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Thread: Lee Boards

  1. #1
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    Default Lee Boards

    A comment in another thread got me thinking about lee boards. I know some people don't like them, but I like the look, very traditional.


    Not having a centerboard trunk in a small cruiser is also appealing. Does anyone have actual experience with them they would be willing to share?

    Thanks,
    Perry

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    Default Re: Lee Boards

    I love Gretchen and Helga!
    My experience with leeboards has been with canoes and they are very handy. One board adequate, mounted to port is the canoe tradition.
    Some use twin but I prefer one.
    Maybe someone with a Dovekie will chime in.
    Live and let live

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    Default Re: Lee Boards

    I believe leeboards lend visual interest to an otherwise plain sheer. I may be prejudiced; most of the sailboats I've owned had leeboards; a kayack, a canoe, a 14 skiff, a Dovekie, and a Shearwater Yawl. You are never in doubt as to how your leeboards may be fouled; not like centerboards, especially when they get tangled up in trailer cross members at a launch ramp, or in shallows choked with weed. And Leeboards are always a good conversation sparker in any marina.

    Moby Nick

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    Default Re: Lee Boards

    I've used them. I found the performance to be poorer than that of the identical boat with a daggerboard. I actually did the experiment with a Bolger Teal, and then retrofitted a DB case to a Chamberlain Dory-skiff that had started life with leeboards, both with utterly clear results. The explanation that seems to fit the phenomenon is that a surface-piercing foil like a leeboard has an inherent disadvantage over an end-stopped foil like a CB or DB or a fixed keel. Because of the vortex that can be dragged down the leading edge at the air/water interface, a leeboard needs to be relatively larger and thus have more wetted surface area than an equivalent end-stopped foil. The faster and more performey your boat is, the more of an issue this will be.

    Depending on your other requirements, you might be content with trading some drag and extra wetted surface area towards opening up the inside of your boat for cruising purposes. But for myself, I found the losses to be intolerable. I do think they look pretty darn cute on a genuine Dutch botter or hoogaars though. (But those ain't no high performance racing sleds, neither!)

  5. #5
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    Default Re: Lee Boards

    What's an "end stopped foil"?
    The cure for everything is salt water - sweat, tears, or the sea
    Isak Dinesen

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    Default Re: Lee Boards

    One where both ends are immersed in the fluid in question, as in a centreboard or daggerplate. Leeboards have the lower end immersed in water but the upper end in air.

    I've also used leeboards in sailing a kayak, twin ones in my case. The designer recommended that the weather one be raised, so each was pivoted. But it was such a business that in the end I just left them both down. They certainly increased drag, but on the other hand they made sailing possible -- no room for a c/b in 27" beam.

    Mike
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    Default Re: Lee Boards

    thanks for the replies everyone. i'm a little confused about the "end-stopped foil" comment.
    Quote Originally Posted by Wooden Boat Fittings View Post
    One where both ends are immersed in the fluid in question, as in a centreboard or daggerplate. Leeboards have the lower end immersed in water but the upper end in air.
    doesn't a daggerboard also have it's upper end in the air? in this picture of another Atkin design, it appears so to me (but since i know next to nothing about sailboats i could be wrong, once again).

    thanks again,
    perry

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    Default Re: Lee Boards

    My experience has been the opposite...I prefer the manner in which the canoe sails with my single leeboard to windward. It was once explained to me that the when the foil is to windward of the effective center line of the sail rig, the forces generate more forward propulsion as compared to when the foil is to leeward of the rig........obviously I'm no naval architect here...I'm just going with what it feels like underway.

    The explanation went further by comparing converging forces of lift from the immersed foil and the airborne foil (leeboard to windward of sail rig) to a banana being squeezed out of its peel as compared to scenario when forces of lift are diverging (when immersed foil is to leeward of airborne foil). I have often thought about mounting the mast offset to port closer to the port side leeboard and seeing how that effect canoe sail performance. Note how daggerboards and centerboards are for the most past aligned athwartships with the sail rig.....I recall a Lake Champlain Sail Ferry ressurected by DOuglas Brooks having the mast to one side (perhaps to allow for uncluttered ferry deck).
    Live and let live

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    Default Re: Lee Boards

    Quote Originally Posted by potterer View Post
    CB cases always wring and, eventually, leak.
    CB cases silt up, and jam, with mud and stones.
    Just curious if these disadvantages would still apply to the Paul Fisher designs I've been studying?

    From the description of his Sandgrouse 16: "The centreplate is ‘L’ shaped so that it fits low down under the cabin sole and does not intrude into the cabin space and the pivot is outside the hull through the integral keel so that there is no chance of annoying leaks."

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    Default Re: Lee Boards

    Quote Originally Posted by P-man View Post
    thanks for the replies everyone. i'm a little confused about the "end-stopped foil" comment.

    doesn't a daggerboard also have it's upper end in the air? in this picture of another Atkin design, it appears so to me (but since i know next to nothing about sailboats i could be wrong, once again)...
    The 'end-stopped' part of the foil is where it enters the board slot. The board 'should' fit tightly.

    Of course, it's all a matter of choosing the compromise which suits you best - centerboard case intrusion vs. daggerboard rigidity in shallow water vs. leeboard inefficiency due to not being 'end-stopped'.

    I suspect that a successful boat designer is the one who juggles the compromises with sufficient skill to produce a design whose performance is pleasing to the client. No wonder they all seem to have greying beards and receding hairlines!

    Tom

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    Default Re: Lee Boards

    thanks for the reply Tom. that makes sense. it would have to be a tight fit.

    perry

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    Default Re: Lee Boards

    Re: Lee Boards

    Advantages
    They open up the interior of the boat for cargo or people.
    CB cases always wring and, eventually, leak.
    CB cases silt up, and jam, with mud and stones.
    The inside of a CB case is difficult to defoul and paint.
    Leeboards can be shaped to provide positive 'lift'.
    Lovely, 'salty', appearance.

    That's an interesting observation. Does anyone care to proffer the merits of a foil-shaped leeboard versus a slab-shaped end-stopped foil like a DB or CB?

    Kevin
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    Default Re: Lee Boards

    Quote Originally Posted by MoMan View Post
    Just curious if these disadvantages would still apply to the Paul Fisher designs I've been studying?

    From the description of his Sandgrouse 16: "The centreplate is ‘L’ shaped so that it fits low down under the cabin sole and does not intrude into the cabin space and the pivot is outside the hull through the integral keel so that there is no chance of annoying leaks."

    MoMan, i can't speak from experience, but i can see how that design might help reduce the chance of leaking. you would still however have a case that could get rocks and mud in it.

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    Default Re: Lee Boards

    Quote Originally Posted by MoMan View Post
    ....centreplate is ‘L’ shaped....

    That gap between the board and boat may jam with weed......in Barnegat Bay for example eelgrass would build up on the pendant of a straight board, and eventually make it difficult to raise then jam it in the slot.

    The leaking pin you avoid with this kind of arrangement, should be in the list of disadvantages for most boats. Though I've been sucessful at making some watertight. Still an issue though in most centerboarders.

  15. #15
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    Default Re: Lee Boards

    This Egret does pretty well beating, compared to a Rhodes 19 centerboard sloop. But her lee chine probably helps too. A round bottom boat with leeboards wouldn't do so well, I would think. She had the advantage over me in water less than 2-1/2' deep (most of that lower Bay).


  16. #16
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    Default Re: Lee Boards

    Small world....... I know Zingaro and some of its owners (maybe different composition now). She's moored here in Barnegat Bay, actually Manahawkin Bay, off North Beach section of Long Beach Island, NJ. I have come up on her in my lateen rigged leeboard equipped canoe. IIRC, Zingaro is based upon Munroe's Egret. She's a lovely sight to see under press of sail on that lovely bay. As much as I like a single leeboard on a canoe, think it's safe to say that on a vessel of that size, twin leeboards is probably a requirement.http://web.me.com/geisser/Site/Photos.html#grid
    Last edited by David Geiss; 11-04-2011 at 06:01 PM.
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  17. #17
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    Default Re: Lee Boards

    One thing I like about the Leeboard on the Egret which KAIROS posted is the sweep of the leading edge. That sweep will maximize the area of submerged leeboard when swept way aft in shallow water.

    Moby Nick

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    Default Re: Lee Boards

    The leeboards on the Black Skimmer I built sold me on them, more or less. A (snooty voice) "proper leeboard" is canted outward so that it's close to vertical when the boat heels. That's a big advantage over daggers/centerboards/keels. Another nice thing about a big boat with leeboards is that the windward board, which (according to me anyway), ought to be tended every tack is about a 100 pound hunk of ballast as far out as it could go, while the leeward one is almost completely immersed and weighs quite a lot less. Win win. As for surface-piercing turbulence... who cares. It's a square edged sharpie with external chine logs that got most of it's speed from it's large, low rig. The bigger the boat, the less that kind of stuff matters as it becomes a progressively smaller factor in the overall scheme of things.

    Also use a leeboard on the Defender that I sail and that boat reaches hull speed pretty much all the time, on every point of sail, and it's close winded, so over all I have no complaints. (other than it's tender as hell because it wasn't ever meant to sail) That rig consists of one clamped-on leeboard for both tacks (though a lot of that boat's lateral plane is in the skeg in the first place).

    They're pretty OK in my book, but if I had the perfect boat, it would have a well-integrated off-centerboard hidden in the interior cabinetwork somewhere. Bolger's the first guy I'm aware of who did that, there are definitely others.

  19. #19

    Default Re: Lee Boards

    Quote Originally Posted by P-man View Post
    ..lee boards. ... I like the look, very traditional. Does anyone have actual experience with them they would be willing to share?
    Absolutely, leeboards are ancient and very traditional in shallow waters. Ask any Dutch sailor, or anyone sailing the Thames estuary. Also, leeboards are very common in sailing canoes.

  20. #20
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    Default Re: Lee Boards

    Quote Originally Posted by brucehallman View Post
    Absolutely, leeboards are ancient and very traditional in shallow waters. Ask any Dutch sailor, or anyone sailing the Thames estuary.
    An astonishing number of people sailing the Thames estuary have the wrong boat!
    Many look like they're designed for the med.

    I am interested in how long and thin you can make them. Or is that deep and narrow?

    Zingaro could probably accommodate significantly longer/deeper boards. How much would high aspect ratio leeboards, almost vertical in the water, help windward performance?

    St.J

  21. #21

    Default Re: Lee Boards

    Quote Originally Posted by St.J View Post
    An astonishing number of people sailing the Thames estuary have the wrong boat!
    Similar for the San Francisco Bay (estuary). Probably 90% of the surface area of the water of San Francisco Bay is shallow mudflat, inappropriate for almost all of the deep keel sailboats common around here. I think the average depth of the SF bay is 12 feet, and the southern half, it has an average depth of 6 feet. The deep fin keel sailboats are confined to the dredged channels, and most don't even dare to try. Leeboards make a lot of sense, yet the modern locals don't use them.

  22. #22
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    Default Re: Lee Boards

    Quote Originally Posted by brucehallman View Post
    Similar for the San Francisco Bay (estuary). Probably 90% of the surface area of the water of San Francisco Bay is shallow mudflat, inappropriate for almost all of the deep keel sailboats common around here. I think the average depth of the SF bay is 12 feet, and the southern half, it has an average depth of 6 feet. The deep fin keel sailboats are confined to the dredged channels, and most don't even dare to try. Leeboards make a lot of sense, yet the modern locals don't use them.
    Maybe that's 'cause there aren't any commercially made. One of the reasons I like multis btw...fast and shallow draft.

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    Default Re: Lee Boards

    While it would be easy to say high-aspect is better than low-aspect for minimizing leeway, when a high-aspect leeboard, or centerboard is pivoted aft, the center of lateral plane moves aft, also.

    For maximun efficiency, you really ought to try assymetric foil leeboards which can maximize lift to windward on alternate tacks. You won't find much written about this, as there is such a huge prejudice against leeboards among the "experts", and BVolger himself was fond of short, flat, broad leeboards.

    Moby Nick

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    Default Re: Lee Boards

    Anyone contemplating leeboards should read this: http://www.duckworksmagazine.com/01/...ards/index.htm
    basil

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    Default Re: Lee Boards

    I would take exception to several points in the Duckworks articlel for which goodbasil posted a link to.

    First, canting the leeboard inward toward is not as bad as the writer says. Proof? Edey & Duffmounted their leeboards directly against the flared sides of their Dovekie, and it works fine. I cruised in Dovekie #56 for 12 years, and I'll bet dollars to doughnuts that is WAY more experience than the Duckworks writer has with similar leeboards.

    Peter Duff even wriote about the benefit of such cant. When the lee board is immersed more deeply due to heel, it is still effective on the light displacement Dovekie. When the leeboard is used on the "wrong" side (windward) the leeboard is immersed significantly less, however kthe board is then about vertical, giving the boat a good gripe on the water.

    While the idea of a curve on one side of a leeboard, with a flat on the opposite side, may go way back in history, that actually involved only a simple arc on the curved side, and sometimes just a long bevel, not even a blended curve. Thw "wing-like" chord shown in the drawing of a Dutch boat would not have been done untill after the invention of the airplane. Scow "Square Toed" Schooners in Maine had leeboards, too, and they were mounted so as to give the lee board a bit of positive angle-of-attack for added lift to windward. Chapelle points out this feature in American Small Sailing Craft. Those SAcow Schooner leeboards also had bevels, or a curve, on the windward side of the lee board, and a flat on the opposite side, in addition to the angle.

    Plenty of the Dutch boats today have flat leeboards with the forward edge rounded and the trailing edge beveled. That aircraft-like wing is not nearly universal.

    I may have a few things yet to learn about leeboards, however, I have been studying them rather intensley for decades. My Shearwatrer Yawl had a pair of laminar flow leeboards (laminar flow airfoils became common after they were used on the P-51) which were a huge success in minimizing leeway.

    Use of any foil other than a NACA-0012 for sailboats is almost unheard of. One need look at what the hydrofoil folks are doing for state of the art stuff, and that is where someone suggested I try a laminar flow foil for my Shearwater.

    Moby Nick

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    Default Re: Lee Boards

    I have a lot fun experimenting with various leeboards on the identical canoe. By keeping the hull constant, you can learn some interesting things about how particular boards behave. It's only a few minutes to beach and switch a board allowing comparison between boards in identical conditions.

    I prefer modestly a high aspect leeboard which, in profile has its aft edge plumb and the fore edge nicely tapering from wider at top (near leeboard thwart) to narrower at the bottom. Wider seems better for light winds and really high aspect seems better when it's really blowing. Naval architects please hijack thread here........

    I generally mill a flat on the inner surface, about 8" in height, where the board mates to the bearing surface of the leeboard thwart I also drill a series of holes, all parallel, each sized for the leeboard thwart (protruding hanger bolt). Reason being is I like to deploy less board for a smaller rig and more board for a larger rig. Yes, you can reduce immersed surface of the board by titling it aft but you also affect the helm whereas with the series of drilled holes you can modulate how much of the board is immersed when it's in its vertical position.

    Vertical or close to vertical lee board seems to me to perform better to windward. At 45 degrees seems good on my canoe for most reaching, except for broad reaching, and of course before the wind (or nearly so) when all I want immersed is only the leading edge of the board nearly parallel to the canoe gunwale.

    Best,
    David
    Last edited by David Geiss; 11-10-2011 at 03:46 PM.
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  27. #27

    Default Re: Lee Boards

    Quote Originally Posted by Nicholas Scheuer View Post
    While the idea of a curve on one side of a leeboard, with a flat on the opposite side, may go way back in history, that actually involved only a simple arc on the curved side, and sometimes just a long bevel, not even a blended curve. Thw "wing-like" chord shown in the drawing of a Dutch boat would not have been done untill after the invention of the airplane. Scow "Square Toed" Schooners in Maine had leeboards, too, and they were mounted so as to give the lee board a bit of positive angle-of-attack for added lift to windward. Chapelle points out this feature in American Small Sailing Craft. Those SAcow Schooner leeboards also had bevels, or a curve, on the windward side of the lee board, and a flat on the opposite side, in addition to the angle.

    Plenty of the Dutch boats today have flat leeboards with the forward edge rounded and the trailing edge beveled. That aircraft-like wing is not nearly universal.

    Moby Nick
    About the wing shape not evolving until after the airplane, what is your source for this? I don't know either way but I don't see why it couldn't evolve by itself. I have a book from the 70's or so which is unfortunately a bit vague, but it states that most boats (this is fishing vessels, not recreational) have the inside front rounded, and the back inside feathered out, like a wing shape. It also says that some boat builders even made a hollow in the outside of the board. The rule for how deep it should be was that you should just be able to empty a single bucket of water in the hollow to fill it completely. So that is quite sophisticated, and I doubt that some of the boatbbuilders around the time the book is talking about (also vague, I think basically between the two world wars) were up on high tech aerodynamics.

    I have another very detailed book on dutch boats (around 300 pages), but haven't really read it yet, so can't confirm what this says on the subject.

  28. #28
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    Default Re: Lee Boards

    I have quite a bit of experience with leeboards. Many years ago I had a small skiff with leeboards which I sailed a lot and cruised a little in smaller lakes in northern Ontario. At that time I had no reason to doubt the efficiency, and it allowed me to roll out a sleeping bag in the bottom of the boat comfortably.

    I now sail a Herreshoff Meadowlark "Whimbrel" I can offer more insight on the overall plus's and minuses.

    Herreshoffs design shows leeboards less than 6 feet long. These were clearly not up to the job....too small. Mr. Herreshoff later recommended boards about 1 foot longer. Mine are almost 10 feet long but they are mounted on a welded hinged bracket on deck instead of the big eye bolt through the sheer strake. My boards are cambered on the inside and flat on the outside, and toed in about 2 degrees. These boards do swing out 'broken wing' when on the weather side for short tacking. I read somewhere the area of the board('s) should be 4% of the sail area. Mine are shy of 3% and less than ideal in light conditions. If I find time I will modify them, increasing the area 20% or so. Once I reach 3 to 3.5 knots I am getting enough lift to be useful. Slower than that the foil is stalling. This is also exacerbated by the interference of the main sail on the mizzen. In light conditions plenty, maybe most boats can pass us at least when close to the wind. Off the wind the issue is less apparent. When the wind gets up a little we are fast and efficient. I have made passages pretty much straight 20 odd miles to windward in 20 odd knots of wind, say distance over the bottom 30-ish miles in 4.6 hours. I have tacked to windward in 30 odd knots of wind under full sail, tacking through ~95 degrees, averaging over 7 knots and spurts over 8 knots. The point here is we get to windward quite reasonably, even in light wind conditions, we are just slower in light conditions. Once the wind pipes up we do not give up much to anyone. My boards are high aspect ratio. When fully down I draw about 6 feet. This is both good and bad. the length is useful for adjusting the balance, giving me quite a range when playing with sail combinations
    On any point of sail, close up or running free we can sail hands off after a few minutes of fiddling with sheets and leeboards etc.
    When short tacking, say out the harbour, I leave both boards down. Once I am clear the windward board will be hauled up after each tack. They are similar to handle to an overlapping jib but less time critical when tacking. You drop the windward board before putting the helm down, and haul up the other board after you have filled away on the new tack and the sheets are all tended.
    I'd really not want a centre-board or dagger board trunk in the cabin .
    I'll have to go now but if you have questions please ask....

  29. #29
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    Default Re: Lee Boards

    I don't have a link. However, I've been reading aviation and sailboat books for over 60 years. Early aircraft all had comparatively thin-chord wings having a concave underside (high pressure side). The illustration of the Dutch boat appearing at http://www.duckworksmagazine.com/01/...ards/index.htm showing what appears to be a NACA foil (not yet invented at the time of Lillenthal and the Wrights) shows a chord thickness quite a lot thicker than leeboards on ordinary Dutch sailboats.

    My Laminar Flow leeboards incorporated a very slight, narrow hollow (concave) along the trailing edge of the high pressure surface. BTW, the most conspicuous feature of Laminar Flow foils is the maximum chord thickness being located almost halfway back from the leading edge instead of approximately 30% aft of the leading edge with a NACA foil. The radius on the leading edge is also somewhat smaller.

    I was very interested to read gilberj's experience with his Meadowlark Ketch. When we cruised across Vineyard Sound in my Dovekie we were dramatically outsailed by a Meadowlark we encountered on our way to Tarpaulin Cove form Katama Bay. that ML appeared to have leeboards reflected in the original design. Tenfeet seems awfully long for a ML leeboard, especially when swept aft in shallow water, but I'm sure would perform very satisfactorily when vertical. I wonder whether more ballast is required at the lower end of such boards to keep them down whn underway at speed? I like the idea of stouter pivot anchors.

    The chord centerline of my Laminar flow foil leeboards are parallel to the keel because the foil's designer said the foil itself incorporated a 3-degree positive angle attack. My Shearwater's progress is virtually straight ahead when sailing close hauled in winds over 10-knots.

    Moby Nick

  30. #30
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    Default Re: Lee Boards

    thanks everyone for the excellent information. apparently there are more leeboard fans out there than i realized. this gives me a lot of information to digest.

    these are some comments from WB #27 about Atkin's Gretchen:
    [IMG][/IMG]


    perry

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    Default Re: Lee Boards

    There's a million successful centerboard boats and satisfied owners out there and the disadvantages are being overblown. Sandgrouse is a charmer and I wouldn't let the centerboard stop me from building it for a second. I've had a centerboarder for many years and not a hint of trouble or anything getting jammed in the trunk. In the bay I mostly sail in there are signs asking boats to stay out of the eelgrass. Its important natural habitat and should be avoided anyway.

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    Default Re: Lee Boards

    There are thousands of boats of all descriptions. I have also had a very successful centreboarder. A person makes a choice. I like leeboards, not to the exclusion of anything else. It makes a big difference not having the cabin encumbered by a trunk. I go into shallow waters pretty regularly, though seldom take bottom, which is one of the qualities Meadowlarks were designed for. Waiting to be set free by the tide requires attention to the clock, and the boat is often less accessible than afloat because of the muck. Hard sand and fine gravel are fine, though not a common as I'd wish . Some folk consider leeboards ugly. That's OK, does not bother me. Some folk think the leeboard is vulnerable when docking. Mine are long and hard and strong (pardon the allusion) and protects the sides of my boat. I do use fenders of course, but my point is they do not seem vulnerable to me.
    Whatever method you might use to prevent your boat from sliding sideways when sailing, keel, centreboard, dagger-board, leeboards, chine rails. Each has advantages and disadvantages. you simply celebrate the good qualities and accept the not so good qualities.

  33. #33
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    Default Re: Lee Boards

    My boat is a traditional Dutch " Lemsteraak" which is fitted with traditional dutch lee boards (" zijzwaarden" in dutch). Boats like mine where designed as fishing vessels on the shallow coastal sea's around the Netherlands an the north of Germany. The current shape of the so called seagoing leeboards ( relatively narrow and long, on the bigger boats up to 5 meters long) orignated in the middle of the 19th century, long before aeronautical wing shape designs.
    In the Netherlands the leeboards are widely used on traditional ships, the ships wich are used for competition use high tech developed lee boards wich generate so much lift that they can point as high as modern keel fitted racers. An example

  34. #34
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    Default Re: Lee Boards

    Very intresting photo, dudchpp! It appears that one sode (with the decorative star at the pivot) is almost flat, but with an incline giving the board some pitch, or "angle-of-attack", while the ohter side has a curved chord. The curved side appears to me to have its thickest point near the center, which would make it significantly different from NACA foils.

    Even though my Laminar Flow foils are thickest near the center, they differ markedly from your leeboard in that the high-pressure side of my boards is nowhere near flat.

    Your leeboards reflect one property stressed by the fellow who advised me on laminar flow, that the shape should be as accurate as I could possibly make it. Lifting foils in water is no place for rough workmanship.

    As for comparing high-performance leeboards with "keel-fitted racers", I would expect that to be the case. Except in designs where the shape of a daggerboard can be changed while underway, those fins need to be symetrical whereas leeboards and bilge boards can be shaped for optimum lift on just one tack; that is to say they can have assymetric foil chords.

    Moby Nick

  35. #35
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    Smile Re: Lee Boards

    Nicolas, the shape of the cord differs along the lee board. Near te upper end of the board the thickest part of the coard lies near the center, while at the end of the board ( the " wingtip", or the deepest part when deployed in the water) the shape is more ore less similar to a NACA foil.

  36. #36
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    Default Re: Lee Boards

    I like the way the thickness near the lower end tapers off toward the edge all around the curve, so that when the leeboard is angled aft the water flow is allowed to slip off the board almost as nicely as from the aft edge.

  37. #37
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    Default Re: Lee Boards

    Quote Originally Posted by dutchpp View Post
    the ships wich are used for competition use high tech developed lee boards wich generate so much lift that they can point as high as modern keel fitted racers.[/IMG]
    dutchpp can you point me in the direction of these competition leeboard yacht?

    St.John

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    Default Re: Lee Boards

    Quote Originally Posted by Nicholas Scheuer View Post
    leeboards and bilge boards can be shaped for optimum lift on just one tack; that is to say they can have assymetric foil chords.
    While trying to answer my own question, above, I stumbled on this page from Van Oossanen & Associates which shows how asymmetrical leeboards can be and how much lift they can create.



    How much lift would you need before the disadvantage of the turbulence created by the air-water interface was counterbalanced?
    James McM, do you know of any work that's been done on the air-water interface or have any links to help me find out?
    Many thanks,
    St.John

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    Smile Re: Lee Boards

    More information on the racing leeboard yachts is available at www.va-klassenorganisatie.nl I'm afraid it is in the dutch language, but if you need translation just let me know. I will take some pictures of my own ship with leeboards later today and post them here.
    The construction of the leeboards allows them to be adjusted in the fore-aft way to fiddle around with the centre of pressure.

  40. #40
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    Default Re: Lee Boards



    Here is a sketch showing how my Laminar Flow leeboards differed from the original flat leeboards designed for Dovekie and Shearwater by P. Bolger. The tip of my leeboards are shaped similar to the illustration dutchpp posted, that is with the foil crossection blenbding into a curved taper all around the lower end of the board.

    dutchpp's post showing a colored illustration of a lifting foil is the only other I've seen which shows something other than a leeboard being flaty on one side, with a simple arched curve on the other.

    Moby Nick

  41. #41
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    Default Re: Lee Boards

    I should point out that the origianl leeboards (as well as all other Dovekies abd Shearwaters) have a 5/8" 3-strand twist Dacron rope tackle leading through the hole in the board, stopped with a figure-8 knot.

    Mine have 1/8" stainless cable passing through a small fiberglass-reinforced hole in the board, stopped with a swage fitting that lies below flush with the foil surface. The countered hole was filled over with silocone adhesive-sealant, so that the board has a optimum surface extending over the swaged cable.

    Moby Nick

  42. #42
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    Default Re: Lee Boards

    In the Netherlands some design offices have gathered considerable scientific knowlegde of leeboard design and the associated optimalization of leeboard yachts. Examples are www.oossanen.nl ( as mentioned earlier) and www.hoekdesign.com ( both websites in English)
    If you need some realy scientific knowledge just mail them, perhaps they are willing to help you (St John)

    As promised some indicative pictures of the leeboards on my yacht.

    A small overview:



    And a picture of the leeboard <>ship construction:
    This construction exists of two axels to allow the board to move along the vertical, a necessity in heavy seas (ship weight is 11 metric tons). The leeboard can slide fore/aft along the horizontal axel to adjust for changes of the centre of pressure of the board and/or vessel.
    The boards are made of European oak ( white oak), the dimensions are approximately 330cmX80cmX7 cm, weight around 70 kg each.
    In shallow waters you can use the boards as altenative depth indicators, if the boards come up, you should tack.

  43. #43
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    Default Re: Lee Boards

    In the USA one of the Herreshoffs (Designer of the Meadowlark Ketch) is credited with having invented a two-axis pivot which is merely a T-bolt with the "cross" segment fixed to th4e straight edgew of the boards with U-straps, while the vertical section of the "T" pivots through a reinforced wale, then secured with a threaded nut. This type of mount is why we call them a "broken wing" pivot because if the windward boaRD IS LEFT IMMERSED, IT WILL TRAIL OFF SLANTWISE INSTEAD OF BEARING AGAINST THE HULL LIKE THE LEEWARD BOARD.

    I like the double pivot, or T-bolt" mount, despite P. Bolger (most prolific American Designer commonly incorporating leeboards) fondness for rigidly mounted boards like mine. In fact I broke both of the original lkeeboards on my boat due to flexing while underway in seas. My new foil leeboards are very stout and will not break off like that. (Don't ask how strong my hull is. "Hope springs eternal.")

    I very much appreciate the links you've provided, dutchpp. I found nothing like them when researching leboard and assymetric foil data before building my foils. The only things I could find about Dutch leeboards was a very limited quantity of old traditional leeboards.

    Moby Nick

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    Default Re: Lee Boards

    No thanks Moby Nick, I tried to find a readable construction drawing of a dutch type of leeboard. This is what I found in one of the dutch databases, it gives a good impression of the curvature:



  45. #45
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    Default Re: Lee Boards

    Wish I could read that drawing! The aspect ratio of the leeboard is way beyond any I've seen in photos of boats. The board appears to have much more dramatic curvature on both sides than what I've seen previously, also.

  46. #46
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    Default Re: Lee Boards

    On my Meadowlark the leeboards are mounted with bi-axial brackets allowing them to swing away broken wing on the windward side, but are held against the hull when on the lee side. These brackets were similar to ones drawn by Herreshoff on later leeboard designs. When short tacking in the harbour I leave them both down so the windward one simply flies out to the side. The additional drag is not worth the trouble to hoist them when short tacking. I have fitted a strip of wood along the trailing edge of the leeboards to assist the lift as per a Gurney flap. This modification is relatively recent and I am not sure what, if any improvements this has made.
    Our leeboards are flat on the outside and curved on the inside, hull side. When peering over the side it is easy to see the lift, with the water level several inches higher on the high pressure outside than on the low pressure inside curved side.

  47. #47
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    Default Re: Lee Boards

    I have two sailing dinghy's. The Goat Island Skiff has a daggerboard. The Puddle Duck Racer has a clip-on leeboard. The leeboard was an experiment. It has a 'near-NACA' shape, but I had no expectations about how it'd work or if I could make it stout enough to not break. Turns out the MarkI version did break (up high at the cleat connecting the board and the clip), in winds that I probably shouldn't have been out in anyway. I am remaking it.

    Regarding the performance, though, I've been pleasantly surprised at how effective and effortless it has been. Despite my rudimentary skippering, I credit the foils - along with a large-for-the-class Storer balanced lug rig - with propelling me to a 4th place finish at the nationals despite getting tangled at the start and getting a very late start on a very short course. I don't have experience with other leeboard boats, but will give a tentative thumbs up based upon my expience with the PDR.

    Oh... and I happen to be one who really likes the look of leeboards. At least, most of them.
    David G
    Harbor Woodworks
    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)

  48. #48

    Default Re: Lee Boards

    If you have ever beached your centerboard boat in a little swell and had a pebble get stuck in the centerboard box and not be able to get the board down again you will always think kindly of leeboards! It's amazing how impossible it is to get one out! The most important thing to think about when your deciding on the shape of the leeboard is how much you will need to adjust the CLR to balance your rig. A high apect ratio will allow you to move it way back or forward. It's also nice not to have the centerboard box spoil the cockpit! It sure makes building a lot simpler too. Daggerboards, are just a disaster waiting to happen and they have happened to me many times!

  49. #49
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    Default Re: Lee Boards

    Sailing with Leeboards is a lot less trouble than sailing with a typical overlapping jib/genoa. You have to handle them when you tack, but it is not time critical. On Whimbrel, (single handed a lot) I drop the windward board shortly before tacking, something like 30 seconds to 1 minute, so there is time to secure the pennant. When I am ready I get both jib sheets in my hand, and push the helm a-lee with my butt. Whimbrel is slow in stays, slow to turn, so I keep the helm a-lee and handle the jib, at just the right moment, so I can sheet in on the new tack without using the winch, let the tiller go so she meets the new course. After all the sheets are tended and secure, I raise the new windward board, unless I expect to tack again within a few minutes. This procedure works equally well whether the wind is blowing 5 knots or 35 knots ( actually easier as the wind increases). I have never had another boat as easy to sail in gale force winds, either to windward or running. There is no question that a keel boat might be a little easier to manage, at times. Tacking a jib, and leeboards are what they are.....eliminating either or both would make sailing a little easier. I have had two boats that were self tacking/tending....just put the helm down and mid-ship the helm when you are through the eye of the wind.
    Dagger boards and the trunk allow for a much stronger structure around the box than you might have with a similar keel boat. There is a better way of spreading the stresses throughout the whole structure. That said a dagger board trunk must be built stronger than a centreboard trunk, to allow for the occasional sudden stop.

  50. #50
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    Default Re: Lee Boards

    Deleted by the author.
    Last edited by upchurchmr; 12-12-2011 at 08:37 PM. Reason: I need to read the complete thread before opening my mouth.

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