Kites

Wha?

OK, can you give any examples of "self pumping" rigs that make the main and jib more efficient? With all your AC involvement can you explain why they are making the mistake of ever stiffer rigs to glean the most power out?

With the Tour de France in the news, why don't the bike designers incorporate "pumping" technology into their frame designs? This effect must make a far better climbing bike, yeah?

 

No, I cannot. They do not exist yet.

I do not understand your comparison of stiff rigs and stiff bicycle frames to the aerodynamics of hysteresis. I'm guessing you are still confused regarding energy input/output versus transient aerodynamics.

Let's try it this way: Do you understand that, when pumping for instance a J105 mainsail (a boat and sail far too large for a human's relativfely puny input to have much direct effect), that the energy actually harvested and applied to the yacht's hull is greater than that input by the crew? Let's try to establish this first, shall we?

Dave

 

I don't feel confused at all.

I'll intently watch the next round of AC action to see if the competitiors there are smart enough to understand this hysteresis effect. That is the top of the research game, and a stone this big surely won't go unturned.

I'm wondering, if you get hit with a puff and your boat heels over (decreasing power) then comes back upright ("increasing" apparent wind) is that better than if the the boat didn't heel and used the available power? If the boat heeled, righted, heeled, righted, ad nauseum would that promote this hysteresis effect?

Have you ever been able to measure the power out of a spring greater than the power in? Nevermind.

Good luck with proving your theory. I hear there's a guy in FLA who is now in the business of making RC models to prove these sorts of theories out, so they can be patented and sold to investors more easily. Maybe you shold contact him.

 

It's not "my" theory, Paul, but an established field of aerodynamics. Have you read Marchaj? Or try googling aerrodynamic hysteresis; see if you can learn something new. In the meantime. thanks for your comments. Have a nice day.

Dave

 

I like learning. I tried to google aerrodynamic hysteresis but only seemed to come up with hysterical and hissyfit.

Do you think a self pumping rig would be able to power an AC boat at 7 knots? Would it be eligible for a Guiness Record?

If you design a self pumping rig maybe Langman will put one into his new, larger Zena/Grundig/AAPT.

 

F'ing troll. Climb back under your rock.

Dave

 

"Paul B"

Hah! Dave you hit the nail on the head with that one!!

 

Hey Dave, would you mind explaining this "self-pumping" rig to me? I find the concept interesting even though it would probably be illegal for racing.

Thanks

 

Pumping is currently illegal in almost all racing classes, but the definition of the term varies, so it's hard to guess. Sometimes "pumping" is defined as crew-supplied input to the rig and sometimes it is defined as any rythmetic motion of the rig--likely anything which makes the boat faster will be found to be illegal... ;-)

"Self-pumping" is any method of using wind power to "pump" the rig. A conceptually simple one might be a wind vane on a long boom extension, with a mechanism to alter its attack angle and also sense the boom's current position. It isn't hard to imagine designing a series of rods and cranks to have the boom's position set the attack angle on the vane, causing the boom to pump in and out on its own (It's useful to rememberr that pumping does not require large amounts of force--you don't, for instance, need to cause the boom to exceed the wind speed in order to gain power--you do not need to "air row")

Another approach would be to use an "aerorig" type of rig, where the jib is mounted on a forward extension of the boom. Such rigs are almost balanced to begin with; causing them to "autopump" would require much less energy than the first way.

A third would to be to use a fully balanced, rigid wing sail. These have almost zero tension on the sheet, and would require very little imput to get them to pump. You could even (perhaps) design a wing sail with negative stability which will auto-pump itself, with proper linkage. There has been some question (on internet fora) regarding whether the movement of the leading edge to windward during the pump (or the whole jib if an aerorig) might upset the hysteresis aerodynamics. I think not, but others disagree.

What is uncertain, but unlikely, is whether the drag of the vane will exceed the increase in total power to the system; not only are the physics complex and little understood, there's going to be real-world losses in efficiency in any vane system as well. What is likely is that the self-pumped rig will be more powerful than a static rig; the boat will accelerate and you'll be promptly banned. ;-)

For reference, see C.A. "Tony" Marchaj's 'Sail Performance', Part 3, Chapter 5, "Pumping--a Legitimate Technique?" ISBN 0071413103

Or just ask Paul B to take you for a sail on his ACC yacht and show you how...

Dave

 

Wow, that's some weak sauce.


Let's take a J24 in 10 to 12 knots of breeze as an example.

What's the required amplitude and duration of the pumps of the main and jib to create the hysteresis effect upwind?

What is the load on each sail?

What is the power input from the boom-mounted vane? How large does it have to be to provide this amount of power? How well does it work in the gas of the main? What k do you calculate in for mechanical losses?

Do the sails receive input to have the required twist as the open and close?

So many details in the physical world.

 

Interesting boat.

I have been thinking about a kite sail as a jury rig for my 20ft mini cruiser which I someday hope to design and build. Something like Ive seen in Ft. Lauderdale where they use it with what looks like a small surf board. I like the idea that the thing can be rolled up into a real small package and not take up too much space when not needed.

My boat design calls for an unstayed mast, so it is highly likely that if it were ever rolled it would come up minus the mast. The kite, even if its good for only down wind, could get me somewhere.

I then started thinking about making it more controlable. I grew up flying kites so I know all about bridles. I thought why not have two. One fore and aft and one athwartship on the kite. The fore and aft one would be adjustable only with the kite in hand. The athwartship one would have an electric 'bridle creeper' which would be controled from a radio transmiter on the boat.

The bad thing about this idea is that the 'creeper' would need batteries and a way to charge them. All would add weight. The good thing would be that the kite would be attatched to the boat with only one line.

Along with this rig, the boat would have tandem dagger boards to minutely adjust the boat's CLA for course setting purposes. It would have a rudder as well for quick maneuvers. I have also thought about using hydrogen rather than helium for the lifting gas. Hydrogen can be made on sight; helium can't.

Any way. I like your boat and can't help noticing that it would fit nicely within in the rules of my proposed 1x19 class offshore sailboat (see Proposed Class of Small Off Shore Racing Sailboat thread). The main idea of this proposed class is to encourage sail design developement beyond the usual sloop rig (while keeping the costs down) by measuring the entire sail area, not just the foretriangle and mainsail.

The kite could be a great off shore sail development. I wouldn't want to see them racing in crowded coastal or inland waters (especially with power lines about). But I would much rather see them than the Canting Ballast Twin Foils that really look like I'm about to see.

Bob

 

I wouldn't know much about hysteris if I sat on one (I think it's in a later ed. of Marchaj than my one) but don't we all know that on windsurfers, Lasers etc in light air you can get a considerable increase in speed from a minor amount of pumping? I know those are not the most precise and quantifiable of terms, but doesn't it indicate the efficiency of hysteris and therefore that a (partly) self-pumping rig would be possible?

Then again, one reason not many people have investigated it thoroughly is that unrestricted pumping is pure shyte. I mean, really, really bloody unrewarding pain in the arse sort of hard work. I mean, not wimpy stuff like grinding a big boat or straight-legging a Laser to cube level, but the hard work where an Olympic class puts out a bulletin warning that deaths may occur if RCs hold too many races in hot weather. The hard work that leads even Olympic medallists to say that the pumping is killing the popularity of the class.

And if you allowed pumping and a top offshore racing crew were becalmed in an offshore race, they WOULD pump and roll a 40 footer until they dropped. It would be more effective to just pump and roll and ignore most of the subteties of light-air trim and tactics. OK, older crews would be left behind, skill would go down to fitness, and we would basically end up with very innefficient rowboats, but they would do it and everyone would hate it and fleets would drop. It would be much more efficient and honest to just put bike-driven propellers out the back.

So how you balance the self pumping rig with that problem, I dunno.

 

Too right, Chris. I'm certain that's why it is so broadly outlawed--the line between "efficient" pumping and air rowing is too narrow.

OTOH, if you built a self-pumping rig, the crew need never touch it--which would make the nice clean line--if the wind causes all movement, it's OK; if the crew gets involved; it's illegal.

This is the whole reason I'm looking at self-pumping rigs.

Dave

 

I'll give an example of an "almost" self pumping rig. If you sail a Laser upwind or close reaching you can do the "pop". In moderate wind so that you aren't quite fully hiked you bounce on the rail with a very small bounce. The trick is to bounce at the rigs' natural vibration frequency which seems to be about 1-2 seconds in a 6-8 knot wind. This will start the flexy mast fanning like a birds' wing and with each bounce the amplitude will increase until after a few bounces you can get the rig going back and forth about 3 feet or more at the tip. And does it ever increase your speed and pointing- you will blow by anyone not doing it- that's why it is against the rules. You literally have a flapping wing with practically no energy input- here again the trick is to pop at the resonance frequency of the rig.

 

Hmmmmm, interesting stuff Dave. Intriguing. My gut feeling is that sailing with a rig that self-pumped gently may also not throw tactics out the door as much as unrestricted pumping does, and that would be a good thing too.

When beating and pumping in very light winds in boards we sometimes actually aim to sail in the dead calm lulls, rather than the 1 knot puffs, because it's easier to pump dead "upwind" in a calm than in one knot. There are certainly some possible tactics going on, but the problem is that (say) 95% of the race is fitness and pain and only 5% is the tactics and trim etc. The tactics and trim are still there when pumping, and if we could get rid of the fitness and pain element they would come back into significant play.

I came across a heated thread discussing whether a windmill boat could sail directly upwind and thought it was funny, because when we stand on the foredeck and roll a Laser home in a calm, we do exactly that. Totally irrelevant to the thread apart from the fact that we're talking pumping, 'scuse me.