What type frame tubing for skin on frame 16 foot dinghy? Wood, carbon or fibreglass?

Discussion in 'Boat Design' started by Matt Thompson, Sep 13, 2017.

  1. Matt Thompson
    Joined: Sep 2017
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    Location: North Berwick, Scotland

    Matt Thompson New Member

    Hi all,

    I am planning (in my head so far) to build a double ended skin on frame Yole-ish type dinghy. I want to use carbon or fibreglass tubing for the frames braced with kevlar string (like in Plat Monfort's brilliant designs), with 8 oz ballistic nylon skin. I do not want to use wood for the frames as I want it to be very robust and with minimal upkeep. Is that a good idea? It doesn't have to be as light as Plat's boats but a lot tougher.

    Now the tubing...Fiberglass is more flexible than carbon but heavier. Any thoughts on which I should use - or a mixture? I haven't a clue on what dimensions of tubing to use - where should I begin? I know there are a lot of variables such as how many frames.....again any advice would be hugely welcome.

    I want the boat to be fairly bulletproof for coastal sailing and camping in Scotland. I love the Mirror which weighs 165lbs but is too small. I would like this bigger boat to weigh about the same so I can drag it up beaches. The rig would be a balanced lug.

    Thanks in advance for your thoughts,

    Matt
     
  2. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    You might think about aluminum tubing. Not as expensive as CF, about the same weight as fiberglass tube - if you actually do an engineering design.

    Hope you think about dragging a SOF boat up on the beach. The skin may not be very abrasion resistant, depending on the coating used.

    Yostwerks.com had kayak plans built out of aluminum tube - you might take a look. Kayaks are much lighter without a sail, so the tube size won't work exactly. Just an example to start from.

    You might also look at gentrycustomboats.com . His boats are wood framed, but you might be able to use aluminum tube of comparable stiffness. Do you know how to do a moment of inertia calculation?

    Wood frames with epoxy or epoxy/ glass coatings might be durable. Glass on a frame might be really a lot of work.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If going the light weight canoe/kayak/dinghy route, why the bother of carbon frames and a SOF build? Consider a single skin composite instead,which will be tougher, lighter, have less parts, etc. Single skin composites have been around a long time and molds are available and it will likely be near half the weight of a Mirror.
     
  4. Matt Thompson
    Joined: Sep 2017
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    Location: North Berwick, Scotland

    Matt Thompson New Member

    Thanks very much for your speedy responses.

    I hadn't thought about aluminium thinking it was mainly used for folding kayaks and would be difficult to bend without kinking. Very good idea looking at their designs and working backwards. I have to admit I am a total amateur having only some limited experience helping make a St Ayles Skiff. St. Ayles Skiff - Wikipedia https://en.wikipedia.org/wiki/St._Ayles_Skiff. I like the idea of single skin composite but would be daunted by the prospect of making it unless I could buy ready made sheets and stick them together like plywood. I am of the 'Dynamite' Payson school of boat building. Likewise I have no clue about moments of inertia. Maybe someone has done those calculations and I can look them up in a table?

    Good point about abrasion! I was thinking of a hypalon keel and 'garboard' strip. Or light rollers. The rocks round here are often covered with abrasive barnacles some broken into tiny knife edges..
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Given your understanding, you shouldn't be thinking about self designing, just a build method you can live with.

    A one off single skin will give the faster bang for you buck, with far fewer parts to make and install, again given your needs. SOF regardless of fabric, isn't very tough.
     
  6. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    I would get a decked sailing canoe like the Shearwater The Shearwater - decked sailing canoe http://www.solwaydory.co.uk/products/sailing-canoes/shearwater-decked-sailing-canoe/ with outriggers and ideally second hand. Or build something similar in plywood if that is your thing, there are plans available.

    Making a SOF dinghy "bulletproof" is impossible given razor sharp barnacles. It will have to be picked up in the water and carried ashore so it's either light enough for one person or you have crew. You can use beachwheels or trolleys to ease the task. Draging would be my last option.
    You still have to watch your gear weight, it's amazing what people can put in a 16ft boat.
     

  7. Matt Thompson
    Joined: Sep 2017
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    Location: North Berwick, Scotland

    Matt Thompson New Member

    Good points - I was thinking of copying a traditional Shetland boat rather than starting from scratch. I have used rollers before which have worked well. I take your point about gear weight having done a trip in the said Shetland boat. Maybe I need to rethink the toughness/lightness factors.
     
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