venture 21 daggerboard question

Discussion in 'Boat Design' started by j.bonner, Dec 11, 2014.

  1. j.bonner
    Joined: Dec 2014
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    j.bonner Junior Member

    I'm new to the site but I have found much useable info on here for my projects. So thanks in advance for the feedback.

    I have an old venture 21 with a swing centerboard, the board measures 18" × 4'. I wanna rip er out and install a daggerboard trunk.

    Problem is...the daggerboard would have to be shorter because of the headroom in the cabin. It would be 3' long, with 8" left in the trunk.

    How much width should I add to the daggerboard? Should I just make it the same area as the old swing keel?

    I thought I would pour a lead bulb at the end of the steel daggerboard Im thinking of building.

    Any thoughts on my plan? I want my boat to load on a short trailer, and be able to beach it. We just camp cruise around the outer banks. Performance as far as racing is not whats on my mind, and I dont mind using the outboard.
     
  2. tdem
    Joined: Oct 2013
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    tdem Senior Member

    You can continue the daggerboard case all the way up through the roof of the cabin. This way you are able to raise it even higher than the cabin if you recess the pulley system for raising it into the board a bit. (Cut a channel into the board, so it is shaped a bit like a U, and attach your pulley system to the bottom of the channel so it sits "inside" the board when fully raised.)
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Daggerboards are used in small craft, because their footprint in the boat, makes less of an impact, which is important in a small boat. High performance boats also employ daggerboards, for slightly better performance.

    A centerboard is the logical choice on your boat, as the momentum in a bottom strike on your boat, will easily snap off an appropriately sized daggerboard. A loaded Venture 21 will displace the better part of a ton easily, so some simple cantilever math, will show you how much force will be applied against the end of a daggerboard, in a bottom strike (read tons).

    What is the logic behind this conversion?
     
  4. tom28571
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    tom28571 Senior Member

    I agree with PAR. A Venture 21 is has limited righting moment and is not immune to capsize as many have done so. Even with a stock centerboard, it should always be locked down in use.

    If your idea to change to a DB is to make beaching easier, it would be more prudent to wade the extra inches to shore. Only by extending the DB trunk to the cabintop could it be made strong enough and the issue of damage due to grounding or hitting stuff would still remain. A bulb at the bottom would also have some limit to beaching.

    Fully raising a ballasted DB on a Venture 21 would decrease righting moment to a serious safety issue in my opinion.
     
  5. j.bonner
    Joined: Dec 2014
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    j.bonner Junior Member

    Well, the reason behind my potential modifications would be for beaching, and so I wouldnt have to put my brand new GMC off in the salt water every time we launch. I have already worked the trailer over (tongue extention, lowered bunks...ect)

    If the db trunk is connected to the cabin roof, and incorporated into a bulkhead it would be strong. Could the lead bulb not be incorporated into the trunk as well by shapeing the trunk to accommodate it? I know the hull might need reinforced around the base of the trunk.

    The idea Tdem had about extending the db on out the roof would work but the cb is right under the mast step. It would have to be moved aft.

    Tom and Par also have a point about the safety issue, that should most certainly be considered.
    My mind is not made up to go through with this yet, weighing the pros and cons is why I started this thread.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    My understanding of these puppies is, this is the predecessor to the MacGreggor 21 (1979), which was very similar, with some updates (new liner and slightly changed deckcap). The centerboard up draft is 12" or there about, so calf deep water when aground. These where never spectacular boats to begin with and had a bout a 20% ballast ratio on a moderately narrow hull form, so as Tom mentions, they tend to capsize if you get ballsie with one.

    A trailer tongue extension is a good idea, but hoisting the board up further then it's current CG is located will present some issues, though it will reduce draft. If you want to beach this old gal, you might consider a stub keel around the existing centerboard, where it protrudes from the hull. This keeps all the moments and centers where they need to be and would be a whole lot easier thing to do. Some foam, a bit of laminate and paint. Many designs employ this trick to lower the centerboard case's impact (foot print) inside the cabin. You can also add some ballast to the bottom of this new stub keel, which the boat will thank you for, when a breeze pipes up.

    Additional thoughts to beaching would be some props when you run her aground, to keep her from flopping over or possible a couple of short bilge keels, so she can flop over on these. All of these are easier to do than make a whole new case, further aft and a new 400 pound appendage to fit inside it, not to mention hoisting gear.
     

  7. j.bonner
    Joined: Dec 2014
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    Location: north carolina

    j.bonner Junior Member

    Didn't think of the stub keel, thanks Par.
     
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