Skiff Design

Discussion in 'Sailboats' started by bobby_mcgrath, Jul 30, 2006.

  1. bobby_mcgrath
    Joined: Jun 2005
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    Location: Newfoundland, Canada

    bobby_mcgrath Junior Member

    Hello Again Everyone,

    I am here to seek a little more expertise. i am hoping to start a design on a skiff, something to fit in between a 29er and 49er, something that a bigger crew can sail, but not as aggressive as the 49er. Any ideas on what areas I should be focusing on? I realize that I will gain more stability and a smoother ride for the bigger sailors by having a length near to the 49er, but a larger beam. I am concerned though using the larger beam and its implications on the wetted surface area in the aft planing sections, and everything playing back into at what point the hullwill jump from displacement to planing regimes. As well, ideas or pointers on the rig/sails would be great. Any help or insight would be greatly appreciated. Thanks

    Bob McGrath
  2. frosh
    Joined: Jan 2005
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    frosh Senior Member

    Hi Bob, from your other posting you say that you are doing naval architecture so you should specify whether you are doing a one off or trying to sell the design/boat.
    I would look at the 505 for inspiration for an excellent performance boat for two people too heavy for a 29er. I know it is an old design but has been modernised in a number of ways, and the hull shape has always been a winner. Mostly the rig shows the age of the design and this is where the biggest improvements could be theoretically made.
    The other possibility in hard chine with more sail power and larger waterline beam than a 29er, is the Javelin. Sort of a detuned International 14.
    If you are maybe thinking of going commercial, then only the Bethwaites seem to have struck gold, and many others have been disappointed. :)
  3. bobby_mcgrath
    Joined: Jun 2005
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    Location: Newfoundland, Canada

    bobby_mcgrath Junior Member

    Right now, i am looking at one-offing some prototypes. I have a design I have been working with, but am just looking for some input on what really makes a skiff a skiff, and what I should be looking out for. Particullarily in skiff hull form characteristics, construction, and rig design. I have some captial to make up some molds, and some technical help lined up for construction. It looks like I will have some moderate financial support for the next while. so am looking to start a career in design. Again, any help would dbe greatly appreciated.

    Bob McGrath
  4. Doug Lord

    Doug Lord Guest

    Design and Technology

    Bob, are you going to build the Bluenose and a skiff?
    If I were you I would look carefully at what lessons of small boat design can be learned from the modern Moth-some call it a "skiff". It achieves speed beyond many other small boats with incredible efficiency. Perhaps that technology could be(or should be?) of benefit in any consideration of a new design for a modern skiff.
  5. CT 249
    Joined: Dec 2004
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    Location: Sydney Australia

    CT 249 Senior Member

    "What makes a skiff a skiff?"

    One of the most debated questions on the internet, that one! Some say it's any fast dinghy, some say it's just an Aussie 12, 16 or 18, and there are many positions in between.

    Personally, taking a detailed long-history view, I reckon you can say it's design-wise, it's an unballaste centreboard boat with more crew-induced righting moment for length, and more sail area for length, than anything that's definitely a dinghy (ie 505, FD, Kiwi Javelin). When you plot "real" skiffs - ie the ones that are definitely skiffs as we mean the term today (12s, 16s, 18s, 14s)- in terms of SA and RM for LOA, you'll see they sit quite distinct from the fast dinghies that are totally outside the skiff line of development. These factors more than any other seem to drive their development.

    However, the Aussie skiff sailors had a very good case to say that a "skiff" AS WE USE THE TERM IN SAILING TODAY is a development-class boat with multiple rigs, no sail numbers, fast and high-tech, and part of the "skiff" tradition. Problem is, language evolves and so do skiffs and now 16s and 18s have one design hulls so they have changed themselves and that seems to make the old definition unworkable, or at least underline the fact that definitions change as language evolves.

    Sorry about the longish answer, but it's a hard question and one thing's for sure, any easy answer is the wrong one! Any simple answer like "a flat hulled boat", "a boat with everyone on trapeze", "a fast boat", "something like a Jersey skiff", "a boat with an assymetric", "a boat that planes upwind and tacks downwind" etc is easily proven wrong.

    2) There aren't really any "skiff hull form characteristics" as far as I can see, having spoken to most of the major designers. Some skiffs have chines, some have round bilges, some have dead flat planing panels down the centreline, some have Vee deadrise through most of their length, some have racks, some don't. Some have very low freeboard, some have very high freeboard. Some are One Design, some aren't. Some are wedge-shaped in plan form, some are much less so. Some are self draining, some weren't until very recently. Most were designed to plane early (as in in fairly light winds) in the past, now most are designed as "slicing" or "displacement" hulls, like the way the 9ers stay off the plane as long as possible. This is just within the 3 main "traditional Sydney Harbour skiff" classes!

    Displacement-length ratio has a major impact on design and DLRs on skiffs vary enormously, a 12's DLR is about 144 or so while an 18s is about 70 (off the top of my head).

    Just to show how confused the issue is, the "standard" 12' Skiff hull races as an R Class (like a skiff but with small working sails) and wins, a Cherub dinghy hull can race as a 12 and do well, and a UK National 12 hull can be modified to (edit) do sort-of-okay in Cherubs.

    The most detailed piece on how to design a skiff was written by an Aussie naval architect, Rob Widders, in Australian Sailing magazine a few years back, including info like chine heigths, deadrise etc and lines for 16s and 18s. Most other guys start with an existing design and sail it to get some knowledge of its weak and strong points. Even a guy like Iain Murray (top designer in 12s and 7 time "world" champ in 18s) got to the stage where he wouldn't design a boat unless he really knew the exact class of skiff already.

    It sounds like you're creating something like a slightly blown-up B14, perhaps.
  6. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    I'm with him

    I second the above bloke ( he is my brother). Look really hard at the B14. It is often sailed with male/female crews and Julian Bethwaite and Frank Bethwaite really know how to design a boat that is ergonomic to sail. When I sailed 16s I was always tripping over a fitting or block but go out on a Bethwaite boat and they fit very well. I am a big TASAR fan for sailing with your partner and the B 14 is a TASAR on steroids.

    Sail one or something like it until you know what you want. My guess is you will like it and keep it if this sort of scene is your bag.


    Phil Thompson

  7. TaSSie_deVil
    Joined: Jan 2004
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    Location: Launceston, Tasmania, AUS

    TaSSie_deVil Resident Boataholic

    Definately agree with the B14; sure it isn't as user friendly as the '9ers, but it was developed many years beforehand (so kite bags are the order of the day and no one-line up/down kite controls) but it was the first boat to bring 18 footer performance to the masses and this is what makes it great. It is also the only true "mini 18" in existance. Only problem is that the class has really strayed from its original one-design roots to the point where CST carbon masts and big head kevlar sails are the order of the day which means that it isn't easy to get a good cheap 2nd hand one anymore. Also the boat has only got a decent fleet in the UK and a fairly good one in AUS; that's about it. If you want one in the US; it's a matter of either finding the Alvis Marine moulds (thought to be destroyed; and even if they do still exist they're outdated as the structure of the boat has changed over time also...) or importing one from the UK or AUS.

    Aside from a misguided attempt to get some boats into Japan and Hong Kong (which resulted in about 10 boats going to asia), there are only 200 or so in the UK/France and about the same in AUS; with less than 1/3 of the existing boats actually racing.

    So... great boat, but not without it's flaws.

    Also, there is a new bethwaite boat... the 29erXX... that is trying to muscle in on the B14 scene. Throw the rig from the flunked 59er on the 29er and add twin traps to act as the big brother 29er/little sister 49er kinda thing.

    If you really want a simple answer as to what to sail as an intermediate thing between the 29er and 49er... the answer is take a I14 and drop a slightly smaller rig on it.
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