Sailing Dinghy Design

Discussion in 'Sailboats' started by Tim B, Mar 12, 2003.

  1. Tim B
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    Tim B Senior Member

    I'm starting this thread, so that all us dinghy sailors have somewhere to discuss dinghy-specific issues, including design of the boat and systems. If anyone else thinks its a good idea, we may also try to do something like options 1+2 and do a collaborative design. Any one who sails a dinghy can participate, wheter mono or multi-hull and of any class (but don't get classist please), Anyone else who has any ideas can also join in. Please do in fact. We'll run this, and see what happens.

    Have Fun,

    Tim B.
     
  2. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I'd like to encourage you to share links, Tim. I know there are some really good dinghy sites out there. Here are some I like:
    www.ruach.net
    www.bana.com
    www.tboat.com
    see also http://boatdesign.net/forums/showthread.php?threadid=1070

    Are you a fan of Paul Bieker's International 14s? I think Bieker is the best dinghy designer in the U.S. right now.

    Do you prefer boats with or without double trapezes?

    Do you like the Johnson 18 (designed by Rodger Martin)?

    Do you like the 49er? Have you sailed one?

    I have a colleague who wants to see a fleet mini transat boats racing in the NY area. Do you think that's a good idea?
     
  3. Tim B
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    Tim B Senior Member

    Thanks Stephen.

    I'll certainly share the links I have when they are relevant. I have to admit that I find search engines very useful!

    Sadly, I have to admit that I have not sailed the I14, 49er etc. but I will post my opinions when I do get to sail them. Who knows what will happen this season.

    I did say that we'd try to run a collaborative design didn't I? now don't get me wrong, I'm not saying that a 6m mini-transat is impossible, but I feel it's going to be a bit too much of a risk. A six to seven-metre coastal racer style thing may be good. Who's going to sail this thing anyway...

    If we get some more interest, we'll have a poll and see what we want. The other difficult thing, and I may be thinking way too far ahead, is who's going to pay to build this boat, once we've designed it? Anyway, we can think about that later.

    Hope we can get something on paper,

    Tim B.
     
  4. DavidG
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    DavidG Junior Member

    National 12

    Hi Tim,

    How about designing and building a National 12, they are cheap to build, have a great fleet, and are probably the most cost effective way of practicing the designers art!

    Apart from which designers like Jo Richards, Phil Morrison, Hugh Welbourne, Uffa Fox, Ian Proctor ... all cut their teeth in the class!

    But I am biased.

    David
    N3461
     
  5. Tim B
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    Tim B Senior Member

    David,

    I like it. 2 : 3.3 beam:length seems large to a LARK sailor (we are at about 1.5 : 4), but I don't mind that at all. I presume you sail the National twelve, and so have more experience than I do with it. I like the idea of going for a developement class, and I can't find any that I like any more than the National 12. Could you post some rules. We'll start at the hull and work up, if that's okay.

    Cheers,

    Tim B
     
  6. Stephen Ditmore
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    Stephen Ditmore Senior Member

  7. Tim B
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    Tim B Senior Member

    Stephen,

    I take the point about the comparison of classes, but we must bear in mind that we are more likely to design a good boat in a class that we, collectively, have some experience in. I have looked through your links, though, and I feel that the I14 (which I was avoiding slightly) would be a good contender to the National 12.

    At two feet longer and a little narrower, we're back to a ratio of about 1.8:4.3 , which, to my eye is quite nice. Looking at the rules, LWL should read LOA (excluding spinnaker pole), other than that the vital statistics are self-explanatory and listed below:

    Number of crew 2
    LWL 4267mm 14ft
    LOA (including retractable spinnaker pole) 7010mm 23ft
    Beam 1830mm 6ft
    Mast Height above hull 7626mm 25ft
    Hull weight (with fittings) 74.25kg 164lbs
    Sail area (main and jib) 18.58sq.m 200sq.ft
    Spinnaker unlimited, typical size 32sq.m 350sq.ft

    Let me know what you think,

    Tim B
     
  8. Stephen Ditmore
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    Stephen Ditmore Senior Member

    The advantage of the International 14 from my point of view is that it's sailed in the U.S. while the National 12 is, to my knowledge, only sailed in England. A disadvantage is that I feel hopeless about ever doing as good a 14 as Paul Bieker.
    http://www.48north.com/may96/bieker.htm

    I'm a fan of Phil Morrison's work, too. Here are his thoughts on the I14:
    http://www.eclipse.co.uk/rowsell+morrison/MK8Design.shtml

    I have to thank you though, Tim, for getting me interested in the Moth. I'd seen a letter to the editor about it in a recent issue of Sailing World, and your post about dinghies caused me to go back to it. I've since decided I really want to design and build one, and the morning after that decision I woke up feeling like a new man. I'm going to attend the nationals in Brigantine NJ on June 14 to learn more. Interestingly, the design that became the Europe, now the women's olympic single-hander, came out of the Moth class (many years ago).

    I may not have the skill level required to sail a narrow "Modern Moth," so I may wind up trying to find someone else to race my boat. The nice thing, though, is that I think I'll be able to get it in and out of my apartment! I might make some floats for it and sail it as a trimaran when not racing.

    Anyway, I'd like to do an I14 or a National 12 as a group project, and a Moth on my own, so feel free to choose whatever class you want for the group project and count me in!
     
  9. Tim B
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    Tim B Senior Member

    I14

    Phil Morrison's general attitude towards the design certainly seems to be about right, to my thinking, low beam : high length has been proved many times to be the way to go. As for the bows, I'm completly in agreement there as well. Having sailed a fine-bowed LARK and other broader bowed boats (eg. 420) the Lark is dryer and faster through waves.

    As far as which class is concerned, I like the extra length afforded by the I14, as opposed to the National 12. I'd like to hear what DavidG has to say, since he offered an opinion on the Nat. 12. I'll drop him an e-mail and see what he thinks. I have a feeling though, that whichever class we go for, we're going to have to use a bit of computing power to help! There is a free version of Hullform (Version 6S) around on the web, but I can't work out how to use it properly! There's been a fair bit of talk about using Rhino recently, especially among the big-boaters, that could probably help us here, it'll get some pretty pictures anyway!! I daresay,though, that if we can get DavidG and anyone else who are yacht/racing yacht/dinghy designers by trade then at least we'll hit the water with something good whatever class.

    With the moth, do post questions, who knows, there might be some cross-feed of ideas (and that's one reason I never work on one thing at a time!) which could well benefit all of us. We'll try to answer them whatever they are! I'm glad I could have provided the impetus for a new bout of interest.

    Cheers,

    Tim B
     
  10. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Stephen Ditmore says:
    Do you like the Johnson 18 (designed by Rodger Martin)?

    Well, to be accurate, it was designed by "Rodger Martin Yacht Designs", which at that time consisted of Rodger and myself, as equal partners. We both had a lot of input, but still much less than Skip Johnson. The boat was designed for "a fairly athletic 55 year old" who didn't want a trapeze. They have clocked one at 20+ knots (downhill in a good storm) but it just never caught on, probably because the 49er came along,. and the Laser 5000, etc.

    Steve Baker
     
  11. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I wonder if it might have been the without a trapeze part. What's wrong with a trapeze, at least for heavy air? I think my abs would prefer to be with than without, and I suspect that'll remain the case when they turn 55.

    Anyway, glad to hear from you, Steve. How's Richard Roake progressing on that wacky hydro-ski thing? Has he given up on sailing? I know Dirk Kramers and the Halls have been racing A-class catamarans; has Richard considered getting into that?

    Note for the purpose of establishing connections that I'm dabbling in brokerage with Ted Fondulas.

    Tim: on the subject of software I'm about to demo TouchCAD on a Mac. I gravitated to that because it will unroll surfaces, but I see from "Polarity"s posts that Rhino will also unroll developable surfaces.
     
  12. Tim B
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    Tim B Senior Member

    Rhino/Prelim Design

    I take it Polarity is now somewhat ahead of me in his capability to use rhino, I had been enjoying a been there, done that phase, but now I'll have to learn about unrolling surfaces. It's good to know you can do it though.I've posted a (very) preliminary I14 sketch ( http://www.boatdesign.net/gallery/showphoto.php?photo=792&password=&sort=2&thecat=512 ) I know the waterline looks way off, but the rest of the hull could be about right to my eye, for a very basic sketch. Do not take the Length/Displacement ratio too seriously, is is liable to change, especially if I work out a real volume, not just an approximation.

    Length/Displacement = Length / (submerged volume)^1/3

    Cheers

    Tim B
     
  13. Tim B
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    Tim B Senior Member

    Sadly I have not yet had a lot more time to play with the I14 design, so I'm still at a fairly preliminary stage. I am assuming (since nobody has objected) that everyone is at least reasonably happy with designing an I14. I'm going to start using Hullform 6s (still free off the web) to begin something of a more workable design. I'll post a couple of pictures as I progress
     
  14. dishsail
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    dishsail Junior Member

    Hello Everyone,

    I really like this posting so far. I am new to design and haven't really started to design any boats yet in my life, but would like to start. I was wondering if someone would work with me to help me design an I14 within this post. Please let me know.

    Thanks,
    Joseph
     

  15. Tim B
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    Tim B Senior Member

    We always welcome new input with this project, Stephen and myself are pretty keen on the I14 design as a collaborative project, so if you want to join you're more than welcome. Unlike I said in a previous post, I am now working on a Rhino design for the I14 rather than a Hullform design. Thus far, the difficulty has been to keep to class rules with respect to hull-shape. Prior to this, I did a sketch of a preliminary design. It's a good starting point and it allows you to get ideas in order. See ( http://www.boatdesign.net/gallery/s...rt=2&thecat=512 ) for the sketch. From this sketch, which will have been drawn to max length and beam, though not necessarily section data, you can start to work it through on CAD, which is where we are now. Be warned, CAD may take some time, especially with the I14 Hull.

    'Principles of Yacht Design' by Lars Larson is well worth a look, it is very easy to follow, and although not dinghy specific, a lot of the theory is the same, and some examples (mostly graphical) are given down to about 5m boat length which is not too far off where we are. I think, to be honest, the Hull design in itself is simple enough from an empirical point of view, the foils, which we will also try to optimise, will get into more complex theory, but I'm sure you'll be able to follow it.

    I don't know how used you are to dinghy sailing, again there is a multitude of books and websites about the subject. A lot of which are very useful if only in as much as they put alternative views forward. If you want to go for an I14 design on your own, do feel free to bounce ideas off us, and keep us posted on what you're doing.

    Cheers,

    Tim B
     
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