Cox's Bay Skimmer

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

  1. Doug Lord
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    Doug Lord Flight Ready

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    Those words were not used by me to aid "in determining whether DSS or any other system are worthwhile." They referred only to DSS and to proven elements of the DSS system learned over the years of testing. The point was to attempt to illustrate the known range of effectiveness of the DSS foil system. Sorry if I came across as unclear.
    http://www.dynamicstabilitysystems.com/
    http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html Unmatched race record boat for boat even against much larger boats.
    Infinity 36- http://vimeo.com/45635108
     
  2. Baltic Bandit

    Baltic Bandit Previous Member

    Doug have you actually seen the datasets of the testing? Because as far as I know, DSS still has yet to prove its worth except in very large keel boats. The Quant 28 is a one-off so there is nothing to compare it to. WOXI has its perfs sufficiently modeled that when they say it adds 3% to boat speed I believe them.

    But 3% on a boat doing 14 knots upwind is very different than 3% on a boat doing 6 knots upwind and not being able to fully immerse the foil. In fact I don't think the DSS has been proven on any boat smaller than 30' much less essentially a large dinghy.

    Seems to me a bit presumptuous to be telling other people to spend money on a modification that is "proven" when it is nothing of the sort
     
  3. Skyak
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    Skyak Senior Member

    No apology needed. I was just grumbling at the realization that I was not likely to get any data and nobody has even shown interest in the curves I proposed. I still don't see DSS as a good solution for Gary's skimmer and now it has little to do with my assertion.

    About DSS performance and stability; My thoughts about performance and stability in the 2 chord to the surface depth have changed a bit. Now I think that the DSS foil looses lift progressively and that this is the 'grove' or stability bump that they are operating in. At high speeds and relatively light righting force and variability (gybing downwind) this is very easy. Upwind with large variation in wind force and lower speed would be much more challenging, playing the sheets constantly. The damping effect of the DSS foil makes control manageable.

    About Crossbow, I think that the main hull and DSS are about as good as you can get in a light boat and still the cost/performance could be lowered. For example, leave DSS off and put bruce foils like I describe off the floats at the ends of that beam. With the correct rig this could sail faster easier, and it would cost significantly less.

    I don't know how crossbow is supposed to work but I think the main hull would be on top of the surface at a fairly low speed, turning the expensive DSS into a lossy planing board. Have you calculated the speed at which that DSS foil could lift the entire boat (assuming fully immersed foil)? The DSS foil is ahead of the mass center so the DSS foil will surface sooner than this velocity.

    You could go the other way and eliminate the crossbeam, put a little weight at the bottom of the daggerboard and have the smallest DSS boat made but I think it would cost more and perform less. Your model can determine this.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Skimmer + DSS

    Skyak, as I've been saying DSS is a well proven but a young technology. Things are constantly being learned about the foils and the right foil positions, the best foil sections are currently designed by Hugh Welbourn. For a year, as far as I know, the Crossbow fl has been the smallest boat designed from scratch for DSS and because of my study and the team I have helping with the project, I expect the DSS system will be an important addition to the boat with increased speed due to increased RM, increased pitch control, improved ride especially in chop-- in other words it should have the advantages proven already in boats like Brace, Brace, Brace(25' LOA), Quant 28, Quant 30, Infinity 36-all boats designed from scratch for DSS.
    It's my opinion from all the work I've done on Crossbow fl and all the study I've done with a lot of help in learning from Hugh Welbourn and Michael Aeppli(developer of the Quant 28 and Quant 30) that there is an excellent chance that the system would work on Gary's boat and for sure on the 6.5 if the elements important to DSS were incorporated from the start. I'm 100% positive that Hugh would work with anyone trying to expand the knowledge base on DSS by trying the system on smaller boats.
    Here is the "two boat" description of DSS from Michaels book:

     
  5. Baltic Bandit

    Baltic Bandit Previous Member

    how is it "well proven" Doug? particularly on a high performance dinghy? and frankly the foil shapes ought be no mystery NACA sections all have known drag/lift curves which very easily and quickly let you calculate RM increase (which indirectly gives you velocity increase) vs drag increase. there isn't that much to be studies.

    So Doug are you saying that you are actively engaged with Michael Aepelli?

    we know what your opinion is. But as you are seemingly unable to provide any sort of quantifiable numbers behind it, Its a bit dubious to lend that opinion the kind of credibility that is necessary to take a sawzall to a hull
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Skimmer

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    Gary, looking forward to the Skimmer video!
     
  7. Skyak
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    Skyak Senior Member

    Doug, crossbow is not an example of DSS in it's current form because it is a multihull. All of the real DSS boats have weighted keels and none have crossbeams with floats.

    There is a very important statement on Hughs DSS site "DSS is IRC legal." This is the root of DSS success. Multihulls are excluded, DSS is not.

    Regarding DSS on Gary's boat, the negatives I mention still warrant consideration, particularly in light of the cost. It appears Gary has moved on. You can take crossbow and DSS back to their (your) respective threads. I still would like to see an attempt to apply DSS to Gary boat to show the problems so we can have a small boat discussion you don't make about DSS.

    BB, about the foil profile for DSS, the latest 10M DSS appears to have a high lift at low Re profile. It's definitely not NACA. I have forgotten the name of the guy that did the series, begins with an S...
     
  8. Baltic Bandit

    Baltic Bandit Previous Member

    Skyak I think you are confusing Doug's current 4 year multihull model project with his next project - the one he plans on crowdsource funding. That's the CrossBow X - which used to be called the Trapwing X... it has both the DSS and the automated flying weight system. Doug assures us this will be his immediate next priority

    I'll admit there are other foil shapes besides NACA and a high lift low Re profile with a fairly narrow drag bucket should be ok for that usage. Its still not rocket science to build an experiment
     
  9. Skyak
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    Skyak Senior Member

    BB
    I was referring to the pictured model he posted on this thread. I could be confused but there is no way I am going to read 50+ pages with no supporting calculations or data -too much work, too little value. If none of them touch the water does it mater?

    I mention the profile just FYI. The IRC rating info is more informative. My concept of a wing dingy with surface piercing stabilization foils off the outside edges of the wings -do you think it would always be ruled a multihull?
     
  10. Doug Lord
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    Doug Lord Flight Ready

    ================================
    Crossbow fl(the fl in honor of my brother) most certainly is the smallest DSS design that I know of. http://www.boatdesign.net/forums/sailboats/crossbow-fl-43615.html
    It is not, in any way shape or form a multihull.
    There are differences and similarities between my design and other DSS boats:
    1) Crossbow fl is the smallest DSS design that I am aware of,
    2) Crossbow fl ,like other DSS boats(Quant 28 &30, Brace Brace Brace(25'), Infinity 36) uses movable ballast. However, it is in the form of the Trapeze Power Ballast System(Trapwing),rather than a movable crew(even though crew may be able to move a small amount),
    3) Crossbow fl does not require keel ballast for self-righting as do other DSS boats: the Trapeze Power Ballast System allows the boat to be righted by the crew(with no crew body movement)-an advantage of it's size and the buoyant wing that is the key element of the Trapeze Power Ballast System.(Ballast is sealed inside the wing and both the wing and the ballast move. The buoyancy of the wing is substantially greater than that required to float the ballast and wing. The outboard ends of the wing are supported by Trapeze wires.)
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    Last edited: Feb 5, 2014
  11. Baltic Bandit

    Baltic Bandit Previous Member

    Well that's an interesting question. I could see someone protesting Speed Dream's rating as a mono-hull the moment that out of the water bulb touches down into the water...:)

    but if you go to "first principles" - a multi-hull is a vessel that uses more than one immersed "hull" to prove RM stability in place of a heavy center keel. Under that line of reasoning, outrigger foils are a form of hull - regardless of whether they can support the whole weight of the hull. After all the ama of a Proa typically cannot support the whole weight of the rest of the vessel either.

    So then the fact that your outrigger foils take more advantage of dynamic hydrodynamics vs. static hydrodynamics is a matter of tradeoff. Those still then are outrigger amas
     
  12. Doug Lord
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    Doug Lord Flight Ready

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    Probably. There are at least two trimarans referenced in the "Multihulls" forum that use only foils at the end of their crossbeams :"Broomstick" and a British Americas Cup challenger "Blue Arrow"(see link below). The first Moth to use surface piercing foils(Brett Burvills "Windrush") was ruled to violate the Moth class rules against multihulls and that ruling ended the use of surface piercing foils in that class.
    http://www.boatdesign.net/forums/mu...ng-hydrofoil-trimaran-without-amas-23293.html
     

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  13. Baltic Bandit

    Baltic Bandit Previous Member


    Doug could you possible try to not disrupt this thread with your personal self-promotion please? This post has been reported to the moderator as an attempt to disrupt the thread
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Skimmer/ DSS

    =================
    Generally, Hugh Welbourn designs the DSS foil sections himself. He allowed me to use one of those sections for the DSS foils on Crossbow fl and would more than likely help Gary in the same way.
     

  15. Baltic Bandit

    Baltic Bandit Previous Member

    Hmm he must be an amazing man to be able to outdesign the smartest guys at Electric Boat and Boeing etc.
     
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