Small single handed skiff

Discussion in 'Wooden Boat Building and Restoration' started by Jamesblack, Apr 7, 2014.

  1. Jamesblack
    Joined: Jun 2013
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    Location: Victoria, Australia

    Jamesblack Junior Member

    I'm currently designing a single handed skiff. I want to make it fairly short and light, about 10 or 11 feet. I like the hull shape of many modern skiffs like the 29er. Ideally it would not have a trapeze and only have a mainsail. I'm having trouble working out beam and rig dimensions for a crew weight of 65kg. I want to avoid as much CAD for simplicity.

    Some help would be useful as I am rather clueless.
     
  2. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

  3. JRD
    Joined: May 2010
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    Location: New Zealand

    JRD Senior Member

    James there are plenty of books that will define the physics of sailing, but you will need some ability with maths and engineering to put together the pieces.

    RW is right you need to find an existing design if not an existing boat. If you want to learn about the design factors you could start with a close look at all the comparable existing designs and figure out what makes them tick. For every different design feature you will observe a different sailing characteristic.
     
  4. Jamesblack
    Joined: Jun 2013
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    Location: Victoria, Australia

    Jamesblack Junior Member

    Would frank bethwaites book higher performance sailing be useful for me?
     
  5. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    Mmmm, tricky one. Bethwaites High Performance Sailing and its sucessor are good books without any doubt but they are not per-se design books. Well worth reading though. In High Performance Sailing, I have a few issues with subsequent developments in lower or medium power hull shapes that Bethwaite ignores, because of the age of the book and the fact he had moved onto fast skiffs. The skiffs have problems of their own in terms of nosediving so you need to be very careful in the aft volume distribution and forward lifting sections to resolve this. Less static than 'dynamic' problem, check out both the RS100 (Paul Hobson) and the Devoti D1 for newer skiff types that are not quite as badly behaved for nosediving. Note the problem is not eliminated (probably impossible) but it is easier to handle. Primarily the problem is the lever from the force (on a gust) at the topmast forward pushing the bow down. All boats get this but if you cannot move aft or sink the stern sections by moving your weight aft? how does it react - pitchpole.

    So there are a few choices, he (FB) is pretty much correct in the Sail Carrying Power ratio of 30%. Which side of that do you want to go? An 11' International Moth is pretty much cutting edge stuff. If I was to try a design of one of these I'd definitely sail a few first. I'd also expect to build 5 or 6 different foil sets to get it to work somewhere near max. If you are below that 30% it is a bit easier but you will still find there are quite a few new tricks since his book was written. Also worth googling the PlusPlus at 14' that fell too much in between the two sides of the ratio and is interesting, in just that. Check Keith Callaghan's Hadron as even a scaled down version would actually work pretty well. Depends on what you want and the waters you expect to sail on.

    If you are going to design a boat, that's fine but check where the loadings go. If you understand these well, then you should be able to resolve things to come up with a design.
     
  6. WhiteDwarf
    Joined: Jun 2011
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    Location: Sydney

    WhiteDwarf White Dwarf

    Please define your design further

    James, a design which is excellent in some conditions can become downright dangerous in others and that which is excellent for an experienced sailor may cure a novice of sailing for life. You need to tell us what conditions you expect the boat to sail in and give an indication of your experience, if it is for your own use.

    Richard Watson's advice is spot on. If everybody had to start at first principles we would still be voyaging on rafts.

    In total ignorance of your situation and resources, may I recommend that you look at Richard Woods' Duo. It is 10 feet LOA and conceived to be built from two sheets of 4mm ply (plus wings). It might meet your needs, or you might straighten out the run to get better planing performance at cost of reduced load carrying capacity. http://boats.woodenboat.com/?p=3924

    Richard is one of the professional designers who contributes generously to this forum so you might get some outstanding advice.
     
  7. joz
    Joined: Jul 2002
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    Location: Melbourne, Australia

    joz Senior Member

    James

    have a look at the 12 foot skiff association website you can pick up a skiff for $ 2,800 why design one when you can buy one cheaply and modify it.

    http://skiff.org.au/category/for-sale/
     
  8. Jamesblack
    Joined: Jun 2013
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    Location: Victoria, Australia

    Jamesblack Junior Member

    Nice idea joz. I'll get in contact with the owner to see where it's located
     
  9. JRD
    Joined: May 2010
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    Location: New Zealand

    JRD Senior Member

    A 12 foot skiff of the type in the links is not for the faint of heart. It is a two person dinghy with both on trapeze, so does not really meet any of the OPs stated criteria.

    There is no off switch once you are on the water, they have to be sailed flat out all the time once the rig is powered up. If you haven't sailed a high performance dinghy with trapeze before, you will be doing a lot of swimming.

    If you are thinking of buying one, first get hold of a club where they sail and see if one of the guys will take you out for a sail. Sailing this kind of boat is addictive, but not for everyone.
    Good luck
     

  10. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    James I don't get the impression you have a lot of experience in either sailing or building. Your other threads seem to have an emphasis on keeping the costs down. Maybe the best approach would be either to join a club and get hands-on as crew or build a simple boat to a plan.

    I built my 10 footer for around $200 and had a lot of fun and learned a great deal.

    Designing a decent boat with paper and pencil requires a few years of study under an expert or a formal college degree. I enjoy designing as much as I enjoy building and boating; if that is where you want to be you can't do better than get a computer application, there are several free ones. Carenne2008 is limited but very intuitive and straightforward, you can get something out of it in less than an hour I would guess. FreeShip is more powerful and a little counter-intuitive but there are good tutorials on the web that will get you going. An early route that I took to boat design was to use Carenne to develop a quick prototype, export an offset file and then import that into FreeShip to get access to its more powerful analytical features.
     
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