The article mentions a promise for the new battery, not a reality.
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a promise, not a reality - sounds familiarâŚ
This inflatable sail was already realized for a small boat:
Laurent de Kalbermatten was a co-inventor of this sail. Previously he was the designer of Woopy, an inflatable wing according to the same concept, using also a small blower to stabilize the pressure, and a spar who became a telescopic mast for the sail. SALSA / KALBERMATTEN LAURENT (Fabricant de deltaplane) :
According to Laurent de Kalbermatten, the fabric of the sail (or the wing?) is much less stressed thanks to the inflation.
A lead for AWES for more durable and scalable flexible kites?
In kiteboarding many tried to make a dual layer inflatable kite to account for the inefficiencies of the single skin status quo. History shows that they were not actually solving a problem, rather they did not understand that a single skin inflatable kite was actually superior.
I also remember seeing a dual layer sail on TV as a child. But nothing came out of it.
I have the same feeling with the inflatable sail. A normal sail seems just better to me.
Hang glider sails have a top surface and a bottom surface these days. Easier-to-fly models have a dual-surface at the front, and a single-surface extension to add more surface area and maneuverability at the rear. âHigh-performanceâ hang-gliders have less surface area, with most of the wing being dual-surface. Without the large single-surface trailing edge, the high-performance hang gliders have a higher aspect ratio and a better glide ratio, but with stiffer maneuverability.
Most paragliders are ram-inflated with a top and bottom surface.
Sometimes its not easy to spot the best design. For paragliding it may be a ram air, for kiteboarding kites currently I believe the single skin inflatable kite is preferred for general use. I think by now there is little point in discussing, just look at sales numbers. All the flies cant be wrong on thisâŚ
For a shipâs sail the single skin sail has a long history and 3D sails have been around. I would expect its quite likely the single skin sail will continue to dominate. Why?
What problem will an inflatable sail solve for a cargo ship? Single skin sails seem to be sufficiently effective even for super fast hydrofoil racing ships. That to me leaves only practical or price issues as winning points for the 3D sail. And I cant see any real benefits. As always, Id love to be proven wrong
This is surely true.
However, inflatable sails would perhaps be interesting for AWE use as kites if they make it possible to attenuate the mechanical tensions on the fabrics, with an appropriate method of fixing the tether and the bridle.
Shipping is required to reduce reliance on fossil fuels. And saving fuel saves money.
No comment on this product, but in general, I think:
The more you inflate a structure, the stiffer it gets and the more wind it can take. So an inflatable sail, if pressurized enough, should be more robust than a sail. Also less flutter. So better durability. The claim here is also that it needs less crew. If an inflatable sail can be deflated and stored, thatâs a good safety feature. If it can be replaced on shore quickly, that reduces maintenance costs.
I donât know how many bridges a container ship encounters on its journey where storing the sail makes a difference, which they claimed as a benefit. Maybe thatâs a feature for smaller boats.
Questions Iâd have: how does the sail retract safely in high winds? Does it keep the same pressure while it retracts? How big do you have to make the sail to make the ship tip over or otherwise fail? And of course, how durable is it?
Good point. My info is kitesurfing uses inflatable spars for convenience: the kite floats instead of sinking in the water, and maintains its shape so it is easier to launch instead of sinking. But the inflated sections often explode during use, which is not fatal because the person is not flying high in the sky.
Paragliders found that inflated spars can prevent small canopy collapses, but make more serious canopy collapses worse, and the relative pressure gets too high when they ascend thousands of feet into thinner air. A burst spar at altitude could make the glider unflyable.
From what I see of these inflatable sails, they appear to have little-to-no camber, which is an important component of lift.
Also, a telescoping mast is possible without an inflatable sail, for deploying and furling the sail, going under bridges, etc.
Challenges with inflatable sails might include higher cost, more weight, more material, leaks and unplanned deflation, complete failure if a seam blows open, old sails unable to hold air, etc.
It also appears that no guy wires are used to stabilize the mast, so the mast must be more rigid, even while having telescoping capability, AND the attachment/support area of the hull where the mast is mounted must be stronger, heavier, more expensive, etc.
They should have a race and see how the Michelin-man sailboat does against a regular sailboat. Isnât comparing performance a main reason why they have sailboat races? To see which designs work best? Well, have the race!
The inflatable sails and wing in the previous videos have built-in blowers, which ensure pressure control. They are therefore not completely closed, unlike the inflatable spars of wings for kite surfing. So they can more easily be deflated. Perhaps an option of a Tensairity ⢠beam as the mast (or spar for a wing) could be studied.
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Thanks a lot for sharing this article. Both informative and provoking.
So a full sailboat still produces 1/3 enissions of a huge container ship of today.
Also seems a clear business opportunity for AWE to generate both electricity and propulsion in a way that may not be feasible with the alternatives.
Iâd also like to add that renewable steel production could swing this calculation in favor of the sailboat. Though the numbers mentioned in terms of cargo carried in a shipâs lifetime and number of ships needed make this scenario seem less likely
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I think Peter Lynn himself replied to the initial question:
Below is the article. Nothing to add, nothing to take away. I put in bold characters the passages which seem to me the most interesting:
Kite Power for Commercial Shipping.
Can kites be economically viable for propelling commercial shipping in mainstream applications?
In my view there are two chances of this happening in the foreseeable future: Zero, none, and a teensy possibility that indirect kite propulsion by way of on-board kite generated electricity driving a conventional propeller may work. Whoops thatâs three, but youâll get the drift. But this is not to say itâs not worth trying. Development work in this field, providing itâs eventually shared, will undoubtedly advance kite flying in general, and greenwash money seems to be available right now to support even more unlikely ideas than pulling ships around with kites. Just donât get suckered into using your OWN money. Disposing of the indirect possibility first; the principle here is that one of the kite energy systems currently being developed by various project teams in Europe and the USA could be mounted on a ship, and the electricity generated then used to propel the ship via an electric motor and conventional screw propeller. This is certainly technically achievable, but whether it can be economically viable is in doubt. The advantage of an indirect system as compared to using kite pull directly for traction is that all courses become possible- even directly into the wind. However, whether a ship driven in this way can be fast enough over a wide enough range of wind conditions to make commercial sense is far from established. For starters, none of the kite energy systems projects have yet been able to demonstrate a fully functional system- with practical kite launching and retrieval, some degree of autonomous flying, adequate reliability and useful power generation across the available wind range. They all seem to be still some way from meeting even these relaxed criteria, but eventual success canât yet be ruled out. My concern is not so much that they will fail to solve the technical challenges- though developing autonomous flying (kite auto-pilots) that will operate reliably in marginal and turbulent conditions is probably unachievable- but that in the end they will be defeated by windâs inherent variability. When thereâs too much wind, above 40knots, kites cannot usually be flown safely. Even by 30knots, experienced kitefliers generally start to pack up. When thereâs too little wind (less than 6 or 7 knots), kites fall into the water. Until there is 15knots or so they donât develop useful pull. This leaves a useable range of approximately 15kn to 30kn; the âsteady mid range windsâ that I have not often experienced in my kite flying life, not yet anyway, though I live in hope.
That winds are so variable and unreliable also makes using kites to directly pull commercial ships unworkable in my view. Itâs not believable that âjust-in-timeâ, customers will accept 5 weeks plus or minus 3 weeks instead of the 10 days to-the-hour trans Atlantic delivery schedule that internal combustion power allows. And, such delayed and irregular schedules would be the reality if kites (or sails) were used now instead of diesel motors. In the 19th century, sail power lost out to coal fired steam power, completely and irrevocably. By 1895, there were almost no sail powered ships plying the North Atlantic in mainstream applications (military, freight or passenger). From the mid 20th century, steam power (even powerful and efficient steam turbines) then lost out to diesel power. Large diesel engines have now exceeded 50% efficiency, an amazing accomplishment considering that Sadi Carnotâs second law of thermodynamics sets an absolute limit for practical heat engine efficiency of not much above this. Kites have yet to show any form even by comparison with sails, not that they might not some day. Their various inherent disadvantages (like that kites fall into the water when the wind is light), have so far prevented them being even nearly as practical as conventional sails at converting wind into propulsive force. To suggest that, for commercial shipping, kites can not only work better than sails-on-masts, but also recover the deficit between sail power and steam power, then the deficit between steam power and diesel power is dreaming. Sailing craft took anywhere from 75 to 200 or more days, averaging around 100, to get from England to NZ in the days of sailing ships- and there was a fair chance of their not arriving at all. Container ships today stick to a contractual schedule of 40 days for this passage- while diverting to four or five extra ports along the way. As well as unacceptable reliability because of wind variability, there is a technical reason why kite power cannot be useful for commercial shipping- unless container ships change to submarine form so as to reduce their above-water-line drag profile. Aerodynamic drag is the killer. A largish container ship, with containers stacked up 15m and more above deck level can have side area above the water line of about 5000sq.m. Even if itâs kite is also 5000sq.mâs (5 x larger than any kite thatâs yet been built, but probably possible), the shipâs superstructure drag will reduce the efficiency of the kite/line/ship system (measured by lift to drag ratio, L/D) to less than one, and options for upwind courses will fade away. This will be so even if this kiteâs stand alone L/D is 5, (a little above current state of the art for traction kites). When other other inefficiencies, such as hydrodynamic drag, are also allowed for, even if the apparent wind strikes the shipâs superstructure at 45degrees rather than the worst case of beam-on, upwind sailing will still not be achievable to any bankable extent. Additionally, the usefulness of kite power for container ships is restricted because they travel FAST- and customers will not generally accept slow because the cost of holding stock while in delayed transit exceeds the extra cost of cranking up a few more knots. Fuel use per tonne km is perhaps 70 times better for a container ship than for a truck or train- theyâre VERY fuel efficient. Under kite power, it canât be expected that a commercial ship will be able to achieve sustained travel at wind speed or above. Even for dedicated performance oriented recreational sailing craft, exceeding wind speed is never easy, and especially not over any sustained period. So, the wind speed will have to be 25knots or more if kites are to propel ships at the speeds the market demands. And unfortunately, this is true even for kite assisted motoring. Except on reaching courses (cross wind), and barely even then, if the wind speed is less than the boat speed, the motor will effectively be towing the kite along rather than the kite assisting the motor. Putting this limitation together with the likely upper wind speed limit of 40knots suggests that the wind range for using kites to pull such ships is say, 25kn to 40kn at the outside.
OK, so say kites are only used when the wind is appropriate by direction and strength? Hmm, for downwind sailing, is the wind in a useful direction 35% of the time, and in a useable strength range for 10% of the time? Letâs be generous and say itâs going to work for one day in every 25. Are ships owners going to install the equipment, add extra crew, and supply specialist training for some kite assistance barely one day a month? And then thereâs the associated reduced load capacity- and the downtime from running over the lines etc, and the risks to the boat itself and its crew and to other craft from out of control and escaping kites (which will happen sometimes, no matter what fail safe systems are installed) -more costs. Oil is so effective and efficient for shipâs propulsion that commercial shipping will be the last transport mode to switch to alternatives should oil prices ever climb to unaffordable levels again. But I expect that oil will hang in at bearable prices at least long enough for our nuclear phobic generation to be but a bad memory, and kites will not be competitive against nuclear power either, so will still not be able to find a role in commercial shipping. Come to think of it, Iâll take a small bet on viable (that is long term stand-on-itâs-own-feet, non-subsidised) kite power for commercial shipping not happening for now (leave me a small out for some minor, and as yet unidentified niches). There are things that kites can do superbly- recreational kite sailing, kite boarding, buggying, sports kite flying, snow kiting, possibly kite energy systems and so on- more than enough for a kite industry many times its current size, but powering commercial shipping is not one of them.
Peter Lynn, Ashburton NZ, February '09
PS, Iâm an optimist
Yes there it is again from one of the top âkite godsâ. Logic and facts (ouch!) We canât progress without dreamers, yet it takes more than just dreaming to make dreams come true. It also takes at least some basic arithmetic. AWE as a topic seems to encourage âflights of fancyâ in thinking, which is great, but itâs also important to realize, as Clint Eastwood famously said âA manâs got to know his limitationsâ - substitute âtechnologyâ for âmanâ? Nice to dream, and dream big, but not to the point of making a whole new art look foolish again and again. But we do have kite-surfing which does prove advantageous, at least for the very smallest craft. Iâd say, try to work your way up from there, step by step, and forget jumping right from mini-surfboards to container ships. Seems logical, doesnât it?
Come to think of it, kitesurfing is usually pursued in specific places where the winds and all other factors are favorable. Nobody would try to utilize a kite-surfing setup for general transportation, but kitesurfing works great at favorable sites at favorable times in favorable weather. Maybe a more realistic approach to kite-powered craft would be to target niche applications where conditions are favorable.
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I agree container ships are not where you would start. But most container ships and other ships as well spend a bulk of their times in quite favorable conditions for kite wind power - lots of space and maybe ok winds. And alternative energy price is generally expensive as wellâŚ
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Well it seemed like Peter Lynn of all people made a pretty good case, from multiple angles, against kites for container ships. If that post was really from 2009, itâs even more surprising. We had a lot of what can now be seen as goofy AWE ideas floating around and raising millions back then. Meanwhile, where is a kite-power rig for a small sailboat or motorboat? Besides some high-profile feel-good publicity-seeking symbolic demo? Iâd think maybe some class of racing sailboat where a kite could fit the rules, if such a class exists, might be one starting place. Consistent wins might lead to further development. Or some ferry or inter-island scheduled ferry or delivery service that happens to be located where the route in both directions is reliably crosswind. Peter Lynnâs off-the-cuff analysis sounds similar to the synopsis for small wind turbines in general, which is only a tiny fraction of households are suitable for wind power. First, most people do not live in an area with a good enough wind resource to make it economical. Out of the people who DO live in a sufficient wind resource, most have lots too small to put up a high enough tower within development codes that require a fall-zone big enough to contain a fallen tower within the property lines. And out of the small fraction of people who live in a sufficient wind resource AND with enough land for a wind turbine, a good proportion are surrounded by trees, buildings, and other obstructions that spoil the wind for power generation through blockage and turbulence. This is one reason why most small wind turbine manufacturers have gone out of business during the time AWE has enjoyed its recent popularity. The other two reasons are the drop in prices for solar, and the well-intended but destructive certification schemes that lock out most small manufacturers from tax incentives, favoring, in the U.S. at least, a single surviving manufacturer over everyone else.
Anyway, it does seem that using a kite to pull a boat is low-hanging fruit for AWE. There must be some situation somewhere that it could make sense to develop a kite-powered boat. I mean, really, all you would need in many cases would be an off-the-shelf kite and an off-the-shelf boat.
Hereâs one analysis of actual kite boating
But a more extreme version was done by Don Montague 7 years ago
Interesting Roddy. Seems like there is no good reason we donât see more kite-powered boats, at least for niche applications. Looks pretty fast. After watching these videos, youtube spoon-fed me this one of a couple of guys kite-sailing partway around the Isle of Wight - you probably know them?
Well looks they ran out of wind. Luckily a boat showed up willing to give them a tow. One more case of needing a tow back to shore once the fun and/or wind has expired. They sound Australian?
Note: In the early days of hang gliding we had a pilot killed by a helicopterâs downwash, while filming a commercial at our hang-gliding club. Lesson: keep heck-of-a-lopters away from hang-gliders unless you want someone killed. Today with drones the dangers are probably more about collisions.