wood boat as fiberglass mold

Discussion in 'Boat Design' started by jumpinjackflash, Apr 22, 2014.

  1. jumpinjackflash
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    jumpinjackflash Junior Member

  2. rwatson
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    rwatson Senior Member

    This technique will work for any boat - and is a great way to 'steal' the hard work away from carefully finished compound curved hulls, avoiding all the hard work.

    Doing the hull from scratch however, is dubious time saving. You are not saving much effort over say strip planking techniques, and you run the risk of building a heavier hull unless you know your way around re-inforcing thin fibreglass shells.

    As for ballast on a Micro 8 - its not a big problem.
    The blocky keel can handly adjustment of the 250 kilos of ballast, and removing unwanted weight will be easy to judge.

    BUT - the Micro 8 would be a very unsuitable hull to build from plain fiberglass as it is designed from flat panels - which would not translate well into glass.

    It would be hard to justify doing the Micro 8 in any material other than plywood - unless you were rich and wanted to do a foam sandwich build.
     
  3. jumpinjackflash
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    jumpinjackflash Junior Member

    would it work with the welsford fafnir? or is it also too flat?

    [​IMG]
     
  4. rwatson
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    rwatson Senior Member

    I think this is a far better candidate, and frankly, if you did round off some of the chines, it wouldn't matter at all for buoyancy and sailing ability.

    The big question remains as to why you want to build using a temporary internal mould in fibreglass for little boats like this ?

    What, apart from the challenge of it, is the big appeal ? It certainly is not time and material saving.

    As mentioned before, the 'scantlings' ( design strength ) of the hull has been calculated in ply - and if you did it in glass, you would need an experienced person to specify the size and thickness of the glass layers, re-inforcing ribs and stringers - and a whole lot of localised loading points. The original designer would be the first person to ask if you did proceed though.

    "she’s built of stringers and plywood planks over plywood bulkheads. This makes her very very strong, and a lot more capable than most would think a boat of this size could be. "

    http://jwboatdesigns.co.nz/plans/fafnir/index.htm


    Its a major design challenge.

    Given that these ridiculous boats are floating coffins for potentially heavy weather, you cant do what you can in other small boats - just guess on the re-inforcing.
     

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  5. jumpinjackflash
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    jumpinjackflash Junior Member

    I am just not a fan of the maintenance a wood boat requires. they rot while a fiberglass boat has a near indefinite lifespan
     
  6. rwatson
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    rwatson Senior Member

    Thats a valid point of view - the 'average' fibreglass boat can be expected to have a life of 40 - 60 years with care. Mind you, plywood and epoxy versions can be expected to last that long with a bit of extra care.

    The only downside with expecting to keep a boat that for 50 years, is that the economics arent favourable if you include your labour, design and setup costs for fibreglass.

    With the money and effort put into a glass boat could pay for 3 or 4 plywood hulls in that time - but most boat owners upgrade or sell their boats within 10 years.

    Its actually cheaper to build from plywood, and scrap the boat in 10-12 years.

    Though in your case, this is a boat that will probably be out of the water for much of its life between trips. If its well epoxied, the maintenance and care is very small. If you were building a big boat, that was permanently moored, you would have a better business case for glass.

    My advice would be - build the first hull in plywood and epoxy, and get it on the water. If you are so enthusiastic about the concept in a year or so, then get the designer to do the calculations for a glass version. Then, when you have paid him for the work, and can afford to build in glass, pull your plywood version out of the water, turn it over, then clean and dress it up to be the plug for your fiberglass version.

    This way, you will get 4 or 5 years sailing from your 'plug', and still have a good hull to sell after you build you glass version.
     
  7. jumpinjackflash
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    jumpinjackflash Junior Member

    how would I go about rounding off the chines?
     
  8. rwatson
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    rwatson Senior Member

    The trick is that glass fibres will bend around quite small curves.

    When you build the mould, you can either fill in the corners with goo, to make a smooth radius about 15mm, or if you are building a male mould, make sure you have some say 30mm wide timber, so you can get a plane and put between a 7 to 15 mm curve on the sharp edges.
     
  9. Poida
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    Poida Senior Member

    Another problem could be, a frp mould is made for the finished product to be extracted from it. Unless the angles on the original boat are suitable you may not get your new boat off.

    Poida
     

  10. rwatson
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    rwatson Senior Member

    Yes - it might have to be done in two halves, say if the tumblehome is negative.

    makes for a lot of extra work.
     
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