Monohull Speed: Speed Dream by Vlad Murnikov

Discussion in 'Sailboats' started by Doug Lord, Jan 8, 2010.

  1. Munter
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    Munter Amateur

    Hi Dave,
    Some friendly advice that you are probably already across. The frequency of posting and sheer volume of words on a topic isn't necessarily a good measure of one's competence in a field. You will find posters on here at both ends of the credibility spectrum. As with the rest of the internet, apply an appropriate filter to the (quite expansive) information on this site.

    Lifting hydrofoils are a very interesting development in sailing and no doubt will be integrated into all sorts of future designs. Experimentation has yielded all sorts of configurations and the drawbacks of many of these aren't understood until they are experienced first hand.
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    Obviously the answer is going to depend on the yacht type, size etc. As Doug noted, the gain is from the reduced friction of the wetted surface to the extent that it is reduced by the foils, less the friction of the foils. Lifting a boat a few inches might reduce drag only a few percent while the displacement of the boat is greatly reduced; since the boat's weight hasn't changed the loss of bouyancy must be replaced by foil lift and the net result could easily be more friction. Once the hull is flying entirely on the foils the speed increase will be more dramatic, but not all hulls will react kindly to such treatment.

    The greatest cost factor may well be the damage to the yacht if something nasty happens.
     
  3. Perm Stress
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    Perm Stress Senior Member

    Advantage of lifting foil to lee of the hull is NOT reduction in resistance. Resistance could be easily more with additional foil as without it.
    Advantage is greatly increased RIGHTING MOMENT, what mean greater force (both heeling and driving, as they remain roughly proportional) on the sails could be developed. In the end, we have much greater driving force at the cost of modest increase in resistance. As driving force is increased more as resistance, speed is up. As speed is up, righting moment is increased once more, because lifting foil moves faster trough the water, creating more righting moment and allowing more driving force. At some considerably higher speed, acceleration stops. :)
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ============
    According to its inventor, DSS increases stability and reduces wetted surface-and total drag. (see link below)
    Other forms of "foil assist" can also reduce resistance such as the rudder T-foil on the I-14 and National 12. The curved daggerboards on the A Class, Nacra 20, Orma 60, Banque Populaire, Sodebo etc. also reduce wetted surface-and total drag.
    On the Orma 60's the single "foil assist" curved foil lifted up to 70% of the weight of the boat drastically reducing resistance. "Foil Assist" whether it is used primarily to add RM, reduce resistance or both is one of the most exciting avenues of hydrofoil development with more and more boats taking advantage of the careful design of such systems.

    http://www.harken.com/Interviews/DynamicStability.php
    ============================================================
    As to the boat that is the subject of this thread, heres what Vlad Murnikov(the designer) says foils will do for Speed Dream:

     
  5. Perm Stress
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    Perm Stress Senior Member

    From the link in the previous post:


    "Can you explain what accounts for the dramatic increase in upwind VMG when the wind speed increases from 10-15 knots? Presumably, that is when the boat becomes fully powered up, but why is there such a dramatic increase in stability?

    HW: The improvements to upwind VMG are from two separate effects of the deployed foil. the added stability on a correctly configured system gives the boat more power to carry sail and thus speed. This outweighs the cost of additional drag. One can also see that you can achieve a degree of stability at a lesser angle of heel with the foil deployed, so the boat is being sailed in a more effective trim for speed.

    Secondly, the dynamic damping of the boat in both pitch and roll significantly improves the rig efficiency. This also reduces the amount of corrections required by the helmsman or autopilot – again, less drag and greatly reduced power requirements.

    What accounts for the greater performance increase downwind as opposed to upwind?

    HW: The lift of a foil is proportional to the square of the velocity, so as soon as the boat is moving faster then the foil effects rapidly mount up. So the added stability comes into play, and also the reduced displacement of the hull as seen by the water further reduces drag."

    As could be seen, inventor itself quote increased sail carrying power first, reduction in roll and pitch second, and reduction in resistance (hull only? total?) third, and only for downwind sailing.
    However, it should be remembered, that really fast boat sail fastest downwind by broad-reaching back and forth, instead of dead running.
    Further, dead running is about the only sailing mode, when righting moment is of trivial importance.
    While, broad reaching at high speed (same as wind speed or higher) apparent wind will blow forward of the beam, and righting moment again became of primary, vital importance. I.e. we are again in "more righting moment for modest increase in total resistance" situation.
    To sum up, DSS in most cases give her benefits by creating more righting moment for modest increase in resistance, and only occasionally - by reducing resistance (of hull?).
    So much could be seen before detailed number crunching.

    Regards.
    Nothing personal to anyone, just physics.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ================
    I don't think its possible to separate functions too much with a DSS type foil: when the foil is working either upwind or downwind it will tend to lift the boat
    as it creates RM.
    Just another "foil assist" application for hydrofoils and a brilliant system from Hugh Welbourn. It still concerns me that the location of the foil seems like it might wind up too close to the surface in real world applications in ocean racing.
    But on "Brace, Brace, Brace" ,the Wellbourn 25, it seems to work perfectly. I'm looking forward to seeing more results on different boats.
     
  7. TokyoBay
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    TokyoBay New Member

    A few reflections on the MX-Ray from an original owner

    As an original buyer and owner of what may have been among the last MX-Rays that Vlad shipped from his workshop near Boston, I want to add a few thoughts to put the boat, its design, and its builder in proper perspective.

    First, the build quality of the boat is and was excellent, with first-class trusted suppliers for the sails (North) and two-piece carbon mast (FibreSpar) and of course deck fittings (Ronstan, I believe). Just the idea of borrowing sail and mast design fm the windsurfing industry was a step forward and at that time, I don't recall any other dinghy with mylar sails.

    Second, the boat arrived at a time when the performance dinghy market was in a period of transition - and when I say performance, I mean the intense discussion underway to select new designs for the Olympics. It is perhaps now forgotten that it was an open field until the Bethwaites came along with what, in retrospect, was THE radical innovation of its day, the 49er. But I recall that for a time, the MX-Ray was considered a contender.

    Third, speed contests and outrageous claims were part and parcel for people at the ragged edge of the sport, as it was among wind-surfers, Bonneville bike racers, and those guys in the high-risk extreme motorboats. GPS as we know it today was just coming into the hands of sailors, and frankly I think any sailor who takes claims of that or any era without a grain or two of salt ought to hear the story about the fish that got away...Lighten up folks!

    Finally, Vlad. He was attentive, thorough, and generous when I needed a key part that had broken in shipment of my boat to Japan. (Peter Fuchs)
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Attached Files:

  9. cardsinplay
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    cardsinplay da Vinci Group


    OR, you just weren't paying too much attention to your own posts on the topic. Go back to the last week in June and take a good look at the pdf's you posted for everyone to read. The May press release by Speed Dream clearly announces Cam Lewis' participation. (Post #54 on page 4 of this thread) http://www.boatdesign.net/forums/sailboats/monohull-speed-speed-dream-vlad-murnikov-30880-4.html

    I find it truly hilarious that a guy who regularly lectures other members of this forum with dismissive commentary such as this: "Obviously you haven't read, much less understood, the material previously presented" and "Ct did did you read the pdf in the very first post? I don't think so" and "If you read the press release..." and "If you didn't read it then you have made these comments without having all the facts. I think you owe Mr. Murnikov an apology" and yet, here you are, having apparently not read your own stuff, much less understood it comprehensively.

    Kinda losing your grip, there, Doug?

    Perhaps it's time to apologize to each and every person who got this ugly, trite treatment from you in the past?
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    He's gotcha there, Doug

    ... BUT -

    - this sounds just as bad to me; just my impression ...
     
  11. cardsinplay
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    cardsinplay da Vinci Group

    Just your impression, indeed. Look to the originator of the issue to which you wish to respond and make your comments there. And you wish to blame the messenger... really?

    Come on, Terry, you've got more going on than that would indicate.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Speed Dream

    Fairly interesting article on the front page of SA by Brian Hancock: http://www.sailinganarchy.com/index_page1.php

    Biggest news is that they will be building a 35' test boat to work out the concept for the big boat.
     
  13. Gary Baigent
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    Gary Baigent Senior Member

    Good on them - but I think more recognition should go to the French 60's where they have almost the same configuration: bulb keel rotated out of the water, angled dagger boards to stop leeway, chined after section hulls - damn near the same thing. The difference is that Murnikov is hoisting the bulb keel up, which makes theoretical sense but tricky to implement, extra equipment and complexity, On the point of the near horizontal leeward lifting foil; it was also tried here on the Ross 45 M1 several years ago (but was not really successful) by the present owner of Geant/Vodafone ORMA 60.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ===============
    Well, according to a bunch of people including Hugh Welbourne the DSS foil, which is very similar to Murnikovs foil, works and is PROVEN to work. How fast it really is is still up in the air but the first indications are excellent. The Vlad's 35 footer seems like a damn good idea.
    Have you seen the Whitehouse design:
     

    Attached Files:


  15. Doug Lord
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    Doug Lord Flight Ready

    ================
    Did you mean the Verdier/VPLP collaboration on Open 60's using lifting foils?

    see: http://www.boatdesign.net/forums/sailboats/open-60-using-curved-lifting-foils-35710.html
     
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