Another Bolger lapstrake, Nord Coaster, 16 foot Cat Yawl

[James McMullen]

Having done essentially that very experiment, I'll take that bet. I'm willing to publicly put my money where my mouth is right here. I'll put up $100 right now on the DB boat beating the leeboard boat. Let's make it a best 4 out of 7 races to dampen out noise and get a more accurate sample size.
(And I'll bet another $50 that it doesn't take the whole series for the DB to come out on top!)

Who's up for it? We just need someone to step up and build a couple of otherwise similar boats. PD Racers? Goat Island Skiffs? Any takers?

[boat fan]

That would be great to see.

Poly tarp sails would be ok , as long as they were identical.

In the end ,it`s all about using the boats , after all.

I wished I was over your side of the pond.......

[Nicholas Scheuer]

That PD Racer bet might be worth taking, provided the leeboard boat can utilize assymetric foil leeboards, while the daggerboard may use a symetric foil that is not equipped to pivot on a logitudinal axis.

Everyone MUST be aware by now that a PD Racer kicks up WAY more disturbance at the square bow than any "surface piercing" leeboard might.

Moby Nick

[DGentry]

Having done essentially that very experiment, I'll take that bet. I'm willing to publicly put my money where my mouth is right here. I'll put up $100 right now on the DB boat beating the leeboard boat. Let's make it a best 4 out of 7 races to dampen out noise and get a more accurate sample size.
(And I'll bet another $50 that it doesn't take the whole series for the DB to come out on top!)

Who's up for it? We just need someone to step up and build a couple of otherwise similar boats. PD Racers? Goat Island Skiffs? Any takers?

Sounds fun, but, realistically, if there's an appreciable difference in racing skills, the better skipper could/should win every race, no matter which boat he or she is in. In racing, there are just way too many variables besides foils.
Better to move back to the two boat testing idea, side by side with identical settings.

[James McMullen]

Swap skippers and boats, even swap rigs to even out differences in sail shape and cut. Do a whole series to get a good sample size. My money is on the DB.

But hey, I'm not the one who needs convincing that the "conventional wisdom" is some big conspiracy of cluelessness. Since both scientific theory and the organic evolution of small boat design both seem to favor the non-surface-piercing foil, the smart money is on the null hypothesis.

[brucehallman]

Since both scientific theory and the organic evolution of small boat design both seem to favor the non-surface-piercing foil, the smart money is on the null hypothesis.

It is hard to believe that water tests have not been done. That is what I would like do (or see). Tease out exactly why, (or not) leeboards are deficient. Design some experiments, and drag them through the water with a scale measuring the forces.

[slidercat]

Ray , I think your claim that lee boards are "an abomination " may be a little strong , IMHO.

It would be nice to see two identical Bolger Light schooners , or Michalak Lagunas racing , boat for boat.Swap crews too.
One fitted with the Michalak lee board , the other with a Bolger style dagger board.

Personally , I would have to give slightly shorter odds to the dagger board boat as the favorite ,but I`m not sure that one would be much slower than the other.

You're probably right. Did I call leeboards an abomination in this thread, or was that in some other rant?

I would love to see a couple of Lagunas with those mods go at it. The leeboard on the Laguna is pretty clever. I don't think Jim Michalak gets enough credit from Bolger acolytes. I seem to remember Bolger referring to Michalak as his go-to guy when engineering issues came up that were above his paygrade. Heresy, I know, but I tend to like Michalak's designs a little better than Bolger's, though maybe that's just my inner engineer trying to get out.

Here's a candidate for a trial:



Right now, the only leeway prevention devices are the rudders, and the boat still goes to windward sort of okay. I've actually considered putting a central foil on the little boat-- which would be just like a leeboard, but without the boundary layer issues, if it were far enough forward to be in clean water.

[slidercat]

Sounds fun, but, realistically, if there's an appreciable difference in racing skills, the better skipper could/should win every race, no matter which boat he or she is in. In racing, there are just way too many variables besides foils.
Better to move back to the two boat testing idea, side by side with identical settings.

Have you seen that old test, sponsored by a philanthropic organization interested in helping third-world fisherfolk? They were trying to determine the best rig for a sail-powered fishing boat. The test is 30 or 40 years old, judging by the somewhat old-fashioned rig they called Bermudan, but they got two identical catamarans (on the theory that these boats were more sensitive to small differences in rig efficiency) and tested three "archaic" rigs against the Bermudan-- gaff, sprit, and lateen. To their great surprise, the sprit rig was by far the most weatherly.

Anyway, the two boats were sailed side-by-side in the Solent, so that conditions were the same for both crews. The crews were exchanged to level out differences in skill, and while the sailors were encouraged to add sail-control bits, they were also instructed to take a sort of reverse-racing attitude to the other boat-- no covering, for example.

So it would be possible, I think.

Probably a much simpler test would be to have two identical foils, one end-stopped by a solid chunk of wood to simulate a hull, and one supported on either side by small pontoons of the same area as the simulated hull, so that it operated in surface-piercing mode. You could tow both behind a power boat and see which developed more drag.

[boat fan]

Hello Ray .

Actually , you are right , you called lee boards an abomination on another thread...

All agreed about Michalak`s work too.
I actually thought that his Laguna gave a very credible account for itself at the Duckworks events. Its performance got noticed .

I guess that was my point really , not disputing that dagger boards are the better way , just saying you can end up with a half decent boat , with care , either way.

How is the new cat project going ?

[coucal]

Frank Bethwaite's tow testing for surface-piercing rudders was complicated by the presence of a fine-grain turbulance layer from the hull forward.

But he was adamant that there is an adverse surface piercing effect for foils.

Fully immersed bodies (he argues) recover much of their energy; the energy spent in the acceleration of water around the front of a submerged foil is recovered as "..it slows and stops, its pressure rises, and this increased pressure forces the tapered after part of the shape forward. In this way, the tapered after part of the (fully immersed) streamline shape recovers almost all the energy which the forward half expended in accelerating the water 'backwards'. The greater the energy recovery, the less the drag"
From 19.4 Modern Foil Development, High Performance Sailing

In 19.6 The Drag of Surface Piercing Foils in Wake , he argues that this pressure energy is lost in surface piercing foils due to the escape of energy at the surface of the water as spray (or the formation of waves as the water is pushed upwards & outwards at the top of the foil).

[brucehallman]

Frank Bethwaite's ......argues that this pressure energy is lost... as the water is pushed upwards & outwards at the top of the foil).

If that is true, then a surface piercing foil could be developed which mitigates this leading edge pressure wave. This is remarkably similar to the problem with leading edges of wings in supersonic flight. The ideal shaped wing for supersonic flight is knife edged fore and aft, and diamond shaped. I would be fascinated to see a test of this in water, where about 12 inches of the leeboard (at the air-water boundary line) is diamond shaped, and the deeper portion of the board is foil shaped to give left hand or right hand lift to windward for each side's leeboard. I could imagine this could give an advantage to a leeboarded boat, relative to a neutral lift single centerline foil.

[slidercat]

Frank Bethwaite's tow testing for surface-piercing rudders was complicated by the presence of a fine-grain turbulance layer from the hull forward.

That's true, but isn't this the situation with a leeboard, or for that matter, a transom-hung rudder? They both must operate within this turbulent boundary layer.

What struck me about this research is that the differences in drag were far from subtle-- drag increased to several times the calculated drag. If I recall correctly, calculated drag was supposed to be one-sixth of a pound, but actual measured drag was over a pound.

[slidercat]

All agreed about Michalak`s work too.
I actually thought that his Laguna gave a very credible account for itself at the Duckworks events. Its performance got noticed .

I guess that was my point really , not disputing that dagger boards are the better way , just saying you can end up with a half decent boat , with care , either way.

How is the new cat project going ?

I really like the Laguna. John Wright stopped by the house on his way to the EC a couple weeks ago, and showed me his boat. Very impressive. The leeboard was pretty brilliant-- something only an inventive engineer would think of, I guess. The board is pivoted low on the hull, and the top is restrained by an outwale-- makes much more sense than the usual approach. If I were going to put a leeboard on something, I'd definitely steal that idea.

New cat is progressing slowly. I'm trying to get a free day to start cutting bulkheads.

[Dan St Gean]

Ray,
Why not conduct a super easy and low cost experiment with Slipper? You could build in a daggerboard trunk on one hull using no more than a pound of material, and you could build a Michalek leeboard using the same board. In fact, other than the small hassle of the leeboard mount possibly becoming obsolete, you're out nothing. On top of it you could do some GPS tracks to windward before any board as a baseline, leeboard, then daggerboard. Mighty fine thought expeiment IMHO. One other thing to think about is that there have been numerous cats with no board--but most were v hulled. Teh more recent examples have been the Dart, Escape playcat, Wave and Getaway. All these seem to rely on rudders as foils for their windward bite more than their hull shape (although it does play a part). What would be more interesting is your dory shaped hulls should be poor windward foils--really revealing the efficiency of good rudders OR the need for a dagger/center/leeboard.

Dan

[brucehallman]

... a leeboard, or for that matter, a transom-hung rudder? They both must operate within this turbulent boundary layer.

How thick is this boundary layer? I can see for sure that the water behind the hull has been stirred up. But the water to the side of a boat? Perhaps an inch or so, but depending on the leeboard mount detailing, it is imaginable that the leeboard could be extended to relatively clean water out to the side.

I still am imagining the competitive advantage potential with the use of a matched set finely shaped leeboard asymmetrical foils, one of left hand lift and the other of right hand lift.

[Nicholas Scheuer]

Anyone desiring to judge the maximum benefit of a leeboard should try an assymetric foil (even if it's only one). It will significantly reduce drag, while minimizing leeway.

Of course such a leeboard will take at least twenty times the hours to construct, compared to a flat one, because true chord curves are critical.

IMHO a flat leeboard is just an exercise in antiquity.

Moby Nick

[brucehallman]

an assymetric foil ...will take at least twenty times the hours to construct..,

Perhaps it could be quicker. If you had a series of CNC cut templates, you could quickly rough out the shape using a angle grinder with 36 grit disks aiming to overcut by 1/4 inch, then skim on some Bondo for the final shape, sanding it with finer grit to exactly match the templates. This could be pretty quick work, assuming you got the templates right using CADD, this could go relatively quick.

[Nicholas Scheuer]

My Shearwater's leeboards were made with fixtures designed to guide a hand router over the desired chord of the wooden core, minus the planned thickness of the fiberglass sheath. After the fiberglass sheath had been applied, the final shape was sanded using another set of CAD-designed templets for the high and low pressure sides. None of this was quick. I did get a pair of leeboards shaped exactly like the CAD drawing.

The first board has a Balsa core applied to both sides of 1/2" marine plywood. The second board has a Cedar core applied to 1/2" plywood. The Cedar weighs little more than the Balsa, and was not only easier to work with, but soaked up less Epoxy resin.

Moby Nick

[brucehallman]

...shaped exactly...

Exactly? What kind of tolerance is appropriate. +/- ten millimeters? one millimeter? a hundred microns? Does the theoretical and optimal foil shape vary with anticipated speed of the boat? Hence, does the optimal foil shape have to be a compromise based on "anticipated speed"?

[Nicholas Scheuer]

I believe my foils, having a chord length of 20", are correct within one milimeter. Furthermore, the finish is very smooth, having used "filler primer" and lots of hand long-board sanding.

I know nothing about how foil shape relates to speed. I needed a pair of new leeboards, and did not want to build another set of flat ones. My Shearwater is 28-ft LOA, displaces just under 3000-lbs, and has a maximum speed on a reach of right near 7 knots.

Moby Nick

[slidercat]

Dan, I imagine that would be interesting for Bruce. But considering my personal experience with leeboards I'm just not willing to spend any time on an experiment that seems pointless to me. If there were any real controversy on this matter, it might make a more interesting experiment for me, but I doubt you can find a single naval architect who believes that leeboards are as efficient as daggerboards. That doesn't mean they aren't a good compromise sometimes.

Right now I'm thinking either LAR keels or a centerboard in one hull. We went out again today and this time the GPS was working. The tracks are nothing to write home about, so I'll have be doing something. I'm tending toward the centerboard.

[Dan St Gean]

Dan, I imagine that would be interesting for Bruce. But considering my personal experience with leeboards I'm just not willing to spend any time on an experiment that seems pointless to me. If there were any real controversy on this matter, it might make a more interesting experiment for me, but I doubt you can find a single naval architect who believes that leeboards are as efficient as daggerboards. That doesn't mean they aren't a good compromise sometimes.

Right now I'm thinking either LAR keels or a centerboard in one hull. We went out again today and this time the GPS was working. The tracks are nothing to write home about, so I'll have be doing something. I'm tending toward the centerboard.

Just sayin'. Unless you have a pretty well shaped centerboard, it's likely to be no better than the leeboard unless employing flaps to close the slot. Drag is drag. Why not a dagger? You've had good experience with it in Slider in exactly the same waters. I personally like the kick up feature of centerboards--I'm going to have to decide on what to do with my Tamanu cat pretty soon.

Dan

[slidercat]

Dan, you're probably right. One of the issues is structural. The boat is very lightly constructed (cartoppable) so my thought was that a centerboard would be less strain on the structure in the event of a grounding. Slider's built like a tank-- probably a good bit heavier than she needs to be. Maybe I just need to make the daggerboard a bit delicate, so it snaps off instead of the case rupturing. Have you seen these guys:

http://www.flyingfoam.com/QuickOrderDetails.html

I was thinking about them when Nick was talking about the effort he had to put into his assymetric leeboards. For a smallish boat, you could order a 72" span which would give you 2 36" cores, glass them onto ply stubs, and there you go. Effortless perfect foils.

[James McMullen]

Just sayin'. Unless you have a pretty well shaped centerboard, it's likely to be no better than the leeboard unless employing flaps to close the slot.

Not my experience. Mind you, I'm not saying that a centerboard won't benefit from being carefully shaped or that flaps to close the slot aren't beneficial. But reducing drag is not necessarily the same thing as increasing lift, and it is the degradation of lift that is the primary disadvantage of a surface piercing foil.

You can get lift from a symmetrical foil or even just a completely flat plate due to nothing more than angle of attack. There's plenty of boats that have no particular shaping at all--just a steel plate, or a big timber keel in the case of some very traditional boats. They'll go to windward too, though of course they are generally not as efficient at doing so. An asymmetric foil is an attempt to increase lift even further than the component associated with angle of attack. For sails this is quite important. For underwater appendages there are many other structural and operational constraints that seem to limit the practical utility of it compared to the expense and complication.

[slidercat]

Surely someone must have tried assymetric bilgeboards. I wonder why they aren't more common, since Nick's Shearwater is much more weatherly with assymetric leeboards. Racers wouldn't mind fiddling with boards at every tack, if they could get an extra degree or two out of it.

In fact one of my design heroes, Thomas Firth Jones, did a pretty goofy thing, putting a single daggerboard in the float of his Trimaran Hummingbird. When racing, one of the crew was detailed to pull the board and trot across the decks to drop it in the other case on the far float. When he came to draw his little Night Heron tri, he used a single case in the cabin. He rationalized this by saying Hummingbird was a long-distance cruiser that might stay on one tack for days, but Night Heron would be used mostly in restricted waters where tacking was more frequent. I think maybe it was a case of sadder but wiser.

OOps. Google is my friend. Scows use assymetric bilgeboards very effectively. Now I'm wondering why the idea hasn't spread to sportboats.

Oops again. here's an interesting piece on twin keels and their various incarnations:

http://www.docstoc.com/docs/50407974...-Development-o

It reads a bit like a promotion for the UK firm Hunter, but lots of interesting info, all the same.

[Dan St Gean]

Ray,

I've seen them before, but I think I'll be bookmarking that site. Thanks! My next rudder will be an order form them + a bit of carbon.

As for daggers with intentional weak spots...they work as advertized as long as the boat's case is stronger than the board AND the board is still strong enough to do it's job. I sailed on a redesigned Tennant Tourissimo 10 that had breakaway daggerboards. They must have worked great because we flew upwind at 10-12 and off the wind up to 18. No breakage. However the owner forgot to pull one up and entering his tidal mud mooring, and it snapped off just like it was supposed to. Reattaching it and fairing it might be a pain though, so some sort of kick up sounds good to this shallow water sailor.

Dan

[Nicholas Scheuer]

I know of one builder who has assymetric Bilge Boards in a racing boat on the market. I'll have to hunt around for the literature, but the boat is built in Minnesota.

I chatted over the phone with the builder a couple of years ago when discovering his literature and he said he was using NACA00 foils. He also said there was no question about the bilge boards promoting superior performance.

One obstacle to any of this is the "conventional wisdom" that anything other than a flat centerboard is not worth the bother due to a sailboat's relatively slow speed. Peter Duff, builder of my boat, is one who told me that.

Anyone who "pushes the envelope", in any discipline, will encounter plenty of contrary "conventional wisdom".

Moby Nick

[Nicholas Scheuer]

FOUND THE LITERATURE! She's the Victory-38 Scow (V38 on her sail) and a brochure can be secured at www.VictoryByDesign.org

A bullet point list of features says "Sideboards: draw 5-ft (profile looks like a Spitfire wing), easily retractable, asymetrical". Another area of the literature says "Carbon Fiber Sideboards: The carbon fiber elliptical design provides not only lift, but gives a high strength-to-weight ratio."

There is not a lot of text in this brochure.

Moby Nick