Tips on Dagger Board Trunk Construction?

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

  1. CatBuilder

    CatBuilder Previous Member

    Still Can't Figure It Out

    Here is a diagram of my trunk wrapped around my board, as seen looking up into the trunk from below the hull:

    [​IMG]

    Questions I still can't figure out are:

    1) How much gap do I need between the board and trunk sides?

    2) How do I make the transition from core to solid glass for the forward rounded end and the aft rounded end?

    3) How do I know how much glass to use in order to get the same thickness? The thickness of the cored flat side walls is 1/2" plus 34oz on each side of the core, plus some extra 6oz cloth to make things smooth and water tight.

    The next picture is from the side... looking at the side of the trunk. The bow would be to the left in this picture, facing the same way as the first picture.

    [​IMG]

    1) How can I do the tapers both from the blue cored panel area to the green solid glass curves around the nose and tail of the board AND for the orange/yellow taper to full glass where the trunk meets the hull and deck? Do I even need to do a taper at the blue/green boundary to go from cored panel to solid glass, or is there a better way of doing it?

    2) There is a tremendous amount of glass carried from the inside of the trunk, out and over the outside of the hull and deck. How do I make this fair?!? I already have a hull and I'm cutting a hole in the bottom of it to put the trunk in. The glass layers required outside the hull around the trunk are: 2 layers of biax all around and 10 layers of 6oz cloth. That's a lot of glass. It'll surely make a huge hump. What do I do with that? How do people usually make these flush?

    3) I am infusing this whole thing in one shot. Any tips on how to get all of this glass (plus several other layers not even mentioned here that are reinforcement) in place, dry around the dagger board without them falling all over the place? Dagger board is currently laid flat on its side with a 4" PVC pipe in place aft of the trailing edge to make that area for the foam crash block and some bubble wrap around it to provide some spacing. Need to secure all of this glass (including those solid glass rounded ends) and get them all into a bag with core and infuse. Thoughts?
     

    Attached Files:

  2. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    Have you considered solid glass thru and thru? Stronger. And eliminates transition problems from foam cored to pure glass.
     
  3. CatBuilder

    CatBuilder Previous Member

    It sure would weigh a lot, so, no, I hadn't. Has any catamaran builder here built them solid?
     
  4. rberrey
    Joined: Oct 2010
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    rberrey Senior Member

    I cant see where a foam crash block will do any good. If the sharp edge of the profile is in the box at time of impact it will act like a wedge and foam will do little good. I dont think you need sloid glass for the sides. With an impact the box willbreak at the weakest point. Stand up a 4x8 sheet of ply and put a 45 degree kicker on it , do the same with a piece of 4x8 steel plate. The two will take about the same force to cause them to fall. Your piviot point of the board on impact will be at the joint of the case and hull. Reguardless of what damage is done to the other areas of the case the only area to concern yourself with is where the water will be comming in at. To keep a case from failing the case must be stronger than the dagger board and the dagger board must fail first. This is no differant than rigging on a crane, or wiring your house so the breaker kick off before the wire burns. Rick
     
  5. CatBuilder

    CatBuilder Previous Member

    Hey Rick, hope you are feeling better. Saw that post a while back.

    I hate to b*tch slap the thread, but I need to. This thread is in the "boat building" part of the forum, not the "design" part of the forum. The boat has already been designed.

    I asked very specific questions about how to build this and am looking for very specific answers, please.

    I am not designing a boat. I'm building one.

    Rick, the crash blocks work amazingly well. What I didn't draw (in the interest of time) was the hard plate on the front of them that goes across the whole trunk. The crash blocks work because they allow your dagger board to take a tremendous impact, not break... and at the same time not break your trunk. The energy of the impact goes from the trailing edge of the board to a flat face on the front of the foam crash block and compresses it toward the back of the trunk. It absorbs all the impact, instead of your board or trunk breaking. The trailing edge doesn't bind in the foam because of the flat panel between them.

    Best overall solution. Neither the board nor the trunk breaks on an impact. The foam does.

    You pull the squished foam out (without hauling out) and stick one of your spares in. Back in business in 10 minutes.
     
  6. rberrey
    Joined: Oct 2010
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    rberrey Senior Member

    The hard plate would make sence, I can see that working. I feel better just a little discomfort. Thanks . Rick
     
  7. Charly
    Joined: Dec 2009
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    Charly Senior Member

    I don't have my plans in front of me, but I believe that there is a good bit of clearance between the trunk and the side of the board. If you are laying up multiple layers at the openings and staggering the biax pieces then it will be narrower at the openings and more open on the middle of the trunk. Then if you put a plate or something or just bog to within 1/8 of the board at the bottom opening (like Rick said) the inside of the board trunk will have a gradual constriction down to the opening, which is what you want (?) You wouldn't want the board tip hanging up on a lip there as it tries to go out.

    On the outside of the hull I had no problem fairing the glass into the hull bottom.
     
  8. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Its interesting that the trunk constuction must be questioned ?

    Most yacht designs Ive dealt with have very detailed drawings of technical constructions.

    I'm surprised your designer didn't engineer this for you ?
     
  9. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    Use to have a toyota compact car. Only been in two accidents in 49 years of driving. I'm 63 and got a daylight only license at age 14.
    Both accidents I was hit from the rear. The Toyota was rear ended on the expressway. I was driving 70 mph. When I was hit, I found myself off the road doing 95 mph slaloming around bushes and trees. I estimate the car that hit me was doing well over a hundred, to add so much speed to me.
    Whats that have to do with your catamaran?
    Once I was stopped back up on the highway shoulder, I checked for damage.
    Only damage was rear bumper was moved 3 inches closer to body. The bumper had steel wedges that fit into square tubes on car frame. The wedges had driven in to and flared/spread the square tubes. That absorbed the impact energy. Don't think you need steel tubes and wedges on dagger board. Hopefully you wont experience any 100+ mph collisions.
    Matbe the wedge of the board edge and the foam will work similarly. Merry Christmas
     
  10. CatBuilder

    CatBuilder Previous Member

    My designer leaves a lot up to the imagination. :D:p

    His designs are great, where it counts, but I think he expects you to know a little bit more than I do about actual construction techniques.

    His detailed drawing show just what I've shown on this thread. Not much else. It is kind of up to me to figure out how to do the various tapers and various little bits to make it right. Being that I'm an "on the water" professional and not a builder, I have lots and lots of questions to fill in the details where many pros would already know the answer.
     
  11. CatBuilder

    CatBuilder Previous Member

    I think you're right, Charly.

    I should probably make 1/2" clearance from the board inside the box the more I keep going over this stuff and taking all the advice into account. That leaves some room for the extra laminations to attach it to the hull on the inside as well.

    I did find that the laminations carried onto the hull that I was worried about being hard to fair in are only 4mm in thickness. They are also staggered (tapered, like stairs), so I guess this won't be too out of fair. I am probably over thinking.

    I do like Rick's idea for bogging in the lip as a sacrificial surface. It seems like the way to go after you get everything else in place. Nice and soft, so that wears off instead of the board.

    Thanks. I'm nearly understanding this thing 100% here. I think I'm at about 75%, since those complicated tapers on the board itself seem tough.

    Did you say you *HAD* no trouble fairing your trunks in?!?!?

    You're already done?!?! :eek:

     
  12. Charly
    Joined: Dec 2009
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    Charly Senior Member

    The trunks are roughed in, inside the hull. I still have to do the deck opening, and figure out what, if anything I will do at the bottom outside. I guess I will be laying the hulls back down on their sides at some point, and that is the only way I will be able to test the boards fit. I haven't started the boards yet.
     
  13. CatBuilder

    CatBuilder Previous Member

    That's still a big (huge) amount of progress. Congrats!
     
  14. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Since a Daggerboad has nothing to do with the seaworthiness of the boat, you would think that the best protection would be a dagger board that simply broke away before it damaged the hull, trunk. This is how a rudder is engineered. The rudder blade fails before the rudder stock , rudder bearing , watertight integrity of the hull is breached.
     

  15. tunnels

    tunnels Previous Member

    I asked this very same question a while back and am still surprised he even had to ask or post the question asking for advise .
    Got to have clearance with anykind of board they always get crap and growth in qute a short time !, Had swing keel once and was forever having to Drop it to clean the wearing faces for rubbish .
    Plastic bags can be a nightmare if they happen to get stuck and dragged up inside . :D:p:p
    .
     
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