Dinghy Design: Open 60 influence?

Discussion in 'Sailboats' started by Doug Lord, Jan 22, 2011.

  1. Doug Lord
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    Doug Lord Flight Ready

    It's occured to me with the Barcelona World Race where the top three boats today are all using lifting foils that maybe there is some potential design trickle down possible for dinghy/daysailer design.
    Years ago the Open 60 trimarans used curved lifting foils on the amas to reduce wetted surface and keep the lee bow up. In fact those foils would support up to 70% of the weight of the boat. Now there are quite a few smaller multies in the C Class, A class and others who have adopted curved lifting foils years after their big sisters proved they work.
    The Open 60 monohulls are using either straight angled boards or in the case of V3 curved lifting boards to aid control, reduce wetted surface and go faster.
    There are all kinds of options available now to planing hull monohulls to add speed with lifting foils-t-foils on the daggerboard and /or rudder, a DSS foil extending out from the lee side (which adds RM in addition to the other potential benefits) or the curved/ angled twin foils used on Open 60's.
    Does anybody see any potential in the trickle down affect of these design innovations resulting in new dinghy/daysailer designs?
     
  2. Cheesy
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    Cheesy Senior Member

    Not really, the hull shapes are wrong to start with. There have been quite a few boats designed to look like the open 60s but they dont go as fast as the scaled up skiff designs. Asymmetrical boards may be of use but the weight penalty, complexity and cost would rule them out.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Dinghy Design: Technology trickle down.

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    I wasn't thinking that there might be a trickle down of the "look" or hull shape of the Open 60 just the foil technology as happened in multihulls: pioneered in 60' tri's and now used on a growing number of small tri's and smaller catamarans....
     
  4. Cheesy
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    Cheesy Senior Member

    Kind of my point, their successful utilisation of these foils is in a lot of ways due to the hull shape and large canting keel. Skiffs (and all fast small boats) are sailed flat so they dont need the canted boards, there is even debate as to whether gybing boards are advantageous
     
  5. Doug Lord
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    Doug Lord Flight Ready

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    The key to this technology is that it physically lifts the boat. That would work with curved foils placed outboard pretty much regardless of the hull shape. A canting keel is not part of the technology or required for it to work on a dinghy since RM comes from the crew. Scows already use dual retractable boards. The trickle down that I think might be possible would be with dinghies designed to use retractable curved lifting foils in order to reduce wetted surface and increase speed-and I don't think the boat would have to heel a lot(like scows) for the foils to work. However, there are other technologies that might accomplish the same thing or even have better benefits like DSS- so I don't know. One thing about the curved or angled boards is that they would provide lateral resistance AND vertical lift whereas with DSS there would still have to be a daggerboard.
     
    Last edited: Jan 29, 2011
  6. CutOnce

    CutOnce Previous Member

    Square pegs for square holes

    Doug:

    Open 60's are ballasted keel boats where heavy canting ballast is used to solve a righting moment problem. This heavy ballast has the negative side effect of increasing displacement, wetted surface area and affecting planing performance downwind. Hence the benefit of lifting foils - at the price of some added drag and complexity in maneuvers, it reduces displacement and brings the planing performance up. Since Open 60s sail offshore, and course changes are infrequent by dinghy standards, the increased complexity maneuvering is acceptable.

    Dinghies built for high performance are as light as possible, have no ballast other than crew, and therefore do not have the same set of problems to solve and compromises to compensate for. Dinghy maneuvers are frequent, and crew are busier - as they are effectively replacing the canting ballast on the Open 60, as well as everything else they are doing. Adding one more task (dealing with tack-specific boards) to the list of things needing attention isn't easy.

    I think to some degree adding dual curved lifting boards to dinghies is putting a square peg in a round hole. There isn't the same problems to solve, and as a pure planing hull (unlike cats & Open 60s) decreasing displacement does not show the same level of benefit due to the added drag and complexity.

    I'm not convinced that a T-foil daggerboard used in a "foil-assist" capacity will provide serious net benefit as well. If full foiling is the objective, yes, the T-foil daggerboard provide huge speed benefit once lift-off is achieved. But until foiling it is a drag. Someone doing tank tests measuring drag, speed etc. might be able to convince me otherwise, but just from the conjecture posted I'd bet it a net loser.

    I do acknowledge the benefit of a T-foil rudder in making pitch control possible on planing boats - but that is not to reduce displacement - it is actually to maintain optimized pitch and minimize drag when planing.

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    CutOnce
     
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  7. Doug Lord
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    Doug Lord Flight Ready

    1) The fact that lifting foils work so well on Open 60's is a good reason why they should work even better on lighter weight boats.That they work so well on relatively heavy keelboats is truly an extension of the revolution in sailboat design that lifting foils represent-most people discounted the potential when I suggested this years ago. I'll post a rough sketch of a potential dinghy version of a curved lifting foil later today.
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    2) You might be aware that most scows use dual main centerboards and the Melges 17 uses dual main, asymmetric daggerboards. To have a daggerboard
    that can be toed in as well as have the ability to lift X percentage of the boats weight can't help but be advantageous as proven on the Nacra 20, A Class catamaran etc. The addition of a lifting foil to a dinghy has to be done carefully-the rule of thumb is that if you reduce wetted surface by 4 times the planform of the foil then you probably will have a cost/benefit ratio that adds speed in excess of the drag it creates. Examples already include the I-14(see page from Biekers paper below) where the foil lifts 400n(89lb) upwind at 9 knots. The sailing technique on the foil equipped 14 has changed to have the crew move max aft upwind so that the foil supports some of their weight. Other examples include the cats mentioned earlier and the National 12.
    You say "there isn't the same problems to solve", I beg to differ:the problem that curved lifting foils solve on V3 is SPEED and that problem exists on almost every dinghy -more speed is good. New dinghy designs that could produce higher speeds will generate interest and are a good rationale for exploring new speed-producing technology.
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    3) Well, the Bieker foil is not exactly a t-foil but close enough for jazz and of course it works well as does the National 12 foil. I don't know how much reading you do but there are numerous examples of Moths and R class boats partially foiling( "foil assist") and being faster than the version of the boat w/o foils. It is a matter of careful design and good engineering. "Foil assist"
    is not voodoo and its benefits are not hype: it can be applied successfully in a number of different configurations to a wide range of boat types. It cannot be applied beneficially to every boat but would be likely to benefit most planing hulls.
    =========================
    Whether the "trickle down" use of the lifting daggerboards from the Open 60's
    is viable or not is yet to be seen. My gut feeling is that versions of those foils
    may play a role in dinghy design-we'll see. It's taken 10-15 years for the lifting foils on big tris to "trickle down" to small cats so there's plenty of time.
     

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  8. CutOnce

    CutOnce Previous Member

    There is a fundamental disconnect here in how we think. Just because one technology provides a functional solution to one set of problems does not mean the same solution will work as well or better in a different situation. You see both situations as the same, I do not. I'll agree to disagree.

    As I wrote in my earlier post, the situation with a catamaran's displacement hulls is different than a dinghy's ultralight planing hull, which is different again from the canting ballast planing hull of the Open 60. What is advantageous on a Nacra 20, C Class is not the same thing on other boats.

    Scows are a different breed entirely from high performance dinghies. Their wide, hard chine hulls have far more form stability (and lower top end speed potential) than a planing skiff, and using twin asymmetrical foils to generate lift to windward certainly can enhance a boats ability to hold it's lane and eliminate leeway. Like any force in physics, the lift is accomplished through an increase in drag. I have not seen any scow designs today where generating vertical lift to reduce displacement is a design objective.

    Here where I sail there is an active and growing I14 fleet that includes boats from new Beiker 5s from Object 2 to Penultimates. People here use their T-foil rudders to bring the knuckle of the bow back down to the water's surface going upwind to reduce dragging the stern of the boat and enable upwind planing. Effectively, they are increasing wetted surface by bringing the hull flat on the pitch plain, while reducing overall drag. Yes, there may be 89 pounds of lift at the rudder, but it is done with a fulcrum point such that the lift is accompanied by an increase in displacement forward of the fulcrum. The lift at the rudder can not happen without effect elsewhere, therefore the total displacement of the hull isn't reduced by all 89 pounds. There may be some net improvement in displacement, but certainly not 89 pounds worth. You have to think systemically of the whole boat - lifting just one end isn't happening in isolation. If you've been out on high performance power boats, the same thing is done with trim tabs. Bow drops, more of the hull is wet, speed increases.

    Time will tell, but since there isn't a proportionately similar weight problem to be solved in dinghies, the benefit of a lifting foil will be proportionately smaller. My personal swag (scientific wild assed guess) is that the net benefit of lifting foils (other than rudder T-foils & gybing boards) isn't worthwhile in the face of added complexity, weight and drag. But that's just an opinion.


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    CutOnce
     
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  9. Doug Lord
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    Doug Lord Flight Ready

    Open 60 influence

    From a design standpoint, lift that reduces a boats wetted surface within the framework mentioned earlier(approx. + four times the planform area of the lifting part of the foil) is beneficicial regardless of the type of boat it is on. If designed properly the lift/drag ratio of the resulting boat is improved, it's speed is improved and perhaps it's handling is improved. It doesn't matter if it is a keel boat or a light dinghy, or a catamaran, or trimaran: if a lifting foil meets the proper design requirement the resultant lift will make the boat faster in the conditions when the design criteria are met*.
    Did you look at Bieker's "balance" sketch of the I-14 in my previous post? 89lb lift @9knots upwind.....

    * This should be apparent to anyone that does research on the wide variety of boats already using lifting foils successfully.
     
    Last edited: Jan 29, 2011
  10. Doug Lord
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    Doug Lord Flight Ready

    Open 60 influence: Reverse Curve Foils

    I came up with this last night. This is a preliminary, ROUGH sketch. The first impressions I have of the concept are that it combines the advantages of the curved foils on Open 60's with the potential advantages of Hugh Welbourn's DSS(without the possible disadvantages). DSS has the advantage of moving the center of lift outboard to lee allowing the lift from the foil to be converted to RM by the distance of the center of lift to the CB. I've always been concerned that DSS might position the foil too close to the surface and the reverse curve foils lower the foil while moving the center of lift outboard.
    Both DSS and these foils have the advantage of being retractable but the reverse curve foils have an additional advantage in that they don't require additional lateral resistance as does DSS.
    These foils are not limited to dinghy applications since the probability is they would increase speed and reduce drag on any planing hull boat they were used on. The amount of curve etc can be varied and tailored to the application. The version of the concept in the rough sketch below shows a high lift system with additional vertical surfaces(similar to those included in the Speed Dream concept by Vlad Murnikov).
    The reverse curve foils shown below curve in the opposite direction than do the curved lifting foils on Open 60's-or any other application of curved foils and as a result have greater advantages.
    See page four for more info on the down side of the reverse curve foils.--
    This video shows the "normal" curved foils on the super fast Open 60 V3: http://www.youtube.com/watch?v=-DfoBCIPfJY&feature=player_embedded

    click on image:
     

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    Last edited: Jan 29, 2011
  11. Cheesy
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    Cheesy Senior Member


    To clarify, the foil you have shown in the down position is the leward foil? If so, assuming a constant section (shape dimensions could change) would it not drag the boat to leward??
     
  12. Doug Lord
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    Doug Lord Flight Ready

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    The foil would most likely be toed in-like a rotated gybing board(or Open 60 foil)The section would Not be constant! Starting out at the hull as an asymetric section(flatish side outboard) then morphing into an asymetrical section flatish side down. Or the whole thing could actually be symetrical without significant loses-if any. The "lifting" part of the foil would have an adjustable angle of incidence by angling the foil fore and aft. The A Class cat "DNA" appears to have a good system for that.....
     
  13. Cheesy
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    Cheesy Senior Member

    Well you best bet would be to build it and see how well it works
     
  14. Doug Lord
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    Doug Lord Flight Ready

    reversed curved foils

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    I agree-maybe somebody will build it and test it before I can get to it. Seems like it has potential....See page four .
     
    Last edited: Jan 29, 2011

  15. Gary Baigent
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    Gary Baigent Senior Member

    Doug, the reverse curve foils are lifting more than creating a to leeward forces (since your drawing of foils are of a tight semi-circumference) - there will be some to leeward force but that will be counteracted by the much larger vertical and near vertical lifting forces. I think it is a good idea (noted that it is also Vlad's) because compared to conventional in facing foils, you get a larger righting arm. But constructing asymmetric (in, that is if you're relying on this section of the foil to counter leeway) to middle curve and then to asymmetric up and out will be tricky ... but not impossible ... perhaps better to keep the case and inner half of the foil symmetric for construction ease. But you're also stuck with an no angle of attack (for the outer asymmetric foil shape to move in the case - and therefore you're not going to be able to get the maximum lift such as an angled case/foil. Or do you see these problems differently?
     
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