Design for DSS-Foil Assist for Keelboats

Discussion in 'Sailboats' started by Doug Lord, Dec 6, 2011.

  1. Doug Lord
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    Doug Lord Flight Ready

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  2. human 1.0
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    human 1.0 Don't mess w/ Humanity

    I think you guys are over thinking this (as armchair-types tend to do).

    The blunt bow reduces the "pie slice" effect that catboats experience (Bolger, et al.) where the keel fights the boat direction by falling over towards the leeward bow. It may also help downwind by keeping the boat from diving into waves. Seeing it beat 2nd by a day and the pack by two days, this might be the shape of the future, which is definately not a Pelican, and probably not a scow so much as an X-33 flying wing.

    Note the cutaway section aft to "fit" it into the "box". Can't call that a chine either, this is definitely a different world than the Friendship Sloops we thought of as having high performance.

    I am writing about it over here and I hope Raison and TeamworkEvolution put out more material.
     
  3. Doug Lord
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    Doug Lord Flight Ready

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    While what David Raison did was fantastic I wouldn't think its neccesarily a revolution in design for future boats. The new Welbourn Mini using DSS has the potential to change Mini design drastically reducing beam significantly while still allowing the RM possible with a wide boat. It will be interesting to see how this develops. I would not think characterizing all mini's as very wide is relevant anymore?
    I think you mis-characterize participants in this thread as "arm-chair types"...

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    Thank you, Daniel!
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    Last edited: Feb 7, 2012
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    Welcome to the thread - and also to the forum since I see you are a fairly recent arrival.

    A brief comment if I may: personally I don't like judgemental words like "over-thinking and "armchair-types" and this thread is specifically for discussion; elsewhere in the forum some of us have active build threads.
     
  5. human 1.0
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    human 1.0 Don't mess w/ Humanity

    problem is... last time I posted here I ran into a pack of lunatics sorry about the reality check, but that is the way it was
     
  6. sean9c
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    sean9c Senior Member

    Pretty small foil to generate a lot of RM. What happens if it were to stall or aerate? The sudden loss of RM would be interesting. It's one thing to have DSS on a sportboat for day races and blasting around but I think it's something else to rely on it in a distance racer.
    Since it is, as yet, unproven it could end up just another wacky idea that didn't work.
     
  7. peterchech
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    peterchech Senior Member

    I was just thinking along those lines. The foil only provides rm so long as it is in forward motion through the water. The slower the boat, the less rm. Under normal conditions this is fine, but what about if suddenly taken aback? Or in extreme gusty/shifty winds? Etc etc... I mean, maybe the boat just heels way over then stands up as speed picks up, but this may make it very vulnerable to knock downs in heavy weather...
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    er, Sean9c, you need to take a look at past AYRS publications, all those wacky ideas from wacky people .... but hold up, not so wacky, they were just 3 decades or more ahead of their time ... because what you're seeing being implemented in yachts of today are the results of their forward thinking of yesterday. Now who's wacky - or backward?
    Enough generalization and a suggestion: high performance, non-aerating, sophisticated foils do not have to be large.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Dss

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    Who says it's unproven? Unproven in the Mini class-well yes-so were canting keels before they were first used but to say DSS is "unproven" as a technology is just not right.
    What happens to a boat with a canting keel if it is taken aback? You can create scenario's that sound bad because they're not based on the real world experience with DSS which has built up over years of testing.
    I'm fairly sure most people know that a DSS keelboat has a keel capable of allowing the boat to right itself ?
    Knowing that the technology has been proven in rc models, tank testing, on the 27' test boat, on "Brace, Brace, Brace", the Quant 28 and a few others one can speculate on the potential of such a proven foil assist system on a Mini given the known factors involved. And the potential is great...
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    - Check out the size of moth foils which lift the entire boat.


    - from Doug’s diagram in Post #83, I understand the DSS foil is deployed to leeward in heavy conditions, it should be traveling fast enough to avoid stalling and not be near enough to the surface to aerate. It it failed to operate for some reason it would be a result of pushing the boat too hard in heavy conditions which should only happen in a race to sailors who will have to take the consequences, as always. I don’t think the DSS is being presented as a safety device . . . moth sailors use the phrse "going down the mine" to describe a related experience.
     
  11. CutOnce

    CutOnce Previous Member

    Like many performance-enhancing technologies in machine-based speed sports, once DSS becomes an integral design element other safety factors are reduced due to it's expected contribution to overall function. Altering passive foil-produced downforce on a current Formula One car can be the difference between a safe ride and a dangerous one. Cars operate in a far more predictable environment and conditions than sail boats.

    In this particular case beam is reduced - and consequently inherent roll-plane stability goes down. DSS also allows higher sail area for a given beam, therefore design power is higher than boats with the same beam.

    DSS is to a great degree a passive set-and-forget technology that depends on predictable flow across the foil. Unlike a person on a trapeze, mechanical canting keels or crew hiking, it does not dynamically adapt to (anticipate and predict) condition changes.

    Sailing is an activity operating in a dynamically changing set of conditions - gusts, lulls, lifts, heads, currents, waves - all these things vary constantly. All these things may affect the predictable steady flow required to make the DSS foil operate optimally.

    I do not doubt that DSS "works" in the conditions it is designed for. I think Sean9c comment is valid and worth consideration. A reduced beam design, carrying a larger more powerful rig than that beam could normally support would not react well to the DSS-provided righting moment varying significantly.

    I (like everyone reading this) have no experience using DSS. Therefore everything said here is speculative and unproven. I do wonder if the passive, unreactive nature of DSS would function as well as more active solutions to the same conditions. I do not doubt the "upside", but wonder like Sean9c about the unknown downside to the technology. Ignoring downsides and embracing only upsides is more marketing hype than objective engineering analysis.

    --
    CutOnce
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Dss

    =====================
    One of the beauties of a DSS foil is that it does dynamically adapt to the speed of the boat- automatically increasing RM as speed increases, decreasing RM as speed decreases-that is about as far as you can get from "passive and unreactive". For very little weight you have a max RM system that adds righting moment only as it is needed while at the same time adding vertical lift to the boat reducing wetted surface-there is no other ballast system that can accomplish this. Further, the foil can be adjusted for more or less lift for different conditions.
    For some applications the angle of incidence of the foil can be adjusted allowing the foil to be better configured to a given set of conditions.
    And again: DSS is not used as the sole righting moment for any boat-any boat using DSS can be sailed in any conditions w/o the foil-just not as fast as with the foil.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    - that is true, but the delay between the additional heeling force from additional wind or sail and the resulting extra speed means that the boat has to be managed carefully, especially if it has been designed to take advantage of the DSS with less hydrostatic stability to reduce wetted area.

    My own small experiment with a Bruce foil brought this home to me; although it would respond to a gust in a couple of seconds, a wind knuckle caused by nearby trees reversed the wind direction and almost swamped me on one occasion. The hydrodynamic drag of a deep keel would have given me more time to react. The Bruce foil required only a few inches per second leeway to generate a righting moment, but it takes longer to build up the speed that a DSS requires to work.

    Depending on the design of the hull per my comment above, a ballasted keel - especially if it is the canting type - would be a useful, even essential safety feature.

    What the DSS allows designers to do, should they choose, is to adopt more extreme boat designs. That is usually the result of any performance development.

    Will this device be adopted for cruisers? I think it is a possibility; but not as shown above. A fixed DSS just below the surface might be accepted by the cruising fraternity; as the boat heels the windward foil would lift automatically transferring lift to the leeward side, a kind of stabilizer if you like. Perhaps the underwater hull shaped could be designed to "channel" additional water flow across the foil for extra lift.

    Alternatively a surface effect foil above the water could be arranged to ride on the bow wave.

    But that's all conjecture (read "BS" until demonstrated to work) from a non-NA, and the DSS could be a nuisance in a marina or when trailering.
     
  14. peterchech
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    peterchech Senior Member


    Some sort of a fixed, but smallish foil would probably be best for the cruiser. Haha I am kind of tempted to play with one for my hunter 25, I am doing so many other mods and refits to it anyway... of course, it would kill any potential resale value of the boat... I like the idea of having the dss foil as an option, for an existing design. Not a necessary part of the boat, but rather just an improvement which allows the boat to be stiffer in a breeze and maybe a tad faster and more weatherly too. A fixed DSS foil would make it nearly impossible to park in a slip though...
     

  15. peterchech
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    peterchech Senior Member

    This should really be continued in the DSS foil thread though, as this conversation has nothing to do with the speed potential of scows...
     
    Last edited by a moderator: Feb 9, 2012
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