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Swing centerboard effectiveness?

Discussion in 'Trailer Sailors' started by Tsam, Sep 6, 2017. Add this thread to a FAQ

  1. Tsam

    Tsam

    Joined Jun 28, 2011
    25 posts, 3 likes
    S2 6.8
    US Long Lake, MN
    Have a hard time determining the effect of the three foot long, 100 lbs. swing centerboard on my S-2 6.8m shoal draft crusing day sailer. The fixed shoal draft keel has 1,000lbs of lead. Overall boat weight 3,000lbs.
    Fixed keel draft is 2ft 4inch. Swing centerboard adds another 2.5 ft of draft.
    Under what conditions should I notice the favorable effects of the swing centerboard?
    Thanks
     


  2. TomY

    TomY Alden Forum Moderator

    Joined Jun 22, 2004
    1,101 posts, 570 likes
    Alden 38' Challenger yawl
    US Rockport Harbor
    You may not notice the effect by how the boat feels. If the centerboard is working - creating lift going to windward - you may detect a change in your boats course over the ground, on a GPS chartplotter or App.
    The boats motion may stay the same(board up vs. board down), but the lift generated by the centerboard, lessens leeway and may show an improved course to windward (I find 5 degrees on the average).
     


  3. Justin_NSA

    Justin_NSA

    Joined Jul 7, 2004
    4,451 posts, 646 likes
    Hunter 30T
    US Cheney, KS
    I agree with Tom. Reduced leeway is the main advantage
     


  4. scoob

    scoob

    Joined Dec 9, 2016
    15 posts, 5 likes
    Sage, Montgomery 17, 15, SageCat and 17
    US Denver
    can also feel the difference in the helm ... depending on the boat more/less weather/lee helm. also the boat's ability to point to weather.
     


    jssailem likes this.
  5. Crazy Dave Condon

    Crazy Dave Condon

    Joined Jun 8, 2004
    6,228 posts, 453 likes
    -na -NA
    US Anywhere USA
    In layman's terms some say it helps the boat from slipping sideways. Use to sail that boat with a friend a few times. Try it with it up and then down and you will see what we are talking about.
     


    jssailem likes this.
  6. SailormanDan

    SailormanDan

    Joined Jan 24, 2009
    404 posts, 76 likes
    1981 Cherubini Hunter 27
    US Belle Haven Marina, VA
    From my C22 days, I would feel it like Dave mentions when the wind blows across the boat. You will also feel it stabilize the rocking after a powerboat blasts by, versus with the board up.
    Conversely, when running down wind, crank the keel up to reduce drag.
     


    Will Gilmore likes this.
  7. Brian S

    Brian S

    Joined Nov 9, 2012
    2,292 posts, 132 likes
    Oday 192
    US Lake Nockamixon
    I have a keel/centerboard combo, and I can tell you that sailing anything closer than a beam reach, the boat goes noticeably faster when I put the board down. All that side slipping gets translated to forward motion. My board is not ballasted, other than weighted to have negative buoyancy. It probably doesn't markedly affect the boat's rolling motion, other than the board would slow down a roll. Honestly, having pressure on the sails probably does more than the drag of the board swinging laterally through the water.
     


  8. Captain Larry-DH

    Captain Larry-DH

    Joined Jun 14, 2010
    309 posts, 109 likes
    Quorning Dragonfly 1200
    US home
    Agree with above posts, but when going downwind (aka "sailing deep") you may find that raising the board allows you to go faster. Dead downwind -- raising it will reduce wetted surface, and you won't benefit from lift when it's down. Deep reach - you would lose the lift but the extra leeway (side slip) will allow you to point the boat so that the jib/genoa has more exposure to the wind (with less of it shielded behind the mainsail).
     


  9. DockH

    DockH

    Joined May 14, 2011
    26 posts, 0 likes
    Abbott 22
    US Lorain, Ohio
    Does anyone know of a listing of vessels by displacement, keel type and draft dimensions? Shoal, fixed, swing, centerboard.
     


  10. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    2,147 posts, 841 likes
    O'Day 19
    US Littleton, NH
    You can also experiment with the swing keel all the way down or part way down. If there is a point of sail where she develops a lot of weather helm, you should try partially lifting the CB. This moves the CLR significantly aft and could help to balance the helm better.

    For a 6.8m boat, 100 lbs of keel weight isn't much, but it is something more than lifting that same 100 lbs 3' higher. The 100 lbs helps with the righting moment and the profile in the water stabilizes the rolling moment.

    You didn't say what the CB model weighs. My Mariner CB model is the same weight as the fixed keel model (1430 lbs). The CB has two hundred pounds of lead glassed into the hull on either side of the trunk as well as a 130 lb CB. The CB has more draft than the FK version. I'd guess they have about the same righting moment. Maybe the keeled version is a little stiffer, but I think the deeper CB offsets that a bit. In general, lighter is faster, but stiffer is also faster and points better.

    -Will (Dragonfly)
     


  11. jssailem

    jssailem

    Joined Oct 22, 2014
    4,824 posts, 1,469 likes
    CAL 35 Cruiser
    US Salem, Moored Port Everett WA



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