Cox's Bay Skimmer

Discussion in 'Sailboats' started by Doug Lord, Jan 11, 2014.

  1. Baltic Bandit

    Baltic Bandit Previous Member

    you are tacking. there is the main sheet, the jib sheets and the rudder to handle as well as the mast rotation. Really there is no additional hassle on the DSS? small boats like yours can tack in 3-5 seconds. Add DSS and that's going to double
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Skimmer

    Gary, when I designed the DSS system for the Crossbow fl, I had help from Hugh Welbourn in helping to place the foil(s) and he donated a DSS section shape that he had designed. I had both foils made from wood and carbon. I determined the foil area and the exact foil location. The most important thing was assuring that the foil would be one chord(minimum) below the surface and that works out to an angle of heel of about 10 degrees(foil is then level-draft of hull at this angle is 7"-daggerboard draws 2'). I'm certain that he would work with you if you wanted him to.
    On the Crossbow fl, the DSS foils don't slide in a trunk-they are inserted in individual trunks and require no adjustment at all while sailing. This was done for simplicity of construction and use though there is room in the cockpit to have included a sliding foil trunk. A sliding foil (or pivoting foils as in the Quant 30) have the advantage of being able to retract but I decided that since the foils on the Crossbow simply plug in, it would be easy to remove them(or not install them) depending on conditions and for trailering. When the boat is heeled 10 degrees the windward foil is clear of the water. So far as I know this is the only DSS boat designed with "plug-in" foils.
    Gary, your boat might be too big for plug-in foils ,but maybe not?

    PS- one of the advantages of the pivoting foils on the Quant 30 that is touted by them is the ability to leave both foils out in their extended position. The "plug-in" system is the only other DSS system capable of that.

    Crossbow fl foils using Welbourn section, carbonated. Built by Rick Loheed, planform/aspect ratio and area my design:
    click-
     

    Attached Files:

  3. Baltic Bandit

    Baltic Bandit Previous Member

    Doug please stop using the idiotic term "carbonated' it means infused with CO2 gas.

    So Doug, how far along is the Crossbow build? Did Hugh help or did he do most of the work?

    Im curious about the 10 degrees of heel, because I know of no dinghy that is fast at that angle of heel. 5 degrees yes, but not 10. And given that in some places the EC challenge is sailing in 3' of water, I suspect that those foils would have some problems
     
  4. Skyak
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    Skyak Senior Member


    I have been wondering something about DSS that I think might help Gary. Why not just put a surface piercing foil at an angle far to leeward? That way he (or anyone else) doesn't have to chop up his fine boat and the result is faster, more powerful, and easier to sail. It has natural heel control. In light wind it comes out of the water altogether and adds no drag -all untended.

    DSS just doesn't fit well on shallow draft hulls like his and most un-ballasted boats. To get the foil deep enough in the water the boat has to heel too much and the DSS foil lift angle has a significant component pulling the boat to leeward. DSS from the hull declines in righting and adds to leeway as heel increases. When the boat is not heeling the DSS foil is too close to the surface and begins to generate wave drag. My proposal would do the opposite, adding more righting and leeway resistance in gusts, cut drag in lulls. In real conditions this gust response is very valuable.

    I think it is clear my proposal is lower cost for more performance. The downside must be perception or rating. DSS LOOKS like a monohull going fast, mine looks like a multihull or foiler going faster.
     
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  5. Doug Lord
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    Doug Lord Flight Ready

    ======
    1) Probably not true. On the Crossbowfl(my 14' DSS equipped design) it appears that it would work well-I have carefully researched the effect of heel on the Crossbow fl and it's relationship to DSS given the extensive study I have done on DSS. I have discussed this design concept with Hugh Welbourn(inventor of DSS) and made the adjustments to the hull shape to allow the hull to work well with DSS. There are many high performance boats designed to sail at an even greater angle of heel than 10 degrees-scows, Open 60's and more. And while 10 degrees angle of heel is ideal for a fully submerged foil the foil will work at a lower angle(see 3 &4 below). Crossbow fl is a ballasted singlehander ,and though it is not a keelboat it uses a unique movable ballast system to dramatically increase RM and provide the capability of righting from a knockdown. The Trapwing Movable Ballast System enhances the effectiveness of DSS is this type of small boat.

    2) Definitely not true-DSS installations are not experimental and have a proven track record of performance. Quant 28 thread.
    3&4) DSS boats are sailed with an angle of heel of not more that 10 degrees usually. In real life the foil has proven to work at less than one chord below the surface-in fact it works well as a planing board. One chord is ideal, but it has a range of less than that or more than that where it is still very effective, particularly off the wind. Off the wind, an angle of heel that causes the DSS foil to have a component of leeway is not a negative and has proven to be fast.
    http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html
    ====
    A surface piercing foil at what angle? Why don't you draw a sketch so we can get a better grasp of your idea?
     
    Last edited: Feb 1, 2014
  6. Baltic Bandit

    Baltic Bandit Previous Member

    "probably no true" - please. Skyack's point is absolutely spot un.

    I'm curious as to what sort of immersed waterline simulations do you have on Crossbow to make the assertion that "it would work well". can you share those images with us please? or perhaps this is just a sketch on paper, in which case I'm curious as to what you base your strong assertion on

    #2 - the Quant 28 is a keelboat, not a dnghy - which support's skyaks point

    #3&4 - dinghies are usually sailed with far less than 10 degrees of heel. I have yet to see a dinghy documented as benefitting from the DSS.

    Its one thing to be a fan of DSS

    its totally another to make statements about DSS that are not accurate
     
  7. Skyak
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    Skyak Senior Member

    Doug, the way you parse my assertions and facts out is to argue against them without logical merit. 1 is the assertion I am making. To just say it is wrong is fallacy known as begging the question. The Quant boats are designed from the start for DSS. The hull is optimized for DSS, is not as shallow draft as Gary's, and thus it doesn't offer anything against my premis. Your 2 again refers to Q28, not Gary's boat. Two three and four should be considered together, on Gary's boat. Lets start with a real section of his boat with it's actual waterline. Foil case at least two hull thicknesses above the edge it exits. Then let's chart the DSS forces vertical and to leeward (as well as drag) at various angles of heel and consider their contributions to performance.

    I was under the impression that a foil needed to be at least a cord or two below the surface to not produce significant wave drag and that is just a rule of thumb based on skinny high aspect foils. I likely got the info from you Doug. If you have good data to the contrary it would be valuable to the thread. From pictures of DSS in action near the surface I see a wave forming.

    The central point I made that didn't make your list is that DSS has poor gust response and off angle performance charicteristics. My suggested concept reverses this negative. You CAN sail at an exact heel but it takes work and sacrifices performance -Gary has his hands full already. The graph I describe is worthwhile if not key for the consideration of DSS.

    About my design proposal -a sketch. For now lets just think about that Moth with foils on the forward outer edge of each wing, but instead of big foils extending well below the waterline lets put smaller ones extending down at 45 deg to vertical just to the waterline. We will need to optimize angle, aspect, profile... but this is a fair start. It's a Bruce foil without the float.

    The last thing I have to say is that I have no interest in arguing with a zealot. I win nothing for correcting/countering you or anyone else. I value your bringing data and news. I see that we are competing to offer solutions to builders (to build vicariously and get better data) but I don't seek to give or get respect. I generally present very straight forward logic and I have nothing but force of reason. I would be happiest to give up this essay format and just trade straight logical arguments. If you have any pertinent data or can quantify any qualitative assertions -great! If you want me to make the logic straight and concise, ASK. Don't rearrange my words into something you can refute. You will get nothing but contempt from me. There is far more value in producing the graph I suggest above to help characterize DSS and my concept of foil assisted stability and we will all have better performance models.
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    Thanks for the suggestions Skyak, if I'm reading you correctly, you're talking about a foil stabized monohull cum multihull - and yes, that is THE way to go.
    But keeping to the subject of a DSS non ballasted dinghy, am wondering whether say, 10 degrees of hull heel with a shallow curved to near horizontal DSS foil, just how much to leeward forces are enacted; my guess is not much and not worth being concerned about because the near vertical lifting moment is large. Also you have a conventional dagger too keeping everything honest.
    On the black Skimmer (unless it is in light airs) the boat is usually powered up and the boat heels; we have to stack hard; maybe the simplest solution is trapeze.
    But the boat was not designed to be a full on race boat, really just an okay performance, simple to sail craft. The fact that it really can perform introduces some "unwanted" more extreme thought.
    But I like the free or almost free righting power and stability of DSS, worth pursuing the extra complications of constructing the system.
    But I have three boats to look after at ther moment ... and I've been fooling around with 10m cruising trimaran foiler sketches too, craziness.

    ps: one point BBandit, the wing masts rotate automatically from tack to tack, gybe also, the only adjustment is to ease the spanners further, then cleat off, when changing from upwind to downwind course - and the other minor point, Skimmer has no headsails - but probably a reacher later.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    ===========
    Skyak, I was trying to help you not annoy you. I've had years of interaction with Hugh Welbourn and learned a lot from him on line and in person. He helped me understand the requirements to make DSS work on such a small boat and I thought that experience was relevant. So far as I know, the Crossbow fl is the smallest boat ever designed for DSS from scratch with input from the best in the business.
    I apologize for annoying you.
     
  10. Skyak
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    Skyak Senior Member

    BB,
    there is a common problem around here. People tend to draw fast powerful sailboats neglecting how hard it is to sail them. From keel boats, to catamarans, to wing dingys, now to foiling and wing sails ...control is getting to be the limiting factor on racers to say nothing about pleasure operating. I am struggling to characterize or even communicate the challenge. I think we need a thread just about quantifying control. I am good for nothing but logic, engineering theory and a little math. I could try to ask the question but do you think there is someone better for the task?
     
  11. Skyak
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    Skyak Senior Member

    Gary,
    I am glad you like both these ideas. I think there is value in quantifying the performance characteristics to more fully understand how to apply these appendages (do we all agree on this?) and the graph I mentioned is the first milestone. What we need from you Gary is the hull section from the point where you would mount the DSS foil. I don't doubt that you can draw a curved foil that makes an impressive free body diagram for one heel angle. What I feel the need to point out is that benefit falls off at other heel angles and a superior solution gains from gusts as opposed to needing the crew to adjust constantly to keep the boat at the best angle.

    Your skimmer is not optimal for my version of dynamic stabilization either, but it is an easy add and it extends the 'easy performance' you have already taken to a high level.
     
  12. Skyak
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    Skyak Senior Member

    Doug, you did annoy me but that is as much about my peculiarities as your actions. Your behavior is common practice on threads, in politics, and life in general. Logic has taken a back seat to argument. Unfortunately for me I cling to logic. From that perspective I see you (on this site) as mired in arguments loaded with fallacy (by and against you) among the tidbits of logic and valuable data. These fallacies were identified and documented thousands of years ago (their names were translated from Latin) but they continue on. I don't know if it will help you get out of the mire, but here is a fine compilation of these fallacies:

    http://www.nizkor.org/features/fallacies/index.html#index

    Please use it for good not evil.

    You don't need to apologize but if it makes you feel better I accept and reciprocate. If you can manage it in the future please try to follow my directions and have me assemble my own logic, and don't assign any emotion to my short contrary logic statements. What I want is good information to use in my logic. Save emotional arguments for bar stools and sales pitches.

    You have or know where to get information about the performance of foils in water near the surface. I need this for modeling performance. Let's start with Garry's boat, model DSS on it and quantify performance. I intend to do the same for my concept and you are welcome to participate. The assertion I made can only be proved considering both.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Skimmer/DSS

    Years ago, I learned from Dr. Bradfield that a hydrofoil should be at least 2 chords below the surface. A couple of years ago, I learned from Hugh Welbourn that the DSS foil could be as high as 1 chord below the surface. Last year I learned that, thru extensive testing, it has been found that the DSS foil will be somewhat effective with just the bottom of the foil wet and effective, to one degree or another, between that and one chord below the surface. When I have time I'll try to find info on the last statement.
    ----
    I should say that anyone considering DSS should get help from Hugh Welbourn-trying to do the system without his help is just reinventing the wheel and depriving whatever project that is being considered of the latest info. DSS is patented and in most cases will cost about the price of a mainsail
    for a licence. But Hugh is open to new ideas and will work with most people.
    Again, anyone wanting comparisons with other boats should read the Quant 28 thread, linked above. That boat has an incredible race record winning most of it's races boat for boat even against much larger boats.
    -----
    Skyak, just a suggestion- you might want to start another thread about your ideas-it's 100% up to you as far as I'm concerned.

    ==================
    Picture's: Crossbow fl DSS foil is 39" long with a 6.5/1 aspect ratio and is slightly more than one chord below the surface at a 10 degree angle of heel with the windward foil clear. Draft of the boat heeled with the foil one chord below the surface is 7" max(+the daggerboard and rudder). On a boat like this DSS does not increase draft when the boat is sailed at it's proper angle of heel. Takes a large angle of heel to even equal the draft with the daggerboard down.
     

    Attached Files:

  14. Baltic Bandit

    Baltic Bandit Previous Member

    "it has been found" IOW Doug you don't actually know this. you are going on claims by the guy touting this technology.

    Gary the thing to realize is that as soon as you start heeling the hull, your CB actually starts counteracting the benefits of the DSS foil so the more you have to heel your hull for the DSS tto work, the bigger a DSS you need the deeper you have to heel it

    Note that at 10 degree heel, the tip of the DSS foil iis 1/6 the length of the foil under water. On a 3' foil that's 6" which isn't even 1 chord length. So doug's claim of 10 degrees of heel is a bit made up. Now if you start with the thing in the very bottom of the bilge (not really practical but lets pretend) and you draw 6" - then you might do that. But I suspect you draw more like 3"-4" and the keel and other stuff will raise the DSS foil at least 2"

    So that puts your DSS at initially drawing more like 3" so you really need about 15 degrees of heel to make it work , OR dedicated foils on each side and you have to deploy one ad retract the other in each tack.
     

  15. Skyak
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    Skyak Senior Member

    Words like 'effective', 'effective, to one degree or another' are useless in determining whether DSS or any other system are worthwhile. I need to get to lift and drag forces to make a model and you and Hugh are the best source I know for foils close to the surface.

    The patent and price of licences are news to me. I suspect the price includes support and consultation. If it is news to Gary I suspect DSS just got far less interesting for his skimmer. I would like to finish my contrast of dynamic stability from down in the hull (DSS) vs surface peircing -produce those graphs. I am pretty sure Hugh does not expect to make money putting DSS where it isn't a cost effective benefit so even if I am right and it's not good for shallow hulls accurate characterization is good to comunicate.

    As long as Gary is still interested and supportive I think this is the right forum.
     
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