Newbee with a brilliant idea needs your help!

Discussion in 'Boat Design' started by kitetug, Dec 19, 2005.

  1. kitetug
    Joined: Dec 2005
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    kitetug Junior Member

    Newbee with a brilliant idea needs your help! (Kite + Water carrier)

    Hi, I'm very new to designing boats, but I have a concept I want to explore. It is about a small water-carrying cargo ship powered by a kite.

    Now I know that something like Skysails exists, but mine is different in that the hull of the ship the kite tugs, is not made of steel but of a fibre-reinforced polymer.

    This means you save on several fronts:
    1. you use wind instead of very expensive oil (which is getting ever more expensive)
    2. you need a lot less power to pull a polymer bag (compared to a steel hull weighing thousands of tonnes)
    3. in short, you would almost ship your water for free!


    The idea is to carry bags full of fresh water to places where water is scarce.

    1. the idea of transporting water in bulk in bags exists: http://www.waterbank.com/Newsletters/nws12.html

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    2. the idea of using kites as traction and tug devices exist:

    [​IMG]


    Now I want to combine both. I would want to find out if a small "tug-boat" which is pulled by a kite, can translate the force of the kite to the bag.

    1. Obviously, in my configuration the pull requirement of the kite is greatly reduced, because we're pulling a lightweight polymer bag, not a steel tanker weighing thousands of tonnes.

    2. The problem is I'm not sure whether the translation of forces works out. As I understand it, a ship pulled by a kite levels out the sideward traction because at the same time there's a lifting force. This is the so-called "heeling moment compensation":

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    So in principle, the forward directional pull of the kite, should be translated through the "tugboat" to the polymer bag. The thing is I'm not sure whether the small tugboat would be lifted out of the water and pull part of the bag with it, or whether it would remain in the water to nicely translate the force to the water-carrier.

    What do you think of this concept? It might be interesting to study its feasibility since it would allow fresh water to be transported on the cheap to water-scarce regions. (E.g. from Alaska to southern California).

    Your help & comments would be greatly appreciated!
     
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  2. Skippy
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    Skippy Senior Member

    If you're talking about a lightweight tug hanging on a huge kite to pull an enormous load astern, then yes, the tug would tend to get yanked out of the water. The whole point of kites is to keep the kite's propulsive forces directly in line with the boat's resistance.

    Also, it looks like the art department at SkySails should consult with their engineers. In the bottom picture, the total force on the kite should be EXACTLY parallel to the line holding the kite, and the line should be exactly in line with the resistive forces of the boat, which probably aren't too far from that little cross-hair symbol they have in the center of the hull.
     
  3. Skippy
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    Skippy Senior Member

    Just saw one more thing, the horizontal and vertical component forces should form a rectangle with the total force on the kite extending exactly to the far corner of the rectangle. Their total force arrow is too small, or the component arrows are too big. Also, those rotational moment arrows are kind of dumb, since the component forces are just mathematical constructions. There are no large rotational moments, again that's the whole point.
     
  4. safewalrus
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    safewalrus Ancient Marriner

    Interesting concept! I'm sure the 'mathamaticians' could prove it would work, but ........ and there always is a but! Practically; too many inponderables. What if's? Think about it logically Skippy has already given a few above; how's about frailtys of wind too much and your off, what controll do you have, the bag snags and bursts, it's possible! Big kite [bloody big to make it worthwhile!] control? some fast and big winches - we ain't talking string here! Break one of these beauties and we're all in danger. Ever see the effects of a parted wire rope! it can be dramatic - now auxilary sails tp help pull your tug ? reasonable sized schooner or brig! now your talking. Also don't forget the Specific Gravity of water. Some years ago the same concept (floating bag or dracone) was used for oil (SG less than water) this gave some flotation what your propsing don't give enough! Funny you don't see many dracones these days (collision, lack of contol etc)
     
  5. kitetug
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    kitetug Junior Member

    Thx Skippy and Safewalrus!
    As you probably noticed from my rudimentary grasp of the concept, I'm really not (yet) into the physics of this concept, I just stumbled on it and wanted to share it rightaway with more people.
    I just thought:

    1. kites at high altitudes (say 500 metres) can create a tremendous pulling force (in theory, thousands of horsepower)
    2. oil is getting expensive and bunker fuel costs make up 50% of the entire cost of international shipping
    3. replace the steel hull of a ship by a polymer bag, and you dramatically reduce the towing force (as in horsepower) needed to transport the cargo (in this case sweet water)

    So I thought, let's combine these different concepts into one!:cool:


    1. Skippy, you seem to understand the physics of kite traction, I don't very well... could you help me finding out whether it makes sense to use a huge kite on a small tugboat which would then tow a cargo in a lightweight bag (with the cargo having a lower specific gravity than seawater)? You see, I just thought that it would be possible to have a big traction force coming from the kite, which could *elegantly be translated into a simple forward pull*, without lifting the entire tug out of the water (which would lift the bag too, snapping it to pieces!)

    2. Safewalrus, you're right, one would need a big kite, but then the kite would need to be much smaller compared to kites like those of Skysails, which are intended to pull ships with steel hulls weighing thousands of tonnes! (Remember, mine is just a polymer bag, gets rid of the thousands of tonnes of steel). Of course, there would be a small engine to keep some kind of control when sailing out of harbors or to give auxiliary power in case of weak winds.
    Kite control would be automated (as in Skysails).

    Did they use "dracones" to ship oil? Cool! Never heard of it before. Why don't they use it more now that oil prices are so high? I heard that shipping costs have *tripled* over the past 18 months because of high oil prices! Of course, when such a bag breaks and you spill petroleum, you have a disaster. With my idea, sweet water, this is not the case...

    Mmm, I'm not sure, maybe as you guys say: too many imponderables... :(


    [Excuse me for my bad English, I'm not a native speaker!]
     
  6. Vega
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    Vega Senior Member

    It looks to me that the weight of the boat is almost irrelevant compared to the weight of the water you want to transport. Or I am missing something?.
     
  7. kitetug
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    kitetug Junior Member

    sorry for being such a total beginner and physics dummy!

    Mmm, I'm not sure: the boat (the tug) needs to be heavy enough to translate the force from the kite effectively to the bag (which contains a huge load of fresh water) without being pulled out of the water.

    See, that's my problem (I hope I'm not repeating myself here too much): can a small boat (maybe with a heavy counterweight) translate the huge power from a traction kite into a horizontal pulling force, without being pulled out of the water? I'm having trouble with these "vectors" of forces here.

    I'm a physics dummy, so really I don't have a clue. But I saw these pics:

    [​IMG]

    [​IMG]

    So I thought, :rolleyes: this is for speed; but what if you just attach a big bag full of water to such a similar vessel and use a much bigger kite, - would the bag of water gently be pulled forward, say at a speed of 3 knots? :D :D I know, I'm a total beginner!!

    Can you convert the power of this kite which delivers for speed, into power which delivers for pulling a large body of water with high drag through the sea?
     
  8. Stephen Ditmore
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    Stephen Ditmore Senior Member

    But the "boat" you're talking about is a tanker (no mater what you make it out of) and tankers are waaaaaaaaaaaay heavier than the hydroplane in the photo (because the cargo is heavy, as Vega pointed out).

    So you're talking about a small boat and a tanker? I think the small boat is useful as a platform for deploying all the essencials, but once underway I think the small boat is supurfluous from a physics standpoint.

    I wouldn't say there's nothing to your idea, but getting enough horsepower from a single kite would require an enormous kite!

    I've heard what sounded like serious proposals for towing icebergs to southern ports. Finding some way to lower the drag of the berg through the water would certainly contribute to the energy effectiveness of such an endeavour.

    But if we're brainstorming wacky ideas, how 'bout this. Start with a hopper ship full of sand or gravel and a set of carefully optimised wings that can be attached to your blimp-like bag, or to a streamlined iceberg, which I'll refer to as a "water tanker". Attach the wings and load giant sandbags aboard the tanker until it's heavier than water, and take her down. If designed for optimum glide ratio the tanker should be able to achieve some forward motion with each foot of decent. When you near the bottom (or maximum depth), drop the sandbags or gravel to the bottom of the sea, and continue to make forward headway as you glide back to the surface. Rendevous with hopper ship and repeat.

    This could be controlled remotely from a small vessel, or from the hopper ship, so you wouldn't actually have to ride the tanker to the bottom of the sea.

    Whaddaya think?
     
  9. kitetug
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    kitetug Junior Member

    True, but mind you: a big oil tanker uses 50% maybe 70% or so of its entire power merely to push forward its steel hull! My hull weighs nothing (a few tonnes, a steel tanker comes it at thousands of tonnes). So I'd at least be saving 50% to 70% of energy, requiring half the size of the kites a company like Skysails proposes.

    Does anyone out there know how much of the horsepower a steel tanker produces, it actually uses to propel itself? (In other words, if an ordinary oil tanker were empty, it would still need thousands of horsepower to push all that steel forward, wouldn't it?) :confused:



    About the sandbag idea: I think it's for fairy tales, but I like fairy tales! :D
     
  10. Skippy
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    Skippy Senior Member

    If the tug is not weighted, it gets pulled up into the air. If it is weighted, then you have a heavy vessel with a short waterline, plus the waterbag. What you need is some efficient way to attach the kite to the bag other than a big heavy tanker. You'll need some kind of hull to deal with the pressure at the bow, then maybe the rest of the bag can somehow trail astern sticking out of the bow/hull. But you still need some kind of framework to distribute the upward component of the kite's force throughout enough of the vessel's weight to make sure no part goes airborne.
     
  11. Skippy
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    Skippy Senior Member

    The only use I can think of for weights would be inside the bow/hull. Basically, the tug is just connected to the waterbag to lengthen the waterline. Then the question would be whether it helps to add enough weight to sink the whole thing. I guess it's possible, it would be kind of like the SWATH designs.
     
  12. Packeteer
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    Packeteer Junior Member

    nobody seems to have considered the drag created by a bag with a large floppy mass
     
  13. tom28571
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    tom28571 Senior Member

    Yeah Packeteer, and can you imagine the strength needed in the bag to prevent it from rupturing when one half of it is on the back of a big wave and forward half is going down the other side. The inertia sounds enormous. The bag could be compartmented or baffled or filled with open celled foam like NASCAR fuel cells but none of this sounds cheap.

    For many years we have seen wind assisted ships of one kind or another like Fletner rotors, Savonious rotors and even the worlds largest jib on a Gulf coast oil rig. None of these seem to work out on the bottom line of money production though.
     
  14. chase687
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    chase687 Junior Member

    What about attaching a foil to the line of the sail that would produces negative lift. As there is more wind you move faster and hence make more negative lift. Would that not solve the problem of the Small Light boat coming out of the water? Just a thought.
     

  15. Deering
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    Deering Senior Member

    If you want to bring water from Alaska to California, your kite concept may prove challenging - prevailing winds are from the SE up here. Besides, who says we want to give away our water to California?

    Look at the economics: It will be really slow, so transit times will be long. Even without engines you'll need a crew to man it. Crews cost money. You'll have to carry enough water to cover their cost so it'll have to be enormous. Enormous means means expensive. There are plenty of other operating expenses besides engines and fuel - those don't go away with your plan. In fact, with your unique concept, they're probably a lot higher.

    Another idea to consider. Rather than towing an expensive bag full of water, go far enough north (or south) and latch onto a large iceberg. If you can tow it fast enough you can get it to CA before most of it melts.
     
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