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And then you have proa! Or you could have. Who said you could do this but it would be wrong? :lol:

 

Or could the freeboard be fairly low in the front and rise up to the measurement station to get the height necessary from the bottom, if the curves awit outside of min radii without the deck rising up too (or in other words the deck remaining flat at the lower dimension)? In other words is the skin of the hull the sides without the deck having to rise too? It's kind of cool looking...

 

The rule says nowhere at the measurement point shall the hull be less than 11" in depth and 30" in beam. Does this mean the sides of the freeboard of the hull, or the deck too?

 

I read it that some point on the hull, meaning hull or deck, must be higher than 275mm (11", if you must) above the keel line. I would interperate it that if, for instance, the sheerline was less than 275 above the keel line, it could still measure in if some point on the deck was more than 275 above the keel line. Or, all of the deck could be below 275 as long as the hull topsides projected above 275. This is all measured at the nominated measurement station which is located somewhere between 1350 and 2600 forward of the stern. Elswhere you can do what you like as far as hull depth is concerned.

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The blessings of a classical education.

 

B)

 

The attention to every possible detail.......

 

"and Alexander wept, for he realized he had no more worlds to conquer."

 

Edit- this is my response to the brain flat out observation.

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I should add that I think the 275mm depth measurement point has to be at, or outside of, the 750mm minimum beam. At least, that's how I interperate it.

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I guess the definition of "hull" and "deck" will be tested in this case.

 

The sheer line in plan view I would expect will define where the deck ends and the hull starts, the BMS and taught tapes are taken from the centre line of the hull, given the 45 degree rule at each end is defined about the centre line of the hull which then in turn requires the hull is symmetrical. Yes you can flare the hull but to create centre line you would have to have the same treatment to both sides of the hull.

 

Now given this exercise is about saving weight all this extra surface area (flares) I'm guessing will be equal to some extra structure internally i.e. a centre case......

 

I learnt allot when designing my boat, the biggest thing I learnt was how much things had to be traded for one benefit over another in the end I had my guess/gut feel for what I thought would do the job the best time will tell. I think I have a good product at least it feel really nice to sail in a good range of conditions.... Sounds like your brain is going flat out at the moment.

 

It is a wonderfully steep learning curve. If a learning curve is steep enough, can you get an endorphin rush?

 

:lol:

 

Paul

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post-2679-058482200 1303397449_thumb.jpg

post-2679-018517500 1303397491_thumb.jpg

 

Dragonfly IC - nearly finished!

 

Perhaps this is a more concrete example: It's kind of hard to see exactly from the pics, but if the tabs for the jib track on Dragonfly are in the same plane as the sides of the hull, would they be considered the hull, or part of the deck? Basically I'm doing a bigger version of the jib track tabs on Dragonfly at my measurement location, only I'm using them as sides of the hull to get to the minimum vertical and horizontall measurement, while leaving the deck in the same lower plane throughout the hull including the section where it passes between my big swoopy vertical tabs. In other words, like the tabs on Dragonfly, the hull rises independently and above the deck. Kind of like bullworks. (Where is my spellcheck when I need it?) I'd like to nail this down, as I have regretfully moved away from LB's, and this seems like the only real issue left. I hope.

 

Paul

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I have built a set of IC sails. I'm still messing with luff curve and mast bend. And trying to get more camber into the jib foot without mucking it up.

Higher hounds, stiffer mast tip and that unusual feature on the foredeck.

post-16686-038009600 1304038900_thumb.jpeg

post-16686-085335400 1304038916_thumb.jpeg

post-16686-059957000 1304038967_thumb.jpeg

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... and that unusual feature on the foredeck.

 

Is that a jib boom? It's a bit hard to tell from the photo.

 

Looks like a jib boom to me, and of course the system would be made beautifully and work just as good as it looks given the builder.....

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Looks like a jib boom to me, and of course the system would be made beautifully and work just as good as it looks given the builder.....

Hayden,

 

Are you saying that MY jib boom is not beautifull?? :lol:

 

Mal.

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... and that unusual feature on the foredeck.

 

Is that a jib boom? It's a bit hard to tell from the photo.

 

Looks like a jib boom to me, and of course the system would be made beautifully and work just as good as it looks given the builder.....

 

I think it's more a sprit. Well maybe a boom. I call it a swing jib. The sprit/boom pivots at the mast base. Kind of like a swing rig but not tied to the main boom.

 

I'm not sure it's fast. I'm not even really sure it's legal.

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This is of course, most excellent.

 

Of course, I nearly gave up LB's. Nearly. That's my theory, and I'm sticking to it. :D

 

Nice curves, Chris, nice curves. If you send me your email address, I'll send some pics of some morphing symmetrical 3d epp sections. They morph into asymmetrical sections. Not nearly as nicely developed as your stuff.

 

More Illegal though. You are using a stick, after all. You feel the madness, though, no?

 

Paul

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I think it's more a sprit. Well maybe a boom. I call it a swing jib. The sprit/boom pivots at the mast base. Kind of like a swing rig but not tied to the main boom.

 

I'm not sure it's fast. I'm not even really sure it's legal.

 

I'd be interested to know how you control that. It looks like the forestay is still attached to the foredeck?

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The upstands on the deck of Dragonfly will take the ends of the jib track, they do not extend / stick out past the line of the silhouette of the hull, so are legal, not sure if it makes any difference if you call them part of the hull, deck or a fitting

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... and that unusual feature on the foredeck.

 

Is that a jib boom? It's a bit hard to tell from the photo.

 

Looks like a jib boom to me, and of course the system would be made beautifully and work just as good as it looks given the builder.....

 

I think it's more a sprit. Well maybe a boom. I call it a swing jib. The sprit/boom pivots at the mast base. Kind of like a swing rig but not tied to the main boom.

 

I'm not sure it's fast. I'm not even really sure it's legal.

That's very intresting, I think i see what you are doing but I am sure all will become clear in a few months, hope you are bringing it to Germany, mainsail looks really good as well. When are you all having to pack your boats up? for me its almost nearer than some of the open meetings in the UK (well driving time anyway)

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The upstands on the deck of Dragonfly will take the ends of the jib track, they do not extend / stick out past the line of the silhouette of the hull, so are legal, not sure if it makes any difference if you call them part of the hull, deck or a fitting

 

I assume they don't stick out looking down on the hull sides from above. And I really like 'em. Elegant design. Can you look at them as a vertical unbroken extension of the hull, or are they inboard of the sheer? If the former, I'm a bit moRe sanguine about the legality of my approach.

 

Paul

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I think it's more a sprit. Well maybe a boom. I call it a swing jib. The sprit/boom pivots at the mast base. Kind of like a swing rig but not tied to the main boom.

 

I'm not sure it's fast. I'm not even really sure it's legal.

 

I'd be interested to know how you control that. It looks like the forestay is still attached to the foredeck?

 

It looks like you're coupling main and jib control to the sheet? If so, this is one of the finest traditional design avenues in sailing dinghy and canoe running rigging design. IIRR the Canoesletter and AYRS have been full of articles about this. When I was a teenager, I was convinced that a gentleman who figured out an elegant solution to this problem could be knighted. :lol: Really.

 

It should be legal.

 

Paul

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The upstands on the deck of Dragonfly will take the ends of the jib track, they do not extend / stick out past the line of the silhouette of the hull, so are legal, not sure if it makes any difference if you call them part of the hull, deck or a fitting

 

I assume they don't stick out looking down on the hull sides from above. And I really like 'em. Elegant design. Can you look at them as a vertical unbroken extension of the hull, or are they inboard of the sheer? If the former, I'm a bit moRe sanguine about the legality of my approach.

 

Paul

 

The upstands/jib track mounts are 1.5mm thick carbon plates, bonded to the inner skin of the hull, and angled so that they lean in a little, so definitely not extending past the sheer line in plan view.

The rules don't really make a distinction between the hull and deck. ( 'hull' kinda covers everything )

 

Leeboards don't sound a good idea to me...

 

My camber-induced unarig was faster than the bolt-rope conversion :angry: , but the bolt rope sail was more managable when tacking, after capsizing, launching, on the beach, rigging and derigging.

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The upstands on the deck of Dragonfly will take the ends of the jib track, they do not extend / stick out past the line of the silhouette of the hull, so are legal, not sure if it makes any difference if you call them part of the hull, deck or a fitting

 

I assume they don't stick out looking down on the hull sides from above. And I really like 'em. Elegant design. Can you look at them as a vertical unbroken extension of the hull, or are they inboard of the sheer? If the former, I'm a bit moRe sanguine about the legality of my approach.

 

Paul

 

The upstands/jib track mounts are 1.5mm thick carbon plates, bonded to the inner skin of the hull, and angled so that they lean in a little, so definitely not extending past the sheer line in plan view.

The rules don't really make a distinction between the hull and deck. ( 'hull' kinda covers everything )

 

Leeboards don't sound a good idea to me...

 

My camber-induced unarig was faster than the bolt-rope conversion :angry: , but the bolt rope sail was more managable when tacking, after capsizing, launching, on the beach, rigging and derigging.

 

 

Thanks Andy, I am officially off DB's. :(

 

And they say men can't commit.

 

One of the big differences between your una rig and Phil's was that you ran your sail pretty much down to the deck, which would seem to give your rig what 15-20% more luff than most of the mainsails out there. (Most, Jim.) So how did you think your rigs did upwind? Was the difference between the Camber Induced and the Bolt sails height and speed? Did your mast rotate on either rig?

 

Paul

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I had many versions... the long luff + vang pusher worked Ok, but the boom was a bit low.

Boom on the crewdeck, pusher on the mast stump, so no vang loads on the mast.

 

The next mod had a shorter luff, but higher boom, but still kicked up for headroom clearance, and this was better. Boom on the mast stump, conventional vang.

 

The next mod was the mast rotating with the boom, conventional vang ( int moth style ) - this worked best. ( i could get under the boom )

 

Next was to convert the sail/mast to boltrope - much better for handling afloat and ashore, but not as fast.

 

The camber induced rig was faster upwind - pointing higher, or going faster - I could feel it was low drag.

But... impossible to turn off the power, and it was always one side or the other, and usually the wrong side when it got difficult.

 

The board is further aft with una rig, and was mostly under the seat when downwind, so could only lift the board a bit.

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I think it's more a sprit. Well maybe a boom. I call it a swing jib. The sprit/boom pivots at the mast base. Kind of like a swing rig but not tied to the main boom.

 

I'm not sure it's fast. I'm not even really sure it's legal.

 

I'd be interested to know how you control that. It looks like the forestay is still attached to the foredeck?

 

It looks like you're coupling main and jib control to the sheet? If so, this is one of the finest traditional design avenues in sailing dinghy and canoe running rigging design. IIRR the Canoesletter and AYRS have been full of articles about this. When I was a teenager, I was convinced that a gentleman who figured out an elegant solution to this problem could be knighted. :lol: Really.

 

It should be legal.

 

Paul

 

Just another reason why I won't be knighted any time soon.

 

The swing of the jib is controlled by p&s guys and is entirely de-coupled from the main boom and sheet. It should make mark roundings a bit of a fire drill. I don't imagine I'll deploy it if it's blowing over 15.

 

You can see why I put such a big window in the jib. Otherwise I can't see where I'm going.

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The swing of the jib is controlled by p&s guys and is entirely de-coupled from the main boom and sheet. It should make mark roundings a bit of a fire drill. I don't imagine I'll deploy it if it's blowing over 15.

 

You can see why I put such a big window in the jib. Otherwise I can't see where I'm going.

 

When in the centerline position, do you lock the tack down to the foredeck somehow? Otherwise, how do you get enough forestay tension?

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The swing of the jib is controlled by p&s guys and is entirely de-coupled from the main boom and sheet. It should make mark roundings a bit of a fire drill. I don't imagine I'll deploy it if it's blowing over 15.

 

You can see why I put such a big window in the jib. Otherwise I can't see where I'm going.

 

When in the centerline position, do you lock the tack down to the foredeck somehow? Otherwise, how do you get enough forestay tension?

 

Yes, the end of the jib boom gets pulled down by what was the old forestay control.

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FWIW I had the first opportunity to sail my wide stern ex one design IC against other ICs this weekend. The weather varied from very windy to extremely windy, and boat speed was largely irrelevant. The best boat handlers did best, and I'm not one of them... Still think its a bit easier to sail with the wide stern, but it didn't stop me falling in enough times that I ran out of energy before making the start of the first race on day one... I honestly have no idea whether the performance vis a vis other ICs has changed I did manage to lead the fleet round the windward mark in one race on day two, but that was managing to get a shift right rather than boat speed I think.

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I have built a set of IC sails. I'm still messing with luff curve and mast bend. And trying to get more camber into the jib foot without mucking it up.

Higher hounds, stiffer mast tip and that unusual feature on the foredeck.

 

Lord, I miss the Salish Sea.

 

Paul

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If anyone is interested, Del sent me back an email on the legality of my Design Thoughts Whilst Tripping Down the Garden Path,:

 

No DB because of projections rule

 

Hull/deck: if I understand it correctly is governed by the fair curve part of the rule, no concave more than 100mm, so some relief there, at least a small compromise on my part.

 

Onward!

 

Paul

 

Oh- is the zipper under the boom, sleeve above the boom still legal? Saw that I think in an early part of this thread. Like page 10 or something.

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Could I get some learned opinion here? By raising the jib foot up off the foredeck I have lost the endplate of the deck.

How important is that endplate? And since I am off the deck now anyway would it be a better use of my limited sail area to hoist it up another 8" or so into cleaner air? Or maybe cut that 8" off the foot of the jib and add it to the main?

post-16686-044917000 1304553798_thumb.jpeg

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Chris,

 

I worry about this too because I use a jib boom. According to Marchaj (from memory) the end plate effect rapidly diminishes as the gap inceases. If you want to make good use of end plate effect, it's important to have the foot sitting right on the deck. So I guess that means that if you have a significant gap already, making it a bigger gap wont make much difference.

 

Mal.

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How important is that endplate?

From what I can make out back in the 60s when jibs were moved down the forestay onto the deck the idea spread amongst classes very quickly indeed, so you'd think the benefits must have been pretty significant, but I have no numbers to offer...

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There is a study done by Bill Hansen that centered around a 25mm gap, which seemed to be significant. I can't find the articles I know I have on the measured difference in pressure between the two sides of a jib, but in my conversations with Bill about a sail, he has said it is amazing what efficiencies you can get with just the first 20-30% of the chord endplated. I used to drive my dad crazy putting tufts under the foot of his jib to see what kind of airflow was going on under there, and even more that an inch would get the tufts moving to the low pressure side, which would be anecdotal to Bill's more formal study. Maybe Bill could chime in here?

 

My personal feeling is that if it isn't scraping the deck at least near the leading edge, there's no endplate. But fences do have some effect on the flow underneath them- I wonder since you're making your own sails now, Chris, if you could sew (glue?) in a rigid piece of shaped foam at the bottom of the jib that might help? Kind of like what the J boats used to call the Madison Avenue boom, which was a T shaped cross section. If it was shaped in such a way that the flow underneath was broken up into small vortices, the pressure difference might get ' stuck' there. At least the high pressure would be attracted to it. I don't know whether low pressure would be, and how much would leak from the vortices themselves into the low pressure area. But it would kind of be like a squarehead main top at the bottom, which would at the least be another vortex.

 

But as long as you're thinking about going up, you could experiment with moving the main sail area of the jib up higher. And there's been a lot of experimentation with that, mainly in the early 20th century, what with quadrilateral jibs, really high clew jibs (like in the middle) etc. Mainly in the J boats again. And that in turn would start influencing your main shape, maybe even encouraging movement to Tom Speer's egg shaped planform.

 

Frankly, given the slow speed of the wind close to the water, and the problems with the low Reynolds numbers that narrow jibs experience, I've wondered for a while why there's more sail down low in a jib, rather than up higher, other than it's easier to design. If you look at spinnaker design, though the most area isn't at the bottom. Look at SailRocket's sail planform. That planform as a jib would be a bitch to sheet, but as long as you're already using a boomed jib, you could just think of it as moving the boom up to the middlish of the jib, and sheeting it off the boom? And how many ounces does one of your carbon jib sticks weigh? Cheasapeake Bay Log Canoes have used quadrilateral jibs and mains for some time now. And they are canoes........ :D

 

Paul

 

Paul

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There is a study done by Bill Hansen that centered around a 25mm gap, which seemed to be significant. I can't find the articles I know I have on the measured difference in pressure between the two sides of a jib, but in my conversations with Bill about a sail, he has said it is amazing what efficiencies you can get with just the first 20-30% of the chord endplated. I used to drive my dad crazy putting tufts under the foot of his jib to see what kind of airflow was going on under there, and even more that an inch would get the tufts moving to the low pressure side, which would be anecdotal to Bill's more formal study. Maybe Bill could chime in here?

 

My personal feeling is that if it isn't scraping the deck at least near the leading edge, there's no endplate. But fences do have some effect on the flow underneath them- I wonder since you're making your own sails now, Chris, if you could sew (glue?) in a rigid piece of shaped foam at the bottom of the jib that might help? Kind of like what the J boats used to call the Madison Avenue boom, which was a T shaped cross section. If it was shaped in such a way that the flow underneath was broken up into small vortices, the pressure difference might get ' stuck' there. At least the high pressure would be attracted to it. I don't know whether low pressure would be, and how much would leak from the vortices themselves into the low pressure area. But it would kind of be like a squarehead main top at the bottom, which would at the least be another vortex.

 

But as long as you're thinking about going up, you could experiment with moving the main sail area of the jib up higher. And there's been a lot of experimentation with that, mainly in the early 20th century, what with quadrilateral jibs, really high clew jibs (like in the middle) etc. Mainly in the J boats again. And that in turn would start influencing your main shape, maybe even encouraging movement to Tom Speer's egg shaped planform.

 

Frankly, given the slow speed of the wind close to the water, and the problems with the low Reynolds numbers that narrow jibs experience, I've wondered for a while why there's more sail down low in a jib, rather than up higher, other than it's easier to design. If you look at spinnaker design, though the most area isn't at the bottom. Look at SailRocket's sail planform. That planform as a jib would be a bitch to sheet, but as long as you're already using a boomed jib, you could just think of it as moving the boom up to the middlish of the jib, and sheeting it off the boom? And how many ounces does one of your carbon jib sticks weigh? Cheasapeake Bay Log Canoes have used quadrilateral jibs and mains for some time now. And they are canoes........ :D

 

Paul

 

Paul

 

 

I think the interaction with the main plays a big part in determining the best planform for a jib and that the jib and main planform needs to be considered as a whole rather than two separate sails.

Sticking some sort of endplate on the jib foot seems like it might work but I'm pretty sure I've read of reasons why an endplate wouldn't work on the head of a sail which, if true, would probably be the same reasons an endplate wouldn't work at the foot of a sail. Does anyone know where to find that information?

 

It would be fun and easy to test though.

 

Manfred Curry would have had the jib clew up as high as the main tack and if the jib isn't endplated on the deck anyway that idea has some appeal. From what I can tell though Manfred believed a lot of things just because his reasoning told him they must be so. Not because he proved it.

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But, Manfred had a really good time. I mean, brakes on a canoe?

 

:lol:

 

Edit- forgot while I was posting here. One of the reasons I've seen that the endplate is a problem on top is upwash is hard to manage, which is one of the reasons you see so much variation on airplane wingtips. Depends on planform too. I've never seen anything on, uh, downwash?

 

Or maybe the flow sneaking around to the low pressure side at the foot causes upwash down lower, and faster?

 

Now I'll have to spend hours in my office looking for articles. Darn. Purcell and Aero. B)

 

Paul

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But, Manfred had a really good time. I mean, brakes on a canoe?

 

:lol:

 

Edit- forgot while I was posting here. One of the reasons I've seen that the endplate is a problem on top is upwash is hard to manage, which is one of the reasons you see so much variation on airplane wingtips. Depends on planform too. I've never seen anything on, uh, downwash?

 

Or maybe the flow sneaking around to the low pressure side at the foot causes upwash down lower, and faster?

 

Now I'll have to spend hours in my office looking for articles. Darn. Purcell and Aero. B)

 

Paul

 

Couple of ignorant questions here...

 

How would a "Madison Avenue Boom" be measured WRT Sail area? If its not measured, rather than just foam, wouldn't a series of mylar "T Tabs" (each say 1/2" long to allow shape of the sail to still work fine) say about 4" on each side of the bottom of the sail work better?

 

As for Upwash - I always thought that what was causing the upwash was the "sweep" of the LE of the jib (caused by the angled forestay) and the resulting skew in flow. And that on aircraft, wingtip endplates reduced drag by reducing tip vortice energy rather than by reducing "pressure leakage" - So wouldn't the same issue apply to a sailplan with a forestay mounted jib?

 

IE "upwash" increases drag at the mast tip not so much "leakage"?

 

If this is so, I'd be curious about the dif between the impact of a fractional rigged foresail vs. Masthead. And it would also seem that a Masthead rigged foresail would benefit from a "winglet" plate at the top of the Mast. D'ya know of any experiments with a flat plate on the top of the mast reducing drag? I know that in the era of AL masts, that's a lot of "weight aloft", but for "endplate effect", you could just glue a 2ply sheet of CF up there which would add less weight than the Tricolor

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In the mid-late '80's, a Naval Architect student at UC Berkeley did a CFD study on 'closing the gap' with a windsurfing rig and found significant gains in the last few cm's of gap closure with a 6.5sqm sail. Anyone who has windsurfed with performance equipment in marginal conditions has experienced this effect and found it dramatic.

 

post-9717-094236200 1304614690_thumb.jpgpost-9717-081712700 1304614954_thumb.jpg

 

In post #47 by SlackWater_SF on 31 December 2005 - 10:33PM in this thread: http://forums.sailinganarchy.com/index.php?showtopic=27993&st=25 I found the following attributed to Tom Speer:

 

End-Plate Effect = Good ?:

An equation on drag, lift, gap ( E ) follows, along w/some of Mr. Speer's words:

Image351.gif

 

"E is the Oswald efficiency factor, and is a function of the planform geometry and the surface effects. The value of e for the minimum drag planforms is shown in Figure 5. For zero gap, e is two, which is in agreement with classic wing theory. With as little as a 1% gap, however, e drops by two-thirds to 1.36. "

Unfortunately, the above applies to una-rigs. My guess is it also applies to jibs but Tom could no doubt confirm and expound on the subject.

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Jib endplate is really nice, but it doesn't trump other factors.

I am more confused by what happens at the head of the jib and how that ripples across the lee side of the main.

What goes fast, never seems to be what looks right, and vice versa.

SHC

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But, Manfred had a really good time. I mean, brakes on a canoe?

 

:lol:

 

Edit- forgot while I was posting here. One of the reasons I've seen that the endplate is a problem on top is upwash is hard to manage, which is one of the reasons you see so much variation on airplane wingtips. Depends on planform too. I've never seen anything on, uh, downwash?

 

Or maybe the flow sneaking around to the low pressure side at the foot causes upwash down lower, and faster?

 

Now I'll have to spend hours in my office looking for articles. Darn. Purcell and Aero. B)

 

Paul

 

Couple of ignorant questions here...

 

How would a "Madison Avenue Boom" be measured WRT Sail area? If its not measured, rather than just foam, wouldn't a series of mylar "T Tabs" (each say 1/2" long to allow shape of the sail to still work fine) say about 4" on each side of the bottom of the sail work better?

 

As for Upwash - I always thought that what was causing the upwash was the "sweep" of the LE of the jib (caused by the angled forestay) and the resulting skew in flow. And that on aircraft, wingtip endplates reduced drag by reducing tip vortice energy rather than by reducing "pressure leakage" - So wouldn't the same issue apply to a sailplan with a forestay mounted jib?

 

IE "upwash" increases drag at the mast tip not so much "leakage"?

 

If this is so, I'd be curious about the dif between the impact of a fractional rigged foresail vs. Masthead. And it would also seem that a Masthead rigged foresail would benefit from a "winglet" plate at the top of the Mast. D'ya know of any experiments with a flat plate on the top of the mast reducing drag? I know that in the era of AL masts, that's a lot of "weight aloft", but for "endplate effect", you could just glue a 2ply sheet of CF up there which would add less weight than the Tricolor

 

 

Ignorant questions from you. Right. ;)

 

I really meant the "Madison Ave Boom" as a historical example of an attempt at an endplate. Hard to know what the ratio of endplate to chord

to fence? endplate? would have to be.

 

But I'm still looking..

 

Every time I have seen a description of tip vortices, the reason they start is high pressure stuff going to a low pressure area by going around the tip. Control of that vortice, or maybe a better word is management of that vortice seems to be the aim. The strategies go from multiple foils sprouting at the end of the wind, to curved up, etc. I've assumed that upwash makes things more dynamic, but does it change the equation? Does the energy of a tip vortex become less if it is smaller? Or broken up into smaller vortexes? Leakage is an old fashioned term for it, but I have been reading Munk lately, so I apologize. It seemed descriptive.

 

I messed with an endplate in my windsurfer days, but I out thought myself, in hindsight, and proved nothing. I became obsessed with up wash and down wash until I though an endplate was only better in a small range of rig inclination like when the flow was right across the luff at right angles to it. At least the Ampex Grand Master 1/4" recording tape I had up at the tip of the mast seemed to indicate that. I then tried an endplate that rotated around the end of the mast in the same plane as the sail fabric (up and down), but then thought it had to be held at some angle to the flow in order for it to work, and thought that small bungie chords might work, but then became convinced that they were screwing up the flow, and then I mangled everything during a nice face plant and gave it up.

 

The end.

 

Paul

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I checked out Marchaj. In "Sail Performance" pp 178-186 there is a section on a wind tunnel experiment to determine the effect of gap below the sail and also hull interaction. The test was conducted using a rectangular planform solid untwisted wing. The gaps tested were 0%, 13% and 29%, with the base plane being the wind tunnel turntable.

 

The results show that even with no gap, the increase in effective aspect ratio is nowhere near the theoretical value of 2. Furthermore, the efficiency of the foil with the 29% gap was better than for the 13% gap. Marchaj attributes these results to the significant wind gradient effects. The theoretical effective span value of 2 is only possible if the (infinite) reflection plane is frictionless and there is uniform flow over the whole span. In reality, the reflection plane causes a velocity gradient, which significanly reduces the expected benefits.

 

Reading between the lines, it would be very difficult to draw any hard conclusions from these results because there are a lot of variables: planform; twist; actual velocity gradient on the day. Further reading also shows that the presence of the hull itself can significantly effect the efficiency of the sail, in a positive way, and not necessarily just becuase it can be used to close the gap.

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Jib endplate is really nice, but it doesn't trump other factors.

I am more confused by what happens at the head of the jib and how that ripples across the lee side of the main.

What goes fast, never seems to be what looks right, and vice versa.

SHC

 

Steve, when Lorrie and I first had Amati, anyone who saw her will tell you I had a, er, large amounts of telltales on the main and the jib, to 'investigate' that very thing. I wish I had pics, but they got lost when I lost my iphone with the pics. No download.

 

We had a normal pinhead jib at the time. The results were that the Ampex Grand Master on the lee side showed flow disturbance, and over a pretty wide area- like 12" to 2', depending on how straight the leach of the jib was relative to the mast. So I started adding more twist until the tape showed a nice line across at that point. Having a bunch of tape at the top of the jib showed a real mess, and I had to shorten the tape from 12" to 8" to 4" to keep them from knotting up. a couple of times the 12" tape actually wound up like a trailing vortex, which was exciting for me, at least. Flow was never really smooth for very long down to about 1-1.5' below the tip. My grand plan was to have a square top jib built, but Lorrie was not, um, enthused about losing the self furling function as a result. So I never have seen what a smaller tighter vortex might look like going across the main.

 

To describe the flow across the main at the point of the jib head, which was at 3/4 up the mast? It was always changing. I could not get a steady state other than when the jib head was really close to luffing. And it was a cruising jib, with lots of laminations at the top, so I could get it so It would be weather vaned without shaking that I could see, and I could get the twist so there was no shaking in the leech.

 

This is kind of hard to explain, so I'll try to break it down into the telltalles that were directly behind the tip of the jib, and then the telltales that were above and below that area. It helps to know that Amati has 8.5' of draft, a pretty high sail AR, and when she's going upwind, the Windex points straight forward. I had to learn the difference between wind shifts and velocity shifts big time. Anyway, there were a few what I call conditions- and this is all on the low pressure side of the main; 6" long telltales; the main planform is close to looking like a Hobie 16 mainsail, and is full battened. Ballenger rounded square section 4" wide, 8" long. She weighs 9600lbs, and the mast is near 55' tall. The sloop part of the rig is very IC like, although the hounds are a bit higher, and she has a stiff mast. When I found out how much a compliant rig would cost to develop, we went to stiff mast concept. B)

 

-the tufts standing straight out

-the tufts standing straight out and the last inch or two twirling. I shit you not. This is while the rest of the tufts on the mast were streaming straight back.

-the tufts standing kind of half way out, and then banging against the sail, sometimes in a rytthm, from slow, ~2 seconds or so, to shredding the telltales

-the telltales staying plastered against the main, but oscillating up and down, grinding against the sail

-the telltales kind of staying about an inch above the sail as if suspended, but then the leach telltale would swirl I think clockwise

The area this all happened in was 6" for the first two, and the last one, and a much bigger area for the 3rd and 4th one. Sometimes it fanned out a bit, from the the mast out.

 

Above this point, the telltales would sometimes point towards the imaginary line of the jib turbulence

sometimes dance up and down while on the sail.

They never pointed away for more than a second or so.

The telltales above the next batten (full length) up didn't seem stirred by all this. It is about 3' above the jib hounds.

 

Below this point, the telltales were not as involved, although sometimes they would dance a little, pointing towards and away from the line.

But usually pointed towards the line.

 

The next full length batten is 3' below the jib hounds. Tufts below this point not interested.

 

The condition I like on the main is with the tufts streaming straight back, and the leach telltales lifting a tad around to the low pressure side. But just a tad. I have a full width traveller, so that is incidence control, the sheet is leech control.

 

The first 2 and the last one usually tended to happen in steady air, which is our North wind (which is kind our sea breeze), the 3rd and 4th one in more lumpy air, which is our South stuff. I mean Puget Sound.

 

So I think that there was a band of the main that was effected by vortices generated by the head of the jib. You could see stuff happening, but it wasn't very steady state, and changed sometimes slowly, sometimes rapidly, depending I think on the type of wind, North or South. If we don't sell her, I would like to get a square head jib and go Gentry on the sails again, but I took everything off for now so as not put off prospective buyers. I thought I could detect differences in heeling in different vortex patterns when wind velocity didn't change, which would imply drag changes. Whether I'm right that keeping the head of the jib not drawing is a good thing is anyone's guess- my gut hunch, and one I've stuck with since I posted it many moons ago is that if the vortex off the jib top is coherent enough, it acts as a type of dynamic fence that can suck in high

pressure as well as pushing away low.

 

Our mast is very vertical, and if there is any upwash on either the main or jib, it's not very obvious.

 

Anyway, anecdotal evidence. Don't know if it's what you wanted........

 

When Stradivarious passed us, they had some tufts up by the jib hounds. I think you can see them on Youtube on the 'close encounters' part of the vid.

 

Paul

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Every time I have seen a description of tip vortices, the reason they start is high pressure stuff going to a low pressure area by going around the tip. Control of that vortice, or maybe a better word is management of that vortice seems to be the aim. The strategies go from multiple foils sprouting at the end of the wind, to curved up, etc. I've assumed that upwash makes things more dynamic, but does it change the equation? Does the energy of a tip vortex become less if it is smaller? Or broken up into smaller vortexes? Leakage is an old fashioned term for it, but I have been reading Munk lately, so I apologize. It seemed descriptive.

 

You are right that the tip vortices do "roll" from the flow from the high side to the "low" side, but the energy in them is proportional to the spanwise flow velocity and not the pressure diff. And yes, the smaller the vortices the lower the energy in them and hence the less drag.

 

But its important to be careful not to read TOO MUCH into the shape of jet plane tips, because some of them are there more for style than any actual benefit. One Boeing engineer told me that the 747s with tip winglets turn out to be a "push" in terms of energy savings. That the drag reduction caused by the reduction in tip vortices was offset by the surface area drag of the winglets themselves

 

And its more than just pressure leakage because some of the designs use tubular ends that trail behind the tip, the idea being a bit like a lighting rod - to FOCUS the vortex into a smaller but more focussed one.

 

Again, I'm not sure how well each of these technologies works, but it would be interesting to see if a lightweight "winglet" bolted to the mast-tip would work. I'd start with a square shape and experiement with wedges, reverse wedges etc. And with a "square top main" you could put that "Madison Avenue Boom" but using Mylar T's right on top of the mainsail...

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But its important to be careful not to read TOO MUCH into the shape of jet plane tips,

The other reason not to read too much in them is that the long distance commercial jet airliner spends the majority of flying time within a narrow speed range, so can be optimised to that in a way that would be quite undesirable for a racing boat.

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Burt Rutan on tip shapes: "I don't care, just make it longer."

The tips of commercial airliners make the wings longer , but due to the limiting factor of airport gates, the actual span can't increase , so they sweep up.

 

On boat with a narrow bow, like an IC, It is pretty easy to think of the lee side of the bow as a continuation of the lee side of the jib. So getting a seal down to the "infinite fence" is imaginable.

SHC

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Burt Rutan on tip shapes: "I don't care, just make it longer."

The tips of commercial airliners make the wings longer , but due to the limiting factor of airport gates, the actual span can't increase , so they sweep up.

 

On boat with a narrow bow, like an IC, It is pretty easy to think of the lee side of the bow as a continuation of the lee side of the jib. So getting a seal down to the "infinite fence" is imaginable.

SHC

 

From that you might infer that keeping the bow down as far as the surface of the water is concerned might be better than bow up, which is what Chris and some others have been doing. Might also infer that for a bow up boat, an endplated una rig farther back might work a bit better.

 

You'll never guess which approach I'm taking. B)

 

Paul

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How wide does the endplate need to be? If you want to move your jib sail area area moved up, you could do a jib that is generally shaped like the sail rocket airfoil, but with square ends, the bottom one endplated, and the mid controlled by a wish boom, the ends maybe 1' wide? Could be more straight edged to match the mast if you want it to act as a leading edge flap .

 

Chris, didn't you have a Birig jib on your Wylie?

 

Paul

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Would a tubular rod extending aft from the top of a squarehead come under rule 11 c "the greatest projected area of spars other than mast, boom, jibstick and the boom of a boomed foresail shall be included in the sail area"?

 

I've seen some literature on this in studies on eagle and hawk and MAV (flapping) flight low re stuff.

 

Paul

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Would a tubular rod extending aft from the top of a squarehead come under rule 11 c "the greatest projected area of spars other than mast, boom, jibstick and the boom of a boomed foresail shall be included in the sail area"?

 

I've seen some literature on this in studies on eagle and hawk and MAV (flapping) flight low re stuff.

 

Paul

What about a foredeck that instead of being concave is convex, I rising to meet the jib and generate "endplate" effect in light to moderate upwind.

 

As for the Ruttan quote - he's a real character with deep insight, but he also makes some wild statements kind of in the manner of a curmudgeon. A "swept up wing" does NOT do the same thing as the wing in horizontal shape.

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Baltic:

Perhaps they do the same thing in a different way?

 

Just saw this quote in a winglet article attributed to Dave Akiyama, manager of aerodynamics engineering in Boeing product development: "We find that it really doesn't matter what kind of wingtip device you use-they're all like span," he says. "The devil is in the details. Span extensions are the easiest and least risky."

 

As for the Ruttan quote - he's a real character with deep insight, but he also makes some wild statements kind of in the manner of a curmudgeon. A "swept up wing" does NOT do the same thing as the wing in horizontal shape.

Burt Rutan on tip shapes: "I don't care, just make it longer."

The tips of commercial airliners make the wings longer , but due to the limiting factor of airport gates, the actual span can't increase , so they sweep up.

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Baltic:

Perhaps they do the same thing in a different way?

 

Not quite. A span extention contibutes to lift. A perpendicular fence doesn't. Therefore if you choose to use a fence it should be because there is a reason why you can't just increase the span.

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I think a forward force vector is ideally generated from the tip vortex wrapping around the leading edge of the winglet, so even if it doesn't contribute much to lift, it has the effect of reducing drag, improving the ratio by recapturing energy normally lost in the vortex and converting it into thrust.

 

Yes more span is better but in reality span is almost always limited by either rules, functional limitations or (rarely) structural considerations. So winglets have their place perhaps, even in sailing, e.g. vestas sailrocket.

 

Anyway what do I know about this stuff? As you were.

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I think a forward force vector is ideally generated from the tip vortex wrapping around the leading edge of the winglet, so even if it doesn't contribute much to lift, it has the effect of reducing drag, improving the ratio by recapturing energy normally lost in the vortex and converting it into thrust.

 

Yes more span is better but in reality span is almost always limited by either rules, functional limitations or (rarely) structural considerations. So winglets have their place perhaps, even in sailing, e.g. vestas sailrocket.

 

Anyway what do I know about this stuff? As you were.

 

Winglet primary function is drag reduction (which a shorter chord, longer span does as well)

Secondary is that by reducing spanwise flow, it "recovers" some of that velocity along the chord (the air that would normally spill over the tip into the vortex HAS to flow somewhere, so aft over the TE is the next place) which means more lift - which a longer span does as well.

 

So winglets create more power (hence the "endplate effect" on sailboards) which is LIKE adding span, but the don't work quite the same way. Which is why I think adding a winglet to the TOP of a fractional jib wouldn't have much effect, whereas adding it to the top of the mast or the top of a "squarehead main" is a different thing.

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Another way of looking at winglets is in terms of span-wise flow. It seems that most modeling in high speed aero is modeled as 2d. If I understand it right, there are 2 reasons

 

- the momentum of the fluid increases it's tendency to flow along the chord of an airfoil

 

- most high speed foils are pretty high AR, so the particles think they are looking at an infinite span foil

 

At lower speeds, in general, neither of these reasons seem as reliable, as re decreases span wise flow increases dramatically across the entire body. (You can look at Sun & Boyd, Simulation of Gas Flow over Micro Scale Airfoils Using a Hybrid Continuum Part Approach)

 

Monttinen and Latek did some work on winglets in low speed flow. Monttinen concluded that winglets slightly increase performance in MAV's:

winglets that reach forward of the 50% chord location work best- winglet height and cant angle don't make much difference. But as far I can tell, the height of a winglet adversely affects drag while increasing lift. CL/CD change isn't much. But winglets seem to change the pitching moment on wings.

 

I do have a question though that is only elliptically related, how do you figure out what the wing loading is on an IC? Is it the foot pounds of my weight at the end of the seat? It seems a lot of efficiencies are gained by lighter wing loading.

 

Paul

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I think a forward force vector is ideally generated from the tip vortex wrapping around the leading edge of the winglet, so even if it doesn't contribute much to lift, it has the effect of reducing drag, improving the ratio by recapturing energy normally lost in the vortex and converting it into thrust.

 

Yes more span is better but in reality span is almost always limited by either rules, functional limitations or (rarely) structural considerations. So winglets have their place perhaps, even in sailing, e.g. vestas sailrocket.

 

Anyway what do I know about this stuff? As you were.

 

Winglet primary function is drag reduction (which a shorter chord, longer span does as well)

Secondary is that by reducing spanwise flow, it "recovers" some of that velocity along the chord (the air that would normally spill over the tip into the vortex HAS to flow somewhere, so aft over the TE is the next place) which means more lift - which a longer span does as well.

 

So winglets create more power (hence the "endplate effect" on sailboards) which is LIKE adding span, but the don't work quite the same way. Which is why I think adding a winglet to the TOP of a fractional jib wouldn't have much effect, whereas adding it to the top of the mast or the top of a "squarehead main" is a different thing.

 

 

I can see winglets decreasing span wise flow, but as atg implies, cant they also exploit span wise flow? That would explain CL and CD going up.

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I think a forward force vector is ideally generated from the tip vortex wrapping around the leading edge of the winglet, so even if it doesn't contribute much to lift, it has the effect of reducing drag, improving the ratio by recapturing energy normally lost in the vortex and converting it into thrust.

 

Yes more span is better but in reality span is almost always limited by either rules, functional limitations or (rarely) structural considerations. So winglets have their place perhaps, even in sailing, e.g. vestas sailrocket.

 

Anyway what do I know about this stuff? As you were.

 

Winglet primary function is drag reduction (which a shorter chord, longer span does as well)

Secondary is that by reducing spanwise flow, it "recovers" some of that velocity along the chord (the air that would normally spill over the tip into the vortex HAS to flow somewhere, so aft over the TE is the next place) which means more lift - which a longer span does as well.

 

So winglets create more power (hence the "endplate effect" on sailboards) which is LIKE adding span, but the don't work quite the same way. Which is why I think adding a winglet to the TOP of a fractional jib wouldn't have much effect, whereas adding it to the top of the mast or the top of a "squarehead main" is a different thing.

 

 

I can see winglets decreasing span wise flow, but as atg implies, cant they also exploit span wise flow? That would explain CL and CD going up. And at a lower re.

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So I've been thinking about Steves question about what the jib top vortex does as it goes across the lee of the mainsail, and assuming that it is induced drag, is it better to have it tight against the main, or farther away?

 

Paul

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The subject of winglets on sails comes up once in a while but IMHO, the highly specific geometric orientation required for a winglet is impossible given the variable heel, pitching and massively turbulent nature of wind. The only water-borne sailing vehicle without pitching is a windsurfer (with a universal joint) or possibly a hydrofoil craft like a Moth or Hydroptère but the the other variations remain. To drag around a winglet on the top of a sail which is likely only operating part of the time or under very limited conditions seems (to me) like a poor solution.

 

Winglet primary function is drag reduction (which a shorter chord, longer span does as well)

Secondary is that by reducing spanwise flow, it "recovers" some of that velocity along the chord (the air that would normally spill over the tip into the vortex HAS to flow somewhere, so aft over the TE is the next place) which means more lift - which a longer span does as well.

 

So winglets create more power (hence the "endplate effect" on sailboards) which is LIKE adding span, but the don't work quite the same way. Which is why I think adding a winglet to the TOP of a fractional jib wouldn't have much effect, whereas adding it to the top of the mast or the top of a "squarehead main" is a different thing.

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I have built a set of IC sails. I'm still messing with luff curve and mast bend. And trying to get more camber into the jib foot without mucking it up.Higher hounds, stiffer mast tip and that unusual feature on the foredeck.

 

it is unfair how nice your first sails are. Those things look stupid fast

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With Chris' boat I think people are missing the really neat thing with his jib boom arrangement...

 

Albacores use a pole that hangs in front of the mast and deploys to either side, with a separate line that regulates the length, to push the clew of the jib down in a very similar way. Might be a simpler thing to do. George had one for awhile. Very light.

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Albacores use a pole that hangs in front of the mast and deploys to either side, with a separate line that regulates the length, to push the clew of the jib down in a very similar way. Might be a simpler thing to do. George had one for awhile. Very light.

I have one, but its really hard to get jib sheet lengths sorted out. I also deplore all the gubbins on the front surface of the mast, and most especially the pole hanging in the slot. I'm still playing with it, but am not totally convinced.

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With Chris' boat I think people are missing the really neat thing with his jib boom arrangement...

 

[Minor point of historical interest just going to show that there's nothing new under the sun]

Looks like "kitty gear", used by the Falmouth fleet of Sunbeam traditional keelboats instead of spinnakers. Don't know how long they've been using it, but the fleet's been around for 87 years.

http://www.flickr.co...rdy/2937265607/

 

Falmouth%20sunbeam%20champs%20june09%20011.jpg

 

Fslmouth%20Danny%20Winning%20Panoramic%20DSCF0044.jpg

 

[/Mpohijgtsttnnuts]

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87 seems like an old class, until one considers canoes with sliding seats are around 130 years old. The jib boom has been on several canoes in the past few decades I think; Jens may have been running one in Bristol in 2002 IIRC.

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With Chris' boat I think people are missing the really neat thing with his jib boom arrangement...

 

[Minor point of historical interest just going to show that there's nothing new under the sun]

Looks like "kitty gear", used by the Falmouth fleet of Sunbeam traditional keelboats instead of spinnakers. Don't know how long they've been using it, but the fleet's been around for 87 years.

http://www.flickr.co...rdy/2937265607/

 

Falmouth%20sunbeam%20champs%20june09%20011.jpg

 

Fslmouth%20Danny%20Winning%20Panoramic%20DSCF0044.jpg

 

[/Mpohijgtsttnnuts]

 

Damn! Can I never be the first? There's always some Brit or Aussie that rolls in and says, " Yeah we've been doing that since 1922". But I guess we can assume those keelboats wouldn't be using it if it didn't work. So that's encouraging.

 

atg, what does "simpler" mean? Where's the fun in that? One of my hopes with the swing jib was that it would be effective on a reach or sailing deeper with lee side flow attached on both sails. That's a little different than simply poling out the jib clew.

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Simpler to put on the boat for sure. George stuck it on with a section of kite tube, string , two cleats, turning block and a mast fitting. Probably lighter also. You can adjust the height and projection of the inboard portion of the pole from the mast.

 

Aero wise no more clutter than losing the jib endplate.

 

I agree it might not put the clew in the exact same place as your setup but it would get close and not require much alteration of the foredeck.

 

Agreed simpler is not always more fun, as my recent moth project has confirmed. But it is usually lighter.

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Simpler to put on the boat for sure. George stuck it on with a section of kite tube, string , two cleats, turning block and a mast fitting. Probably lighter also. You can adjust the height and projection of the inboard portion of the pole from the mast.

 

Aero wise no more clutter than losing the jib endplate.

 

I agree it might not put the clew in the exact same place as your setup but it would get close and not require much alteration of the foredeck.

 

Agreed simpler is not always more fun, as my recent moth project has confirmed. But it is usually lighter.

 

No no, of course you're right. I was joking about "simpler". My system is vastly heavier and more complicated than anything else I can imagine.

 

But you can see that on my system the jib luff and leach are reversed from that of a winged out jib, right? That must be worth a few points if only in the dinghy park.

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Chris.

 

For Pete's sake, post some higher resolution shots of this gadget, preferably with a youtube link w/closeups of the mechanism in action (doesn't even need to be on the water) . You're being so cagey that no one even knows what the hell you're being cagey about. You can't let just PART of the cat out of the bag. Nobody will figure it out in time for the Worlds, except for you, right?

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Chris,

 

Do you use an outer forestay to hold the rig up when the jib is poled out, or do you just rely on your skill i.e. you won't broach and round up into the wind? :D

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Chris, are you defining some sort of progressive or static distance ratio (for lack of a better word) of the projection of the jib to windward of the mast as it works through different points of sail?

 

Or can you tweak it depending on conditions?

 

Paul

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post-16686-053946800 1305213158_thumb.jpeg

Chris, are you defining some sort of progressive or static distance ratio (for lack of a better word) of the projection of the jib to windward of the mast as it works through different points of sail?

 

Or can you tweak it depending on conditions?

 

Paul

 

 

You're right manuel, I'll try to get some better pictures in the next couple of days.

 

Mal, you can see the outer forestay in this picture. You can imagine what a mess it would be to roll in to weather at speed while the jib is swung out if that forestay wasn't there. Not that I ever capsize!

 

Paul, The jib self tacker traveler is fixed to the jib boom so the distance from the jib to the mast remains constant as the jib boom swings.

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Hey Steve & Phil (or anyone else who knows)- I've been doing models based on the G Bros formula of 1" = 1', which means that .8mm = 4mm, 1.2mm = 1/4 ply, etc.. I've seen that models are being made 1/4 scale, and Steve you mentioned you were getting some .8mm aircraft ply and were going to use it for 1/4 models. Does .8mm scale up to 3mm ply at 1/4 scale for IC's?

 

Kind of a basic question, I guess.

 

Working at 1" = 1' is kind of smallish.

 

Paul

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Isn't it strange how there's always 10 knots less breeze on a video than there was when you were out there?

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Amati,

I think my models were 1/5 with 0.8mm ply. They were chewed up by an energetic puppy a few yeras back so I can not check.

Stiffer ply will make sections less rounded but some successful designs show that is OK too.

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Amati,

I think my models were 1/5 with 0.8mm ply. They were chewed up by an energetic puppy a few yeras back so I can not check.

Stiffer ply will make sections less rounded but some successful designs show that is OK too.

 

The blessings of the metric system.

 

Our West Highland White Terrier puppy, well, he's still a puppy, chewed up my wife's Alain Mikli's. But I think plywood may be worse. :angry:

 

Puppy charms. :lol:

 

Walkies!

 

Did the expanded polystyrene you used in the bow stay put? Or wanted to stay put? I printed out your blog. Thank you thank you.

 

As long as I'm online, I may as well ask- since the rules mandate pintails, any thoughts on pressure recovery after the point of maximum beam?

 

Ah, philosophy.....

 

Paul

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Isn't it strange how there's always 10 knots less breeze on a video than there was when you were out there?

 

Puffs to 30. At least. :lol:

 

Nice vid, and nicely edited, esp.the soundtrack as it related to the visuals.

 

 

Paul

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This boat, if you will indulge me for a moment, is an intervention into certain Edwardian views of Intellectual Empire. It is the warning shot of an emerged America. In a political sense it is a cautionary design that addresses the role of complexity and how it relates to the physical world. Hugely progressive, it is, in some ways, a critique of all those predecessors that (historically) vex your creative impulse. It is hugely sympathetic to those of those of us seduced by the notion of what a sailing canoe might be. Not an atavism, but a post modern reaction to the eternal verities of wind and tide.

 

Within the rule, of course. B)

 

Ha!

 

Paul

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This boat, if you will indulge me for a moment, is an intervention into certain Edwardian views of Intellectual Empire. It is the warning shot of an emerged America. In a political sense it is a cautionary design that addresses the role of complexity and how it relates to the physical world. Hugely progressive, it is, in some ways, a critique of all those predecessors that (historically) vex your creative impulse. It is hugely sympathetic to those of those of us seduced by the notion of what a sailing canoe might be. Not an atavism, but a post modern reaction to the eternal verities of wind and tide.

 

Within the rule, of course. B)

 

Ha!

 

Paul

Not sure I completly understand all that but it sure looks like a clever canoe.

 

(And I stick the foam in with dobs of epoxy and QCells and it has always stayed but.)

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As long as I'm online, I may as well ask- since the rules mandate pintails, any thoughts on pressure recovery after the point of maximum beam?

It seems to me that my wide sterned Nethercott has a much flatter stern wave system than the standard one, which I'm putting down to pressure recovery, but I could very easily be wrong (both in observation and interpretation)

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Hollow Log was much pointier aft than most modern boats. Just what I thought would be good at the time without influence form anyone else. The topsides just curved in to the centre from the back end of the seat tracks which were substantially further forward than everyone else. None the less I rarely ever moved the seat more than half way back along the tracks and had very few diving adventures. My perception is that width and volume aft makes for a nose dive prone boat. Narrow stern also has less wetted area. Everyone else seems to have other opinions but thats the diversity that makes home designs so interesting.

 

I thought the water flow off the back was very clean. There was a small wave near the centreline which I considered was due to the fat rudder.

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

 

 

Yes, like a swing rig offwind except the jib swing is decoupled from the main.

 

Right, the tack is tacked down to the bow upwind.

 

Out for a sail yesterday it was surprising how little oomph - I think that's the right term - it added in light wind. Well I guess I'll find out if it works in a couple of weeks when I go down to sail with Erich, Del and Anders. Mikey and Dan too if they can break free.

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

 

 

Yes, like a swing rig offwind except the jib swing is decoupled from the main.

 

Right, the tack is tacked down to the bow upwind.

 

Out for a sail yesterday it was surprising how little oomph - I think that's the right term - it added in light wind. Well I guess I'll find out if it works in a couple of weeks when I go down to sail with Erich, Del and Anders. Mikey and Dan too if they can break free.

 

Chris- Oomph is kind of why I was asking about changing the space between the jib and main as it swings out. I was looking over a paper called "The Low Reynolds Number Aerodynamics of Leading edge Flaps" by Bakhtian and Babinsky (AIAA 2007-662). It occurred to me that your rig actually deploys so much more accurately that the flow in between the main and jib might slow down a lot more than the approximation that is a normal jib and main and put the slot in really low re, as well as much lower attack angles for the jib, and you are getting the usual twilight zone of laminar separation bubble and bubble bursts over the sails.

 

The paper investigates Re 40,000- 120000, and is based on a row of feathers that deploy at the leading edge of some soaring birds at low speeds,

and runs the concept through a wind tunnel to try to figure what is going on. Fixed flap testing showed a distinct performance at these low Re numbers, and at angles of greater than 20 degrees, a regime in which the baseline airfoil experienced detrimental laminar separation effects.

 

Anyway, they tried out 3 basic approaches- a flap attached to the leading edge which worked really well, but would be pretty complex to deploy.

(Ha!- I am talking to Chris!), a tape trip on the sail (smooth electrical tape .12mm thick 19mm wide, total span, at approximately 5% chord) which only worked above 95000 re (but really well), and a wire trip (1.1 mm spanning the entire airfoil) placed out in front of the leading edge right in the direction of the coming flow, and it worked well over all regimes. Placed the wire at the same position as the leading edge of the flap.

 

I think you have a sleeve luff on the jib. And if you do, a simple experiment might be to try a jib with the jib wire exposed, and the jib itself flying

from hanks? So the forestay acts as a trip. It looks like the wire in the wind tunnel was deployed at 5 - 10% of chord length ahead of airfoil. It may be that low attack angles, at low Re, (if your rig has a sleeve jib luff) produce weaker pressure peaks which allow laminar flow which may lead to upper surface laminar separation and bubble burst. At least at low re. Like under 95000 re. To put it simply, you may need some turbulence over the leading edge to encourage turbulent reattachment of the flot rather than encouraging laminar flow which will burst and detaching forever. If the jib is not working, no oomph.

 

Some sort of leading edge flap might help on the mast for similar reasons, a wire trip might be more difficult to pull off. It might be that your mast is encouraging laminar flow at low Re?

 

Paul

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

 

 

Yes, like a swing rig offwind except the jib swing is decoupled from the main.

 

Right, the tack is tacked down to the bow upwind.

 

Out for a sail yesterday it was surprising how little oomph - I think that's the right term - it added in light wind. Well I guess I'll find out if it works in a couple of weeks when I go down to sail with Erich, Del and Anders. Mikey and Dan too if they can break free.

 

Thanks.

 

It'll be interesting to see when you've worked out the tune off the breeze whether decoupling the two is better than just having the jib boom locked to the same angle.

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

 

 

Yes, like a swing rig offwind except the jib swing is decoupled from the main.

 

Right, the tack is tacked down to the bow upwind.

 

Out for a sail yesterday it was surprising how little oomph - I think that's the right term - it added in light wind. Well I guess I'll find out if it works in a couple of weeks when I go down to sail with Erich, Del and Anders. Mikey and Dan too if they can break free.

 

Chris- Oomph is kind of why I was asking about changing the space between the jib and main as it swings out. I was looking over a paper called "The Low Reynolds Number Aerodynamics of Leading edge Flaps" by Bakhtian and Babinsky (AIAA 2007-662). It occurred to me that your rig actually deploys so much more accurately that the flow in between the main and jib might slow down a lot more than the approximation that is a normal jib and main and put the slot in really low re, as well as much lower attack angles for the jib, and you are getting the usual twilight zone of laminar separation bubble and bubble bursts over the sails.

 

The paper investigates Re 40,000- 120000, and is based on a row of feathers that deploy at the leading edge of some soaring birds at low speeds,

and runs the concept through a wind tunnel to try to figure what is going on. Fixed flap testing showed a distinct performance at these low Re numbers, and at angles of greater than 20 degrees, a regime in which the baseline airfoil experienced detrimental laminar separation effects.

 

Anyway, they tried out 3 basic approaches- a flap attached to the leading edge which worked really well, but would be pretty complex to deploy.

(Ha!- I am talking to Chris!), a tape trip on the sail (smooth electrical tape .12mm thick 19mm wide, total span, at approximately 5% chord) which only worked above 95000 re (but really well), and a wire trip (1.1 mm spanning the entire airfoil) placed out in front of the leading edge right in the direction of the coming flow, and it worked well over all regimes. Placed the wire at the same position as the leading edge of the flap.

 

I think you have a sleeve luff on the jib. And if you do, a simple experiment might be to try a jib with the jib wire exposed, and the jib itself flying

from hanks? So the forestay acts as a trip. It looks like the wire in the wind tunnel was deployed at 5 - 10% of chord length ahead of airfoil. It may be that low attack angles, at low Re, (if your rig has a sleeve jib luff) produce weaker pressure peaks which allow laminar flow which may lead to upper surface laminar separation and bubble burst. At least at low re. Like under 95000 re. To put it simply, you may need some turbulence over the leading edge to encourage turbulent reattachment of the flot rather than encouraging laminar flow which will burst and detaching forever. If the jib is not working, no oomph.

 

Some sort of leading edge flap might help on the mast for similar reasons, a wire trip might be more difficult to pull off. It might be that your mast is encouraging laminar flow at low Re?

 

Paul

 

Well okay, but when reaching with the swing jib the main and jib are operating at a similar setting and AoA as if sailing very free upwind - more twist and a freer jib sheet than when close hauled I am thinking is the way to go. So wouldn't the flow through the slot be faster than when close hauled? For a given AWS of course.

 

I don't know yet what the best course is on a run. Try to sail hot enough to get flow across the sails or sail deep and stalled and rely on that increased projected area? Too bad so much of the jib is so low.

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Albacores use a pole that hangs in front of the mast and deploys to either side, with a separate line that regulates the length, to push the clew of the jib down in a very similar way. Might be a simpler thing to do. George had one for awhile. Very light.

I have one, but its really hard to get jib sheet lengths sorted out. I also deplore all the gubbins on the front surface of the mast, and most especially the pole hanging in the slot. I'm still playing with it, but am not totally convinced.

 

I tried a similar system for the worlds in the US 2002 (IC US214).

 

The system was inspired from my 505 days, similar to the pershing spinnaker pole system.

The pole sat parallel to the boom when not in use. If I remember correctly an extra jib sheet went through the pole and then to a block on the mast down to a reachable cleat.

 

When launched i just have to pull the one line and the pole automatically attacheed its butt end to the mast and sheeted in the jib to its tip end. When retrieved, uncleat and a chock cord attached to the butt end pulled back the pole to the back of the boom. The front of the pole was attached to the boom through another small shockcord loop. It was a single line system.

 

As I couldn't dedect a noticable performance gain I removed it just before the worlds. But the system itself worked very well.

 

Cheers, Former Swedish IC sailor

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It's interesting that in some classes the poled out jib is seen as necessary - Star, NS 14 etc., but in the IC the performance gain, if any, hasn't lead to it's widespread use.

 

I wonder if it's just not effective on an IC for some reason?

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So I have a question about this jib boom thing.

 

Will it work basically like a swing rig when off the breeze?

 

Upwind, I presume the tack is at the bow, and the rig is 'normal'; thus avoiding the tacking problems with swing rigs.

 

 

Yes, like a swing rig offwind except the jib swing is decoupled from the main.

 

Right, the tack is tacked down to the bow upwind.

 

Out for a sail yesterday it was surprising how little oomph - I think that's the right term - it added in light wind. Well I guess I'll find out if it works in a couple of weeks when I go down to sail with Erich, Del and Anders. Mikey and Dan too if they can break free.

 

Chris- Oomph is kind of why I was asking about changing the space between the jib and main as it swings out. I was looking over a paper called "The Low Reynolds Number Aerodynamics of Leading edge Flaps" by Bakhtian and Babinsky (AIAA 2007-662). It occurred to me that your rig actually deploys so much more accurately that the flow in between the main and jib might slow down a lot more than the approximation that is a normal jib and main and put the slot in really low re, as well as much lower attack angles for the jib, and you are getting the usual twilight zone of laminar separation bubble and bubble bursts over the sails.

 

The paper investigates Re 40,000- 120000, and is based on a row of feathers that deploy at the leading edge of some soaring birds at low speeds,

and runs the concept through a wind tunnel to try to figure what is going on. Fixed flap testing showed a distinct performance at these low Re numbers, and at angles of greater than 20 degrees, a regime in which the baseline airfoil experienced detrimental laminar separation effects.

 

Anyway, they tried out 3 basic approaches- a flap attached to the leading edge which worked really well, but would be pretty complex to deploy.

(Ha!- I am talking to Chris!), a tape trip on the sail (smooth electrical tape .12mm thick 19mm wide, total span, at approximately 5% chord) which only worked above 95000 re (but really well), and a wire trip (1.1 mm spanning the entire airfoil) placed out in front of the leading edge right in the direction of the coming flow, and it worked well over all regimes. Placed the wire at the same position as the leading edge of the flap.

 

I think you have a sleeve luff on the jib. And if you do, a simple experiment might be to try a jib with the jib wire exposed, and the jib itself flying

from hanks? So the forestay acts as a trip. It looks like the wire in the wind tunnel was deployed at 5 - 10% of chord length ahead of airfoil. It may be that low attack angles, at low Re, (if your rig has a sleeve jib luff) produce weaker pressure peaks which allow laminar flow which may lead to upper surface laminar separation and bubble burst. At least at low re. Like under 95000 re. To put it simply, you may need some turbulence over the leading edge to encourage turbulent reattachment of the flot rather than encouraging laminar flow which will burst and detaching forever. If the jib is not working, no oomph.

 

Some sort of leading edge flap might help on the mast for similar reasons, a wire trip might be more difficult to pull off. It might be that your mast is encouraging laminar flow at low Re?

 

Paul

 

Well okay, but when reaching with the swing jib the main and jib are operating at a similar setting and AoA as if sailing very free upwind - more twist and a freer jib sheet than when close hauled I am thinking is the way to go. So wouldn't the flow through the slot be faster than when close hauled? For a given AWS of course.

 

I don't know yet what the best course is on a run. Try to sail hot enough to get flow across the sails or sail deep and stalled and rely on that increased projected area? Too bad so much of the jib is so low.

 

 

I guess what the results of the paper are saying a few things- one is that when the reynolds number drops below 95000, too little aoa leads to bubbles on the leading edge that burst and prevent the flow from reattaching, which I think is like a stall.

 

the radio control folks have a rule of thumb formula for reynolds number-

 

780 * speed in mph * chord in inches = re #

 

I don't know what you consider light air, but:

 

780 * 5mph * 24" chord = 93,600

 

12" chord = 46,800

 

6" chord = 23,400

 

So given how much slower the flow is down by the water rather than up even 3-4 feet, you may be right about the planform of typical jibs, particularly in light air: in lower winds, it may be that the usual happy accident of more chord in the sails down where the wind is less, and less where there is more wind needs to get turned around, just to get enough velocity to iron out low re discontinuities. I assume you are adding twist at least partly to accommodate wind shear, as well as induced twist from the planform?

 

But it might be worth trying a bit more aoa in the light stuff to see if might give you a bit more power. It might just stall too...

 

As far as the flow in the slot speeding up when you free up the angle between the 2 foils? IIRR, biplane theory gets a bit vague on that one, so I tend to look at the radio control guys who are messing around with biplanes, and I think with your swing rig you are in the realm of biplanes and tandems (the tandem upwind, which is what, say, a regular sloop rig is closer to) . Anyway, there's a lot of conversation that boils down to "everybody has their own ideas on biplane setup and what works for them." Big help, huh? But the farther away the two foils of a biplane cell are, the more they act like a single airfoils.

 

Anyway, if I can get it to work, here's a link-

 

http://www.hippocketetaeronautics.com/hpa_forum/index.php/topic,2497.0.html (edit- damn it doesn't work) I'll try to find it.

 

Personally, I think if you loosen up the trailing edges, you might get more velocity in the aft part of the cell, and then you're into the Kutta conditionand all that poetry. And you lose aoa up front. But that's why I was interested in the article that started these ravings.

 

But longer chord is a way to get higher re, which could help getting you out of some of these issues. And if it matters supports your idea of more chord up higher, where a combination of longer chord and higher velocities might combine towards something better.. Which is where mainsails have been going.. And it helps to remember that when quadrilateral jibs, high clew jibs and that kind stuff were being tired out, aeronautics was in it's biplane era.

 

Paul

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try googling "biplane wing setup hip pocket aeronautics" haven't figured out how to get my ipad to copy and paste yet, and every time I enter the address on the SADIC thread it doesn't work. But it does come up on the google results. First as it turns out.

 

fun stuff.

 

But it might be fun to get an hanked old jib on and see if low wind oomph increases.....

 

Paul

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It's interesting that in some classes the poled out jib is seen as necessary - Star, NS 14 etc., but in the IC the performance gain, if any, hasn't lead to it's widespread use.

 

I wonder if it's just not effective on an IC for some reason?

 

I use a jib boom on my Classic IC, and I believe it is marginally faster downwind, goosewinged, than it is without it. The difference is enough that I have persisted with it. The other advantage is that it makes the jib self tacking, and there is only a single jib sheet to deal with.

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