Rotating Dagger boards on a cruising catamaran

Discussion in 'Multihulls' started by Becaris, Jun 11, 2011.

  1. rayaldridge
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    rayaldridge Senior Member

    I think Red was talking about a different system, with the central board coming down through a small central hull, or through a fence that would prevent ventilation. I believe the Stiletto board is unstopped. The downside is that the central hull increases drag at low speeds-- but so does having two boards, I suppose.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Gents,

    Interesting how many names we can get for the same thing.

    The Tornado cat has "centerboards" no matter that they are not on the centerline. Since they rotate on a pin thats all that matters.

    Tornados have no pin into the inside of the hull, nothing to leak. No gasket at the top, its open.

    A gasket at the bottom is really a pain, long centerboards would be much worse than a Tornado. The only way I would have one is to be offset to one side so at least the slot is not grinding into the dirt if you beach the boat. Growth in the slot is only avoidable if you pull the boat out ( not reasonable in a 60'er) or pull the board out and scrub it out occasionally.

    There is a way to have a batten inside the slot follow the board down when it pivots to "seal the slot" for some distance. This would only really work for a long rotating centerboard, not a triagular low aspect board like the Tornado.

    Marc
     
  3. oldsailor7
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    oldsailor7 Senior Member

    I had a Buccaneer 28 Trimaran with a rotating centreboard and had no trouble with it. I appreciate it was a much smaller boat, but the principle is just the same. It had a neoprene seal on the bottom, (not rubber), and the inside of the box was coated with copper anti fouling paint. The box top was watertight.
    The Up and Down lines passed thru a double sheave and up a sealed tube to the deck where a double turning block took the lines back to two conveniently sited jam cleats. The board wetted area was 2% of the projected sail area and it worked well for me. :D
     
  4. Gary Baigent
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    Gary Baigent Senior Member

    I hear what you're saying, OS7, but it is an undisputed fact that the foil and shape of a pivoting CB does not compere in terms of foil cross section, windward efficiency, less drag (gaskets and slots) plus basic maintenance with a vertical or 2-3 degree raked forward dagger; it's the average compromise compared to the clear thinking purist. The important factor is that you can vary the amount of board you have down on a dagger, depending on wind and sea conditions without altering the centre of lateral resistance; on a CB, it is always a compromise. For example, I heard from an old mullet boat sailor, that to reduce weather helm on the always hard nosed mulleties, (meaning weather helm) you swung the board aft in fresh conditions ... which is a kind of solution ... but a crude one, imo - because they still got blown sideways. But they were happy with that because they still had a a semblance of balanced steering. Agreed, the barn door rudder was/is an appalling hydro-dynamic shape and didn't help - but there you are. Cheers.
    Yeah, I've been drinking strong Belgian beer ... just had to counter your comment. Cheers again. Ahhh, there are no rules, as long as it works. Cheers.
     
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  5. redreuben
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    redreuben redreuben

    I would never argue with a man who drinks Belgian beer. His taste and discernment are beyond question !
    Gary: Strong ? Is there another kind ?
    Cheers to all, and may you all find a little Duvel in your stockings !
    RR
     
  6. Gary Baigent
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    Gary Baigent Senior Member

    Ah, redreuben, a man of impeccable taste and worldly knowledge. Cheers.
     
  7. oldsailor7
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    oldsailor7 Senior Member

    Thanks RR. I'll drink to that. :cool:
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    I was hoping for something in stockings but my friends said it was a DVD of The Rocky Horror Picture Show....I'll stick to daggerboreds, those swinging foils have too much drag for me....
     
  9. caiman
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    caiman Junior Member

    Does anyone remember a Beaneteau First Class something or other mono,that had a 'centreboard' that swung back completly outside of the hull?ie.when the CB was 'retracted',the trailing edge of the CB lay horizontaly along the hull bottom,(making it look a bit like a LAR keel on a Cat).This would give CB performence without the slot,yet still be able to swing back when hitting a 'dead head' or similar.On the boat I'm thinking about,being a mono,the keel was made of steel,with a multi,the foil would be much lighter,and so easier to manage,and possibly could be 'contrived' to be removable from the inside of the boat for beaching etc?
    Just a thought.
    Cheers
     
  10. Becaris
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    Becaris Junior Member

    Thanks for the various opinions on centerboard/daggerboards. If I was to go back to using a more standard daggerboard, what do you think about angles? What I mean is, I've noticed that some boats place the dagger boards at an angle to move them over to one side of the hull so they don't eat up space right down the middle. This puts the daggerboard at an angle under the boat. Does this cause any issue, or loss of performance?
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    They used a similar swing keel on the Venture trailables, half outside the hull when retracted for a LAR, beaching-trailer shoe. Works well, the "case" is sealed and shallow with the inside contoured for waterflow with the keel down. More resistance but those boats still get on a plane.
     
  12. Becaris
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    Becaris Junior Member

    And while I'm asking questions...
    What about offsetting from the centerline of the hull? Meaning, pushing the whole board (still vertical) off toward the outside of the hull vs. being down the centerline? Again, how would this effect performance?
     
  13. caiman
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    caiman Junior Member

    My DB is offset to the port side.I cannot detect a difference,but I'm still a learner.It certainly gives better access.
    Cheers
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    You can put the dagger anywhere and at any angle (within reason) you like, athwartships in the hull that is, not talking fore and aft, CLR position; you'll never notice any difference to helm feel or pointing ability compared to a centreline position - because there is no difference. However, if the dagger exits too high above the keelson, say, close to the waterline, then in a rolling sea, you might hear the occasional gurgle. But no one is going to have a board that high unless it is a near horizontal foil assist design, different animal. The advantage of an exit at the turn in the bilge above keelson is that you'll rarely get mud or sand forced up into the case, boat can dry out without worries.
     

  15. Dryfeet
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    Dryfeet Junior Member

    The only other potential issue with angled daggerboards is to keep that angle minimal enought so that when in the 'up' position, the top of the board doesn't extend beyond the hull side. It makes coming alongside quays and pilings a bit touchy at low water if the board extends beyond the point of max hull beam. Trimarans with boards in the amas can have this issue. Minor, but subtlely annoying.
     
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