Rival 21 from batavento sailmakers brazil

Discussion in 'Multihulls' started by Lucainbarca, Apr 20, 2019.

  1. Lucainbarca
    Joined: Apr 2019
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    Location: Dominican republic

    Lucainbarca Junior Member

    This is my first building and I would like to have other people advise on design and realization. The plan is available for free in the net. At the moment I am worried with the first h IMG-20190401-WA0037.jpeg 20190326_094216.jpg ull weight. Still not finished and already around 100 kg without rudder, daggerboard, deck and any kind of hardware. The project boat displacement is 280 kg.
     
  2. peterbike
    Joined: Dec 2017
    Posts: 32
    Likes: 5, Points: 8
    Location: melbourne

    peterbike Junior Member

    Yes Luca, I agree with you. It is way too heavy already. :eek:
    I suggest that you consider this one as a practice one & start again. using smaller framing timbers & plywood. 5/6mm ?
    Or even forget the timber & just use plywood.
    good luck !
     
  3. Lucainbarca
    Joined: Apr 2019
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    Location: Dominican republic

    Lucainbarca Junior Member

    For the hull I can't find good marine plywood so I used mdf and the only available one was 9 mm ( here is where the extra weight arrives....) The rest of the structure is cedar and 8 mm plywood. Here we have a lot of windy days and my intention is not to race....
    What will be an acceptable weight in your opinion ?
     
  4. peterbike
    Joined: Dec 2017
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    Location: melbourne

    peterbike Junior Member

    Luca, I don't know how long your hull is - but i am guessing 6m/20ft ?
    So 20 kgs would be good, 30kgs acceptable ?
    Can you get a sheet of 8mm ply & weigh compared to 9mm mdf ?
    mdf is a terrible choice ; it will fall apart very soon. :(:(
     
  5. Lucainbarca
    Joined: Apr 2019
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    Location: Dominican republic

    Lucainbarca Junior Member

    Hobie 21 sc 600 pounds 272 kg
    Hobie 21 se 565 pounds 256 kg

    Reynolds 21 900 lb. 408 kg


    ARC 22 450 lb. 204 kg. 39'6" carbon rig. But this is not my target !!!
     
  6. peterbike
    Joined: Dec 2017
    Posts: 32
    Likes: 5, Points: 8
    Location: melbourne

    peterbike Junior Member

    Well then, I guess you need to measure the weight of EVERYTHING else to see what the weight of your hulls can be ?
     
  7. Lucainbarca
    Joined: Apr 2019
    Posts: 8
    Likes: 2, Points: 3
    Location: Dominican republic

    Lucainbarca Junior Member

    I agree...May be in a couple of months I will get a prindle 18, which I bought to cannibalize.
    But I have to wait ....!!!!
     
  8. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    Get a belt sander, planer or router to the hull, 9mm is twice too thick and heavy. Then cut those bulkheads into ring frames - and you only need a couple. You can still save this hull.
     
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  9. Zilver
    Joined: Nov 2007
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    Location: Amterdam the Netherlands

    Zilver Junior Member

    MDF is fine for making furniture. MDF is not waterproof,very heavy and very weak. It will desintegrate soon. I'd advise to stop building and start again with suitable materials.

    Good luck, Hans
     
    Enter Miles likes this.
  10. Lucainbarca
    Joined: Apr 2019
    Posts: 8
    Likes: 2, Points: 3
    Location: Dominican republic

    Lucainbarca Junior Member

    This type of mdf is waterproof and we try to leave it in sea water, after a polyester coat on it, for a couple of months without any problem. I can understad that this is a non structural test. I do not have access to the material specification. I want to use the boat like a beach cat, so not so long in the water. I know it is not the best, but a compromise....another factor is that I glued everything whith epoxy mixed with cabosil, but I want to use polyester on the exterior side of the hull. Now that the weight problem is clear to me I think the right decision was to go for a very thin mdf just to get the hull shape and then laminate to it stopping at a target weight !!!
    Last option may be to make a sandwich on a flat table and use that instead of plywood or mdf.
     
    Enter Miles likes this.
  11. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    If mdf is all you have but you have fibreglass, then use the mdf to make a mould, waxed polyester works great on mdf to create a release surface.
    Waterproof or not mdf of any thickness will end in tears.
    Use a iso polyester if you have it coremat will help bulk up the laminate you can use cardboard tubes cut in half and glassed over for stringers and ribs.
    Keep the resin glass ratio at 1-1
     
    Enter Miles likes this.
  12. Lucainbarca
    Joined: Apr 2019
    Posts: 8
    Likes: 2, Points: 3
    Location: Dominican republic

    Lucainbarca Junior Member

    I would like to test the design first, hope to spend some time in the water....eventually later when the hulls give signs of tyreness make a mould. But I am doing this only for pleasure and I do not see the need of a mould ( I will try to do it if I can encourage any local child go sailing !!!) Finally I have some time and space but around here nobody is intrested in sailing, so little cat construction is completly unknown.
     
  13. Enter Miles
    Joined: Mar 2019
    Posts: 13
    Likes: 15, Points: 3
    Location: Rio de Janeiro

    Enter Miles Junior Member

    I agree with the comments above, that MDF is not at all a good option. And I can understand, that you don't want to loose the work already invested, and you want to go out to the water and have some fun as soon as possible. However, going ahead, and building another hull with equal specifications, doesn't seem to be a wise way to employ your time and money ressources. It will be a dog, and probably disintegrate fast.

    So, why don't you finish this hull, and then make a tacking outrigger of it? Build a small, cheap outrigger hull, put together a connecting platform out of bamboo, and mast and spars also from bamboo. You might find it in your local area for free. You can experiment with that and have some fun. And if you find that the heavy hull works for you, and if it is still in one piece, then go ahead and build the second. .... Seems unlikely, but who knows...
    Just an idea.
    Best regards,
    Peter
     
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  14. Lucainbarca
    Joined: Apr 2019
    Posts: 8
    Likes: 2, Points: 3
    Location: Dominican republic

    Lucainbarca Junior Member

    First of all I would like to thank everybody for advise !! I successfully try to get in touch with the designer and builder of the boat (Sergio Marques and Chico Armond ), and he told me that the complete hull should be between 95 and 115 kg. For a total boat weight between 350 and 390 kg.
    For a few months I have to stop my building project and go to work !!!
    But the next step will be to weight, as soon as it arrives, the complete rig, beams, sails.....
    I understand that my post is not so interesting, but I hope to keep building, and learn the skills to build more light.
    Also any comment on the design will be very appreciated, I am interested in a cruiser racer type of boat that can sail in the bay, but I would like also to be able to go to some sandy islands 8 nm away, and possibly come back !!! Considering that the way back is always upwind in 20 knots true wind or more....and the consequent sea state......Is it possible ??
     

  15. Enter Miles
    Joined: Mar 2019
    Posts: 13
    Likes: 15, Points: 3
    Location: Rio de Janeiro

    Enter Miles Junior Member

    Upwind for 8 miles in 20 knots of TWS. Possible? ...Yes, might be.
    However, looking at the hull shape, the chances are not too great. :) Looking from here, it seems like a flat bottom, and I don't see provision for a centerboard trunk. ... But I might be wrong.
    If not, and if you want to improve your chances, make sure you have a lee board or something to give you lateral resistance.
    Other possibility, is to provide an outboard engine.
     
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