Tips on Dagger Board Trunk Construction?

Discussion in 'Boatbuilding' started by CatBuilder, Dec 21, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    That is one way to do it.

    However, if you want to keep on sailing, rather than repair your foils, there are more sophisticated ways to avoid collision damage to your rudder (and dagger board).

    A better rudder system does not break away, but kicks up when it hits something. It is on a pivot and pops up, rotating around the pivot.

    Notice the dark blue rudders at the stern of this catamaran picture. They are kicked up, rotated, rudder bearings and all, about a pin that allows them to come free of the water when they hit something. Much better than a failed rudder blade to rebuild.

    If you hit something, simply push them back down into position and lock into place.

    [​IMG]

    The dagger board crash box works on a similar principle. Have you ever seen those large barrels of sand at the exit of a highway (or road)? Have you ever seen the very large, sand filled bumpers ahead of a construction crew on the highway? Are you familiar with modern automobile design, where the car is now equipped with "crumple zones" which absorb the impact of an accident?

    The crash box does exactly this. It absorbs the energy of the impact so your board and your trunk don't have to. Instead of stopping to fix your destroyed dagger board (no small feat - trust me, I just built two of them), you simply slide your crumpled foam crash box out of the dagger board trunk and slide the spare in. This takes 10 minutes.

    Making a dagger board takes weeks (and costs well over $1000).
     
  2. michael pierzga
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    michael pierzga Senior Member

    Sure..sounds logical and its been used on hundreds of boats before. Its a shame that its not supplied to you the builder already engineered. Nothing worse than re engineering the wheel.

    Is it possible for you to cruise down to a local shipyard and have a look at a successfully engineered dagger board trunk ? Perhaps a lift keel monohull sportboat.

    A 40 ft dagger board tri was just hauled at my local shipyard. looks well built. If someone is around to let me in Ill take a few pictures.
     
  3. Yobarnacle
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    Yobarnacle Senior Member holding true course

    You're not designing, so this is only for thinking.
     

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  4. CatBuilder

    CatBuilder Previous Member

    I have no idea what the miscommunication is. Sorry.

    I have plans for the trunk, I shared them in this thread. I just don't know how to *build* it. Please see my questions:

    http://www.boatdesign.net/forums/bo...rd-trunk-construction-41023-4.html#post511671

    The rudders, for example, are shown with the kick up pin, but the hard part (knowing how to connect steering so you can kick up and not break it) is not shown.

    Same with the dagger boards. The plans say how the cored panels are to be made, then they say, "taper and thicken glass" and "rounded ends to be biaxial to same thickness as cored panel area." There are arrows pointing from those comments to the diagram of the trunk. This is all find and well, but it doesn't show me *how* to build the trunk. Ie: Doesn't show how to do the tapers and things I asked questions about in the above link.

    Thanks for the offer to look at the tri, but it wouldn't show me how to build it either. It would just show me what it looks like. It's the fiberglassing and setting up of cores I asked about, not how to design the thing.

    Hope that makes sense.

     
  5. CatBuilder

    CatBuilder Previous Member

    Neat idea. Board are already built though, so I'm not changing the plans.



    [​IMG]
     

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  6. rberrey
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    rberrey Senior Member

    If I remember building the bottem of the case out to within 1/8" of the board was for better performance when raceing. Ed,s says in his book to " Trim dager board case to correct length and file in wear shoe slope 5 to 1 minimum so case may be FG or epoxyed in place and sides are parallel. The wear shoe by looking at the picture seems to be an angle cut on one side of the bottem of the case that allows for bend in the board without eatting into the structure of the case. I cant tell much more about it without looking at my plans. The crash block will be an easy add to my case, my cases will be renicell 240E so some of the H80 will work for the cussion. Rick
     
  7. rberrey
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    rberrey Senior Member

    If your going to infuse the best way would be to build a dagger board male form that gives you the desired space you need between the boards and case. I know it will be more than the 1/8" faired into the bottem of my cases. Rick
     
  8. CatBuilder

    CatBuilder Previous Member

    Agreed, Rick. Thanks. I am definitely using the dagger board as a male form. Richard Woods mentioned putting a rope around the board many times to help make a spacer.

    I thought that was a brilliant idea. I will probably be doing that.

    I am shooting for about 1/2" of play inside the trunk, to be cleaned up by a top plate and (from your post) a faired in bottom made from bog (and the crash block in the back). That seems to be the best combination overall.

    Thanks for the posts.
     
  9. waikikin
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    waikikin Senior Member

    You definatley need to taper the core- 2:1 is the minimum, 3:1 is good. For the external tabbing to hulls outer skin, a rebate molded into the dagger cases lower end will assist with fairing in. The crash blocks would be good as a glue in later.
     
  10. CatBuilder

    CatBuilder Previous Member

    Thanks for the input. I just did that stuff today. I tapered the core at 12:1 both inside and out. Old plywood habits die hard! :)

    I also put a taper style rebate at the lower end of the case on the inside, so the tabbing has a place to stagger into.

    Thanks for confirming this. Much appreciated. It's good to know this was the right way to do it.
     
  11. Yobarnacle
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    Yobarnacle Senior Member holding true course

    You were able to do all that after taking on a cargo of Christmass dinner?
    Hats off, gentlemen.
     
  12. CatBuilder

    CatBuilder Previous Member


    Na, I'm living a hellish life right now (explains my b*tchy posts - ha ha ha).

    I'm 1000 miles away from friends and family building this boat because we could afford this build location. Yes, it was a LOT cheaper than building where friends and family live.

    So, I worked all day today, like I do every day, with the hopes of getting this thing done sometime soon and reuniting with my wife, who I miss terribly while building this boat. (she has to work while I build for us to afford this)

    The way I see it, every day I take off is just another day I have to wait to bring the boat home, so I try to work as much as possible.

    No Christmas for me this year and none last year.
     
  13. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    dedication and perserverance pays. Merry Christmas anyway
     
  14. rberrey
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    rberrey Senior Member

    Merry Christmas Cat. Rick
     

  15. CatBuilder

    CatBuilder Previous Member

    My board trunks are really giving me a hard time. I can't figure them out.

    The problem I'm having is I can't figure out how to build them.

    I can't figure out the steps involved. I started setting up to infuse them in one shot, using the dagger board as a male mold, then realized, part way through, that I will never be able to remove the peel ply and flow media from inside the trunk after I am done infusing.

    This caused me to stop and try to figure it out again.

    I have many hours into it, staring at the plans and not understanding how to go about making these trunks.

    Does anyone have general ideas about the steps involved in doing this lamination, either by infusion or hand lamination without vacuum bagging? I'm so very lost...

    Please see this link for the pictures again:

    http://www.boatdesign.net/forums/bo...rd-trunk-construction-41023-4.html#post511671

    I understand that there are cores and tapers and even how to taper the glass. What I still can't figure out is how to do the actual lamination, with epoxy and coming out the other side with a good dagger board trunk.

    Infusion doesn't seem to work since I can't get the peel ply and stuff out of the trunk later. I've already wasted infusion supplies (put inner bag on the dagger board).

    Any ideas?

    How did you build your trunk?
     
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