Bridgedeck centreboard why don't they work???

Discussion in 'Multihulls' started by valery gaulin, Jan 10, 2017.

  1. pogo
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    pogo ingenious dilletante

    It has been tried with success, but
    The centerboard of " shambala" is not gybing, it' s an articulating centerboard ( up to 10 degrees) , see link in post 128.

    pogo
     
  2. UpOnStands
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    UpOnStands Senior Member

    Shambala may not have the traditional gybing dagger board but the basic intent is the same I believe -- alter the submerged thrust line to make better speed to windward.
     
  3. pogo
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    pogo ingenious dilletante


    Yepp, u got it.......nearly.
    Shambala's centerboard additionally can be tilted forward for sailing upwind under genoa or stormjib only.

    pogo
     
  4. UpOnStands
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    UpOnStands Senior Member

    As you said in your first mention - complicated.
     
  5. brian eiland
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    brian eiland Senior Member

    ...just happened across this reference to a rather old vessel that appears to make use of some centerboards on the centerline of the vessel....:)


     
    Last edited: Jan 30, 2017
  6. brian eiland
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    brian eiland Senior Member

    Can this be translated also?
    I'm having trouble understanding how the pivot shaft can be operating in two plains of action??
     
  7. brian eiland
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    brian eiland Senior Member

    Retractable Centerboard

    If I were to go back to the conventional idea of a centerboard trunk in each hull. I might give this idea some consideration as it lessens the drag of those slots in the bottoms of the hulls.
    [​IMG]

    What about adapting something like this arrangement to that flat plate nacelle structure of mine...just brainstorming

    Nah, ...its worth more effort to make the centerline bridgedeck option work.
     
  8. UpOnStands
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    UpOnStands Senior Member

    how's this? the brown stuff is not the water level :D
    the red sealing strip is hinged to the back edge of the board and is wider than the slot opening
     

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  9. brian eiland
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    brian eiland Senior Member

    Is that meant to be a hull mounted CB?

    And if the 'closing strip' is "wider than the slot opening", how does it ever get up into the slot with the board in its up position?
     
  10. UpOnStands
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    UpOnStands Senior Member

    the closing strip works only when the board is down.
    basically when the board is up its front face projects slightly below the bottom of the hull which provides sealing of about 70%. Fore and aft of the board there are matching skegs, not an LAR but more of a beaching strip.
    But boards are not on my list and most definitely not centerboards in the hulls.
     
  11. Angélique
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    Angélique aka Angel (only by name)

    -
    From post #4 of the thread Very Old Catamaran Plan C 1895:

    See also Page 457 (457) (of 667 pages total) in the above linked book of the year 1900....

     
  12. Mulkari
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    Mulkari Junior Member

    I will try to post more details when I get to my other computer. The whole system is very simple centerboard is made from wood with fiberglass glued over. It is mounted between two stainless steel plates with reinforcment ribs. Whole assembly is bolted to mast beam. Hinge on which board pivots also holds side stays keeping board vertical against side loads and also helps resist bending loads coming from mast.

    Hull shape is conventional with V shaped front section, semicircular middle and aft. Rudders are kick up attached to transom like on most beachcats.

    By 80 and 90 degree angles I meant angle between tacks shown on GPS track basically if you are tacking while sailing upwind good boat should make 90 degree angle when beating upwind. 45 degree on starboard tack and 45 degree on port tack.

    I will try to post some sketch. Design is custom made by me with help from another Latvian multihull builder. Hulls are foam sandwich construction.

    The green cat in another video is my first boat built 11 years ago. Hulls are carved from insulation foam then cowered with fiberglass that's why they are so thick.

    The horizontal rods attached to pipe connecting tillers are extensions to make steering easier when sitting on the side seats.

    The red line is to pull the board down and hold it in position. It is stretchy enough so it usually don't break if the board hits bottom. The white line going aft is for raising the board and also prevents the board from pivoting forward.

    It is good enough for cruising and only easy way how to make board that kicks up on impact. I sail a lot in Estonian islands where water over large areas is only 2 - 4 meters deep with large boulders hiding just below the surface. If you go off the marked channels sooner or later you will hit something. I gladly trade half a knot or so of speed for a board that don't break in half or rupture a hull in serious impact.

    The support structure to hold the board weighs around 8 - 10 kg. I doubt the slots and all the reinforcments to mount daggerboards into hulls would be much lighter.
     
  13. UpOnStands
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    UpOnStands Senior Member

    Very nicely engineered, particularly attaching the side stays to the board pivot pin.
    resolves a lot of the stresses.
    Did you design the rigging arrangement to make the centerboard match the mast?
    Most catamarans have the daggerboards forward of the mast but the key point on your arrangement is the centerboard can mount on and stiffen the mast beam.
     
  14. UpOnStands
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    UpOnStands Senior Member

    For general comment.
    To minimize intrusion of the centerboard into the bridge deck, how negative would it be to trail the board as shown here?
    The board (orange) is in the up position -- no support structure shown.
    Getting a little more interested in the idea -- but.
     

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  15. brian eiland
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    brian eiland Senior Member

    There may be a misunderstand here, and if so excuse me.

    I think you said the 'closing strip' is on the back side of the board,...and I believe this is the side of the board that has to come up fully into the CB trunk/slot. If it is wider than the slot/trunk, then how does it get up there?

    There have been MANY slot closure ideas experimented with in past years. Most were not to successful due to their vulnerability to damage.

    And cleaning the slot/trunk and the CB itself during out of the water maintenance is just another reason I chose to mount my central board(s) in such a manner that they are always retracted from the water doing non-sailing times (thus stay clean, and very productive).

    And the maintenance on the control lines is easily accessible. (unlike hull mounted CB's)

    And they kick-up (automatically if so desired) when striking an object or the bottom, unlike daggers.
     
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