Wing Sails on Proas!
Am thinking the cam may be foot operated to remind me of old gearhead days long long ago.
Two pedals ?
Press the one nearer whichever end is the current bow to make the boat go that way ?
Don’t tread on either to give you neutral ?
Am thinking the cam may be foot operated to remind me of old gearhead days long long ago.
Two pedals ?
Press the one nearer whichever end is the current bow to make the boat go that way ?
Don’t tread on either to give you neutral ?
Ian’t that how the original Model T belt-drive transmission worked? Step on the “low” pedal to tighten the low speed pully pair, step on the “hi” pedal to tighten the high speed pair—then step on the “reverse” pedal to tighten the reverse pair?
Dave
Would it have worked better if the flap ran the full length of the trailing edge but tapered, say, to zero at the head? The idea being to retain some of the twist effect but smooth the change in lift along he span.
Here’s a link to the system Steve Clark, along with others, developed and Steve wrote up: http://www.boatdesign.net/forums/multihulls/patient-lady-wing-control-system-34619.html
This setup is complex, but not complicated. It allows one to *remove* twist from the forward element(s) of even very tall wings, and at the same time (or separately) *add* twist to the after element(s). I’m told this system has become more or less the “standard” for controlling complex wingsails. It is very clever (You may need to invert the colors to see the yellow parts of the dwg).
Steve mentions that some/many of the controls can be slaved off each other, or left mostly separate, depending on your tolerance for controllability versus complexity.
And hey Skip! Have a look at Tom Speers’ excellent wingsail pages: http://www.tspeer.com for why you may want to reconsider your flap-to-wing size ratio.
Dave
Would it have worked better if the flap ran the full length of the trailing edge but tapered, say, to zero at the head? The idea being to retain some of the twist effect but smooth the change in lift along he span.
Here’s a link to the system Steve Clark, along with others, developed and Steve wrote up: http://www.boatdesign.net/forums/multihulls/patient-lady-wing-control-system-34619.html
This setup is complex, but not complicated. It allows one to *remove* twist from the forward element(s) of even very tall wings, and at the same time (or separately) *add* twist to the after element(s). I’m told this system has become more or less the “standard” for controlling complex wingsails. It is very clever (You may need to invert the colors to see the yellow parts of the dwg).
Steve mentions that some/many of the controls can be slaved off each other, or left mostly separate, depending on your tolerance for controllability versus complexity.
Dave
Thanks for that link Dave, Interesting stuff but that’s not quite what I meant. The Patient Lady system outlined in the article physically twists the flap, just like a soft sail. It is quite a complex system by the look of it, and there must be a bit of complexity in designing the flap so that it can twist whilst still being semi rigid.
What I was alluding to is that if you vary the percentage chord of flap element vs front element, you should be able to get the same effect as having twist, but with completely rigid elements. On Tom Speer’s land yacht photo, the flap is only on the lower half of the wing, so when deflected the AOA of the lower half of the wing is effectively greater than that of the upper half, and it the lower half of the wing is effectively cambered, whist the upper half is not, which is like having a cambered sail with a twisted off flattened head. As Tom said though, having a harsh transition between the upper and lower halves of the wing is not the best.
Some time ago I sketched out a flapped wing whereby the chord at the head of the forward element was much greater than at the foot (almost an upside down triangle). The length of the foot of the flap element was the greater part of the total chord and it tapered to almost zero at the head. The idea of course was to get the twist effect with rigid elements. The compromise is that you only get camber and twist or no camber and no twist, you can’t get camber and no twist or twist and no camber.
Mal.
Thanks for that link Dave, Interesting stuff but that’s not quite what I meant. The Patient Lady system outlined in the article physically twists the flap, just like a soft sail. It is quite a complex system by the look of it, and there must be a bit of complexity in designing the flap so that it can twist whilst still being semi rigid.
What I was alluding to is that if you vary the percentage chord of flap element vs front element, you should be able to get the same effect as having twist, but with completely rigid elements.
I understood where you were going, Mal, offered the Patient Lady article as a baseline.
No, it is not necessary to build the flap “extra twisty.” Fact of the matter, it is not physically possible to build a completely rigid element. Everything distorts under load. Everything. We are left with the choice of working with distortions on a “native” basis (like a windsurfer rig) or an “artificial” basis, where we induce—or restrain—the distortion by artificial means (The PL method can both induce and restrain twist, beyond what’s already in the wing element). Both alternatives will work, trading off complexity for potentially less-than-optimal shape. I prefer the latter, am willing to work at less than optimal twist for simplicity, but that’s just me. YMMV.
I will likely get flack for this, but I think sometimes, twist is overrated. Wind shear is not the same at all times (it is often markedly less in high winds then in low). It is a big deal in racing, because you’re racing boat on boat, and milliseconds/mile can win and lose races (you only need a few inches of lead to win a many-thousand mile race) In the real world, when one is exploiting a major advantage—such as a wing over a fabric sail which might increase speed 3-5% or even more, getting another few seconds/mile isn’t really something that’s required to design for.
Some time ago I sketched out a flapped wing whereby the chord at the head of the forward element was much greater than at the foot (almost an upside down triangle). The length of the foot of the flap element was the greater part of the total chord and it tapered to almost zero at the head. The idea of course was to get the twist effect with rigid elements. The compromise is that you only get camber and twist or no camber and no twist, you can’t get camber and no twist or twist and no camber.
QED. The problem perhaps wasn’t that you weren’t clever enough, rather maybe you were over-reaching what’s actually possible. 😉
Dave
I will likely get flack for this, but I think sometimes, twist is overrated. Wind shear is not the same at all times (it is often markedly less in high winds then in low). It is a big deal in racing, because you’re racing boat on boat, and milliseconds/mile can win and lose races (you only need a few inches of lead to win a many-thousand mile race) In the real world, when one is exploiting a major advantage—such as a wing over a fabric sail which might increase speed 3-5% or even more, getting another few seconds/mile isn’t really something that’s required to design for.
Twist is much less to do with wind shear than it is to do with heeling moment. My mantra is ‘righting moment is the most important thing’. Anything that helps to increase righting moment or decrease heeling moment pays big dividends in performance. Twist allows us to get power low down whist still maintaining an acceptable aspect ratio.
One of the models I built had a wing-like rig. It was a soft sail but it had a fairly rectangular planform and a rectangular jib, so it was a bit like a slotted wing. I had built it so that it didn’t twist, because with an appropriate planform, less twist is less drag. But on one occasion one of the wire braces failed and the head twisted off. The increase in performance and improvement in handling was immediately apparent and I subsequently modified it so that it could twist off naturally.
You are right though, chasing the last few percent is not really that important if you are not racing to a rule. Even though I think it is a compromise in performance terms, I’m personally attracted to the simple and apparently robust Saildrone style rig, and because it suggests other possibilities such as effective sail steering.
Mal.
Am thinking the cam may be foot operated to remind me of old gearhead days long long ago.
Two pedals ?
Press the one nearer whichever end is the current bow to make the boat go that way ?
Don’t tread on either to give you neutral ?Ian’t that how the original Model T belt-drive transmission worked? Step on the “low” pedal to tighten the low speed pully pair, step on the “hi” pedal to tighten the high speed pair—then step on the “reverse” pedal to tighten the reverse pair?
Dave
I’m not quite that old 😉
First car was an old 46 Ford, gearhead reference was to racing go-carts and hydroplanes in my teens and early twenties.
Proa content; yes I’m thinking two pedals one for each direction possibly spring loaded to neutral. I’ve mentally shunted all sorts of configurations and have never come up with something to do with my feet. Foot steering a proa a little different than twitching a canoe thru a sweeper; could never convince myself that foot steering was the way to go on a proa.
Ah but with a wingsail it’s simple. Hands are free to steer and do whatever needs to be done with rudders and you just step down in the direction you want to go.
As soon as it warms up a bit and the fiddling pieces of the rudders, sail and wing start to get finished I’ll migrate this stuff over to the Broomstick thread.
Cheers,
Skip
Proa content; yes I’m thinking two pedals one for each direction possibly spring loaded to neutral. I’ve mentally shunted all sorts of configurations and have never come up with something to do with my feet. Foot steering a proa a little different than twitching a canoe thru a sweeper; could never convince myself that foot steering was the way to go on a proa.
Ah but with a wingsail it’s simple. Hands are free to steer and do whatever needs to be done with rudders and you just step down in the direction you want to go.
As soon as it warms up a bit and the fiddling pieces of the rudders, sail and wing start to get finished I’ll migrate this stuff over to the Broomstick thread.
Cheers,
Skip
If they’re spring-loaded have some kind of ratchet so you don’t have to push it all the time. Rig up a ‘kick-for-disengage’ pawl so that fast shunts become a matter of kick-stomp… :o)
I guess timing when you stomp for reverse in mid-steer will be the key to a slick shunt.
I’m really looking forward to see how all this develops on the BB.
Peter H
Love the pedals. Its a smart, intuitive way to keep the cam stable in both directions.
The pedal idea could also be used with the more conventional pushrod linkage or some other direct linkage system.
I can see a the benefit of the the cam system for a tacking boat (although I think it’s a marginal benefit with a lot of compromises), but on a shunting boat, I don’t see any benefit. In fact I thinks it’s exactly what you wouldn’t want on a shunting craft, because it increases the risk of backwards capsize.
Mal.
The pedal idea could also be used with the more conventional pushrod linkage or some other direct linkage system.
I can see a the benefit of the the cam system for a tacking boat (although I think it’s a marginal benefit with a lot of compromises), but on a shunting boat, I don’t see any benefit. In fact I thinks it’s exactly what you wouldn’t want on a shunting craft, because it increases the risk of backwards capsize.
Mal.
I’m missing something here, with a cam system that feathers in neutral and freely rotates thru 360 degrees, where’s the risk?
I’ve been backwinded several times (once memorably) using a couple of different sail systems on proas and it wasn’t much fun.
For me the main appeal of proas both generally and specifically is in getting the most ‘bang for the buck’.P52 was the quickest, least expensive, most comfortable craft in a couple of Texas 200 fleets. Also the quirkiest, with handling idiosyncrasies and prone to gear failure. It was a blast.
The as yet unfinished Bionic Broomstick was conceived to test out a few items for a replacement for P52 that would have all the good stuff with a little less quirky, fewer idiosyncrasies and a lot less gear failure. The whole wingsail movement is a side road for me. I’d be really surprised if Nomad ends up with a wingsail system(s) but I’ve been surprised before.
Once the trialing s done the Bionic Broomstick is probably going to a new home because in that size category (so far) all proas suffer in comparison to a small canoe and double blade paddle for ‘bang for the buck’.
Cheers,
Skip
For a tacking boat, neutral is when the boat is head or stern to wind. The advantage of the cam is that the tail automatically tacks as the boat passes head to wind, or stern to wind. To me, this is a minor advantage as it’s not really that difficult to reset the flap for the new tack. For that small advantage you pay the price of have having a flap action which may not match what you actually want for best performance. However, if you want an almost hands free system with just a throttle control, on a tacking boat, the cam system is a good option. As an automated system design, it’s very clever and I like it for that and I like the bit about it being able to hold the boat still when head to wind (in an oscillating airstream).
For a shunting boat, I presume neutral will still be still be when the boat is head to wind. I guess you could align neutral athwartships, but how would that work? You wouldn’t be able to sail on a beam reach at all and to sail downwind you would have to put it in reverse. So assuming neutral is head to wind, what is the benefit? A shunting proa generally should not go past head to wind, so the only function of the cam would be to automatically de-power the wing as you sail higher on the wind. I’m not sure that that is particularly useful. The downside is that if the boat does accidentally go past head to wind, the wing now powers up on the opposite tack, forcing a backwards capsize, which on a Pacific proa means forcing the ama under water and on an Atlantic proa usually just means a rapid capsize.
If you have a direct tail control, when the boat passes head to wind the wing continues to power as before, except the boat goes into reverse rather than continuing forward, which is not such a big deal on a shunting boat.
Mal.
A shunting proa generally should not go past head to wind, so the only function of the cam would be to automatically de-power the wing as you sail higher on the wind. I’m not sure that that is particularly useful.
On a beam reach that part of the lift of the wing which produces forward thrust is maximised while that part which produces heeling moment is minimised. In the head-to-wind state, that situation is exactly reversed - minimum drive and maximum heel. So de-powering the wing progressively will automatically limit the heeling moment. I suspect the balance between the increasing heeling effect and the decreasing overall power won’t be perfect but it certainly seems to be working in the right direction.
As the bow passes through the eye of the wind the wing will gradually and smoothly power up and the heeling force will act to bury the ama. There is no sudden swing of a boom and no sheet to put a high angle-of-attack on the wing and transfer the consequent forces to the vaka.
It is hard to see how the high forces to sink the ama would be generated unless the boat’s heading changed suddenly and unexpectedly (rudder failure ?) by over ninety degrees or the wind suddenly slewed the same amount. A wind swing in the night when single-handing might do it, I guess. A safety alarm rigged to indicate that the tail was now pointing towards the ama would be needed in that instance.
In normal shunting, of course, the bow will never be close to head-to-wind and a change of wing from forward to reverse will brake the boat and then accelerate it in the other direction.
The downside is that if the boat does accidentally go past head to wind, the wing now powers up on the opposite tack, forcing a backwards capsize, which on a Pacific proa means forcing the ama under water and on an Atlantic proa usually just means a rapid capsize.
Now I see, thanks. Not sure it would be much of an issue since centering the cam would automatically feather the wing and depower the thing. With cam in neutral the wing is feathered into the wind no matter what the relationship is between the wing and hull. Sliding the cam in either direction creates a side force more or less perpendicular to the wing chord either left or right. Magnitude of side force is dependent on cam travel and relationship between wing chord and hull axis (hull dead to the wind force is going to be zero).
There are a lot of permutations to be investigated, should be fun. Dave’s idea of having wings in the ends greatly expands the possibilities.
All this theoretical goodness is worth investigating but when we start talking about downwind there is ................silence.
Cheers,
Skip
All this theoretical goodness is worth investigating but when we start talking about downwind there is ................silence.
Cheers,
Skip
Downwind in a multihull—a performance multihull—is a specialized “science.” Off-wind courses—off *apparent* wind courses are spinnaker territory. If the multihull can carry a screacher or genniker, etc, it’s an almost sure bet that she’s pulled her apparent wind around to 100 degrees or less. Even if she’s making a course to leeward, she isn’t sailing “off” wind.
Now, non-performance multis are something else. A big old cat-o-minium never brings her apparent wind around. She’s basically a pontoon boat with a rig on her. Hate to say it, but a lot of hand-buit proas fall under this category too. One of the seminal raisons d’etre for proas is that they’re fast. Fast multihulls rarely sail in apparent wind deeper than about 100-110 degrees. If you’rer gonna contemplate a rig that’s easy to sail, automatically follows windshifts and self-depowers when you get in trouble, wouldn’t you be better served building a *bigger* version of the rig, and leave “off-wind” sailing behind?
If you decide to build a proa for other reasons—like voyaging, or gunk-holing, or just because you want something different, well, you don’t actually need a performance rig now do you? Except for experimenting—or just playing around, there’s no real reason to put a wingsail on a boat that spends 90% of its time at 5-8 kts.
Roundabout way of saying there’s no real reason to optimize a proa wingsail for off-wind conditions. Anything you can do without increasing sail area is going to have small effect because the apparent wind speed on those courses is going to be so small, plus throwing up a spinnaker is sooo much easier to do than fine-tuning the 3rd flap on a wingsail that it’s well, kinda silly.
Just my 2 cents.
Dave