twin daggerboards on a monohull?

Discussion in 'Sailboats' started by TwoBirds, Aug 18, 2017.

  1. TwoBirds
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    TwoBirds Junior Member

    Hi

    I'll be building a 16' skiff soon and I'm playing with the idea of using twin daggerboards instead of the single board the plans call for.

    Leeboards won't work for what I have in mind.

    just wondering if there's any really compelling reason not to, and if two boards the same length as the single board in the plans and half as wide would do the same job?

    2B
     
  2. UNCIVILIZED
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    UNCIVILIZED DIY Junkyard MadScientist

    You'll be adding extra drag & weight more than anything else. Plus you have to build 2 board cases, along with hardware for each board, etc. And to what gain? You're not going to be sailing heeled over far enough so that a centerline board isn't working well for you anyway.
     
  3. messabout
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    messabout Senior Member

    One of the few reasons for using twin boards is to free up the space in the middle of the boat. There are some Inland Lakes Scows that use twin board to good effect. The deal is that these boats are deliberately sailed in a heeled position. The boards are often angled such the the boards are vertical when the scow is heeled.

    If you make the dagger boards half the width of the single board (half the chord) you will have given them more aspect ratio which is technically a good thing, but the stall angle will be compromised. Not good. Best to use the board as designed. If you are determined to get the case out of the center of the boat you can offset the single board to one side without losing much efficiency of the board.
     
  4. philSweet
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    philSweet Senior Member

    No, there is no compelling reason not to. No, you can't make them half as wide and run on both. The details are complicated, but you probably can't build a pair of daggerboards and boxes that are precise enough in use to balance the load, and even if you did, the hydrodynamics don't work that way - the boards interact through induced flow field velocities. Make each full sized and only run on one at a time.
     
  5. Angélique
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    Angélique aka Angel (only by name)

    Some monohull examples with twin daggerboards...​

    Sailboat Data - | - Red Fox 200 - - Twin Daggerboards - (1990)

    [​IMG]


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    [​IMG]

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    Winner Yachts - | - W8 - | - W8-P - | - W9 - | - W9-P - | - W10 - | - W10-P - | - W11 - | - W11-P - | - W12 - | - W12-P - | - PDF

    the W.. number represents the hull length in meters - - - - P = performance version - - - - PDF = brochure

    Winner 8 Twin Daggerboard = W8-D - - ‘‘ will be available as of June - 2016 ’’

    Don't know though if they have met that timetable, as I didn't see any news about it on their website.

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Aug 19, 2017
  6. TwoBirds
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    TwoBirds Junior Member

    Thanks for your help everybody :)



    I should have realized that it wouldn't be that simple after researching twin rudders back when I was thinking about building a Cat.

    I appreciate your help and I'll likely do a combo of what phil and messabout mentioned, make 2 full sized daggerboard cases and one board which I'll leave on one side most of the time and move it if I need to have her heeled over on the other tack to reduce pounding.

    2B
     
  7. OzFred
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    OzFred Senior Member

    One reason is that it won't fit the 16 foot skiff class rules, but maybe that's not an issue.

    An assessment of whether it's a good idea or not should be based on the advantages and disadvantages weighted by what you're trying to achieve. Otherwise you'll just get some comments on what they're good for and what they're not without any context as to whether it matters.
     
  8. OzFred
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    OzFred Senior Member

    Those don't look much like 16' skiffs.
     
  9. rwatson
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    rwatson Senior Member

    That "winner 8" two board version will probably never hit the market. Its probably just a marketing demand exercise. They haven't even canted the boards, which means they have done no real research.
     
  10. Angélique
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    Angélique aka Angel (only by name)

    Hi Fred,

    Often information can be obtained by studying other boats with the configuration which is being considered. That's why the examples were posted. Also free of charge can be learned from the mistakes they made, like the one named in the last above post.

    Good luck !
     
  11. Angélique
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    Angélique aka Angel (only by name)

    Yes, and for this it would be good if the OP posted a SOR (statement of requirements), or maybe just a statement of goals to start with.
     
  12. Angélique
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    Angélique aka Angel (only by name)

    [​IMG] - - [​IMG] - - [​IMG] - - [​IMG] - - [​IMG]

    The avatar looks to me like ‘‘ kill two birds with one stone ’’ but can hardly say that from wanting two boards instead of one, so 2B, what's up . . ?
     
  13. TwoBirds
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    TwoBirds Junior Member

    Hi

    Sorry, I just needed to know if running two daggerboards would work, didn't mean to cause any arguments, certainly didn't want to participate in any arguments either :)

    I did a bit of googling and could only find twin board information about Catamarans so I very much appreciate the time and effort Angelique took to post pics of twin daggerboard monohulls.

    the reason for having twin daggerboard slots is to use them as sockets for a built in dolly system, I can just lean over the side, pop them into place, and hook a bungee over the gunwale to keep them in place.
    the boat launch I use is very busy and I like to get my boat in and out of the water as quickly as possible so I don't honk too many people off, wish there were more people like me

    I did get exactly the info I needed, I can build in two slots and run one board in whichever slot seems to work the best most of the time.
    since it's flat bottomed (3 panel stitch and glue) I'll need to sail it heeled over sometimes to keep it from pounding too hard in chop in which case I can run the board in whichever slot is on the lee at the time.

    It'll be a work boat mostly for crabbing/diving/fishing so it doesn't need to measure up to the class rules, since I'll be saving about 11 pounds on my dolly the extra 6 pounds making an extra daggerboard slot costs isn't a problem, and as I'll only be running one board the extra drag is negligible.

    Yes, it's " Kill two birds with one stone", partly because all the cool names were already in use but mostly because if I had a motto that'd be it :)

    Thanks again for all your help

    2B
     
  14. Angélique
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    Angélique aka Angel (only by name)

    Hi 2B,

    To make double use of the daggerboard slots as sockets for a dolly system is killing two birds with one stone, so you're doing well . . :)

    For more speed see if you can get some vertical lift of your side switch dagger . . :cool:

    See ---> Daggerboards on a cruising cat ---> some vertical lift daggers in post #11.

    Good luck !
     

  15. iskip
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    iskip Junior Member

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