New Idea for dinghys

Discussion in 'Sailboats' started by usa2, Dec 28, 2005.

  1. usa2
    Joined: Jan 2005
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    usa2 Senior Member

    Alright i was thinking about modifying a Vanguard Nomad as some of you may have gathered, and i came up with this proposal:

    Get rid of the daggerboard, and seal the slot for it.
    Then, forward of the mast, cut a hole through the hull. The surrounding area will be reinforced obviously. In this hole a VARA type rudder system will be installed. So it would be like CBTF/TMF on little boats except you dont need the keel which means no lead. You would have control lines running to the helmsman to control this canard. It would retract offwind.
    Has anyone tried this?

    P.S. This idea will not be patented even if it is worth something to someone.
     
  2. Skippy
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    Skippy Senior Member

    I suggested something like this a while back on another thread about a pirogue with spud holes. In fact, I was thinking about it recently. I'm sure other people know about this for sure, but I think you need two controls, one to turn the boat (foils turn in opposite directions) and one to adjust lateral resistance (foils turn the same way). That sounds like an intersting way to adjust or eliminate leeway.

    Other than that, there will be some problems. In addition to the controls being a little complicated, the rudder will have to be bigger to provide more of the lateral resistance. Which will be less efficient, since the rudder doesn't have the hull as an endcap. The main rudder will also be more vulnerable to grounding, and the retractable rudder is another complication.

    But I do like the idea of controlling leeway, and it might tack better. So I like the topic, and who knows, it just might work. :)
     
  3. usa2
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    usa2 Senior Member

    This would be primarily for upwind optimization, as leeway would be virtually zero. Im not sure you would have to make the main rudder bigger, but if you wanted to the canard could be made bigger, and since it is retractable, just pull it up some to achieve the best leeway/wetted surface combination.
    I think the biggest problem would be the control system, as a 17 footer cannot have computers controlling a canard.
     
  4. Doug Lord

    Doug Lord Guest

    Twin foils

    Rob Denney is using a twin foil concept on a new small proa and the idea has a lot of merit.I've been planning to try twin foils on an RC cat to improve manouverability as well as upwind performance. You would more than likely need to make the normal rudder smaller not bigger* and you might consider placing the twin foils in the same place as does CBTF but it's not critical at this size and type boat but it would make the whole system work better.You could more or less easily set up the twin foils to work opposite each other for steering and use a twist grip on the extension tiller to activate collective.
    Are you actually going to do this?
    ------
    *edit: I'm wrong here; the twin foils, if equal in size which is prefered, would be a minimum area of half the original daggerboard area
    Up to half the daggerboard plus rudder area. On this boat I'd go with half the original daggerboard area.
     
  5. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    Bearing in mind that all leeway is is the water hitting the hull at a very few degrees off exactly parallel to the waterline why do you think its an advantage to reduce it? I can't imagine it will make any great difference to drag. After all the boat isn't going to point any higher- that's defined by the relationship between the rig and the foils. Also you have to consider that if you eliminate leeway that means the rudder is going to be running exactly in the turbulence from the centreboard.

    Mind you playing games by steering with both foils either the same way or opposite ways could be great fun - it could certainly be an entertaining beast to drive, it just wouldn't be any faster or point any higher.
     
  6. Doug Lord

    Doug Lord Guest

    Twin foils

    If you place the foils correctly total drag should be reduced on all courses to some extent. Upwind drag should be reduced by correctly using collective. But as Jim says you won't point any higher; you will actualy point lower but if you've set up the system correctly your vmg to windward should be better. Also because of the way the twin foils work when collective is used the downwash of the forward foil is unlikely to interfere with the aft foil-if the foils are designed and placed properly.I'd think shooting for the most span possible and a 6/1--7/1 aspect ratio on the foils would be close. In tactical situations IF you've set up the system to be easy to use you'll be able to move directly sideways for very short periods and your manouverability will be outstanding.
    I think that you face a real challenge to set this up correctly in the first place on a boat of this size especially in setting up and being able to ACCURATELY use the collective.. I apologize to him but I don't remember the designers name(Bob something) but he has posted here before and seems like an open ,friendly guy. If I were you I'd contact him and get his help in setting the angle of incidence values for the collective and his opinion of the whole exercise.
    ------------------
    Edit: The designer is Bob Ames; here is a link to a topic where he posted that includes a link to his comments on the design. I'd contact him if I were you:
    Dinghy Cruiser /Racer Design - Page 3 - Boat Design Forums-SEE POST #37
    Address:http://www.boatdesign.net/forums/showthread.php?t=3491&page=3&highlight=Nomad
     
    Last edited by a moderator: Dec 30, 2005
  7. usa2
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    usa2 Senior Member

    the point of this would be to improve VMG. I dont think the foils need to be in the same place on a CBTF boat because there is no keel or center foil to deal with anymore. Drag may not neccasarily be reduced, but the improved VMG is what matters. I would not be altering the original rudder on the Nomad-thats staying where it was put.
     
  8. Doug Lord

    Doug Lord Guest

    twin foil

    2, the foils on a CBTF boat are where they are because it has been proven that they reduce wavemaking drag when correctly placed.
    Bruce Sutphen of CBTFco helped me on an experimental model where the foils were placed a little further apart than "normal" for the technology but he said because it was a high beam to length model that he didn't expect it would make much difference . The reason for the placement on the test boat was to use a t-foil on a transom hung rudder. Since the Nomad is a planing hull the "normal" CBTF twin foil placement might not be advantageous enough to require moving the aft rudder.In non planing conditions the "normal" placement would probably help a bit. But equal size foils is somewhat important for making the collective work well.
     
  9. usa2
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    usa2 Senior Member

    thats why i was thinking the foil placement didnt matter too much, because the Nomad's wide flat hull. Also, the forward foil will be retracted because the boat will not develop enough power offwind to overcome the drag of it there.
    I agree with you saying the foils need to be equal size, or the lift wont be distributed properly.
     
  10. Doug Lord

    Doug Lord Guest

    downwind

    One of the great benefits of twin foils is downwind handling-it would likely be a mistake to give that up especially in stronger winds...
     
  11. Skippy
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    Skippy Senior Member

    Lorsail: *edit: I'm wrong here;
    OMG! Doug, did someone take over your computer? I'm impressed! :p Thank you for an unexpected breath of fresh air. :)
    As for equal rudder sizes, I've read that large ships sometimes have forward rudders, but they're usually smaller than the the stern rudder. I seem to recall Phil Bolger explaining why that is, but I don't remember his reason. My thought was that you're moving the forward foil farther forward (everybody say that 3 time fast! :)), so if you want to keep the CLR in the same spot with the same pressure on each foil, you need to transfer some area from the forward foil to the after one.

    "if you eliminate leeway that means the rudder is going to be running exactly in the turbulence from the centreboard."
    That's not true. Leeway effectively moves the bow to windward of the boat's path, stern to leeward. Since the backwash from each foil flows to leeward, the aft (and leeward) rudder gets a lot of backwash in the single-rudder configuration. With a forward rudder and less leeway, its backwash is thrown clear of the hull, so the stern rudder gets cleaner water.

    "But as Jim says you won't point any higher; you will actualy point lower but if you've set up the system correctly your vmg to windward should be better."
    I'm not sure how everyone is defining "pointing" here, but I doubt anyone cares much which way the bow points, as long as the true course is higher. Which I think it very well may be, and would be the most likely source of better vmg.
     
  12. Tim B
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    Tim B Senior Member

    I have found (after sailing many dinghy races and full-size races) that the boats that tend to go fast are the ones with the fewest bits of string to fiddle with. There is a lot to be said for progres in the direction of multi-foil yachts, but if it comes with considerable extra complexity it is only lgoing to slow you down.

    I sail a LARK regularly (well, nearly regularly these days) and it seems that the rig setup will give you more of an advatage to windward than any amount of playing with foils will give you.

    Leeway is what actually causes a hull to lift to windward, and is therefore enabling upwind perfomance, the keel and rudder, whilst helping to go upwind are also heeling the boat, so loading them too much will prove inefficient.

    Lead is a term that is often mis-used, or mis-understood. One should consider lead in a similar way to the static-margin on aircraft. That is, start playing with it, and the boat/aircraft won't sail/fly nicely.

    A lot can be done with a simple improvement of the foil shape. The boats with the go-faster stripes usually lose races.

    Tim B.
     
  13. Doug Lord

    Doug Lord Guest

    pointing

    Tom Speer made this pretty clear in one of the best "treatises" I've ever read on the subject. The angle of the hull center line to the true wind is greater with CBTF or something like a gybing board-the boat would be "pointing" 3-5° less but sailing the same angle. But the hull is not making leeway so drag is reduced and since the boat is actually heading lower the sails can be out a touch. This lack of induced drag from the hull and the lower heading of the boat produce greater speed at about the same angle upwind hence greater vmg. CBTF boats, however, can fudge this angle in tactical situations from the extreme of moving sideways a lot to moving sideways a little-whatever it may take in a lee bow situation ,for instance.The downside on a boat this size may be the difficulty of controlling collective accurately enough to not defeat the purpose. But I think it could be done with some sort of stop, ratchet or similar device on an extension tiller twist grip.
    2, it is so simple to run this by Bob Ames-I hope you do it.....
    -----------
    This may help: draw a line(wind) on a piece of paper running up and down the page and draw another line(heading) 45° to the first. On the 45° line draw a "boat"(looking down on it) about an inch long with the center line of the hull at ,say 5° to the line. Then draw another little boat just ahead(!) of the first one with it's centerline ON the 45° line but with a forward foil and aft foil at 5° to the 45° line.Both boats are moving along the 45° line ; one is "pointing" higher; the other is moving faster. Thats the princible...
     
  14. usa2
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    usa2 Senior Member

    The bigger boats may find the canard helps them control themselves downwind, especially with a chunk of lead swung out to windward, but on a dinghy the forward foil will be nothing but extra drag and a hassle. The Nomad can sail with her daggerboard retracted offwind, so obviously she doesnt need a forward foil down.
     

  15. SuperPiper
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    SuperPiper Men With Little Boats . .

    Reducing Leeway

    Holy moly! That makes sense.

    I sail a fat little pocket cruiser that may not have enough keel area. I have toyed with the idea of a t-foil to give it some "bite", especially when heeled. The added wetted surface may easily be traded for reduced hull drag due to reduced leeway.
     
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