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  1. #1
    Join Date
    Nov 2002
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    Colwell Bay
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    5,525

    Default Carbon fibre foam core dinghy.

    I have a Fairey Duckling dinghy, it suits our purpose very well, except, as light as it is, even lighter would be better.

    Could I use it to make a mould, then build a carbon and foam core lighter weight version?

    Or perhaps not need foam core? Just carbon and bucket and brush laminate?

    9' 6" long and 4' wide, how light could it be?

  2. #2
    Join Date
    Oct 2009
    Posts
    2,282

    Default Re: Carbon fibre foam core dinghy.

    Carbon is not ideal as a tender material. I've worked a lot with carbon in development class dinghy circles, and it has poor resistance to puncture type loads. Run it up a slipway, have a stone in your shoe, drop something on it and it will be bad news all round.

    The majority of the weight in your layup will be resin. And unless you are going to get all peel ply/vac bag about things you're kinda wasting your time with expensive carbon. And if you are building a light carbon dinghy, that you're not expecting to take the rough and tumble of life as a tender, why not build something better than a Fairy duckling?
    Bavaria 32 GBR4755L "Adastra"
    49er GBR340 "20KSB"/Fireball GBR14474 "Eleven Parsecs"

  3. #3
    Join Date
    Apr 2006
    Location
    Caribbean
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    2,225

    Default Re: Carbon fibre foam core dinghy.

    Our 125 nesting dinghy weighs 54kg. It is made from polyester with carbon stregthening to transom, daggerboard case and stringers. The locker and bouyancy compartments and bulkheads where it nests are all foam core panels. Ours is built strong as we use a 15hp engine but you could build lighter for a smaller hp engine and save weight in floor stringers and transom layup

  4. #4
    Join Date
    Nov 2002
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    Colwell Bay
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    Default Re: Carbon fibre foam core dinghy.

    Quote Originally Posted by Iain C View Post
    Carbon is not ideal as a tender material. I've worked a lot with carbon in development class dinghy circles, and it has poor resistance to puncture type loads. Run it up a slipway, have a stone in your shoe, drop something on it and it will be bad news all round.

    The majority of the weight in your layup will be resin. And unless you are going to get all peel ply/vac bag about things you're kinda wasting your time with expensive carbon. And if you are building a light carbon dinghy, that you're not expecting to take the rough and tumble of life as a tender, why not build something better than a Fairy duckling?
    It has to be a Fairey because it does. I only have Fairey boats. I have a Duckling, so that can be my mould.

    I was thinking it would be an infused vac bag job.

    Quote Originally Posted by geem View Post
    Our 12’5” nesting dinghy weighs 54kg. It is made from polyester with carbon stregthening to transom, daggerboard case and stringers. The locker and bouyancy compartments and bulkheads where it nests are all foam core panels. Ours is built strong as we use a 15hp engine but you could build lighter for a smaller hp engine and save weight in floor stringers and transom layup
    The duckling is 9' 6" and is 3 layers of hot moulded veneer, its 45kg.

    ideally i'd like to halve that.

  5. #5
    Join Date
    Jan 2005
    Location
    South Coast
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    13,393

    Default Re: Carbon fibre foam core dinghy.

    Quote Originally Posted by burgundyben View Post
    It has to be a Fairey because it does. I only have Fairey boats. I have a Duckling, so that can be my mould.

    I was thinking it would be an infused vac bag job.



    The duckling is 9' 6" and is 3 layers of hot moulded veneer, its 45kg.

    ideally i'd like to halve that.
    Nestaway boats do a "carbon-fibre" lightweight version of their gorgeous skiffs but I believe they put some Kevlar in as well though, which is common in this sort of use case. Although strong carbon fibre is very stiff and brittle, whilst Kevlar is not at all stiff but is very resistant to punctures and tears (hence flak jackets, motorcycle gear, etc.). Would be absolutely pointless doing it unless you did go vacuum/pre-preg though. 22.5kg is a VERY aggressive target. 45kg isn't shabby to start for a fitted 9' 6" dinghy to start with. In Aerospace you can usually get away with just carbon and even then you won't see a 50% saving over grp.

  6. #6
    Join Date
    Jul 2012
    Location
    Riyadh, Saudi Arabia
    Posts
    1,180

    Default Re: Carbon fibre foam core dinghy.

    Quote Originally Posted by burgundyben View Post
    It has to be a Fairey because it does. I only have Fairey boats. I have a Duckling, so that can be my mould.

    I was thinking it would be an infused vac bag job.

    The duckling is 9' 6" and is 3 layers of hot moulded veneer, its 45kg.

    ideally i'd like to halve that.
    Ah, it's the first bit of this post that's important then. To keep the weight down and functionality and durability right up there is where careful design comes in. My friend's old Int. Moth weighed 34kg and was 11' LOA but that's not the sort of dinghy you're looking for. You seem keen on a feather-light high tech Fairey Duckling.

    Depending on where in the country you are there must be a local boat building co that can assist with building a plug and a first off moulding in carbon/Kevlar but it will be an exercise in spending money. You will get the high tech materials and overall design but remember that the design of the dinghy is for wood construction: you won't get all of the benefits of your expenditure on carbon and Kevlar.

  7. #7
    Join Date
    Oct 2009
    Posts
    2,282

    Default Re: Carbon fibre foam core dinghy.

    Quote Originally Posted by grumpy_o_g View Post
    Nestaway boats do a "carbon-fibre" lightweight version of their gorgeous skiffs but I believe they put some Kevlar in as well though, which is common in this sort of use case. Although strong carbon fibre is very stiff and brittle, whilst Kevlar is not at all stiff but is very resistant to punctures and tears (hence flak jackets, motorcycle gear, etc.). Would be absolutely pointless doing it unless you did go vacuum/pre-preg though. 22.5kg is a VERY aggressive target. 45kg isn't shabby to start for a fitted 9' 6" dinghy to start with. In Aerospace you can usually get away with just carbon and even then you won't see a 50% saving over grp.
    To give you some idea, a 12' Cherub popping off the plug before bulkheads, deck and fitout is about 10kg. Min weight for a fully finished, fitted and painted hull is 50kg but most will be carrying a few kg of lead as correctors. A fully fitted Fireball at 16' is 70kg (minus foils, rig, ropes).

    22kg is pretty aggressive but not impossible. However don't forget "strong, light, cheap. Pick two".

    This does seem like an amazing way to burn cash for little benefit. I'd recommend that you start pricing up the cost of weave and resin to make the boat, plus the effort and materials to make the mould and decide if it's worth it for a marginal weight saving. You'd also be hard pressed to find a worse shape to try and make in a female mould with a foam core.
    Bavaria 32 GBR4755L "Adastra"
    49er GBR340 "20KSB"/Fireball GBR14474 "Eleven Parsecs"

  8. #8
    Join Date
    Jan 2017
    Location
    Norfolk
    Posts
    1,237

    Default Re: Carbon fibre foam core dinghy.

    The American Dyer Dhow is of a similar size and shape to the Fairey Duckling. The rowing only version in single skin grp with teak seats and bronze fittings weighs less than 45kg. I think with glass/foam seats you could get it nearer 40kg. Less than that and you've got to re-engineer.

    However a complete foam sandwich in any material is not the way to go as the 'skins' become too thin and fragile. By the time you've made the outer skin robust enough, it's rugged enough to be a single skin. Better to think of a single skin structure with just sufficient ribs and stingers (seat support / bow and stern buoyancy) and gunwale structure to give it rigidity.

    Your current dinghy would make an ideal plug and is probably curvaceous enough to only need a one piece mould. Sometimes making the transom removable helps extraction. The 'flat' moulds for the thwart and seats are easy to make in mdf.

    The good thing about using internal 'stiffeners' is that you can 'engineer' them in the light of experience. I would start with adding an in and out whale in 12mm x 25mm cedar, the central thwart rigidily attached to both sides and a rear seat / buoyancy 'tank'. Then see how it goes. You could then add short foam stringers or a support from the underside of the thwart to keel, etc, if necessary.

    Excellent project.

  9. #9
    Join Date
    Mar 2011
    Location
    The Netherlands
    Posts
    198

    Default Re: Carbon fibre foam core dinghy.

    If you want truly light weigh, maybe consider a skin on frame design.

    If rigid shape+space were not an issue, that would be my choice.

    Edit:
    Unless professionally calculated, adding carbon fiber to fiberglass is usually pointless.
    Carbon fiber has no stretch and will be broken long before the glass has stretched enough to start breaking.
    Last edited by SvenH; 10-04-19 at 09:14.

  10. #10
    Join Date
    Nov 2002
    Location
    Colwell Bay
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    5,525

    Default Re: Carbon fibre foam core dinghy.

    Great inputs. Thank you.

    You see, not only will it be an interesting project for me and my boy, a lighter dinghy will be easier to handle, it would be fab if I could get it to the point where I can lift it onto my roof rack on my own, then lift it off, walk to waters edge and plop it in.

    Also, in time, I'll be wanting to hoist it aboard using davits, the lighter the dinghy is the lighter the davit can be.

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