Radio controlled sailboats

Discussion in 'Boat Design' started by DiasDePlaya, Jul 3, 2012.

  1. DiasDePlaya
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    DiasDePlaya Junior Member

    Hi all,

    I'm a fan of radio-controlled sailboats.
    I have seen many racing yacht designs that I like, and I would build a boat R / C of 1 meter with a hull based on a famous boat.
    But someone told me that this does not work, you can not scale a hull that way it will not work, that in order to scale down the boat would sail in a much more dense than water.

    Is that so? Not enough to reduce the scale?

    Sorry for my bad English.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    --------------------------
    Scaling large boats down to 1m is almost impossible if you want a good sailing model. Sail area varies as the square of length and displacement varies as the cube of length. So what generally happens if you try to do exactly scale is that the model has too little displacement and too much sail area. You may be able to find more info here: http://www.theamya.org/

    also here: http://www.sailboat-technology.com/links/online_articles.php
    And Lester Gilbert had/has one of the best sites around for the design of the IOM but it appears to be down. He is working on what promises to be an excellent book with Graham Bantock of Sails etc.
     
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  3. DiasDePlaya
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    DiasDePlaya Junior Member

    Forget the sails and displacement. The International One Metre rules requires me to build a boat of 4 kilograms and use a very accurate rig, so with these variables I can not play. Also I have to use a rudder and a keel specifically that I can not change much. I just want to know if the lines of a hull designed for a length of real yacht can be reduced to just one metre will work.
     
  4. Silver Raven
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    Silver Raven Senior Member

    Gooday 'Dias' - Your 'english' is just fine - most of us around the world - who speak 'english' as our first language - murder it rather badly. I'm 72, male ex-pat Canuck - living in OZ - & most people don't know what I'm saying - & sometime - not even me.

    DO NOT believe what you have been told - IT IS WRONG - if you do a very careful study in 'google' or other search-engine - into 'A' class model sailing yachts - you will find that - way back in the beginning - these very fine model yachts were a direct development of a - 6 mtr racing yacht. Back in those days a '6 mtr' class yacht was & still is - a most beautiful - classic & fast efficient sailing full sized yacht. These 'A' class yacht are very famous - extremely fast - great to sail - look fabulous - don't cost the earth & have been used by some of the worlds leading yacht designers to do a lot of development work in design testing - in fact some of the most famous design break throughs have been developed using this fine model yacht design.

    I've built many many of them - in several configurations within the class rules. They are great value for money & you can keep it as simple as you like or get very involved - in the 'high-tec' end of designs, weight, sails, masts, rigging & even fit a spinnaker to be radio-controlled & use a 10 or 12 channel radio-control unit. WE had - bending masts, boom vangs, in/out jib trim tweekers, keel trim-tabs, adjustable back-stay(s) - & more - all controlled from the shore - - sure did make for great sailing & wonderful competitive racing - with fleets of 15 & more boats - competing every weekend.

    I wish you much success with your plans to go model yacht sailing. Ciao, james
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ----------------------
    As before ,probably not because of the scale problems I mentioned. At one meter big boats don't scale down well at all. I did an exact scale Melges 24 at a length calculated to work for a model-it was 55" LOA(see below) and had an asymetric spinnaker. Could not of been done at a one meter length. You could, perhaps, capture the "look" of a larger boat without scaling the hull down. On the Melges, to capture the "essence" of the Melges 24 and still be able to use my spinnaker system I got permission from John Reichel to increase the spacing of the bulkheads forward of the midsection so that the hull was a few inches longer. It turned out well and Reichel-Pugh and Melges were pleased.

    Some models I've designed and built, including the Melges with permission of Melges and Reichel-Pugh:

    Pictures: 1-3 Melges 24 RC with Power Ballast System and retractable, gybable asymetric spinnaker, 4-5-Super scow 36 with Power Ballast System, 6-America One(65") and the S 50 with retractable, gybable symetric spinnaker system:
     

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  6. Doug Lord
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    Doug Lord Flight Ready

  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I've never understood how tank and windtunnel testing could

    be of much value if things didn't scale.
     
  8. yipster
    Joined: Oct 2002
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    yipster designer

    we should not generalise! apart from said of the wall here i read:
    "ofcourse linear dimensions only use the scale
    areas be reduced by the square root of the scale
    volumes and weights be reduced by the cube (obviously)
    and all velocity's be scaled by the square root of scaling factor
    and for sails yes, tricky, and i have to read up ;)
     
  9. fredschmidt
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    fredschmidt Naval Architect

    Hi DiasDePlaya,

    What I can help I will with pleasure. The blog stated Doug has some tips, but you can contact me by email or here in the Forum.
    Cheers
    Fred
     
  10. Doug Lord
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    Doug Lord Flight Ready

    ----------------------
    Things do scale-and quite nicely BUT-Dias seemed to be talking about scaling down a much larger boat to one meter. From experience I know that won't work. But you can try to make a one meter boat capture the "look" of a 60 footer without it being to scale.

    Sail area varies as the square of length, displacement varies as the cube of length. Using a generic VOR 70 as an example:
    A) 70' squared=4900, 70 cubed= 343,000
    B) one meter(3.28') squared = 10.76, 3.28 cubed=35.29

    So if the VOR 70 is 30,800lb and has 3357sq.ft. of upwind sail the one meter model will have:
    1) Sail Area=10.76/4900= .0022; .0022 X 3357= 7.38sq.ft. 1063 sq.in
    2) Displacement=35.29/ 343000= .0001 X 30800= 3.08lb

    1& 2 above illustrate that a VOR70 could not realistically be scaled down to one meter. An IOM must weigh 4000g or 8.8lb. A 36/600 competitively must weigh between 5-7lb. An exact scale one meter VOR 70 would not sail. Not enough weight, way too much sail area. To make a "scale" VOR 70 that would sail with radio control the model would have to be much larger or you could try to capture the "look" of a VOR 70 with non-scale parameters.
     
  11. Earl Boebert
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    Earl Boebert Senior Member

    Well, you can't fool Mother Nature, but you can fool the human eye. If your goal is an exact scale model, dimension for dimension, then you're out of luck. If your goal is a boat that "looks like an X" on the water for some prototype X, then there are things you can do. Take for example Yankee III, a 36" model of the J Class Yankee. Sail area is reduced and aspect ratio increased to give the illusion of a tall rig. Draft is increased as is thickness of the keel to give more displacement and a better ballast ratio. As you can see from the first photo, she doesn't look terribly unreal on the water.

    There were two classes sailed in the U.S. that were directly scaled down from full-size rating rules. One, as mentioned above, was the 6 meter class to 1 1/3 inches to the foot. The class rules even required internal ballast to simulate the weight of the crew. The other was the R Class under the Universal Rule at 1 1/2 inches to the foot. Both yielded pretty but tender boats.

    Another example is my 36 inch Sonder boat. I wanted to maintain the look of those great gaff rigs so I kept the sail plan very close to scale. For the hull I used the tricks noted above. She displaces five pounds and change, three and a half in ballast. Hull is self-stick mahogany veneer laid over a fiberglass shell with another layer of fiberglass on top. The second two pictures are her. Next iteration will have more displacement forward and less aft to reduce the tendency to pitch down on the beat. Goes like a bat on the reach or run, but like her big sisters she's a handful on those points of sail.

    Cheers,

    Earl
     

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  12. Submarine Tom

    Submarine Tom Previous Member

    Dias,

    You can build a very nice one meter sail boat that will perform beautifully!

    You have opened a can of worms with this thread on this forum that will go on for many pages in arguement and confusion.

    Save your time and effort and Google up the R/C world for some streamlined advice.

    There are easy ways to do what you are after with terrific results.

    Rcgroups.com is one place to start.

    Good luck and good sailing my friend.
     
  13. fredschmidt
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    fredschmidt Naval Architect

    Hi Earl

    Spectacular. They are gorgeous.

    Fred
     
  14. DiasDePlaya
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    DiasDePlaya Junior Member

    Do you know the Magnun 747 mini transat designed by David Raison? I want to build a RG/65 with this hull lines. I decided not to built it in IOM scale because the 4 kilograms minimun weight.
    The Magnum boat is 6.5 meters and the RG/65 is a 65 centimeters boat. Would work?

    I insist, don't include the sail plan in the problem, just the water lines. The keel and ruder will be out of scale, much bigger as actual RG/65 uses and the rig would be a Swing Rig, out of scale too.
     

  15. Doug Lord
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    Doug Lord Flight Ready

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