Building+Designing a (carbon)Dagger Board and Rudder for my El Toro

Discussion in 'Boat Design' started by dylantorquerol, Jan 26, 2011.

  1. dylantorquerol
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    dylantorquerol Junior Member

    I just got an 8' el toro dinghy for racing. The blades that come with it are wood, heavy, and don't have a good "airflow" shape underwater. I want to build a new daggerboard and maybe a new rudder. They will be the same size (height and length and width) but i want a different airfoil shape.

    The other carbon ones I have seen have a much thinner profile and cleaner shape. Is this a bad thing for pointing or anything? Also, what should I use for the core of the blades? Wood, foam(what kind?)or something else?? And should i use more than one layer of carbon at 45 degree angles? Thanks,
    Dylan
     
  2. dylantorquerol
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    dylantorquerol Junior Member

    Also what cloth should I use? 5.5 oz, 8.3, 10.1 ect.
     
  3. tom28571
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    tom28571 Senior Member

    The dynamic loads placed on a DB of an El Toro are about as small as it gets in sailboats. Find out what others are using that does not break and use that. The greatest load normally faced on any DB is by the crew after a capsize so making a test of that in the shop is relatively simple. As to the thickness of the blade, the trunk is too narrow to handle the best shape so just give it no more than 1/16" clearance on each side.

    You know you are really over doing the El Toro with technology with a carbon DB, don't you. I am surprised class rules allow carbon on the boat since it is expensive and offers no advantage here that I am aware of. Light weight in the DB can be as much hindrance as help since it makes the DB want to float up.
     
  4. dylantorquerol
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    dylantorquerol Junior Member

    Yah, the rules don't have anything to do with materials. I have a fiberglass boat, but everything else is carbon. I just really want to get a better shape on the wetted foil area. How much would the DB want to float up?
     
  5. tom28571
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    tom28571 Senior Member

    Can't say as it depends on the friction between trunk and DB,
     
  6. JRD
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    JRD Senior Member

    Dylan,
    Look up the NACA0010 offsets for the cross section, there are lots of references to them on the net. Make up a half template and compare it to your existing foils. If your existing foils are wood you will be able to attack them with a router or wood plane then longboard to get the cross section as close as you can to a decent shape. Once it is perfectly fair and slightly undersize for the case, epoxy a layer of 100gsm E-glass cloth, this will give you a good base for paint finish, then paint and polish it smooth. You could get most of this done with a couple of days work plus curing time.

    Tom is right, ultra light foils on your El Toro won't improve your speed. Just get the shape as good as you can, keep them smooth and free of damage. Making or buying expensive carbon foils won't make as much differerence as sailing it well, and probably won't make much difference to the resale value unless they are proffesionally built. Save your money for your next boat, which will presumably be bigger and faster.

    Good luck, Jeff
     
  7. dylantorquerol
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    dylantorquerol Junior Member

    Thanks. I just wanted some new ones because the old ones are probably 5-10 lbs each. Could I just make new foils of foam and fiberglass instead of carbon? And isn't carbon only $20-$30 per sq. yard?
     
  8. dylantorquerol
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    dylantorquerol Junior Member

    (and plus i think making some new ones and playing with carbon would be fun!)
     
  9. rwatson
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    rwatson Senior Member

    Interesting project - if you could save 2-3 kilos of weight in your Centreboard it might help a little, but maybe a light weight CB would not be advantageous in windy weather.

    I have owned a yacht with a hollow CB, which fills with water when immersed. This provides some ballast. For very light wind days, you could put a plug in the board, and keep it empty and lighter.

    Keeping the CB immersed is a problem for even plywood ones, as you need shock cord to hold the board down on many dinghys.
     
  10. JRD
    Joined: May 2010
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    JRD Senior Member

    Dylan,

    If you really must build one out of carbon fibre, have a look for some how to guides on the net. It will be easier than a long winded description here. There are lots of sailors building their own gear and quite a few have put their ideas on blogs.

    http://adamscherubhull.blogspot.com/2010_04_01_archive.html

    The lightest boards are built using a female mold, one for each side. The laminates are layed into the mold halves and vacuum bagged in place, then joined together. The mold has to be perfect if you want a good result, therefore is expensive as they are ussually 3D CNC cut.

    For a home build you would most likely use a foam core with carbon skin. This would typically consist of carbon unidirectionals and an outer skin of carbon cloth. Make sure there is a shear web joining the two surfaces at the thickest part, otherwise they can split at the trailing edge if you put a lot of load on the tip due to the two halves wanting to travel in oposite directions (shear stress).

    Have a look at development class websites, some have good technical articles. UK Cherub site has lots of useful building ideas.
    http://www.uk-cherub.org/doku.php/tech/foils

    Youtube video of making a foam / carbon centreboard
    http://www.youtube.com/watch?v=9KK-3kfX7x8&feature=related

    FWIW I still think its a waste of money when you can probably improve what you already have for next to nothing, save your money for a new sail or whatever, it will make a much bigger improvement to your performance. That said, carbon fibre is a cool material and there is only one way to learn about building stuff and thats getting on and doing it.

    Jeff
     

  11. dylantorquerol
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    dylantorquerol Junior Member

    Wow you guys all this info should help out a lot. I know I have to put some bungee around the CB, which I have on already. All of this helps so much! (My dad also knows a guy that works with building kevlar kayaks so that should help)
     
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