Bieker B6

[SimonN]

I think people are trying to make this way to complex and contrary to what some seem to suggest, gybing boards are not complex. I find it particularly amusing that TingTong is prepared to play with something far more complex and unproven yet dismisses gybing boards because they aren't "plug and play". However, I am sure you can go out and buy a gybing board for a 14. Sure, you might have to make a few bits but compared with all the rest of athe things that are custom made for a 14, it really is no big deal. And yes, you need a clever system so that when you pull certain strings, the board stops gybing. However, this is no more difficult than the rest of fitting out a 14 (and yes, I have done that!)

The flap idea is a good one and has been made to work in some boats. I also am amused when somebody dismisses an idea because somebody tried it 10 years ago and it didn't work. Just because 1 person couldn't make it work doesn't mean a somebody else cannot get it to work. My biggest issue with it is that unlike a gybing board which, when you stop it gybing behaves like a conventional board, a flapped board has increased drag compared with a conventional board when it is at neutral because of the flap joint.

 

[BalticBandit]

Zach B had Larry Tuttle at Waterat build him one about 10 years ago - Zach abandoned it as a failed experiment after just a couple of days - he said definitely slower - now perhaps he did not spend enough time to optimize it - but still - he may still have it in his garage if you want to give it a go.

My areo guy, the one built the spreadsheet referenced above, thinks that a leading edge device would be a better way to go - more lift at less drag penalty.

I know about Zach's failed flaps. Poor chap.

A normal board that already works will gain nothing from a flap (beyond any gain that you could attribute to gybing), but with additional drag from the hinge and irregularity itself. Imagine, though, a board with a thinner, lower drag, section and perhaps a shorter chord. At low lift coefficients (high speed or greater area) it will have less drag. At higher lift coefficients you will either need excessive area or, if unavailable, it will have rapidly increasing drag, before stalling. A flap, eg 30% of chord, 4deg deflection, will shift the drag bucket to match the lift coefficient range of the standard board (albeit at a lower angle of attack), but without rising to the higher drag coefficient of the fatter foil.

So i have chosen the same length, but slightly shorter chord and only a 10% thickness (c.f. 12.5% standard). According to very basic analysis, with a 30% flap at 4deg, this should stall at the same lift coefficient as a standard board, but operate in its full range at between 50% and 75% of the crag coefficient. As long as my hinge doesn't add 25%+ to the drag (and it may) i should be quids in. And the hole in the bottom of the boat is just 15mm wide at the very trailing edge.

The lift coefficient at 0deg is similar to a gybing board operating at 2.5-3deg.

yeah but the lift VECTOR is not. and that's part of the problem. I agree with Simon that gybing boards - particularly if you have an NA like Bieker to go back to - are far more sorted out than a TE flap

Simon I think the reason we end up in complex discussions is that at the end of the day, the majority of lift is generated by the foils and people don't see how you can sail the foils "higher" without generating more drag and so we get into a complex set of discussions.

So let me try a different way of describing what I have experienced happening.

Consider sailing a non-gyber "in the groove" upwind. Everything is balanced, you are trapped etc. So now, pinch up 5 degrees. What happens?

1. First off, you DO NOT STALL the daggerboard...It continues to operate in fully attached flow mode (not laminar) even though it angle of attack has increaed 5 degrees. to make the foil stall you have to really spin the boat
   
2. You teabag, because the sails are generating less heeling force
   
3. You slow down, because the sails are no longer at their optimal angle of attack
   

OK, now consider what happens when you bear off 5 degrees

1. Your blade does not stall but it generates less drag
   
2. Your driving force increases and you accellerate
   
3. INITIALLY your heeling force increases
   

But here is the key, on Apparent Wind Boats, the boat very quickly accellerates enough that you have to sheet back in to keep your drive going, and as the AWA shifts forward, your heeling force goes back down.

so now what if you could configure your boat so that it tracked through the water like a non-gyber "in the groove" - but had its sails set and trimmed as though you were sailing "beared off" 5 degrees? What would this look like?

Well your heeling force would be the same, your lift from your blades would be the same, your drive force would be a bit higher and your sails would be trimmed pretty much the same once at speed.
Now what if in this magical configuration you ran into a lull.

AWA shifts well forward but because you have speed to burn, you don't have to "nose down" to keep on the wire, you just let the boat slow down a bit and load the sails up, and when the next puff hits you accelerate back to normal speed. And the trimming is just within the bounds of what you dynamically do for the main anyway.
From a "normal boat" next to you, you would be "nose down" on them but tracking the same CMG - and you would have a touch more speed. And in the Lulls you would maintain point when they have to "nose down".

And that is EXACTLY what you see when you sail a non-gyber next to a gyber.

 

[SimonN]

If the truth be known, while I usually dig very deeply into the technical side, gybing boards are one thing I have simply come to accept based on them giving me improved performance in every class I have tried them. I think this is particularly interesting. The same concepts seem to work on a National 12 (upwind speed through the water of, say, 4.5 knots) and an I14 travelling at significantly more! Sure, the boards are different but the principals are the same. However, despite maybe not fully understanding what is happening, I know enough to see a benefit and there is an old saying - never look a gift horse in the mouth!

 

[mark1234]

BalticBandit - unless I seriously misunderstand you, now you're messing up transients! Whether you're pinched, or footing, the AOA of the board is set by sideload and speed through the water, with sideload directly proportional to how hard you're trapping. Heading up will (transiently) increase the AOA as you turn, due to the turn load. Once you straighten up, it will drop right back in the bucket, unless you slow down a heap. Same footing off.

A gyber of the same form as a non gyber will run exactly the same lift curve, therefore the same AOA for the same speed and sideload. Any gains must come from drag reduction in the whole package (hull alignment to direction of travel), and any improvement in the sailplan. My gut says that a typical dinghy hull is a really bad way of generating lateral resistance compared to a board, and I'm less convinced about the sailplan (I don't know either way).

I would be inclined to completely discount slats (sorry, leading edge devices) - they are high lift features, but critically they work by allowing attached flow at large angles of attack; therefore only come into play when you're way up the right hand (draggy) side of the l/d curve. Add a LED to a standard board, all you'd gain is drag. To make it function, you want to be working a large AOA - that could be done by massively reducing the size of the foil, but to what advantage? Flaps are generally in the same boat(!), although they are made to work on sailplanes - there they are typically a small percentage of chord, over a large percentage of the span, and move through relatively small angles. That approach might work with a dinghy board, however in a sailplane it's typically working with an asymmetric wing with a somewhat reflexed trailing edge. The flap is allowing the wing to stay in the drag bucket more of the time (it runs negative - tail up at speed), and the reflexed TE helps keep the air moving cleanly off the back. Obviously dinghy boards can't do this, being more symmetric.

Of course, all of these things are small percentages, well below the 'noise' factor of individual performance - 99.9% of sailors would be far better served by just sailing what they've got better, staying in sync with the shifts, etc. Still interesting in the abstract though!

 

[SimonN]

Of course, all of these things are small percentages, well below the 'noise' factor of individual performance - 99.9% of sailors would be far better served by just sailing what they've got better, staying in sync with the shifts, etc. Still interesting in the abstract though!

While this sentiment is true, one cannot sail 24/7 and therefore so long as the time spent in fitting a gyber doesn't eat into sailing time, go for it. Even without a lot of tuning, the chances are that a gyber will make you faster more than it will slow you.

 

[mustang__1]

i never got a good look at a gybing CB setup, but how much bigger is the box? is the centerboard still tight with the trunk? ie, a regular board is put into the trunk as tight as possible - with my understanding of how the gybing CB works, im not seeing how that would work.

 

[jfunk]

Mustang

A 14 gybing board setup is different to say a 5oh. With the 14 the board has a tight fit within a cassette - no flop, but the cassette gybes inside a box that is moulded into the boat, hence the discussion about retrofitting 14s'

Whereas in a dinghy, the board is shaped to gybe within the case.

 

[Carbon Dave]

In essence, you build an oversized rectangular centreboard case hole through the boat (say 70mm wide x 250mm long with a thin flange on the outside skin - making the aperture in the outside skin in the order off 50 x 230 for example). Then you make a cassette or inner case, which is shaped so that the foil (typical max thickness around 30mm) is a perfect fit inside it, but the outside profile, while a close fit to the square hole in the boat at the trailing edge, is a loose lateral fit at the leading edge (in our example the gybing cassette might be 60mm wide giving a total lateral movement of 10mm, ie 5mm either side of the CL) The board is well supported under load because the sides are not parallel - ie they are angled inwards towards the leading edge, and the cassette edges are always inside the outer flange detail.

When in gybing mode the inner cassette is free to change angle because the trailing edge stays on the centreline, while the leading edge moves to windward as the pressure on the foil (applied at a net position of 30% chord in effect) is applied from the high pressure side of the foil (ie leeward). Thus as side pressure increases, the board 'gybes' into a +ve Angle of Attack attitude. To reduce this movement, or lock the board off altogether you have a V shaped block which has the corresponding angle of the outside of the cassette machined into it's inner face and is a good fit to the rectangular hole in the boat... The V block can move fore and aft, so when it is pushed backwards, it locks the foil on the centreline. When it is pulled forwards it allows the inner case to move. There is a little more to it than that, but you get the idea I hope.

BTW, To assemble, the basic part of the mechanism is held in the boat by a top plate with similar aperture size to the outside ap. - The cassette is then free to move laterally as described but under the rules is a permanent fitting in the boat. The advantage of this design over a fixed traditional centreboard case is obvious particularly on fast moving design platforms like 14s - Because not only can you make the actual hole in the boat as strong and robust as you like, but you have a standard sized hole which you can make plug and play cassettes for - so you can make cassettes which allow you to move the board for and aft, allow it to gybe, change the design of the board altogether.... etc etc

 

[FearBiter]

2 different i14 set ups.

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[BalticBandit]

BalticBandit - unless I seriously misunderstand you, now you're messing up transients! Whether you're pinched, or footing, the AOA of the board is set by sideload and speed through the water, with sideload directly proportional to how hard you're trapping. Heading up will (transiently) increase the AOA as you turn, due to the turn load. Once you straighten up, it will drop right back in the bucket, unless you slow down a heap. Same footing off.

HUH? How does how hard you are trapping DIRECTLY affect the angle of Attack of water flowing over a board?

A gyber of the same form as a non gyber will run exactly the same lift curve, therefore the same AOA for the same speed and sideload.

A yes on the speed. "side load" is a meaningless term. AoA is based on the vector flow of water over the surface and the lift curve is a function of that curve and relative flow velocity. "side load" has no bearing on it. I suspect that what you are calling "side load" is a combination of the Leeway vector of the lift from the sails, and the AoA - thus it cannot be a factor in setting the AoA.

Any gains must come from drag reduction in the whole package

Nope. You can also make gains if you can increase the amount of power used to drive the boat, which increases speed and changes AoA - AND if you stay within the drag bucket, you may well be able to improve the amount of CMG by sailing a slightly higher AoA...assuming you can achieve it.

I would be inclined to completely discount slats (sorry, leading edge devices) - they are high lift features, but critically they work by allowing attached flow at large angles of attack;

No that is one of their EFFECTS, but it is not HOW THEY WORK. Essentially they are "jibs" and the general mechanism is the same. As for using Sailplanes and similar, they are operating at different Reynolds and Froude numbers so the shapes, sizes and uses doesn't quite translate.

I think I am completely misunderstanding your point because I don't understand the language you are using

 

[BalticBandit]

2 different i14 set ups.

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/monthly_02_2011/post-6638-096423000%201297905125_thumb.jpg

I never cease to be amazed as to how many strings it takes to run a boat that fundamentally runs on 4 settings controls (Rig Tension/Forestay, Vang, Cunno, rudder foil AoA) and 3 sheets.

 

[mustang__1]

thanks for the help understanding these things. however, fundamentally, there is going to be a gap somewhere in the system right? the board is tight with the cassette, but then the cassette is slightly loose in the hull? im just thinking about the gap, and the drag that might be associated with it.

 

[Shu]

thanks for the help understanding these things. however, fundamentally, there is going to be a gap somewhere in the system right? the board is tight with the cassette, but then the cassette is slightly loose in the hull? im just thinking about the gap, and the drag that might be associated with it.

Perhaps these progress photos of my I-14 will help. This cassette is presently set up in non-gybing configuration, but that can be simply changed by trimming a taper on the outside edges of the cassette, and easing-out the daggerboard-shaped hole in the thin carbon plate so that the board/cassette can rotate in the box. There will be a gap, but it is only the depth of carbon plate (a couple millimeters).

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[mark1234]

Mark:

BalticBandit - unless I seriously misunderstand you, now you're messing up transients! Whether you're pinched, or footing, the AOA of the board is set by sideload and speed through the water, with sideload directly proportional to how hard you're trapping. Heading up will (transiently) increase the AOA as you turn, due to the turn load. Once you straighten up, it will drop right back in the bucket, unless you slow down a heap. Same footing off.

BB: HUH? How does how hard you are trapping DIRECTLY affect the angle of Attack of water flowing over a board?

Mark: A gyber of the same form as a non gyber will run exactly the same lift curve, therefore the same AOA for the same speed and sideload.

BB: A yes on the speed. "side load" is a meaningless term. AoA is based on the vector flow of water over the surface and the lift curve is a function of that curve and relative flow velocity. "side load" has no bearing on it. I suspect that what you are calling "side load" is a combination of the Leeway vector of the lift from the sails, and the AoA - thus it cannot be a factor in setting the AoA.

Sideload is the best term I can come up with. Follow me on a thought experiment: You tow a boat with two people standing in the middle. AOA = 0. (hopefully we agree). Now stick some sails up, put it on a reach, and stand in the middle. It falls over - the foil will develop a little (transitional) lift due to leeway, but very little AOA as it will turn the boat over. So you hang out on the wire. Now you're applying a force to balance the rig, the moments resolve through the various centres, and the board 'sees' a force trying to shove it sideways through the water. It's AOA will depend on how hard it is being pushed sideways, the speed, and the lift it is generating. Of course it can't generate lift until it has some positive AOA (being a symmetric foil), but if an equilibrium is to exist, you must trap exactly enough to oppose the couple between the CofE of the rig, and the CofLR of the hull. You may prefer to say how hard you're trapping directly depends on the lift the board is generating - it's all rather cyclic.

Or to put it another way, anything you do to the sailplan does not DIRECTLY affect the board. It effects the equilibrium you maintain. If you bear off, and the rig force vector swings forward, you either power up the rig somehow to restore the lateral component, or you swing in on the trap. Of course, the longitudinal component will affect the speed (so you go faster with less 'sideload', and the AOA decreases.

My point was that the board 'sees' and cares about the lateral forces (and speed) only - the most obvious, immediate measure of that I can think of is how hard you're hanging over the side

Mark: Any gains must come from drag reduction in the whole package

BB: Nope. You can also make gains if you can increase the amount of power used to drive the boat, which increases speed and changes AoA - AND if you stay within the drag bucket, you may well be able to improve the amount of CMG by sailing a slightly higher AoA...assuming you can achieve it.

Ah, come on.. that's a partial quote - I'm agreeing with you: Any gains must come from drag reduction in the whole package (hull alignment to direction of travel), and any improvement in the sailplan.

 

Granted, I'm not convinced about the sailplan arguament, but I don't know enough to refute. Seems to me that when you free off the hull for the same CMG, you may improve the length of the sail drive vector, however, you're also turning it aft a couple of degrees. But that's just gut hunch, I don't know (hence, not arguing!)

Mark: I would be inclined to completely discount slats (sorry, leading edge devices) - they are high lift features, but critically they work by allowing attached flow at large angles of attack;

BB: No that is one of their EFFECTS, but it is not HOW THEY WORK. Essentially they are "jibs" and the general mechanism is the same. As for using Sailplanes and similar, they are operating at different Reynolds and Froude numbers so the shapes, sizes and uses doesn't quite translate.

BB: I think I am completely misunderstanding your point because I don't understand the language you are using

Perhaps I should have said that they work *at their best* at large angles of attack. If a jib isn't a high lift device, I don't know what is - I'd consider the range of AOA the rig is working in to be very much in the high AOA range. One of the things a jib does is allow you to sheet the main harder (increase it's AOA) without stalling out. Granted the reynolds numbers are dissimilar, though I'd wonder for the underwater bits - we're working in a much more dense fluid, and sailplanes are generally low RE anyway (typically around 70kts in air vs 10kts in water for a daggerboard foil. The shapes aren't that markedly different, beyond being assymetric! Anyhow, while shapes and sizes may not translate, however, the principles are the same. I still can't believe in slots and droops in the LE being effective at typical leeway angles. I will grant that might not apply to the trailing edge flap, but my gut still says no.

Hope that's resolved the language differences... in case you've not guessed I'm more of an aero guy.

 

[BalticBandit]

Thanks for clarifying Mark

OK - I see where you are going with this. There actually are THREE effects here that you are conflating. The board will see the normal AoA initially and that will change as it lifts out of the water because when angled the AoA changes. But that's not really the issue here.

The way to think about this is with a notion engineer's call a "Force Couple" - which is a fancy way of describing two forces acting in opposite directions at the opposite ends of a seesaw (ie with a pivot in the middle). In the case of a sail and a daggerboard you have

1. A force acting at the Center of Effort (CE) of the sail pushing the sail directly to leeward.
   
2. A force acting at the Center of Lateral Resistance (CLR) in a direction that in the vertical domain (as opposed to fore-aft) is a vector opposite of the leeforce - and with the blade down, this acts from below the waterline
   
3. The "righting force" generated by your weight on the trapeze.
   

#1 and #2 create a Force Couple http://en.wikipedia.org/wiki/Couple_(mechanics) that rotates around the hull (slightly below the waterline). this Force Couple rotates the boat mast to leeward and the blade upwards. This is Effect #1

Effect #2 is the "righting force" - which is a second force couple that is the force of gravity acting on the Center of Mass of the trapezed crew being off centerline of the bouyancy of the hull. This Force Couple rotatates the boat Mast To weather and the blade upwards to leeward.

When Effect #1 and Effect #2 balance each other, you have a ZERO effective set of rotational forces acting on the sails and the blades.

In this balance of couples you still have the difference in the MAGNITUDE of the vectors of #1 and #2. on a Moth, it turns out that when heeled to weather, #2 is GREATER than #1 and the Moth climbs to weather. In an I14, the balance is close at speed but #1 is still slightly greater than #2 - so the boat makes leeway.

So now we get to EFFECT #3. the balance of lift vs. leeway vectors in MAGNITUDE is what changes how much lift you get to weather. And THIS is the drag bucket tradeoff. Higher AoA of the blade INCREASES Force #2, but, because it induces massive parasitic drag outside the Drag Bucket, it slows the boat down. And when the boat slow down, the Apparent Wind Angle (AWA) moves aft. And that in turn rotates the lift vector of the sails such that you are generating less drive force and more heeling force (Effect #1) - And it turns out that #1 increases more quickly than #2. So if you go outside the drag bucket, not only do you slow down but you also start to make more leeway.

This is why even in non AWA boats, you have to "get the foils working first before you can point".

So there is no "sideforce" here and how you are modeling the forces leads to inextricable complexity that creates a muddle that is almost impossible to think through

Or to put it another way, anything you do to the sailplan does not DIRECTLY affect the board. It effects the equilibrium you maintain. If you bear off, and the rig force vector swings forward, you either power up the rig somehow to restore the lateral component, or you swing in on the trap. Of course, the longitudinal component will affect the speed (so you go faster with less 'sideload', and the AOA decreases.

Here you have it right. And this is what I believe is the primary effect of "gybers" as well as assymetrical/canted foils we see on IMOCA and ACats etc. it essentially allows you to sail slightly "bow down" with the Lift vector (your "rig force vector" which actually is a complex set of vectors) further forward, which reduces the heeling vector. This in turn lets you power up the Sails more, since your righting force is still the same so that the Heeling component of the "rig force vector" increases back to normal.

Another boat we can see this in is the Star - albeit slightly differently. A crew that is 80# heavier than another boat WILL SAIL FASTER, even though they point the same. And this is because they are able to power the sails up a bit more and retain the same angle of heel (Lateral resistance force)

My point was that the board 'sees' and cares about the lateral forces (and speed) only - the most obvious, immediate measure of that I can think of is how hard you're hanging over the side

No, it only "cares" about the angle of attack. Which is the point that Simon and others have made and part of what Hallum cites - namely that the optimal AoA for a set of blades will be the same whether gybed or not. And THAT PART is correct.

[/b]Granted, I'm not convinced about the sailplan arguament, but I don't know enough to refute. Seems to me that when you free off the hull for the same CMG, you may improve the length of the sail drive vector, however, you're also turning it aft a couple of degrees. But that's just gut hunch, I don't know (hence, not arguing!)

No the drive angle is still along the "line" created by the blade travelling through the water. And this is where you get the benefit. Again, the net difference in drive power results in about 5 BL on a 1KM leg... For two identically skilled sailors, that's massive. But for different skill levels, that's not much at all.

Perhaps I should have said that they work *at their best* at large angles of attack. If a jib isn't a high lift device, I don't know what is -

but its not operating at "a large angle of attack". And no the jib does not "allow you to sheet the main harder" - you have to because of the redirected angle of flow. How the jib works is different. If you separate the jib from the main by a very large distance then the air flowing over each surface STARTS at the same speed at the leading edge, Accelerates to a peak velocity at max draft and then DECELLERATES back to its initial speed by the TE.
Now if you glue the leading edge of the main to the TE of the jib (closed slot), you get an improvement because the point at which decelleration has to begin moves aft on the jib and the main doesn't get to accellerate the air as much So you get some additional power but not as much as you could

If you open the slot, what you do is remove the requirement for for flow speeds to match at the TE of the Jib since the air in the slot is being accelerated by the Main. This means that the net speed over the jib is much faster and thus develops more power. Furthermore the accelerated air coming off the TE of the jib helps accelerate the air over the front of the main, thus allowing higher peak velocities which in turn generates more power...

Now your points about slots on the leading edges of blades are interesting. If it were possible to build mechanically, I wonder if assymetrically deployed slots on the LE of the daggerboard would increase lift more than drag. It would be an interesting tow tank experiment.

 

[mark1234]

We're arguing frames of reference I think. It reminds me of being told that there's no such thing as a centrifugal force at school To me it's simple if you consider the board on it's own, separate from the hull. Something causes it to want to move to leeward - a force applied through the daggerboard casing. I'll leave it at that.

A moth is comparing apples and oranges, as we fly to windward on lift from the horizontal, which is a cambered, lifting section flying at a banked angle. I've actually had flow separate off the leeward side of the vertical in extremis.. For the more conventional foil, you can never have lift pulling you to windward, as the foil only generates lift as a function of AOA. No sideslip, no AOA, no lift.

If you look at a rig as a whole system, the AOA is in the reigon of ?25-30? degrees relative to the chord line - to me, that's a lot of AOA. Yes, the entry angle of the nose of the jib, and the nose of the main are relatively small, but that's not what AOA is. Without the jib you have to run a fatter (more cambered) sail, with the draft further forward in order to retain flow.. which makes the jib look an awful lot like a leading edge slat to me

 

[TingTong]

Thanks for clarifying Mark

OK - I see where you are going with this. There actually are THREE effects here that you are conflating. The board will see the normal AoA initially and that will change as it lifts out of the water because when angled the AoA changes. But that's not really the issue here.

The way to think about this is with a notion engineer's call a "Force Couple" - which is a fancy way of describing two forces acting in opposite directions at the opposite ends of a seesaw (ie with a pivot in the middle). In the case of a sail and a daggerboard you have

1. A force acting at the Center of Effort (CE) of the sail pushing the sail directly to leeward.
2. A force acting at the Center of Lateral Resistance (CLR) in a direction that in the vertical domain (as opposed to fore-aft) is a vector opposite of the leeforce - and with the blade down, this acts from below the waterline
3. The "righting force" generated by your weight on the trapeze.

#1 and #2 create a Force Couple http://en.wikipedia....uple_(mechanics) that rotates around the hull (slightly below the waterline). this Force Couple rotates the boat mast to leeward and the blade upwards. This is Effect #1

Effect #2 is the "righting force" - which is a second force couple that is the force of gravity acting on the Center of Mass of the trapezed crew being off centerline of the bouyancy of the hull. This Force Couple rotatates the boat Mast To weather and the blade upwards to leeward.

When Effect #1 and Effect #2 balance each other, you have a ZERO effective set of rotational forces acting on the sails and the blades.

In this balance of couples you still have the difference in the MAGNITUDE of the vectors of #1 and #2. on a Moth, it turns out that when heeled to weather, #2 is GREATER than #1 and the Moth climbs to weather. In an I14, the balance is close at speed but #1 is still slightly greater than #2 - so the boat makes leeway.

sorry. i don't get this. how can, what shall henceforth be referred to as forces no 1 and 2, be anything but equal and opposite? (the couple being counteracted by no3)

if a moth had a net force to windward, would it not accelerate in that direction proportionally to the net magnitude/mass.

similarly a standard i14 with it's force to leeward would accelerate to leeward, presumably until relativistic effects limited it at the speed of light?

surely equilibrium is maintained, typically by the varied angle of attack of the board.

p.s. could you possibly edit your post and replace effects 1 and 2 with A and B or something. My brain almost fried as i read that 1 and 2 create 1(a), while 1(a) is balanced by 3 to create 2b, or whatever!

 

[TingTong]

I find it particularly amusing that TingTong is prepared to play with something...

Always glad to amuse.

As I have already covered, i wasted a lot of a summer trying to get a gybing board working, sometimes when i could have been sailing. I found no benefit, but considerable hassle. When asked if it's worth installing one my honest answer is that i think not. I still find it interesting where any benefit might lie.

A flap on a thinner foil may (or may not) be a lower drag solution, but is one i will enjoy exploring. I thought i may as well get a plug made at the same time as my other foil plugs so it was little effort. I've had a simple mechanism in mind for years.

 

[BalticBandit]

Thanks for clarifying Mark

OK - I see where you are going with this. There actually are THREE effects here that you are conflating. The board will see the normal AoA initially and that will change as it lifts out of the water because when angled the AoA changes. But that's not really the issue here.

The way to think about this is with a notion engineer's call a "Force Couple" - which is a fancy way of describing two forces acting in opposite directions at the opposite ends of a seesaw (ie with a pivot in the middle). In the case of a sail and a daggerboard you have

1. A force acting at the Center of Effort (CE) of the sail pushing the sail directly to leeward.
2. A force acting at the Center of Lateral Resistance (CLR) in a direction that in the vertical domain (as opposed to fore-aft) is a vector opposite of the leeforce - and with the blade down, this acts from below the waterline
3. The "righting force" generated by your weight on the trapeze.

#1 and #2 create a Force Couple http://en.wikipedia....uple_(mechanics) that rotates around the hull (slightly below the waterline). this Force Couple rotates the boat mast to leeward and the blade upwards. This is Effect #1

Effect #2 is the "righting force" - which is a second force couple that is the force of gravity acting on the Center of Mass of the trapezed crew being off centerline of the bouyancy of the hull. This Force Couple rotatates the boat Mast To weather and the blade upwards to leeward.

When Effect #1 and Effect #2 balance each other, you have a ZERO effective set of rotational forces acting on the sails and the blades.

In this balance of couples you still have the difference in the MAGNITUDE of the vectors of #1 and #2. on a Moth, it turns out that when heeled to weather, #2 is GREATER than #1 and the Moth climbs to weather. In an I14, the balance is close at speed but #1 is still slightly greater than #2 - so the boat makes leeway.

sorry. i don't get this. how can, what shall henceforth be referred to as forces no 1 and 2, be anything but equal and opposite? (the couple being counteracted by no3)

Because an I-14 has a net movement to leeward. That means that it is being accellerated to leeward, and thus the force vector to leeward must EXCEED the force vector to weather

if a moth had a net force to windward, would it not accelerate in that direction proportionally to the net magnitude/mass.

similarly a standard i14 with it's force to leeward would accelerate to leeward, presumably until relativistic effects limited it at the speed of light?

And it does.

I'll see about drawing a picture with labels - which should help.

And Moths are NOT "apples and oranges" - the fact that moths can generate enough lift force to weather to accelerate to weather does not mean that I-14s boards are not generating lift to weather. It just means that the net balance of forces is different, but the forces involved are the same (if you exclude the vertical elevation lift forces).

 

[BalticBandit]

We're arguing frames of reference I think. It reminds me of being told that there's no such thing as a centrifugal force at school To me it's simple if you consider the board on it's own, separate from the hull. Something causes it to want to move to leeward - a force applied through the daggerboard casing. I'll leave it at that.

A moth is comparing apples and oranges, as we fly to windward on lift from the horizontal, which is a cambered, lifting section flying at a banked angle. I've actually had flow separate off the leeward side of the vertical in extremis.. For the more conventional foil, you can never have lift pulling you to windward, as the foil only generates lift as a function of AOA. No sideslip, no AOA, no lift.

If you look at a rig as a whole system, the AOA is in the reigon of ?25-30? degrees relative to the chord line - to me, that's a lot of AOA. Yes, the entry angle of the nose of the jib, and the nose of the main are relatively small, but that's not what AOA is. Without the jib you have to run a fatter (more cambered) sail, with the draft further forward in order to retain flow.. which makes the jib look an awful lot like a leading edge slat to me

Well yes this is ALL about "frames of reference" - but that's the key to understanding how gybers work and why I think Hallum's analysis is wrong.

And I see your point about sails operating at high angles of attack compared to aircraft, but remember the wings on Oracle were running much lower AoAs