Ocean Kite Sailing-How to solve the problems with very light airs and sudden squalls?

There is another reason to use Nitrogen, rather than plain air. Nitrogen is close to being a noble gas. It reacts with far fewer elements than oxygen does.

All the very high pressure cylinders on the dies I used to work with, in the stamping plant, were filled with nitrogen for this reason.

Nitrogen is also pumped into near empty fuel tanks on air liners for the same reason.

 

Mot likely the kite/balloon combo will be one in the same, meaning the kite will be the balloon.

This, of course will not produce perfect inflatable NACA wing foil, but may come closer than some might think. Especially if one considers going with a symmetrical foil and a nearly square plan form.

When trimmed parallel to the air flow, it will produce no lift and very little drag. It could be flown from a mast that is slightly more than half its span in height, when sailing upwind or reaching.

It could be flown much higher up when sailing down wind, especially in strong winds.

It could have a bridle designed to let it feather for gusts.

 

The reason for the rant is the original claims of the commercial kite boat. I am angry that they present it as such a smart simple solution. Classic accentuate the positive and just look at them blankly when they ask what happens in less than perfect conditions. I also don't like these
"First Crossing of (insert ocean here) with (insert stupid dangerous propulsion method here) only!" stories which I see this indicating. I would be happy if all of them were required to post bond based on how stupid and dangerous their attempt was.

The Rant was labeled, you were warned, and I think the comparison of the sport bike to the windsurf kite was apt.

Big kite surf kites are about $3k and they are built to about 1000lb strength. Typical lines are 600lb tensile aramid fiber because elasticity is a major control problem. No tension=no control of a kite. When one end or the other gets yanked toward the other, control is lost until tension is reestablished. While there is no control the kite can (and usually does) find a way to give an even bigger yank! Search "kite board teabag" to see what I mean. Anyway, the point is that the $4000 kite and lines are designed to pull a ~200lb boarder, not a 500 to 2000lb displacement boat so it will not last as long and kites do not last as long as sails when used as recommended. There are very talented armature kite builders. I wonder what they would say if you told them you want to pull a 1000lb disp. boat. Beyond the problem of breaking the kite there is the problem of breaking something else. Up in the sky there are gusts and swirls far greater than at the surface. If you leave this foil up long enough something terrible will find it eventually. You need a plan for this to beak safely.

Anyway feel free to brainstorm. But do state what you expect to get out of it and do some calculations.

 

Is that not true of any sail? The trick is to make kite launch/ retrieval/ reefing as simple as a traditional sail.

 

Thanks for clarifying that. From post #1 on the claims in the quote there were questioned, which was the reason to start this thread and discuss it here, you added to that. We need the kite boat claims and the assumptions and speculations posted or quoted on this thread confirmed or refuted by cogent theories, if possible substantiated by calculations and/or testing and experiences, from whoever who can and is willing to do so. So thanks for your input with calculations and theories, and to others for their responses to it.

 

All very true, strange I've never seen it among the claimed benefits. I would put it on the list of benefits if it was my business . .

However, for tires it could be a only theoretical argument because the wear and the UV light and oxygen the tyre is exposed to on the outside makes the outside degrade faster than the oxygen from the inside does, I believe. And for air filled tires that are rarely used, and thus have a long life before the tread is worn, the nitrogen content inside increases anyway to nearly 100% by refilling with air, assumed this is done when needed . . .

 

It is true of sails to a much smaller degree -an order of magnitude less at least. The keel boats the kite boat compared itself to can take a huge gust with just a knockdown and recover intact automatically unattended. I have yet to see a kite setup that could do any better than a complete loss of propulsion (lost kite) and most would suffer structural damage and loss of directional control. Kites are intrinsically weak due to the need to keep mass low for flight and control. Weight and control problems are also the reason that no kites are reefable. Different wind speed requires a different kite. Granted this is all about what has been done in the past while this blog is brainstorming what could be done in the future, but when you get to making real kites I think you will find the current state of the art very difficult to improve. Launch and retrieval could be improved, reefing will be a problem. Even feathering kites is limited because the kite uses lift to maintain shape and control. Low wind is the first problem of kite primary propulsion, but coping with sudden changes in wind speed and direction will be the next.

 

That's exactly what happened to Anne Quéméré in 2008, first ten days without any wind and after that she failed to cope with a sudden squall that tore up the kite and destroyed the pulley system permanently, of which she seemed to have no backup system, and so ended her 2008 attempt to cross the Pacific. There's more info about this in the two linked and quoted articles at the bottom of post #24.

A bit of a pity there's only info about her two successful ocean crossings by kite boat (2006 & 2011) on her website ^{--> Archives}, and no info at all about the failed 2008 attempt from which we all also could learn, but it could be that's not the objective of her website . .

 

Thanks. I like this direction a lot and hope it is not too much to ask for. Kite propulsion is very intriguing but so far I have not seen a way to make it more than an auxiliary means to a safe reliable primary method. I certainly don't mean to disparage development. I would sure like to see data on all attempts. What we need is true wind speed and angle data from all prototypes. It would be helpful to get expectations/projections on concepts for discussion.

 

I feel mixed emotions. Reading these details again I feel anger and the need to go into a two page rant. On the other hand it is soothing to know there is at least one other person in the world that sees the exact point of my pain.

What a screwup. Did you see the part where she got blown back 5 days progress in one day? Did she not have the ability to sail upwind? Who was her NA? Was there any postmortem analysis on the reasons she endangered herself and the crew that rescued her? Thankfully she failed in the doldrums. Actual bad weather could easily have taken her life and made rescue dangerous. And as you say it is all quiet about the failure and it's lessons. All you will find is the small successes. AC....centuate the positive!...

That is one thing I always appreciated about Sail magazine. Every issue had a story of a disaster, how common the problem, what was done right and what was done wrong.

BTW if you appreciate a good postmortem I was fascinated reading about the first Gunboat 55 rescue/loss on sailing anarchy. Brand new multi-million dollar race/cruise cat. Skilled pro crew. Fierce weather but should have been manageable. How could they lose it all? Well after reading I could not find any other way out. Would you send someone over the side to clear rigging from the prop in raging seas? Who? The pros? It's just a job. The rich owner? No way!...

The most innovative post I have seen on this thread was the guy who used a kite on a seabreaze to go fishing offshore without a boat. Brilliant! But of course he pulled in a tangle of line the size of a football along with about 10 Kg of fish. Don't underestimate the challenge of controlling a kite.

 

Excellent explanations.

So I guess the notion of kite sails for light winds is pretty much myth busted.

The size of the balloon needed to loft the kite and to keep it airborne
makes it quite impractical, as stowing all this, once the wind returns, will be a big problem.

100 cf will only loft about 7.44 lbs of sail. That's a lot of gas to have to manufacture or stow, if you're using Helium.

As for Anne's boat. It was totally decked over, so presumably, she would not have been any immediate danger, even if her rig failed in rough weather. She may have been in for a rough ride, as her boat would become a propulsion-less hulk. But she could have mitigated that to some degree with a sea anchor.

I suppose her biggest problem may have been lack of stores, due to the need to keep the boat as light as possible.

I agree with your comments about her boat's designer.

It seems he/she had little taste for back up systems.

I would have insisted on a short mast, with would have been a little taller than half the span of the kite. This would have gotten her through the doldrums, as the kite could have been 'flown' attached to the top of the mast, and not fallen into the sea with each calm.

The mast would have been removable, of course, when good 'kiting' weather returned.

The mast could also have been used to fabricate a jury rig, if the kite and/or its controls were destroyed. Fabric from the ruined kite could be used to produce makeshift sails.

Although I support whimsical adventures such as this, I do lament the lack of self-sufficiency that seems to go with them.

 

As far as "kite sails for light winds" go, if you add the qualifiers -"with currently available kite designs" I would say myth busted. But I also think it is clearly possible to hold a kite up with lighter than air gas, and it is possible to propel a boat with the force from low wind. So the thread did provide a means to hold up a kite per the original question. The challenge of making kites better than sails for cruising is much more difficult and questionable but I don't think I have proved or disproved that thesis. My current opinion is that kites might be a very useful addition to a cruising boat with a more reliable primary propulsion means (cruising boats carry several sails that are useless in low winds). For example a rowboat has reliable propulsion EXCEPT in high winds -a kite would be a fine auxiliary. Solar is another interesting alternative. Low wind is common to high pressure systems which tend to be sunny. When you consider the difficulty/complication of supporting a kite with a balloon you might find that it is much easier and possibly more energy efficient to just power the boat to hull speed by some other method. The weakness of kites in low winds might not be so bad if low wind is uncommon up high. All the times I have seen kites beating sails it was because they were finding higher winds at higher altitudes.

The balloon supported kite has not been given much consideration as far as I can see. Say 7lb net for 100cf X 2 torpedo shaped pods with very reasonable drag, now what can we do for a kite between them. From the start lets keep the balloon simple and large so we can keep the gas handling as simple and effective as possible. The reefing problem might not be so hard. C traction kites only depower a little in gusts but a delta kite can depower much more and in real time. A delta kite is much more stable and easier to handle to boot but also heavier and a bit less efficient.

I am sorry if this seems like I am flip-flopping and just disagree with any conclusion offered. I am not a jerk. I just have high standards for claims and proof. I am not the guy to tell you what can't be done unless I can prove it.

 

Hey Skyak.

If I can brainstorm you can too.

I followed my imagination and ended up with a balloon sail.

It would be nearly square in plan form and have a symmetrical airfoil. A 100 sf one would be 10 ft square and have an enclosed volume of about 124 cubic feet. This would be sufficient to lift a little over 9 lbs.

It would have a center line bridle and two tip ones.

The center bridle would attach to the top of a short mast that is maybe 8ft tall.

When changing tacks, the line controlling the leeward bridle would be slacked, allowing the sail to float over the top of the mast, as the bow came through the wind.

Then the tip bridal on the other side would be hauled in.

In lighter winds, this lighter-than-air sail would be flown high above the boat.

The center bridle would be designed to let the sail feather into the wind, during strong gusts.

The only question is can this sail and its three lines be made strong enough, yet light enough for the gas inside to loft (it all has to weigh less than 9 lbs)?

I'm skeptical.

Now that solar panels are becoming ever less expensive and more efficient, the notion of solar powering through calms seems quite attractive.

For an ocean crossing 'stunt', I'd be all for this.

The boat would have a minimal rig, for sail assist, in lighter winds, and pure sail in stronger ones. I'm thinking of an S/D of around 10.

Expected speed under the sun alone would be roughly half hull speed.

Such would require about one quarter of the energy that full hull speed would. So a boat with a 16 ft WL would do about 2.6 kts under the sun alone, and maybe store enough energy to power through much of the night.

During a 12 hour day, the boat would about 31 nm. If it banked enough energy to run half the night, it would be able to travel another 15 nm.

This gives a total 46 nm, with absolutely no wind at all.

Pretty crappy, eh?

But it's a whole lot better than zero, especially considering that the very best the boat can do is 128 nm/day.

Such a system, if developed would open large portions of the ocean, which are avoided by conventional sailboats, due to chronic lack of wind.

No reason why a kite sail set up couldn't use this system too.

 

I can't completely visualize your proposal but your expectations are low enough that you likely won't be disappointed. 46Nm for a small solar boat is not bad but Why so small? 'Cheap' solar pannels are about$0.9/watt and about 1Mx0.5M for 100w. A 16ft monohull will not have much room for these. I see this thread was spawned by discussion about a ten foot ocean crossing sailboat. I think I have already indicated my feelings about 'stunts' so I will skip the rant and go straight to comments on your proposal
1 -aspect ratio=1 this is not an upwind sailor -as slow as this boat will be I think it needs to tack through 90 deg or less to be safe from lee obstacles.

BTW here is your prototype http://www.bargainballoons.com/10Browse.asp?Search=09362&gclid=CO_ixoDD1sYCFY81aQod14gM9Q

2 your sail/kite gets to a major point -the difference between a kite and a sail is that a sail is righting limited. In light wind even a tender boat can carry massive sail area. In strong wind a tender kite boat can carry a big kite without reefing. This will be the best way to handle wind range on most concepts. The question this begs is why bother with the balloon? You covered the low wind with the mast (note this might not be as easy as you think -the mast must be out of the way to operate without righting limit).

3 your three line control is consistent with today's kites but there are a few problems. Traction kites have a "C" shape that is actually conical so the wind holds the leach out. If your kite is a flat square it will need something to hold the leach out, or it will just fold into a cone too. And to feather in high wind the leach lines need to slack - slack in the bridal increases AOA.

Kites are easy to make but very difficult to make well. I am trying to find a way to make a flatter simpler kite myself. Today's kites are about $200 of material and ~$3000 of skilled labor.

You asked about how much the lines weigh -as I recall 600lb aramid lines are about 0.8mm -so they are pretty light. You still might not be able to fly the balloon/kite very high in light wind due to control issues. When there is no wind there will only be a pound or so of tension and your boat is moving around on the swell which would put your balloon at all kinds of screwy angles and possibly tangle the lines. This may be based on the 'what can happen will' principle, but ...

Lastly, rather than just speculate about a small boat crossing oceans somewhere in the world why don't we try to make real small boats that can safely cross the great lake between us? Michigan is ~50 to 80 miles wide. A reasonable challenge for one day in a small boat. I am working on a 10ft sail kayak that should do 3 knots by paddle or 4 by wind, and I was planning on rigging a kite for high wind days that might get to double digits.

 

Just about any off-the-shelf dinghy, which is not designed for racing , can do this(a racing dinghy can easily make such a crossing too, with reasonably good luck). It may need a few modifications, such as easy to reef sails and a well thought out emergency flotation system. Most to all, it would need a very good tiller nut--one who knows the boats ways exactly.

Since it is impractical to design one that will always right itself, self-rescue is the order of the day. The skipper needs to be able to right the boat in deep water and be able to get back on board with no problems. The Scamp dinghy is a good example of this. It has water ballast, dry storage compartments, and emergency flotation. It is just one inch short of being 12 ft long.

I'm presently designing a boat that comes close to meeting these requirements, but is designed for small, inland lakes. Its emergency floatation system is carefully designed, as I expect to sail it during much of the year. a non-recoverable capsize in cold weather can be fatal, even on a small lake. I had better be able to right it quickly, get back on board, and be able to bail the water out, before I pass out from hypothermia.

I once came close to deciding to cross Lake Huron, when I was a teenager.

The make shift sailing raft, which I had designed and built, was dis-masted in a strong, off-shore breeze. The cotton rope, that acted as a stay, parted. By the time I got the sail back up, I was miles off shore. The bluff I had sailed from was just about to go under the horizon.

If the wind had stayed as fierce, I would have sailed down wind to Canada, rather than try to claw my way back.

Luckily, the wind died down some, and a rescue boat, hired by my exasperated parents, came out to get me and my brother.

Your 10 ft kayak idea seems intriguing. I don't know if you can get the double digit speeds, even with a kite, even going down wind, unless it is designed to plane. I think the 10 ft length, with the weight its supposed to carry will pretty much rule this out, otherwise. My boat will be 10 ft also, but, even though its a scow, I'm not expecting speeds over say 6 kts

If you open another thread on this matter, I will be sure to join you.