Design for DSS-Foil Assist for Keelboats

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

  1. sean9c
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  2. Doug Lord
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  3. Doug Lord
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    DSS- foil assist for keelboats and...

    News: Infinity 36 GT first race (3rd out of 14)

    Infiniti 36GT Palermo to Monte Carlo regatta
    Posted on August 27, 2012 by quin
    Congratulations to Foiled! the Infiniti 36GT on their performance in the Palermo to Monte Carlo regatta, 4th on line, 3rd in ORC and presented with the “fair play” award for their honesty on using a currently unrated sail, thus retiring from the IRC.
     

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  4. Doug Lord
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    Hugh Welbourn answers question:

    steveromagnino, on 06 September 2012 - 04:49 AM, said:

    Hey Hugh

    We raced against the Brace! brace! brace in TOG, Thailand and I took the press boat to follow them downwind as well in another regatta (raceweek). While the boat was very quick in certain conditions (flat water all angles especially at raceweek), it seemed to struggle a bit once the sea became very lumpy as you could see the foil's angle of attack would rotate with the pitch of the boat, so the boat would oscillate up and down as the fin went in and out of the waves; you could see it pretty clearly going downwind that the boat would be fine then they come out of a wave and go down the mine as the foil kicked in, then spring back out, and off they went again; exciting to watch with loads of spray, but probably a tough job to helm the boat in that condition.

    BBB! was quicker than the Shaw 650s downwind in the flat water and the lighter conditions (as it should be as it is 1m longer, more sail area, smaller fin, smaller bulb, wider at the deck, more advanced construction) but when the sea was lumpy enough, it seemed to slow down enough that the Shaws seemed to be going a bit faster and lower.

    Under SMS the foil is not given any rating penalty, and as a result we had pretty close, even racing. Not sure how IRC handles it.

    I know the guys who sail BBB, and they are not slouches (drunken kiwis yes, but not slouches and definitely better sailors than us).

    For a larger boat like the 36, do all these problems disappear (as the boat is a bit more planted in the water and relative to wave height the foil stays in the water rather than skimming over the top like a skiff) or is there some way to eliminate this? I know the moths have a wand, so when they are foiling they don't have to manually try to control it, I cannot see how you could control the angle manually as things happen quickly downwind.


    From Hugh Welbourn:

    Have to remember this was the first real project after the 27 demo boat, so things have moved along quite bit since then. One of the issues with the Brace is the rack angle is a bit too low so there isn't much tolerance in sailing the heel angle that it likes. Then too the foil parameters have developed as we've learnt more but thats something we could well change on the Brace. Finally, it was designed more for flat water sailing and so it would be very effective on the swiss lakes and likewise the Q28 would be a lot easier to sail in those lumpier conditions.
    It really depends on the the mainsail guy being really quick and on the ball to keep the boat in its sweet spot - the later designs are way easier in that respect.
    When you get into the 36, then different animal altogether as it sails with a bit of natural heel angle but doesn't care if you have more or less - not dragging racks in the tide!
    Also, with much higher global inertias then even if the foil breaks surface then nothing much happens before its back in the water.
     
  5. Doug Lord
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    Infinty 36 DSS

    Here are some great pictures of the boat-see pdf below:
     

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  6. Doug Lord
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  7. Doug Lord
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    Mini Transat w/ DSS

    Here is another picture of the Mini Proto built by Isotop:
    click-
     

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  8. Doug Lord
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    Infinity 36 DSS

    News Flash:
    Infiniti 36 GT raced in the 3rd annual Grimaldi Trophy this weekend. The team composed of skipper Gordon Kay, Andy Meiklejohn, Paolo Persi del Marmo as well as four new crew members from Yacht Club de Monaco and the yacht Tuiga. The team took 2nd over the line despite being one the smallest boat in the fleet of over 50 yachts.
     
  9. Stephen Ditmore
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    It'd really be fun to see VPP analysis of the Infiniti 36 GT vs a Skod 36 [Perhaps along with a McConaghy 38 and a Farr 400]. Looking at the mini it's curious to me that Hugh seems to be going narrow rather than wide with his hulls when his own website says the larger the boat the better DSS works. Many early canting keel boats were also narrow, but that doesn't seem to be the trend anymore.
     
  10. Doug Lord
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    Dss

    -------------------
    When Hugh said "larger" I'm pretty sure he didn't mean wider*. The Mini Protos are wide to get RM-with DSS you can use a narrower, easier driven hull because you get RM from the foil not from the beam of the boat. So you can have the RM of a wide hull on a narrow, lighter, low wetted surface hull by using DSS. But probably the most important reason for the narrow hull in the Mini case is the Rule. It will be interesting to see the results when the boat starts racing.
    * Most boats designed with DSS so far have tended to be average or narrower than average for a given length.
     
  11. Stephen Ditmore
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    That's my point. It was the case with many canting keel boats too. I question whether it's the right choice, and in the case of DSS width is the dimension that matters. [And I think a McConaghy 38 or boat like those being designed by Guillaume Verdier or Sam Manuard with water ballast and DSS would be really cool].
     
  12. Doug Lord
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    ========================
    Stephen, I'm curious about your reasoning on this-could you expand a bit?

    rough sketch-click:
     

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  13. Stephen Ditmore
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    Q(a): What constrains transverse foil span?
    case1: When retracted, no projection from hull
    A: Hull beam at location of transverse foil.​
    case2: Foil is allowed to project from both sides simultaneously
    A: Structural requirements of cantilevered extended foil - which ultimately will be related to hull beam at location of transverse foil.​

    Q(b): What determines righting lever from CG to center of lift of transverse foil?
    A: Transverse foil span + hull half breadth at location of transverse foil + transverse distance of CG from centerline (positive value = to windward).​

    In all cases, it's beam that matters. Add water ballast and it matters even more.

    In your sketch you've drawn them with the same foil span. It should show the wider boat with greater foil span.
    Also, the moment couple is not between the foil's lift and the heeled center of buoyancy (you'd have two ups) - it's between the foil's lift (up) and the boat's center of gravity (down).
     
  14. Doug Lord
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    ==============
    Do you have a link to quotes above or are they yours?
     

  15. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Mine. I've edited my previous post in an attempt to make it clearer, and to respond to your sketch.
     
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