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Position Control

Home Forums Archive TSI Engineering Position Control

This topic contains 38 replies, has 17 voices, and was last updated by Avatar of ellmer - http://yook3.com ellmer – http://yook3.com 3 years, 9 months ago.

Viewing 15 posts - 1 through 15 (of 39 total)
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  • #732
    Avatar of deweaver
    deweaver
    Participant

    In thinking about maintaining a specific location, we should note that currents vary with depth. A sail boat obtains energy from the shear between two fluids — air and water — which allows it to move in all directions, except directly upwind. Given a surface current and a deeper current moving relative to each other, it would be possible to construct two wings or keel type devices ( with control surfaces) that can be flown in the two currents and generate a force in almost any desired direction. With the higher mass of water and the lower velocities of currents (relative to wind), you can generate very high force levels per unit wing area.

    For moving around a sea-station, you need very high force with little velocity. Kite type devices (with appropriate controls) flying in the deeper current and a keel on the surface structure would also work to move the structure where you want it. The lift to drag ratio on the wing/kite would determine the minimum angle against the surface current that could be achieved.

    This concept doesn’t require any fuel.

    #4183
    Avatar of Patri
    Patri
    Keymaster

    Yep, we mention this in the book – a reader suggested it awhile back. It is an intriguing idea.

    #4186
    Avatar of
    Anonymous

    I was thinking along similar lines. The seastead book (http://www.seasteading.org/seastead.org/commented/paper/infra-add.html) mentions submerged sails, but it talks about masts extending ~200 meters down. A more kite-like structure connected by one or more long cables to currents several miles down would get better current differences, but would cost more.
    I suspect keels are less effective at very low velocities than at typical sailing velocities. So I’m not optimistic that we can get much choice over the direction the kite pushes in, although changing the angle of the kite will provide some choice.
    I started thinking about this after hearing a far-out idea from Keith Henson about a desalinization method whose source of energy is the current relative to a pipe sitting on the ocean floor. I don’t understand that very well, but if it works it could probably be adapted to be attached to a seastead (but I don’t see many signs that it could be done at a reasonable cost).

    #4187
    Avatar of vincecate
    vincecate
    Participant

    >I suspect keels are less effective at very low velocities than at typical sailing velocities. So I’m not optimistic that
    >we can get much choice over the direction the kite pushes in, although changing the angle of the kite will provide some choice.

    At slower speeds you would need something much larger than a typical sailing keel. But an “underwater kite” could easily be much larger than a normal keel, so I don’t think that is a show stopper.

    A regular in-the-air kite can replace a sail (I and many others have done this). If we replace the sail and the keel with kites that perform the same functions, then we could tack back and forth and work our way upwind or anywhere. Both the underwater kite and the in-the-air kite must be controllable. So the combination of these two types of kites could work really well for seasteads.

    I am confident that seasteads will do this at some point. The electronics to automate these kites is just getting easier all the time. But I also think my first year or two of seasteading will be using a kite to move mostly downwind and motors for going in and out of harbors. I don’t think the ability to go upwind for long distances is important enough to need the underwater kites to start seasteading.

    — Vince

    #4190
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    Maybe it is a good idea in general to build seasteads with some boat-like properties, like having low drag in one direction. To be able to “sail” like this or just to reduce the costs of moving or staying in place against the current.

    You could flatten (elongate, stretch them) the spar(s) and end up with something like those SWATH catamarans.

    Of course this could make it extra sensitive to waves depending on where they come from. Or perhaps it can´t get much worse than a circular spar…

    #5452
    Avatar of wohl1917
    wohl1917
    Participant

    Jacques Cousteau experimented with this about 50 years ago and, I think, still holds the record…

    #5500
    Avatar of Bigbenorr
    Bigbenorr
    Participant

    Most deepwater drilling platforms use Dynamic Positioning systems. This involves using several electric motors on the hull that can be rotated 360 degrees. The computer system acuires a GPS signal and adjusts the motors automatically to maintain position. This method requires a power source though. the platforms just run massive diesel generators, but I am sure it is expensive to keep filling up the tanks. Just thought it would be worth mentioning.

    #5540
    Avatar of wohl1917
    wohl1917
    Participant

    Deep-water drilling platforms pump enough oil to pay the cost of their construction in a very short time so the expense to ‘keep filling up the tanks’ is barely a factor. The single biggest advantage of anchoring is that there is no complex system of computers, controllers, generators or thrusters subject to system failures and blackouts. The routine preventive maintenance on such a system would be prohibitively expensive! For a Seastead to be economically viable anchoring is about the only option. The negatives of anchoring such as limited manoeuvrability etc., don’t really apply because you want people to be able to find you so NOT moving is a good thing. Jacques Cousteau’s ship Calypso weighed in at just over 360 tons, was anchored in 24,600 feet of water to a 3/8-inch nylon line… Most of the ocean on the other hand averages around 13,000+/- or a little more that half of Cousteau’s record…

    #5543
    Avatar of DM8954
    DM8954
    Participant

    When you say that most of the ocean averages only 13,000 feet deep, I believe that is mostly part of the continental shelf. This would technically be within the jurisdiction of another country. An anchor on the seabed of the continental shelf will most likely put you in someone’s territory… but the extent of the control involved might be debatable. It depends on what risks or limitations a given seastead is willing to accept. So, technically it’s doable at those depths but ‘assured autonomy’ would require something much more in line with the record depth in question.

    #5544
    Avatar of OCEANOPOLIS
    OCEANOPOLIS
    Participant

    If yor are 1500nm offshore on a seastead what is the point of spending money (or any effort) on maintaining the position? Is not like you are drilling so you have to keep a certain fix over the location,…LET IT DRIFT, HAVE SOME MARGARITAS,….Keep a watch on your gps, and when u drifted too far(??) start the engines and go back to where you want to be,…It will cost less in the long run.

    #5545
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    Anchoring doesn´t scale very well, I think. How far away from the next anchoring seastead must you be in order not to cross your lines?

    I can´t find any info on Cousteau´s deep sea anchor. Anyone else have anything?

    #5548
    Avatar of wohl1917
    wohl1917
    Participant

    DM8954 said, “When you say that most of the ocean averages only 13,000 feet deep, I believe that is mostly part of the continental shelf.” Actually, 13,000 feet is the average depth of the deep ocean excluding the various trenches. Continental Shelves average around 1,300 feet and yes I agree with you: any Seastead anchored there would be too close to shore.

    Oceanopolis said, “,…LET IT DRIFT, HAVE SOME MARGARITAS,….Keep a watch on your gps, and when u drifted too far(??)” While I think that’s a good idea for smaller Seasteads for a larger Seastead to be commercially viable ‘customers’ would have to be able to find you and the ocean is a BIG place.

    Carl said, “Anchoring doesn’t scale very well, I think. How far away from the next anchoring seastead must you be in order not to cross your lines?” Under normal circumstances, the ‘scope’ or length of anchor line that should be played out is 7 to 1 but I think it’s less depending on the type/weight of the anchor. Even at 7/1 though, if your Seastead was tall enough, you would be within sight of each other.

    To find information of Cousteau’s research in this area, you can’t find it on line or at least I couldn’t find it either: SEE: The National Geographic Magazine March, 1958 and related articles in the February ’56 and January ’54 issues.

    #5557
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    wohl1917, thanks for the info on those issues. I´ll try to check them out.

    Presumably the distance between two anchored vessels can be calculated with the Pythagorean Theorem.

    The distance should be;

    2 times the square root of ((SD)2-D2)

    where D is the depth and S is the scope.

    For a depth of 4 miles I arrive at 55 miles separation, unless I´ve made some error in the formula.

    #5558
    Avatar of OCEANOPOLIS
    OCEANOPOLIS
    Participant

    where did u guys got the ideea of anchoring in 13000 feet of water??? Have u guys anchored before? Do u know ANYTHING about anchoring? If your using 7 to 1 scope, u might need,…91000 feet of rode,…Do u know how much that will cost? Also u will have to use chain, (since rode alone wont do it, because u will DRAG-it is the weight of the chain that’s holding u in place). Lets say u will have1/3 of the 91000 ft in chain. That is 30000 feet of chain. If u gonna use 1/2 inch hot galvanize “BBB” @ $5/foot (and that is CHEAP) ure looking @ $15,000.00 for chain alone. Also that chain will weight around 270 lbs/100′, so u will be carring ,…oh,… 36 TONES OF DEADWEIGHT. Good luck!

    #5559
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    Why would you need 1/3 of the full length in chain? If the purpose of the chain is to provide weight it should be sized according to that and not the length of the rope, right?

    FYI I´m personally sort of sceptical to anchoring. But doing some calculations and research doesn´t cost anything. Chances are the ropes today are both cheaper and stronger than whatever Cousteau used.

    What is the harm in doing research?

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