell with 600 gsm biax

    or strip with 400 gsm biax (or maybe 280 uni actually this isn't a specific design and different ones call for different layups...)

    Or 6mm ply glassed with epoxy.

    I've run equal weight of resin with the glass and 1.5. I know foam needs more than strip or ply but I'm wondering what's reasonable ?

    Ply comes out cheapest although you have to be careful what you source as there is a lot of dodgy BS1044 in australia. The thing that surprised me is that strip seems to be dearest and foam poly isn't much dearer than ply/epoxy.

    I don't know if it's appropriate to put prices up here ?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

  3. redreuben
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    redreuben redreuben

    Timber

    What timber are you costing ?
    Not from personal experience but I believe the price of wrc has gone through the roof here Paulownia should be a bit cheaper, further you will pay a huge premium for machining, if you buy large boards and cut them yourself you will save a lot.
    Ps when I was involved in building strip Farr 9.2' they used double bias outside and uni inside.
    Cheers,
    RR
     
  4. redreuben
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    redreuben redreuben

    Ps, I wouldn't put cheap poly on expensive foam, at least go vinyl ester for osmosis protection and mechanical properties that will get the best out of stitched fabrics.
    Of course if your going cheap and using woven cloth then maybe poly is justified ?
    Your call.
     
  5. guzzis3
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    guzzis3 Senior Member

    Yes 1088 sorry. I've read the boatcraft article and some others. Boatcraft have not been my favourite supplier and I take what they say with a grain of salt but in this case there are plenty of reputable suppliers singing the same tune. I've also seen some of the cr*p they label marine ply so...

    For strip I was costing kiri but yes I know if you buy blocks and machine it yourself you can save. I've got the gear to resaw it myself, hell I could fell and mill it, but you can disappear down a rabbit hole getting into stuff like that. You need to factor losses also.

    I've costed vinylester as well as poly. Not all resins are created equal and you have to look at finishing aswell for blister resistance. You can build a good boat with poly and I bet people have manged to build poor boats with epoxy :) (just watch me)

    Obviously all this is rubbery but the rates I got were about:
    strip $96, poly/foam $66, Vinyl $73, ply $55.

    So poly is about 10%more than ply, vinyl another 10% or so then a pretty big jump to strip. This is based on 1.5 resin to glass ratio and buying a drum of resin. Vinylester is dearer than poly of course but the really big jump comes with epoxy. It's almost double the price of vinyl. Of course you'll probably need a lot less. Another surprise was corecell is little more than half the cost per sqm of strip (46 vs 70).

    So does anyone have an opinion on a reasonable resin to glass ratio especially for foam ? am I miles off ?

    And thank you for the replies.
     
  6. waynemarlow
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    waynemarlow Senior Member

    You also need to expand your data base to include carbon / epoxy, remember a 600gsm biax is really about the same as a 200gsm carbon cloth, do add a light 120gsm outer glass skin to give it a bit of protection but that will save you heaps of filler and paint to prevent imprinting of the weave. We are paying only £ 10.00 a sqm metre here in the UK for 200gsm carbon cloth and a 2 x 300 gsm glass is about £ 8.00. The cost of the epoxy falls by over half as you are halving the layup. The other bonus is speed of construction, half the layup means usually half the time if you are laying it in by hand.
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

    Stripping the hull you have a lot of spare time waiting to the glued strips to set so there's plenty of time to machine the strips for the next patch during that time. Freshly sawed strips are also quite straight and don't lie around drying and bending.
    Also can sand allready finished parts of the hull meanwhile..

    BR Teddy
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    You have to look at more than just the material cost per square metre of hull shell, to make a meaningful comparison.
     
  9. redreuben
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    redreuben redreuben

    Get a price on epoxy from fgi/nuplex
     
  10. redreuben
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    redreuben redreuben

    Carbon

    Wayne. Totally get what your saying but if impact is a concern surely just carbon the inside ?
    I'd be looking at basalt fabric perhaps for external, as good as s glass or better but cheaper.
     
  11. guzzis3
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    guzzis3 Senior Member

    Thank you for the further replies.

    I had thought about carbon/epoxy but hadn't got that far yet. I was still reeling from the cost of strip. I did this exercise years ago and strip was almost as cheap as ply then. Maybe even cheaper...

    redreuben I was wondering if FGI even still existed.The used to be down the road from me (about 20 kms) and I did a lot of business with them once upon a time, but I couldn't find them. New name ?

    When you say carbon cloth is that a woven cloth or stitched ? I don't know that much about carbon.
     
  12. guzzis3
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    guzzis3 Senior Member

    18 pounds x 2 is $60 for the skin material before you add foam and resin. Carbon is nice but it's still not cheap enough to compete with e glass.

    The 10% increase for vinylester over poly is probably trivial but the step up to carbon or strip is significant.

    All the web sites quote 1:1 ratios for glass to resin but I wonder if that's realistic ?

    Also I realise there are other costs, fillers paint etc and that these are significant, but I wonder if the variations between them are large in the different methods ? You use more filler between foam sheets but maybe make more fillets for a ply build...depending on the specific boat.

    Anyway the other thing I'm fretting over atm is beam design. Designing beam in fiberglass, with joins in them... :D
     
  13. redreuben
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    redreuben redreuben

    Years ago I remember trying to get 1:1 in a mould with csm, hard but doable, never worked it out with stitched fabric oddly enough maybe because I was just labour !
    I think given foam or timber absorption 1.5:1.0 is reasonable if you are hand laying.

    Beam design, what are you building ?
    Ray Kendricks Scarab trimarans have a moulded glass beam. Plans are cheap.
     
  14. redreuben
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    redreuben redreuben

    Fgi

    I googled FGI and it took me to Nuplex resins.
    I used it at Peter Milner Yachts and was quite impressed with it vacuum bagging over foam.
     

  15. guzzis3
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    guzzis3 Senior Member

    I think I'd need to start a new tread for that. And maybe I should I'm sure someone here will tell me why my idea won't work.

    I've got a set of F82 plans, it's not trimarans, it cat beams. I'll try to explain clearly, but don't get your hopes up... :D

    I looked at the nuplex site and it appears they have been absorbed by another mob. Corporate machinations....
     
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