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Thread: Which naca profiles for sailingboats

  1. #1
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    Default Which naca profiles for sailingboats

    Hi
    Could somebody explain me wich naca profiles are used for rudders , keels, centerboards and daggerboards.
    What are the pros and cons of these different types of naca profiles.
    A simple explanation would be appreciated.

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    Default Re: Which naca profiles for sailingboats

    I've forgotten all the details, but recollect being told by experts that for boats of anything but extreme performance, the NACA 00xx series are within a hair of optimal.
    For greater stall resistance, go thicker on a rudder than on a board.
    Damfino's daggerboard is NACA0009 and the rudder is NACA0012.

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    Default Re: Which naca profiles for sailingboats

    Max,

    I studied the book, Principles of Yacht Design, by Larsson and Eliasson, and found it quite helpful. There is a whole chapter on keel and rudder design, so it would be hard to reduce it all to a few simple statements. My boat, WindSprite, appears very close-winded, so apparently something worked out reasonably well. My copy of POYD is the 2nd edition, but a 3rd edition is now available.

    Frank

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    Default Re: Which naca profiles for sailingboats

    Rowan's CB and rudder are both NACA 0012
    If this post did not meet all of your needs, please consult this thread for more options.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by Max F View Post
    Hi
    Could somebody explain me wich naca profiles are used for rudders , keels, centerboards and daggerboards.
    What are the pros and cons of these different types of naca profiles.
    A simple explanation would be appreciated.
    The simple explanation... it's a mental thing, people feel good about having a "scientific" advantage in what ever sport they participate in and knowing you have a Space Age type foil sclicing through the water under your boat is a huge psychological benefit for some people, not so much for others.

    in reality on our home built wooden boats that generally sail at 5-12 mph...
    the finish/smoothness of the surface of the foil likely has much more effect on it's efficiency than a foiled shape.

    As long as your under water foils are rounded or oval shaped on the leading edge and tapered at the trailing edge there is little - no benefit from a meticuliously developed foil shapes.
    especially high aspect foils do benefit from shape but most of our boats do not have such needs.
    I have sailied several craft with flat plate type centerboards in company with craft with foil form boards and have seen no marked superiority in the foil boats...the plate boats often out pacing foiled ones.

    A foiled shape can have a negative effect on performance in that often foil shaped boards are wider than simple plate type boards, this added width means a wider centerboard slot and hence more turbulance around and in the slot when the board is lowered.

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    Default Re: Which naca profiles for sailingboats

    I used to sail anShearwater Yawl by Edey & Duff. Another boat had a pair of NACA-00XX foil leeboards which made the boat sail circles around my boat equipped with the original flat leeboarsa. Instead of semetric foils, the owner built assymetric foils based on a NACA-0009 foil, but with one surface being increased by 20% and the opposite surfaCE BEING DECREASED BY 20%, AMKING THEM ASSYMETRIC LIFTING FOILS. I wanted assymetric foils, but is casting about on the internet I met a fellow named Tom Speer who suggested a Laminar Flow Foil of his own design which he had tested on a sailing canoe. I used his profile design and my boat became competitive with the earlier boat, clearly outperforming that boat on one occasions over a course of 10 miles.

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    Default Re: Which naca profiles for sailingboats

    This is the foil shape (NACA0008-34) selected for the offset centerboard of John Welsford's SCAMP, a 11' 11" micro-cruiser.


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    Default Re: Which naca profiles for sailingboats

    I'm not hydrodynamics expert, but my limited experience... and all the reading I've done... suggests that a shaped foil can make a big difference.

    One thing I've learned form Michael Storer is that it's not necessary, for most of our boats, to have a perfect NACA foil shape. He has a scheme for home building that leaves the middle 30% or so still flat (and thus easier to clamp to a table and machine). The front 30+% is rounded and tapered. The back 30+% is likewise tapered down to about a 1/8" flat. What you end with is an easily machined blank that gives you a NACA shape minus the most bulbouse width in the middle.

    That shape gives the builder much less hassle to fabricate, and gives the skipper maybe 80-90% of the performance of a true NACA shape.

    I've used this scheme on two of my personal boats, and am quite happy with it. I've raced the one (PDR), and credit the good results to both good foils, and a large, professionally designed, balanced lug rig.

    Oh... and the scheme for these near-NACA foils can be had from Storer for about $20 by purchasing the plans for an OZ-Racer.
    David G
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    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: Which naca profiles for sailingboats

    Here's a link for a router jig that can enable one to shape NACA foil sections and it's free.

    http://www.duckworksmagazine.com/09/...oils/index.htm

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    Default Re: Which naca profiles for sailingboats

    Thanks for the replys.
    Very interesting to hear different opinions and experiences (like from Nicholas and Daniel).
    Please more!!!
    It seems to me that, if not a scary fast high performance boat, the naca 00XX series is very much recommended!
    I had a look at the huge french racing trimarans some time ago. Man, they do have VERY special looking foils!!
    But why uses Mr Wellsford the 0008 34? What is the supposed difference?
    Something very interrresting that Daniel wrote:
    The simple explanation... it's a mental thing, people feel good about having a "scientific" advantage in what ever sport they participate in and knowing you have a Space Age type foil sclicing through the water under your boat is a huge psychological benefit for some people, not so much for others
    in reality on our home built wooden boats that generally sail at 5-12 mph...
    the finish/smoothness of the surface of the foil likely has much more effect on it's efficiency than a foiled shape.
    I was asking myself that question too.
    Does it make that big a difference to have a propper made naca foil instead a foil shaped roundet and tappered by eye ?
    And how much affects a centerboard slot the speed of a boat?
    I suspected the latter an important issue too, so I closed mine with slightly overlapping mylar strips at the bottom.



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    Default Re: Which naca profiles for sailingboats

    OTOH, Tom Speer, the fellow who gave me the profile coordinates for my laminar flow assymetric foil counseled that the shape and finish of the foil was critical.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by kenjamin View Post
    Here's a link for a router jig that can enable one to shape NACA foil sections and it's free.

    http://www.duckworksmagazine.com/09/...oils/index.htm
    I've used this scheme for some Welsford foils. It does give an accurate rough shape, which one then cleans up. It's still time consuming and tedious - as well as very dusty and noisy. But... it works a treat for getting the shapes nice and symmetrical.
    David G
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    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: Which naca profiles for sailingboats

    Max, I offer just a thought, or three, regarding foils and section shapes, or otherwise...

    If your boat is going to scoot around in the lower speed regimes of say, 4-7 knots, then a stringently shaped board isn't going to make much difference for you... unless you are also going to race against fellow owners. If it's racing and you are looking to win, then the science of lift and laminar flow definitely come into play as an advantage... should you make use of the info that is available. If you are going to recreate, in a non-racing fashion, then the extra work and handling involved for truly well-fashioned foils will be unnecessary. Both of these points go out the door if you are a person who prides themselves on having a properly tuned and efficiently performing vessel, no matter the application. That position fully supports accurate planforms, section shapes, finish and well constructed foils.

    If you own a boat that is capable of higher speeds while sailing... as in more than 10 knots and upward, then a set of really good foils is a great benefit, whether you intend to race it, or not. They just simply give the craft better manners and look like they belong on a boat that projects power and efficiency through the water. If we were talking cars here, you wouldn't be putting the tires and wheels from your Mom's Toyota Corolla on a Porsche 911 and asking it to do remarkable things on your favorite twisty highway. So it's; Faster the boat, the more critical the appendages.

    The observation regarding NACA 0009 keel forms and 0012 rudders is a very good place to lay your hat. Different designers will prefer other sections for varying applications, but I think that you will find that they do not differ very much in the real world. Racing, is another matter and unless class rules stipulate, you will see folks experimenting with a variety of foil sections and planforms until one boat emerges as having the best overall set of foils. When winning is involved, a fever sets in and itís hard to shake.

    Daniel's comment about science in our psychological satisfaction zone is probably more correct than most of us care to admit. We humans are a smug lot. I would take Daniel's idea and apply it across the board to hardware, finish, details of construction, sails, spars... the whole tamale. All of boating is about science, one way, or another and we modern men have helped ourselves to a whole convoluted pile of interactive scientific issues every time we take the boat off the trailer to get on the water.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by Nicholas Scheuer View Post
    OTOH, Tom Speer, the fellow who gave me the profile coordinates for my laminar flow assymetric foil counseled that the shape and finish of the foil was critical.
    Yes... critical. But critical for what? For which boats? Under what circumstances? It's such an ambiguous word... and subject to context. It certainly seems to have made a big difference in your situation.

    My own impression is that the faster a boat goes, the more important the nuances become. My impression also is that some less sophisticated hull designs have enough built-in limitations that adding nifty foils or racing stripes will not help. Another impression is that having a nicely shaped foil at all (no matter which profile you choose, and assuming no other limitations) will be more effective than having a flat plate, and way more effective than having a badly shaped (rough and uneven) foil. Further impression is that smoothness helps a lot. I suggest carefully sanded glass/epoxy covered by a 2-part polyurethane to accomplish this.

    ETA - I see that Chris just expressed much of what I was getting at... and far more coherently!
    Last edited by David G; 04-07-2012 at 11:55 AM.
    David G
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    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: Which naca profiles for sailingboats

    This topic is among the most infuriating of all, I think. Nearly equal numbers of evidently intelligent and literate people fall to either side of a line and argue for flat plates vs. NACA 00##. The only agreement seems to be that gouges, bumps, and 60 grit finish on boards are always bad :-) -- Wade (now finishing an 'almost' NACA 0010 3:1 (wetted under boat) aspect ratio leeboard with a planned final coat of epoxy-graphite)

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    Default Re: Which naca profiles for sailingboats

    It takes very little extra work to produce good foils rather than just using a plank with the edges softened,in the overall scheme of building a boat.The first time you find yourself beating home against the tide and with the wind dropping as the light fades you will be glad of every bit of hydrodynamic efficiency.Make a choice and live with the result.You can always sail a fast boat slowly,its hard to make a slow boat go fast.

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    Default Re: Which naca profiles for sailingboats

    flat boards/rudders with a bit of edge round are ugly.
    foiled boards are pretty.
    that is all . . .

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    Default Re: Which naca profiles for sailingboats

    What I found VERY surprising was a series of posts here a couple of months ago from a guy in Europe showing us some VERY NICE Dutch assymetric foil leeboards for use on traditional Dutch Botters, etc (they have different names for different size boats, and I'm not convewrsant concerning them). These boards seemed state-of-the-art, yet the style of boat goes way, way back. The surprizing thing to me was that a few years ago I was casting about all over the internet, specifying things "Dutch" in the process of gathering background info, and none of this foil stuff came to the fore on Google.

    Considering the capability of assymetric foil leeboards, I'd never consider building a centerboard boat, however a guy in Austrailia mounted a pair of centerboards in the same case. Each had the kissing sides flat, with the outboard sides foiled. He would drop one or the other on the appropriate tack for more "lift" as he proceeded on a particular tack.

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    Default Re: Which naca profiles for sailingboats

    I helped with the rebuild of a rudder on a home designed small cruiser, the boat wouldn't tack reliably.
    We built a new rudder with an approximated foil and cleaned up the back of the skeg/propellor aperature.
    The results were dramatic, we copied off a well regarded woodie in the yard so I don't know the exact nature of the foil but the results justified all the work
    I would always take the trouble to put foils on any fin/rudder.

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    Default Re: Which naca profiles for sailingboats

    You confirm my suspicionsd, BriMac! I wanted to change my Shearwater Yawl's rudder from a rounded and tapered 3/4" flat board to a NACA0009 foil for a long time, but ended up selling the boat before that happened. Due to her long, straight, flat bottom, the boat always tacked slowly. I was convinced a foil rudder would have her tacking more quickly.

  21. #21

    Default Re: Which naca profiles for sailingboats

    I would say that there's more to the question than speed. It might well be the case that a slow boat that is inherently weak to windward will not benefit as much from good foils as a faster boat, but I can give you one datapoint that may be illustrative of another quality that can be enhanced by good foils. My little beachcruising catamaran Slider is notable for her good behavior under sail, and unlike many cats, she tacks well and easily, never missing stays except when I forget what I'm doing halfway through (fish on, other distractions.) She has good foils-- a NACA 0009 daggerboard and NACA 0012 rudders. But at least one of the folks who've built sister ships did not shape the rudders as carefully as I did, and his boat does not tack as reliably.

    In thinking about this, I've come to the conclusion that the less carefully shaped foils tend to stall and lose lift earlier in the turn, and this probably accounts for the not-as-snappy tacking.

    Slider is not a particularly fast boat, being undercanvassed for carefree cruising-- her fastest burst so far has been a little over 11 knots surfing down large waves. But she is amazingly well-behaved, so I think it's worth the small extra time to have good foils.

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    Default Re: Which naca profiles for sailingboats

    Thanks for your input Gentlemen.
    I still wonder what made Mr Wellsford choose naca 0008-34 for his SCAMP?
    Happy easter.
    Max

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    Default Re: Which naca profiles for sailingboats

    Lot'ta interest at present concerning SCAMP. Why not contact Welsford and get an answer right from the horse's mouth? I've tended to believe that the slower the boat, kthe thicker the foil profile. That is of course tempered byy other considerations such as the width of the CB case slot, the thickness of a pivoting rudder fin, etc. My Shearwater had laminar foil leeboards fully 2" thick. The other Shearwater with NACA 0012/09 (assymetric foil profile) had 1-1/2" thick leeboards. My thicker leeboards were not slower.

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    Default Re: Which naca profiles for sailingboats

    I worked in aerodynamics for a number of years in the aerospace industry a number of years ago and have followed this kind of discussion for many years. Foils shape is one of many factors that contribute to performance, but it is not the only one. The old NACA sections are certainly well tested and reliable, with optimized shapes for good performance. The laminar sections improve performance a little, but at the sacrifice of sensitivity to clean flow conditions. Personally I would not go with laminar sections unless you are trying to squeeze the last micro-knot of speed out of it, they are sensitive to shape, surface finish, and must be always keep clean to work. Upstream flow conditions must also be smooth (free stream flow). A laminar section that trips the boundary layer because of bad shape, or poor finish (or a dirty surface), will behave much worse than a non-laminar section and sometimes give twitchy performance, transitioning back and forth between laminar and non-laminar flow unpredictably. Just not worth it for a fun recreational boat.

    The thickness of the foil does not have as much affect on stall as much as the plan form aspect ratio, you go with the thicker sections where you need the extra strength of the foil. Thinner usually results in better performing foils, but you either need much more costly materials to make the thinner sections strong enough to work. So usually thickness is a trade off with cost vs. performance, not stall characteristics.

    To make the rudder more stall resistant go with a lower aspect ratio plan form (Length to width ratio). The higher the aspect ratio the surface, the lower the induced drag, but the more sensitivity to stall. Usually what you want is as high an aspect ratio on the dagger board as you can build, and than use a lower aspect ratio rudder. That way the rudder will not stall out before the dagger board does.

    The fit of the dagger board slot around the dagger board is also very critical for good performance, and has as much an influence over drag as anything else. Centerboard slots are far more draggy than a dagger board, and should be avoided if you want performance. A rudder mounted on the bottom of the hull is also more efficient than one hanging off the back, it gets advantage of the end plate effect of the underside of the hull. They both increase effectiveness of the surface and reduce drag, a double benefit.

    That said, any rounded leading edge, and pointy trailing edge surface will work as a foil. And on a low speed sailboat you will not notice a lot of difference. If you can make an accurate foil section without too much trouble, than you have it made, but just "eye-balling" the shape (perhaps with a foil template for reference), you will make a reasonably performing dagger board or rudder that will work fine with a low speed sailboat. If you want to win races in one design class however, you will need the accuracy of an optimized foil.

    And do not neglect the actual "engine" of the sailboat, the design of the sail and rigging. Some recent tests seem to indicate there is as much to be gained by paying attention to aerodynamic drag of the sails and rigging as much as the hull, which is something I have always suspected, but was always poo-pooed (or just ignored) by the sailboat builders.

    Good luck.

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    Default Re: Which naca profiles for sailingboats

    When you are shaping a pivoting centerboard to whatever NACA shape it is you've decided on, where do you set the curve? Parallel to the waterline with the board in the "down" position or across the shortest width of the foil? Dagger boards and rudders, being fixed in their relative positions to the waterline would seem relatively straight forward, set it to the waterline, but how do you account for a board that won't be in the same plane all the time?

    Steve

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    Default Re: Which naca profiles for sailingboats

    Petros - Thanks for sharing your expertise with us.

    stromberg - I simply make the foil normal to the position the blade with most typically set at.
    David G
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    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: Which naca profiles for sailingboats

    But things are never equal...

    I was always for profiled boards untill I sailed our Tirrik with a metal plate. The plate is 6mm thick compared to a 30mm thick profiled wooden centerboard. In the words of Chuck Paine "what isn't there, the water doesn't have to go around...."

    Our Tirrik sloop with a metal plate and new sails, outpoints a 420 with a Milanes centreboard (very expensive profiled blade) with old sails. Both going at the same speed upwind.

    Its made me question whether it's worth the time, materials and trouble making profiled centreboards since I have to make it, especially with narrow tippy light plywood sail and oar type boats that can usually do with a bit of ballast and extra stability of a metal plate also. Our Tirrik sloop seems to go to windward as well as any sloop does: 30-40 degrees off the wind. And that's higher than a low aspect lug rig, no matter what you do to it. A true NACA shape is going to require CNC machining in most cases as it tapers and gets thinner towards the tip requiring a change in shape and thicknes - a complex thing to achieve with a hand plane.

    Profiled boards no doubt do make a difference, but that's assuming the other boat is the same design, same crew, same crew position, same sail planform, same sail adjustment, same sail entry adjustment, same foil adjustment, same sail age and same helm balance set up etc. I think the advantages for rudders are clearer as they are used at much high potential stall angles when turning sharply and benefit from being thick(er) and rounded leading edge to hold the water flow around the blade as it turns.

    Bottom line, sailing a boat with a metal centreplate in practice for the first time, made me re-think: simple metal plates can work very well if the rest of the boat is well set up and not be a limiting factor at all. For most 'cruising' types building a wooden boat for pleasure, often under crewed, they deserve serious consideration: the thinness, ballast etc must give gains in other areas and there's less labour to make one. The ballast affect of a metal plate compared to a floating wooden board can contribute performance in other ways: sailing more upright also helps the boats wave making resistance, wetted area and sail exposure when its windy etc...the thinness must reduce turbulence, wave making resistance and wetted area. There's no worry of dinging it either, though I accept the bending risk.

    In the local 12ft scow racing, new boats with metal plates have beaten boats with profiled centreboard blades, and the racing is serious. These are lugged rig boats, so maybe the sail planform limits pointing before the foil shaping does. High aspect foils have to match high aspect sail plans etc for it all to work optimally. These boats are all travelling at low speed 2-5 knots.

    Most text books are written from a keel boat perspective, where the ballast has to be put in down in the keel, this take alot of space and so the keel had better be shaped rather than a wide brick shape. Not so with small centreboard dinghy designs where the keel or centreplate can be made very thin as its not having to contain large amounts of ballast. I think there are 'unknown unknowns' with them. I'm certainly not dissmissive of thinner metal centreplates at all. That and metal alloy spars and you'd be out with it quicker...boat building is fun but so is being out there. Working away to get a project finished through a cold winter isn't much fun. Easy metal centeboards also offer less potential 'drag' in that regard. After actually using one, I wouldn't think twice about using one now for a traditional sail and oar displacement lug rigged type boat.

    Ed
    Last edited by keyhavenpotterer; 04-10-2012 at 05:37 AM.

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    Default Re: Which naca profiles for sailingboats

    If you accept the one size fits all quote from Paine, then why in the world are you bothering to sail monohulls? Multihulls are whole lot skinnier through the water than those tubs you describe. ;-) Building a proper foil isn't any more difficult than sorting your rigging, routing sail controls, building your boat, or maintaining the thing in good working order.

    One does not need to go the CNC route to get a terrific foil, either. A simple set of templates, a scribed, or pencilled, centerline on the exterior edge of the planform blank and a few tools that one probably already has in their pile of stuff out in the garage... that's it. There's no big voodoo with a fermented drink ceremony and some scary old broad with her hair in rollers waving a spatula at the process. Just straight forward and very easy shaping work that can be reduced to a mostly mechanical exercise with a little prior planning.

    I wonder if that Paine quote will work for the sail, as well?

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    Default Re: Which naca profiles for sailingboats

    Hi Chris,






    I can make a nice foil...

    Trouble is...to get that...its old growth tight grained yellow cedar (30 rings per inch) quarter sawn, then cut into strips and grain alternated (to be sure it won't warp)...then its planform cut (minus the trim strips) then the sapeli - hard dent resistent cover clamped on - all glued with resorcinol so it'l last...and so the bottom strip covers the grain over the strips...then you have to mark it out for NACA'ring, then cut into into with a japanese back saw for markers, then plane it with a block plane with the grain to avoid and tear out...then be careful at the ends planing into the piece. Then it gets sanded..60 then 120 then 200 grit. Then it gets vacc'd to remove dust and the first of 10 coats of Tung oil varnish. The first one slightly diluted to soak in. Oh...and the bronze bush and pin had to be purchased before starting, the hole drilled from each side to avoid tear out perfectly 90 degrees to the planform and the bronze bush epoxied in the correct width as the finished blade. This is the rudder. The centreboard needs three layers of glass and epoxy with carbon additive, then priming coats, top coats and a final matting finish.. A wash and a sand between each layer. Ideally leaving it stiffer at the hull exit point than the blade tip so it'l flex just a bit, but still hold my weight on it when pulling the boat up and not get dinged to easily.

    Its work.

    Trouble is...I did it like you say...I knew at the time and know its imperfect.

    To do this properly...we are going to the trouble of NACA 'ring it...the planform seems best if its eliptical. Now that means it gets narrower as you go towards the tip (and I'm assuming this is a high aspect foil thats almost straight down so it knocks up still if it touches). Now if it gets narrower, to be correct, as I remember when I researched into all this, the blade should also get thinner in cross section, additional to its naca profile. So, if its going to be perfect you've got to thin your board down perfectly flatly as it narrows too. That's possible by pulling it up through a thicknesser or going at it with a plane or router jig, but I felt that was getting out of hand...a 3d CNC milling machine is the tool here to get perfection. Going at it with a plane will leave it with dips and hollows.

    Just sayin..after a sail in our Tirrik with a thin metal plate, it pointed 30-40 degrees off without all that trouble anyway, so I'm just not sure its worth it. The trouble with naval architecture...its a retrospective science...we know what we know, and its presented as all there is to know, but don't know what we don't know.

    As mentioned earlier, for a centreboard, the moment its half up on a reach, the NACA section streaming through the water is now going at 45 degrees, and its all wrong: one advantage to the daggerboard, at least you keep your 'NACA' profile no matter how much is immersed.

    To get upwind, we adjust sail camber with outhaul adjustment, to go from a fat sail to a thin narrow entry one to point higher. Well that flat narrow metal plate has a narrow entry and there's a fifth the cross sectional area to pull through the water as we go forward...water is viscous stuff, maybe there's less drag there...

    If I build a Tirrik for myself I'd include a metal plate having sailed one, I'd just go to a metal shop with a patten, pick it up in the afternoon, galvanise/ paint it and stick it in and save myself a months work of weekends. No slot gasket, just a nice tight 10mm gap maybe, a quater of the usual space generating turbulence. I'm converted to metal plates now from that NACA bother after a life of sailing profiled boards, just sayin. I'd say its at the bottom of the list, after sail plan, hull design, how its sailed, rig set up etc, in terms of what it achieves: our sloop Tirrik points higher with a metal plate than can be achieved with a lug rig and a profiled board, and I wouldn't expect it to point higher than it was doing: it was going like only a sloop can. Maybe it matters with two identical boats on the same course with the same crew, but for a home built boat as a one off, usually cruised, low aspect sail plan, needing ballast, sailed alone...not sure its actually worth the trouble, now having sailed a boat with a 'plate (and know whats involved profiling a centreboard properly) and that the weight of a plate might make some boats better for what the owners are doing with them.

    Cheers

    Ed
    Last edited by keyhavenpotterer; 04-10-2012 at 12:19 PM.

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    Default Re: Which naca profiles for sailingboats

    Looks to me like you are describing a labor of love. I'm just wondering if maybe you also loaded-up the process with the labor's expectations while you were at it? A board of equivalent capabilities can be made a whole lot faster and be just as durable.

    Of course, you are allowed to use any methodology you like, no matter how out of kilter it may be for a proper comparison. I'm not gonna agree that a metal plate that gets galvanized and painted is going to give you that something extra. Let's also note that the boats you chose for comparison originally... The, "Our Tirrik sloop with a metal plate and new sails, outpoints a 420 with a Milanes centreboard (very expensive profiled blade) with old sails. Both going at the same speed upwind." is as far from scientific as one can get save for not going sailing at all. New sails vs old sails... really? and the result points to the metal board as the reason? Different hull shapes, different trim states (due to sails), different crews, different just about everything?...

    I mentioned multihulls to you as suggestion about boats that are skinny. Take a monohull with 220 ft. of upwind sail, race it against any of a number of beach cats, which are not known for their hard nose pointing ability, and send them off upwind to a mark somewhere across the bay. Pointing, or not, I'll wager that the cat will get there first by a very wide margin and that the precious ability to outpoint is rendered moot by your example. By the way, pretty much all modern beach cats use foil shaped boards in a sport where even small amounts of lost performance show-up as huge issues at the finish line.

    I'm kinda preferring the lengthy studies having been done by the Bethwaites, thousands of working NA's past and present. The entire collection of NACA work, the extensive work by Eppler, et.al. etc., as being more dialed-in to the essence of the argument. It may just be instructional to note that the 49er sailboat, as designed by the Bethwaite clan, uses shaped foils of precision specification in order to extract their remarkable sailing capabilities. It might be interesting to show-up at a 49er regatta with metal plate boards and give it a go, new sails, or not. I'm betting that you won't be able to hang with the fleet. Boat speed and lift to windward are not the realm of flat plates.

    Ed, this isn't new stuff here. I love that you have a desire to go where your investment in time takes you, but it's off the beaten track in the industry. Surely you know that? Just curious, but is it because your boat needs the extra, added weight to behave better?

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    Default Re: Which naca profiles for sailingboats

    My problem with the NACA-knows-best school of thought is based on where those foils come from.

    NACA designed aerofoils (up to the 50s) for a medium which is compressible and of a very different density and viscosity to water. Wing designs for high-speed flight in a powered aircraft in more-or-less stable air would suggest that slavishly copying designs for low-speed sailing in choppy and moving water, each operating at quite different Reynold's numbers, are not optimal.

    Call me a luddite, but the objective of the centreboard is to prevent leeway when sailing upwind - its job is to provide the "reaction" to the sail's "action": that subtle imbalance of forces which results in forward motion.

    Granted, basic experience of drag would give us the sense to round the front edge of a centreboard, and shave off a blunt rear edge, but I wonder if more extensive shaping provides any perceivable benefit in real world use at typical wooden boaty speeds?

    Andy
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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by AndyG View Post
    ..... I wonder if more extensive shaping provides any perceivable benefit in real world use at typical wooden boaty speeds?

    Andy
    I suspect that the answer might well depend on what you were using to do the perceiving....

    KHP's comparison of a sub-optimal foil teamed with good sails outperforming nice foil and poor sail doesn't really come as much of a surprise.

    I suspect that while the simple flat plate is often "amazingly adequate" - it might not appear on his racing scow.
    Even when they work, they don't work well. I blame engineers.
    The only thing engineers have done to the toaster in the last 80 years is make it disposable. I think it applies to a lot of things

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    Default Re: Which naca profiles for sailingboats

    Chris,

    I think we're trying to say the same thing.

    A NACA foil is efficient, but its more efficient to choose a good boat design, a high aspect rig, rigging controls and flatter cut sails if you want to go upwind well.

    My comparison with our Tirrik to the 420: I'm trying to show that just putting a nice foil in a boat, isn't going to make it outperform something with a metal plate if you've chosen poor or old sails, a low aspect sail plan, a boat design that won't point or is insufficiently crewed.

    You will also get passed by someone whose chosen to build a long thin boat with a LWL than a short dumpy one of equal materials and weight, when max velocity come into play. So by inference a NACA foil is low down the list of importance to how your chosen transport goes upwind.

    I'm talking absolute terms.

    Our sloop rigged Tirrik with a metal plate will out point James McMullen's lug rigged CNC NACA foiled Rowan. He's chosen his lug rig (as I would) for its many advantages and decided that he's prepared to loose 10 degrees of pointing for all its good points. Our high aspect sloop rig trumps the NACA foil (by my estimation about 10-15 degrees) but we have to put up with all the rigging hassle. James can show me his NACA CNC centreboard, but I'd still outpoint him in real terms on the water. So if you want to outpoint James, don't slave a NACA foil for a month, just order a set of bermudan sloop sails when your choosing.

    In another example close to your heart, quarter tonner with a high aspect foil and rig gets to New York upwind at the same time as a Tiki 21 when raced accross the atlantic. The Tiki has no 'foils' at all. None. Its just fast. There's no point in pointing to the quarter tonners realtive efficiency upwind with maybe a NACA keel. It was no better than a Tiki 21 in absolute terms. A boatbuilder can just cut to the chase and build a design that's fast or points well in absolute terms even if its less efficient: he's only interested and measuring absolute performance.

    The theoretical comparison of competition is always identical boat v identical boat, crewed identically on the same course at the same time. In relavence to our Tirrik, we'd only be theoretically worse off in a race, with another identically built Tirrik, with the same rig, same sails, same crew, same adjustment going in the same direction, before the NACA foil came into play. I doubt I'll even ever see another Tirrik. I'm not dissmissing what's know about NACA foils, just that woodenboats are built by individuals in such an individual way that no two are at all the same. So the typical home builder wants to know will my sailboat go just fine on the water when I'm out on my own, if I cut out a months work and pop in a quick metal plate to save me trouble. And yes, they do go very well, And the time saving is very real. Rigging a clew outhaul adjustment to reduce sail camber or a cunningham are other examples that could make a big difference and are far more efficient in time to help upwind. Nobody on this forum can be interested in match racing, or they'd be somewhere else. Any custom one off builder free from one deign racing is free to make gains in boat speed, with bigger light air sails for example or more crew in high winds or make it give it a longer LWL to raise its top speed, add a cunningham or clew outhaul, all those will have a greater say than a NACA foil. Its more important to choose other things like a higher aspect rig and have decent sail adjustment etc first than NACA'ing the centreboard if you want to point 30/40 degrees off, like our Tirrik does (with plate).

    That the boat might behave better with a heavy metal plate is perfectly justifiable reason for having one. Beyond the speed of assembly (an afternoon), if it keeps it more upright and at correct displacement, she might be stiffer and stand up to a blow better than a wooden unballasted floating (and trying to upturn the boat once its off centre for example) foil. If she's more upright perhaps it has less wetted area and less wave making resistance too. Metal 3ft down might be leave it stiffer than metal in the bilges.

    Most home built wooden boats have lower aspect sail plans and lower aspect foil plans, and are cruising not racing. I'm just saying, its my observation that you can save yourself a heap of work, stick a flat metal plate in for a centreboard, and go sailing. If your boat is a good one, with good sails, well rigged and with a high aspect sail plan, you can still be pointing respectfully high. Those things matter first.

    You can point with a thin flat metal plate. There just not cool. Now I know how much time you save over a making a NACA wooden foil, next time I pick mine up from the metal shop, it'l be with a sly smile. They go just fine in Tirrik's anyway. Oh yes indeedy. See you out there!


    Ed
    Last edited by keyhavenpotterer; 04-10-2012 at 03:16 PM.

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    Default Re: Which naca profiles for sailingboats

    1. Thumbnail(75 x 100)


    1. Small 240(181 x 240)
    2. Small 320(241 x 320)



    1. Medium 500 (377 x 500)
    2. Medium 640(483 x 640)



    1. Large 1024(772 x 1024)









    Here are the facts regarding a pair of assymetric, laminar flow foil leeboards on my 28-ft Shearwater Yawl. I measured the leeway over a course of several miles in a fresh breeze and found virtually no leeway using the foil leeboards. With the original flat leeboards the leeway was significant.

    The well-rounded leading edge (profile) was most certainly done on purpose, so that when the leeboards were raked for shallow water, the tip would present a nicer flow of water at the lower end of the leeboard.

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    Default Re: Which naca profiles for sailingboats

    I wouldn't really use a 420 for comparison purposes.If memory serves,they have a parallel board with tapering allowed over a specified distance near the edges,some way removed from a full foil section.
    The practical problem is the need for a really fine trailing edge,which if you don't glass or carbon sheathe it,will be very delicate.I can only agree with the point about valid comparisons needing to be validated by watching the results of a number of races.Which may be why I know of no racing classes,in which a choice is allowed,where lug rigs or metal centreplates are preferred.Obviously a good rig is important as well but the foils in the water have to work in conjunction with the foils in the air.Deficiencies in either can only impair the potential performance.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by keyhavenpotterer View Post
    A NACA foil is efficient, but its more efficient to choose a good boat design, a high aspect rig, rigging controls and flatter cut sails if you want to go upwind well.
    By pure symmetry, it's pretty much arbitrary whether you think of the wind as pushing the boat through the water, or the water as pushing the boat through the air. That little centerboard, only 4% the size of all the sails (or so) is doing exactly the equal amount of effort! Minus that which is attributable to the hull, of course.

    They both deserve equal attention to detail, in short.
    It will all be OK in the end...so if it's not OK, you're not at the end.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by Y Bar Ranch View Post
    They both deserve equal attention to detail, in short.
    I'm just not sure they do.

    Our 150kg 17ft Oughtred Tirrik gunter sloop dinghy goes upwind at 30-40 degrees off the wind in a Force 2 with two people in it, with a thin 6mm wide flat high aspect Oughtred planform metal steel centreboard with little appreciable leeway with good speed powered by new professionally made sails:a bermudan main and jib. I know its contrary to what the text books would say. I've read them too. But that's the reality and an honest observation. It's left me thinking foiling centreboards might be a bit of a waste of time, as thin flat centreplates seem to be able to achieve perfectly good performance in actuality, if everything else is right, and its no work. I was very surprised. Boat turns fine too, doesn't stall. Before the Tirrik, I would have been equally dissmissive, but not now. I'll leave it at that.

    Ed
    Last edited by keyhavenpotterer; 04-10-2012 at 05:35 PM.

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    Default Re: Which naca profiles for sailingboats

    There may be lots more unknowns than is generally recognized. Boat design seems to me an inherently conservative preoccupation, in the sense that few designers are willing to diverge wildly from the work their peers are doing. Longtime members here may recall that I caught a lot of crap for putting a sprit-sloop rig on my little cat, because, the experts said, it wouldn't point and it wouldn't be fast.

    Neither turned out to be true. The boat is very conservatively rigged, with 140 sq feet of sail, and as a cruising boat, is much heavier than beach cats with the same length and beam and well over 200 sq. feet of sail, so I didn't expect beach cat performance. Naturally, I didn't get it. But it has been surprising to me that to windward at least, the boat points higher and goes faster than Windrider 17s, the little rotomolded plastic tris that are a hoot to sail. The Windriders have almost exactly the same amount of sail in a high-tech, fully battened main and fractional jib, but instead of a daggerboard, they have a molded in minikeel. They weigh substantially less than Slider as well.

    Anyway, it's at least another datapoint in support of the idea that foils (and hull shapes) are equal in importance to rigs and sails.

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    Default Re: Which naca profiles for sailingboats

    Quote Originally Posted by keyhavenpotterer View Post
    NACA foil is low down the list of importance to how your chosen transport goes upwind.
    "hit the nail on the head"

    thats exactly what I was trying to say (in many more words) in post #5

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    Default Re: Which naca profiles for sailingboats

    "Hit no nail on the head"... and wandered around the landscape making comparisons that hold little connective tissue, calling them valid points in a disconnected argument. The, "Our Tirrik sloop with a metal plate and new sails, outpoints a 420 with a Milanes centreboard (very expensive profiled blade) with old sails....". I'm fascinated that a displacement sloop of the variety called-out and a trapeze rigged planing craft, such as the 420, are even mentioned in the same breath, much less compared on any level. That the argument is so drifty to include the admission regarding state of sail condition, and still goes on to use the event to justify a barely worked metal keel form, is less than well-founded. If there is a nail in that jumble, it's invisible... as is the hammer used to strike it.

    What is absolutely remarkable here in all this flat plater stuff, is the nearly complete disregard for all the research done on section lift, drag buckets, Reynolds numbers, foils as tested over the years by countless tank sessions for the AC, as well as other racing classes... and the critical study work of thousands of Naval Architects since day one on this topic. Let's just toss that whole body of work in the bin and instead opt for the no-tech answer when all the science has long been done for you and it's easy to replicate with a modicum of toilage and skill. Something saddens me when I see these kinds of discussions and there is a cadre of flat platers, for instance, who are adamant about their low wattage solutions. These are the same folks, mind you, who will diddle around with one knot, or another, for a given task, or how many coats of varnish are needed to seal a soft wood core from water entry, or, who is going to build their retro sail kit and with what cloth will it be made, or which seat thwart arrangement is going to give them that saltier than thou look when they arrive at the ramp. It would be sad if it weren't so amusing.

    And Ray, I think that you will find that the designers aren't conservative at all. One look at their private portfolios will show you the facts in the matter. The conservatism is in the end user who tells the NA what kind of boat he wants and that's where the snappy fresh ideas get rubbed right off the page. If one wants to advance the craft with fresh big stick ideas, it is best to approach this kind of consumer by bending them into the fold, so to speak, one increment at a time. Large leaps do not make for excited buyers. The tire kickers will be salivating to death over a bitchin’ cutting edge ride, but they aren't the ones who actually snatch-up the plan sets.

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    Default Re: Which naca profiles for sailingboats

    This has been an interesting discussion. I had an inappropriately made mostly flat center board that cupped so badly it was hard to raise and lower. As a result my Caledonia Yawl pointed noticeably better on one tack. I made a nicely shaped board sheathed in a layer of glass and epoxy to replace it after reading a little about foils and I was amazed at the difference it made. I'm not sure where that puts me in this discussion, but I am definitely a believer in devoting some attention to the shape of center boards.

    Jim
    Eternal optimist and a slow learner.
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    and a new SOF Whitehall too.

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    Default Re: Which naca profiles for sailingboats

    ...some attention, yes. But I'd argue that the rudder's the first thing we should think about optimising: this plate needs to be angled to the direction of travel, without stalling for as long as possible, in order to do its job.

    The centreboard is fixed to the long axis of the hull. Does it ever operate at angles of attack above a few degrees? Always in a low-speed regimine? Flat plates work ok in certain circumstances.

    Andy
    'There isn't a lovelier place in all the world,' thought Dorothea.

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    Default Re: Which naca profiles for sailingboats

    Keep in mind that the leaders in assymetric "lifting" foils use them on the most "conservatively designed" types boats extant, the Dutch Botters and similar gaff-rigged, bluff-bowed, extreemly massive, shallow draft ilk.

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    Default Re: Which naca profiles for sailingboats

    This is a cool little web app. Obviously not to be used for design! Didn't check the reynolds number ranges, but you can compare L/D for different shapes to include flat plate and something that ia probably close to NACA 0012. The flat plate is idealized, of zero thickness.

    http://www.grc.nasa.gov/WWW/K-12/airplane/foil3.html
    It will all be OK in the end...so if it's not OK, you're not at the end.

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    Default Re: Which naca profiles for sailingboats

    A lot of this is not very rigorous armchair theorizing, gentlemen. Comparing one boat with another, different boat is not all that useful in figuring out this question because you haven't limited and isolated all the variables. The correct experiment is to test two boats that are otherwise identical except for the foil, or to test one boat where you first install one type and then test again with another type installed.

    I have actually done this sort of experiment with a leeboard versus a daggerboard in both a Bolger Teal and a Chamberlain Dory Skiff, and I have done another experiment with a flat plate centerboard with rounded edges versus a carefully shaped foil in a Ness Yawl.

    When I built Rowan a few years ago, the culmination of 41 previous false starts, approximations and accumulated boating and boatbuilding experience, I most definitely did not settle for either a leeboard or a flat plate. I agree with jsjpd1 and think a properly shaped foil is totally worth the effort.
    Last edited by James McMullen; 04-11-2012 at 08:10 AM.
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    Default Re: Which naca profiles for sailingboats

    As did I, James McMullen, sailing my Shearwarter Yawl TRUE NORTH sailing abreast of another Shearwater Cat Yawl, ARDEA. I sailed my boat in company with the ARDEA in circumstances both with, and without "lifting" foil leeboards. The results clearly favor assymetric "lifting" foils. The only significant difference between boats was my Yawl rig (an Edey & Duff experiment) against the other's Cat Yawl rig (as designed my Bolger). The total sail areas were comparable.

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    Default Re: Which naca profiles for sailingboats

    Sailing in a straight line at or close to hull speed with a well balanced rig, any reasonable sized fin will do fine, flat plate or elegant foil. the fins, whatever their shape, are generating all the lift required. Where a good foil shape is important is at lower speeds and higher angles of attack, especially if the foils are undersized. I turned a dog of a boat into a decent sailor by making a slightly larger daggerboard with as good a foil shape as I could get in the narrow slot. I've been frustrated enough by centerboards and/or rudders stalling at inopportune moments to be firm believer in the value of a well shaped foil.

    Allan

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    Default Re: Which naca profiles for sailingboats

    At something less than hull speed in a force 2 wind the difference in VMG between my boat and the ARDEA was something like 10-degrees, and I was significantly slower.

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    Default Re: Which naca profiles for sailingboats

    James,

    By choosing a low aspect lug rig, you've lost more to windward than my high aspect bermudan and choosing a flat plate.

    My Tirrik will outpoint Rowan by 10 degrees. The flat plate is ZERO work. In a race to windward I'd beat you by some distance.

    My boat will take fewer hours to build.

    The three spars of a gunter are the same length as a lug. You just say bermudan main and jib to the sailmaker not lug. No work there either.

    My choice is more efficient to windward than yours in absolute terms and in speed to windward per man hours invested. I might be 3% less efficient than if I had a NACA foil, but I'll still be outpointing you to windward because of your rig choice.

    I'll only be worse off if I meet another sloop rig Tirrik, built, rigged and crewed like mine, with a NACA board and we're going upwind, racing and in close proximity. Then his NACA board would come into play and he theoretically might outpoint me.

    A low aspect sail plan looses far more to windward than using a flat plate. Your CNC NACA centeboard might be optimum to windward but your low aspect rig isn't. There's a reason low aspect sail plans were dropped overnight when bermudan's came along...sail planform and adjustment is a much more important variable.

    Really, as I've found out, don't snigger at someones metal plate next time your on a beach looking at boats, because if he's got a bermudan, and your in a lug or gaff, he'll still outpoint you, no matter what foil you've got. An uncomfortable truth I know. NACA away boys!

    Ed
    Last edited by keyhavenpotterer; 04-11-2012 at 10:37 AM.

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    Default Re: Which naca profiles for sailingboats

    Is it really only to windward when a foil comes to work ?
    What about a beam reach?
    The conversation gets a little hot tempered Gentlemen ;-).
    Sure, many factors come into play to get a craft sailing fast and comfortable.
    And I guess all of us know that.
    I would prefere to keep the focus on foils isolated.
    cheers
    Max

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