Design for DSS-Foil Assist for Keelboats

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

  1. CutOnce

    CutOnce Previous Member

    AK:

    My post is just documentation of easily confirmed and long repeated history. This battle has been ranging since the first log floated, and it continued to the establishment banning Herrishoff's catamaran Tarantella. A recent skirmish resulted in the Moth class banning three element wing sails.

    I've built and will continue to build and sail boats that incorporate technology improvements. I do not think that experimentation and innovation is dead - but I do know it has a much higher infant mortality rate than following the herd. Right now we are in the midst of a perfect storm for innovators - poor economy, global resentment of the wealthy for overstaying their turn at the trough, a devastated recreation sector and public decline of interest in extreme designs that are out of reach for most people.

    I feel that the people interested in this forum are better served by gaining a frank understanding of the tough arena they are playing in. Once you realise the reality of this market, you can focus your development and fund raising efforts far more effectively. You can take on projects of manageable scope. Perhaps people will get smart and facilitate shared development of interesting concepts by co-operating together.

    Most of the serious progress made in technology development has been made through public academic projects and shared public business interest. The Internet was a public, open, shared innovation. Tim Berners-Lee worked at CERN in Europe, Vince Cerf worked in North America - and these guys shared their work to create something beyond a private company's imagination.

    The recent rebirth in the C Class Catamaran is the result of open and public sharing by Steve Clark and Fred Eaton. This forum is the kind of place where that type of non-commercial leading edge development can emerge.

    I do highly dislike the people on this forum who want to see only positive comments on technologies - because without critical review and intellectual honesty it just becomes a free on-line commercial like a Sham-Wow promotion. If a technology discussed here can't withstand any questioning of it's function, it doesn't belong here - or this is not a design forum.

    Don't pack in your projects - make them more public and publish results - good, bad or indifferent. Serve as inspiration for all the timid folks who "design" and fail to build. It is far more fun to build and fail, rebuild and get better, rebuild and succeed than it is to never fail at all.

    --
    CutOnce
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Dss

    It's ok to criticize technology if thats your mission but lets try to get this thread back on to the topic of DSS design. My compliments to AK, Perm Stress and last but not least to Gary! Lets keep this discussion on DSS design for better or worse. If you dislike innovation and the effect it has on sailing start another thread about that. If you have technical design reasons why you don't think DSS is a good design solution then speak up-but before you do please read the previous posts.
    ----
    Comments were made about DSS upwind without reading the information that had already been posted-and that was clarified by reposting the information.
    The point is that there is more to the positive effects of DSS than just RM.
    However, this post is about RM for small boats:
    There are areas of design where very little to no experimentation has been done with DSS and that is with very small boats-particularly upwind. RM generated by DSS happens because of the speed of a foil thru the water. Very small boats-say with waterline lengths between 10' and 16' and theoretical hull speeds between 4.23 knots and 5.35 knots are somewhat limited if DSS alone is to provide upwind RM. This kind of speed limits the effectiveness of a DSS foil to some extent. For instance, on the 12 footer I'm designing to use DSS, the upwind righting moment from DSS( + crew+ hull only) is limited to 47% of total RM upwind compared to 80% of total max RM down wind when the boat can plane. But at the same time total RM, especially upwind, is more limited than it should be for a high performance dinghy when using DSS alone for RM.
    On larger keel boats the DSS RM is supplemented by a movable crew and a keel bulb that moves to weather upwind. Downwind when the keel bulb plays much less of a role DSS is able to substantially supplement the RM because of higher speeds.
    A small boat with a sit-in crew that can't move side to side like the one I'm designing needs some form of RM in addition to DSS to allow maximum performance. If the boat was not a "sit-in" design the crew could move and provide the additional righting moment required to allow close to maximum performance for a given length and weight of boat. Or a keel could be used to add to RM, or sliding on-deck ballast for that matter. Whatever is used would allow improved upwind power in the same way a keel and movable crew does on a larger boat.
    So for a very small design DSS has to be coupled with other forms of RM to achieve maximum power just like on larger boats but the choice of what kind of additional RM is the question- particularly on a small boat where the crew can't move side to side.
    The other proven benefits of DSS-vertical lift for lower wetted surface, enhanced pitch and heave control would be at least as effective at this small size as on a larger boat if not more so.
     
  3. Paul B

    Paul B Previous Member

    I think you need to look up the definitions of "proven" and "claimed".
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    Getting back to design details, from what I recall reading in past foiler threads the threads were surprisingly small, not much more than a square foot or so to support the entire weight of boat plus sailor. A small DSS may not be as fast as a foiler but then the DSS foil does not have to generate enough force to lift the boat.

    However, the foil in Doug’s post #46 was 1.5 square feet which seems a lot to develop only 58% of the total righting moment; I’m guessing around 150 lb (100 lb/sq.ft) based on reverse engineering back from a 200 lb sailor on the gunnel of a boat with 4 foot beam providing the rest. It also seems far more Rm than necessary to achieve a rather modest 10 k. Doug, is that lift due to the proximity of the surface or are you being conservative? It would be helpful to see the calculations if you did any.

    I was thinking about what I wrote in my last post and wondering about adding a DSS to my own small, long suffering - subjected to all kinds of experimental abuse - sailboat. It is very light and only draws about 3" so it doesn’t need a lot of sail to barrel along merrily. A DSS-generated RM of 150 lb would supply all the Rm needed I suspect. I would like to keep the DSS and its trunk as small as possible and I have some nice foils for a Bruce Foil project that might work but they are not very large.

    On the operational aspects, deploying the foil at speed might be a handful for a single-handed sailor to do from a hiked position and likely lead to a soaking. So the thing to do presumably is to deploy it long before reaching speed and haul in the mainsheet for more drive as the RM builds. The boat turns on a dime so changing tack when going to windward will require dexterity hence I think it would be best to remain on the centerline within reach of the various controls and let the DSS supply all the RM, except perhaps on a long reach.

    No promises yet, I haven’t got back to boating yet (and I have a shipload of other things I wanted to try as well as long-delayed builds) and need to ask my doctor’s opinion after the last couple of years on the sidelines but hope springs eternal . . . oh God, I’ve been bitten!
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Jim Young has been playing with various foil monohull designs, both power and sail in canting keel/board versions, on small boats (and although the opposite to DSS, could easily be adapted to the concept - he uses simple lines over the side to move the foil/keel); he has been doing this for decades now and here are a few examples - taken from the forthcoming biography. By the way, he recently received Queen's honours recognition and is now called Lord Jim; I bought him the Conrad. Sorry, Doug, slight hijack.
     

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  6. Doug Lord
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    Doug Lord Flight Ready

    ======================
    Ak, the figures in post 62 are more accurate. In the earlier post I was estimating the DSS RA(righting arm) in post 62 I have it exactly= 2.6875' @ 8.25 degrees angle of heel.
    The simplified formula for lift is: L= V^2 X S X Cl
    where L= lift
    V^2= speed in ft.sec. squared
    S= area and CL= coeficient of lift=.6 in these calcs though it is adjustable by adjusting the angle of incidence.
    So, upwind hull speed for a 12.75' waterline(may change)= 4.8knots
    Converted to MPH= 4.8 X 1.15= 5.5mph
    Converted to feet per second= 5.5 X 1.47= 8.085
    8.085 squared = 65.36
    So, 65.36 X 1.5(foil area in sq.ft.) X .6= 58.82lb foil lift.
    The righting arm is the distance of the center of lift of the foil from the heeled center of buoyancy and that = 2.6875'.
    So upwind RM from DSS on this boat = 2.6875 X 58.82= 158 ft.lb..
    Total upwind RM with just crew and boat:
    350lb @ .5'= 175ft.lb. + 158 ft.lb DSS= 333ft.lb. which means DSS provides 47% of upwind RM.
    Now, I mentioned in my previous post that just DSS in a small boat does not provide enough upwind RM for a small boat that wants to be "high performance", so I have made the decision to use the "Trapwing" that places 80lb of ballast 8' to windward for an additional RM at 8 degrees of heel of 8.5
    X 80= 680ft. lb..
    TOTAL UPWIND WITH SLIDING BALLAST:For a total upwind RM @ 8 degrees angle of heel of 1013ft.lb. of which DSS is 16%.
    ----
    Additional RM at different speeds from DSS:
    6.95 knots=8mph=124lb lift=334.6lb RM
    8.69 knots=10mph=194lb lift=521.4 ft.lb RM
    10 knots=11.5 mph= 257lb lift=690.7ft.lb RM
    --
    TOTAL DOWNWIND At 10 KNOTS, DSS with the sliding ballast at max(as above) and an angle of heel of 8 degrees the max RM is :
    1) crew and hull 350lb. @ .5' = 175ft. lb.
    2) wing 80lb @ 8.5' = 680ft.lb.
    3) DSS 257lb @ 2.69' = 691ft.lb.
    TOTAL RM = 1546ftlb with DSS comprising 45% of total RM


    =======================================
    Note: for more info on the simplified formula including the effect of Reynolds numbers go here: posts, 2, 3, 4. I think post 2 or 3 has the address for the bible of small hydrofoils by Ray Vellinga "Design Build Fly". http://www.boatdesign.net/forums/hy...ler-design-foil-assist-full-flying-40894.html
     
  7. ancient kayaker
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    ancient kayaker aka Terry Haines

    Gary: the flattie skiff looks remarkably like mine.

    Doug: sorry - I missed those numbers buried in the middle of a para. Thanks for the other data, I reworked them for my smaller boat and it shows DSS may not do much in my case, just allows me to sit one foot closer to the center line which doesn't seem much of a gain. Of course that is for upwind; on a reach (or if the boat will plane upwind - unlikely) it may be far more significant. I would have to increase sail area a lot to get enough speed to take advantage of DSS on this small a boat. I can do that, the boat will handle at least 50% more handily but it means a new rig . . .
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Dss

    ===============
    AK, I added the figures for downwind using the sliding ballast to my last post and also some reference info on the simplified formula.

    Yahoo-more power! Go for it..... Make it reefable-maybe you can just add to the current rig?
     
  9. Doug Lord
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    Doug Lord Flight Ready

    ========================
    Gary, this design is very similar to the 12 I'm working on-how long is it-any details? It has the chine in an ideal position for DSS on a 12-14 footer:

    click on image-
     

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  10. Submarine Tom

    Submarine Tom Previous Member

    Just found and read this thread, fantastic!

    To you open minded, pioneers, bravo, good for you.

    Too bad nay-saying politics has to muddy the waters.

    I've learned a new technique to read threads however:

    Don't look at the name of the poster just go directly to reading the text,

    within moments the "gold-or-garbage" detector triggers and I can eagerly read what's written or just skip the crap.

    That way I don't get dragged into the politics or develop a distaste for that particular anti-contributer.

    Besides, there is always hope that they'll change their narrow-sighted, closed-minded ways...

    -Tom

    It's brilliant if I do say so myself.
     
  11. Gary Baigent
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    Gary Baigent Senior Member

    The Lord Jim flatty is also designed to sail on its hard (and as straight as he could make it) chine; see the slight keel curve in the plan view. That means, if you have DSS, you could perhaps, dispense with the vertical dagger for anti-leeway and rely on the triangular long keel, cross section shape for going upwind. Downwind a flatty has no problem, can't help but go fast.
    Thinking of DSS on my Cox's Bay skimmer, I'd go to fixed DSS (but shallow angled) sort of inverted V foils, set at the narrow WL - that means, to those who worry about tying up to wharfs or pontoons, the foils would only protrude a little beyond the wide overall deck beam. I could live with that. The upwind Y would clear the water surface while beating, the leeward one would be always doing its job - therefore no moving foil problems. But there would be more drag. Also could be dangerous to curious swimmers wanting to get close when sailing past at speed though, which is what happens often with the skimmer. Must be the red sails.
     

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  12. Doug Lord
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    Doug Lord Flight Ready

    ================
    Gary, how long was/is the original "Lord Jim"? Can you sketch your fixed foil idea-sounds like maybe one side would be developing lift to leeward?? Take a gander at the Quant 28 sitting quietly with the foil sticking out either side:

    click on image-
     

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  13. Doug Lord
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    Doug Lord Flight Ready

    Dss

    An area of real world experience with a DSS foil(or any other foil) I'm interested in learning more about is the efficiency of the foil on the surface when it is acting as a high aspect planing surface. I've been told over the years, when I was just getting into hydrofoil design, that proximity to the surface is very important drag wise. I was told that a foil should be designed to be 2-2.5 chords below the surface yet I've learned that DSS works well shallower than that as well as working reasonably well right at the surface where it is planing.
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Doug, when I say angled V, I mean a very shallow angle, beginning just above the WL angling down so the tips are a little above the hull keel rocker line (for sitting on the hard without damage, a basic). And set at angle of attack of 3 degrees. The only time you could get negative angles there would be acute bow down (which probably wouldn't occur beating because the foil (set slightly forward of mid sections) would keep the bow up and near level. The windward foil, of course, is just clear of water surface. However the drag thing would be up. You also have to carry a conventional dagger. Whether the righting moment of the lee foil would compensate for the extra surface area drag? ... one would have to just S&S. However, in terms of self righting (actually great stiffness would be more correct) and getting rid of unnecessary ballast weight like a bulb keel, a sort of DSS system would be the way to go. I'm thinking dinghy more than keelboat. Get rid of lead, eh?
    The Lord Jim Flatty is around 15-16 foot.
     

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  15. Doug Lord
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    Doug Lord Flight Ready

    ==========
    Thanks-getting the lead out is surely a good thing! But I'm still having a problem: if you draw that hull heeled at 5-10 degrees and then look at the lee foil it will have a small component of lift to leeward, won't it? Do you figure it won't affect upwind vmg very much? Maybe you could zero it out with a gybing daggerboard?
     
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