sailboat design for 2 meter boat.

Discussion in 'Sailboats' started by Projectnick, Oct 2, 2013.

  1. Projectnick
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    Projectnick Junior Member

    I have model a sailboat hull of 2 meter. I would like to design a sail. In this process i have pretty much estimated the sail Area required from my righting moment, however, I want to know how high is the mast needs to be and what should be the diameter of the mast if possible?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    1) Is it a keel boat or multihull?
    2) how much weight in the keel bulb(assuming there is one)?
    3) How deep is the bulb?
    4) Because of the nature of models most racing boats use more than one rig or a reefable rig in order to have maximum power throughout the wind range. 50" racing Marbleheads genrally have around 5 rigs.....
    5) Is it intended to be radio control?

    -----
    Hope it works out well!
     
  3. messabout
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    messabout Senior Member

    So if you have established how much sail area you are going to use, you may be doing this backward. Tell us what the proposed sail area is. Is it to be sloop rigged, ketch rigged, cat rigged, or whatever.

    As for the mast, tell us whether it will have uppers, lowers, diamonds, backstays, forestays, jibstays or just generally how you plan to build the mast. Then we could make a reasonable guess as to how big a section it must have. A two meter RC boat will have as much as six feet of mast height. That will give you a starting place.

    But the height of the mast determines the height of the center of area (or center of lateral pressure if you prefer)., That has to be calculated back against righting moments.
     
  4. Projectnick
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    Projectnick Junior Member

    Doug lord, Messabout, Thanks for the reply
    this is a keel boat, of about 10 kg on keel bulb and the lightship is 20 kg, and displacement is 47 kg
    Height is .565 m from the base of the hull
    It is intended to be radiocontrol later, if possible..
    I have basically designed the hull and from the parametric studies of the boat of my sizes, i have estimated area to be around 2.4 m^2. I did take victoria-18 to be my parent model for the sail and i did ratios to find I, J, E, P for my boat. This is where i am. I am wondering if i can take my I to be the mast height. suprising my I is 6.18 ft which is as high messabout talked about.


    So, messabout, i have not really decided on the rig, but so far i am going with fractional sloop. I am in this stage right now.
     
  5. messabout
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    messabout Senior Member

    If you use proportions from a Victoria or other established RC boat you are going to have a very tall mast it would seem. At 2.4 meters that comes to almost 3700 square inches which is a bunch of sail. For an RC boat you will want the jib clew,to just clear the front of the mast when tacking. That is so that you can use a club and thereby simplify the control mechanisms. Do the arithmetic and you will probably see that 2.4 meters is going to present some interesting layout problems, namely that the mast will be a skyscraper if the sail aspect ratios are similar to the ones you mentioned.

    If you have designed for 47 kg displacement and lightship is 20 kg do you intend to add more ballast to get to the 47kg design displacement? Your rig and all the control mechanism plus batteries will probably not weigh more than 3.5 kg.

    Can you post a picture of the hull or at least some drawings?
     
  6. Projectnick
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    Projectnick Junior Member

    Thanks Messabout
    I will post them as i get the to my computer. I am sorry, the payload is 34 kg, and lighship is 20 kg. So, with ballast and mast 47 kg.
    i used the linear porportion when i do mine I J E P from victoria. AM i doing it wrong by using linear rations?
    By the way i am trying to use maxsurf vpp to create plot for this size boat, but i get an non convergence error. Is that because the boat is really small for Maxsurf VPP, or the i just used I, J, P, E, LP, Boomheight, and mast diameters in the inputs. Did you even happen to have such problems?
     
  7. messabout
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    messabout Senior Member

    I am several hundred years old and some say curmudgeonly. Thus I do not use computer programs. Well not many of them anyway. I certainly respect the capacity and wizardry of some of the computer programs but in any case it is GIGO. I can not help with maxsurf but many of our other members are very good at that sort of thing. Perhaps one or more of them will help you.

    Start with a hand calculator. We have to do some preliminary guesswork and make some preliminary assumptions. Assume that you want sails with an aspect ratio of somewhere around three to one. That is to say, the luff is three times longer than the foot. Just to make the arithemetic easy, figure on 3600 square inches which is near the 2.4 meters that you started with. Now make up a little chart. Let the jib be one third of the total area for example. OK 1200 inches square. That leaves the main at 2400 inches square. Fiddling with the trial chart you will see that the mast is going to be ten feet high. The center of lateral pressure will be something like four feet above the waterline. If you make some kind of wild guess about the sail pressure in knockdown situations then you have about 48 foot pounds. That means that a 10kg bulb is going to be way down below the CB. This is oversimplification but it is the general idea.

    Bottom line, You are probably anticipating too much sail area for a two meter,37 kg, boat. Never mind what the computer program tells you. Be practical and you will have fewer disappointments and lots more fun.
     

  8. Projectnick
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    Projectnick Junior Member

    Thanks,

    What do you mean by i am anticipating too much sail area for the 37 kg boat? you mean by boat cannot take that much sail area?
     
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