another frp schedule question...but for a beach cat

Discussion in 'Fiberglass and Composite Boat Building' started by boatymcboatface, Jul 17, 2018.

  1. boatymcboatface
    Joined: May 2016
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    boatymcboatface Junior Member

    hello and I thank you in advance for any response or intrest but I have one of those "what schedule" questions. well here we go, I have a fiberglass mold I picked up for a 15ft square front beach catamaran hull. its symmetrical so I have to make 2 boat hulls and I got a lot of info of the original owner who made the boat about the schedual he used as well as stringer and plate placements etc

    he said he laid up in polyester 2x 225gsm csm then used some core board about 3/8inch for the flat sections to stiffen them then another 2x225gsm csm. so knowing that a total of 900gsm chopped strand mat at 30/70 hand lay up will need 1.8kgm of polyester for a total weight of 2.8kgm(estimate).

    the cat hull is 4.55 long and about 1m circumfrence average as you make your way down the length of the boat (but am using 4.5mx1m for rough weight calcs cause I can work these out in my head quick) so half a hull will be 12.6kg out of the mold and 4 of these is a bit under 50kg with no stiffners or strengthening in stress parts like under the bridgeing points for the tubes(mast section cut going from side to side for the tramp mat to slide into front and back) and rudder guddgens etc. sorry about the poor terminology. but with rigging was told he achieved 80kg rig weight.

    but I don't want to use polyester for the build for various reasons (smelly to use, low strength) and am leaning towards epoxy because it is easer to use and I am familure using it for repairs on stealth fishing kayaks and am able to get near 50/50 hand layup with epoxy and cloth(maybe more 55/45).
    and was thinking if I have 2.8kg/m2 for a lay up to play with and wouldn't mind going a bit heaver for strength like 3.6kg/m2 for a total hull weight of 16.2kg for a hulf hull making it 65kg with out stifners and strengthening and estimating 30kg for riging that's still a riged weight of 95kg. I think around a 100kg is a good weight for a riged beach cat.

    now the new composite schedule I was thinking of using is 3 layers of 600gm.m2 quadaxial wet out with epoxy 50cloth/50resin and am leaning to make it a solid core through the hull waterline section with extra internal stiffners/partions. the original has 5. one under each bridgeing tube one infront of center board hole and 2 in the bow.
    I am thinking about a foam core between layers 2 and 3 for the flat sections. so that would be gelcoat 2x600gsm quadaxial then foam core then final 600gsm quadaxial. and using maybe 3 stringers in the front and one front and back of the centerboard hole.

    now after explain myself I can ask

    1# can 3 layers of quadaxial be handlaid over each over with epoxy for a good inter layer bond.

    and 2# what thikness coremat should I use because it needs 600gm/m2 for each mm of thickness to wet out its weight it self is minimal at 100gm/m2 so any core mat I add will be weight in resin as well and if I am going to add weight I would rather add cloth to add strength and an extra partion or stifiner.

    if you have gotten this far I thank you for takeing the time to read this
     
  2. Richard Woods
    Joined: Jun 2006
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    If you are building in epoxy and use a gelcoat then check compatibility with your suppliers, regular gelcoat and epoxy don't work too well
    One layer 400g biax each side 6-8mm foam will be strong enough

    don't use coremat with epoxy, I wouldn't use it with polyester as it soaks up so much resin and thick coremat is hard to wet out properly. so you have a heavier more expensive boat than using foam core

    Richard Woods of Woods Designs
    www.sailingcatamarans.com
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Excuse my ignorance, but what is a "square front" catamaran ?
     
  4. Richard Woods
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    Richard Woods Woods Designs

    It's a normal catamaran being sailed backwards. proving how silly ratios like Bruce Numbers are, because the Br No is the same whether it goes forwards or backwards

    real answer is "I haven't a clue"

    RW
     
  5. boatymcboatface
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    boatymcboatface Junior Member

    hahaha nice I got a good laugh out of that. sorry for using slang local to south east queensland austrailia but it is like a nacra 5.2 shape at the front is the easiest way to describe it but this one is 15ft long.

    I thank you for your help Richard your advice is appreciated very much. I was familure with the gelcoat epoxy issue not really sure what to do. my supplier says they have gel coat for epoxy applications in white or was going to maybe spray down some epoxy with pigment in it then I can do a red front fadeing to yellow like my stealth yak. I would luv to just use some of this stuff Aramid Carbon Hybrid – 190gm/m² | Trojan Fibreglass Online https://trojanfibreglass.com.au/product/aramid-carbon-hybrid-190gm-m%c2%b2/ (sorry don't know how to add a link)with clear epoxy as the first layer but cost is bit prohibitive. resale in a few years after I have had my fun with it will probably be easyer in just plain white. but custom colours narrows down your market and carbon/aramind often scare people away thinking there to fragile.

    I will look for other foam core materials and suppliers on line just my local supplier only has coremat but am sure they have acess to other brands/products will email them for product availability etc.

    yet again thanks mate
     

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  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I take it a "square front" is a plumb bow. Epoxy is no good exposed to the sun, pigmented or no, certainly not the Queensland sun. You can always paint them after pulling from the mould, you will save a little weight, too, compared to gel coat. 2-pack PU is usually the choice in such situations.
     
  7. Richard Woods
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    Richard Woods Woods Designs

    I agree re the painting, although you may find you have to fill pin holes in the laminate which gel coat hides. What people do here when making repairs is to put a thin layer of body filler on the laminate as a barrier before gelling. But that won't work on a full moulding. It would certainly be a waste of epoxy/good glass, never mind carbon to also use coremat

    Richard Woods
     
  8. boatymcboatface
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    boatymcboatface Junior Member

    I thought clear epoxy is uv stable is that not what they use on those foiling catamarans when laying carbon??? or being race breed, arnt expected to be raced for more then a couple of seasons and scraped so clear coat is then used to save weight and doesn't matter if it perishes???

    I have roll and tiped a previous beach cat in 2pac pu nice job very tough and still on there today and very robust. and I did think of painting instead of spray coat but remembered the fumes from last time and find epoxy less noxious to use so was going to spraycoat with a compatible/suitable product for epoxy construction of course and make sure I ask the simple questions when purchasing "is this the right stuff for this other stuff"

    I haven't found much info online but have found epoxy flowcoat and brush on but not really a spray coat gel coat in epoxy, there is polyester spray coat modified with epoxy suitable for epoxy builds and my local supplier says they can get stuff that works. not sure what that means. this project is still in the planning and research stage and some time from construction
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Send member ondarvr a message, he is something of a guru on these matters, he'll point you in the right direction. Speaking of epoxy modified polyester, I am told that "colorbond" coatings are just that, though I am only repeating what I was told. That, of course, is an exterior product on roofing etc.
     
  10. ondarvr
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    ondarvr Senior Member

    You can get polyester gel coats from ATL in AUS that work with epoxy, it comes in clear, plus white and black, well, actually any color, but for a color match a drum needs to be ordered.

    It can be used in-mold or when post coating the part. Clear makes a great looking carbon fiber part, but getting the carbon placed perfectly so the fabric looks great can be tough for a rookie on big parts.

    Many companies use polyester primers of the same brand as the in mold coating even if the parts are going to be post coated with paint. With no in-mold coating the entire surface of the part tends to be cover with very tiny defects that making painting a nightmare.

    So you have the option of in-mold clear or color, or in-mold primer and then post paint.
     

  11. boatymcboatface
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    boatymcboatface Junior Member

    epoxy paint for metel is the bees knees always use a super etch(just etch modified with epoxy) on aluminum after washing it with something with phosphoric acid in it like aly bright and never had an adhesion problem with paint falling off from corrosion traped under the paint. bit of topic now.

    thanks ondarvr I haven't found atl befor looking for composite suppliers on google. and there just down the road, well sort off. there site is comprehensive and they have structural foam as well. was lots of good things to read on there site.

    I am leaning toward gell coat only because it gives an easy to care for finish and is an easy step in lay up process where painting(from past experience) always seems to be a production with board sanding and then over spray on every thing in the garage because its the only place I have to paint. I could get the painting done by a local boat builder/painter who also has a booth to heat the hulls. I under stand this is also beneficial for the post cureing process of epoxy to achive full strength.
     
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