Foil for current-driven propulsion?

No. I realize before you can calculate anything you have to have a basic understanding of what is happening and the underlying principles. The moment you suggest what is shown in the Artemis video is breaking laws of physics and representing "The perspective of perpetual movement" there is nothing to calculate.

Not really. I mean there is potential to extract energy from the relative movement between two trucks. Like there is potential to extract energy from masses of water and air moving at relative speeds. You have to realize this is the driving force behind every sailboat (not sailing directly downwind in still water).

 

And yes, even that! Why not? The energy from the air is being used to overcome the drag of the hull.

 

This example is indeed really interesting. Thank you RMLOCK, for the opportunity to re-work again basics in Mechanics. Also, with your diagram, I am able to better understand the wording "Upwind" and "Downwind" that you use, as it is evident that english is not my mother language. With this discussion, thanks to you and whole of you, I am increasingly interested in calculating, at least for my own purpose, the problem posed. When done, It will be a pleasure to share it with you al. Although I don't really know if the solutions, even trivial ones, could be accepted as true solutions. Anyway... I have taken the liberty to analyse the diagram that you kindfully made (again, many thanks for this, it is great), which is very clear, even though simple. Simple is beautifull. No problem with your composition of vector, nor VMG your calculations...If only the forces generated by such a movement would allow this possibilty, given the inputs. Down below, I made the assumption of the direction of the airflow and waterflow, with regards to the vector sum you gave. I gave an orientation of the boat, such as to be able to make her way upstream. I also represent the drag, lift and total forces generated by the sailplane, and the vertical portion of the two foils. I assume that the drag forces are greater than the lift forces, given the incoming angle of flows. Vectors are arranged such as both their projection (sailplane & foils) would give a driving force of the boat, accordingly to Tiny Turnip comment :"The (hydro)foils are behaving as the sails on my boat; they are generating lift in the water, with an upcurrent component, from the real and virtual current.". Before getting any further, please bear in mind that what I'm writing is an ad absurdum argument. Even if the representation downbelow would tend to show, that, indeed, it would be possible for the boat to make his way @constant speed following the given trajectory, multiple errors are made in this representation. If you try to correct them, you will find that the given inputs do not allow the boat to sail in opposition with the current. Of course, it does not mean that other inputs would not also allow the boat to make such a way, in front of the current, 3 times the wind speed. But again, this still has to be proven correctly.

 

Yes... but with no wind at all.... I mean True Wind, the same as define as the "True Wind Speed" in every book.

 

Some scientist say that, before beginning of their calculations, that they have already found the result. Most of the work to be done is demonstrating the result. And, as RMLOCK says, avoid "tunnel effect", that may compromise your judgement. This is the hardest part. Even great scientists have fallen into this trap, some for years long. Some other are long dead, and no one has been able to overcome the "tunnel effect" they have made in their calculations, especially when they are difficult. I trully appreciate exchanging with you, Flotation, because I have the faith that everybody holds a piece of the thruth. It is our capability to discuss and collaborate that makes the impossible possible. I will keep thinking about your idea, because our future desperately need to overcome our actual bounds. To make possible the impossible !
Again, thank you.

 

I might be missing something but I don't think when going directly downwind in still water your are extracting "energy from masses of water and air moving at relative speeds". As the underwater foils are not generating lift in this scenario.

If I understand correctly this is what limits a craft's speed when going directly downwind to something below windspeed.

 

The boat will not be able to maker her way upstream exactly in the direction the water is flowing from (if there is zero wind) I admit this is not very well represented in the Artemis video. What is represented correctly is it will be able to make speed upstream at a higher speed than that of the current because of how efficient the craft is.

Like @Sailor Al explained on page two of this thread:

"My only gripe with the video is that whilst Artemis might be doing 30 kts through the water, it's not sailing DIRECTLY upstream - they have fudged the apparent wind angle. They would have to put in a few jibes (tacks) to make any progress up the river."

To be able to make way exactly upwind or in the direction of the current something like a propeller/propeller driven craft is needed, see (among quite a few other threads on this subject): Finding the best way to sail directly upwind https://www.boatdesign.net/threads/finding-the-best-way-to-sail-directly-upwind.67271/

 

No tacks, just jibes! C'mon we're all sailors here! You don't tack downwind you jibe (unless doing a granny in a stiff breeze)

 

Isn't the apparent wind speed coming from the bow when sailing up the river?

 

Yes the TWS is the speed limit directly downwind, but you're still extracting energy from the wind to overcome the drag of the hull.

 

For me, it was obvious this was a figure of style from Arthemis, the fact was is they were able to progress against the current with no wind. As I said in my former explanation they had to broad reach downwind through the river flow (and jibe oviously !) as multihull use usually to get their best vmg downwind.
Basically, Arthemis are right, they are able to progress upstream the current with no wind. The vmg they are able to progress relative to the shore is their vmg downwind with the true wind equal to the river velocity, less the river velocity. Assuming they are doing 2 time the windspeed at 135° course their velocity upstream should be 2.v.cos(45)-v # 0.4 v , were v is the river stream.

To my knowledge, windmill (air) sails, transmitted to screw propeller (under water) driven sailboats are able to progress directly against the wind (wich puzzle me !), but we have to check foilers with
windmill propulsion are able to do so directly downwind !

 

Sorry AI.... Language.... I meant No wind at all !!! Please skip the True Wind Speed word. It is just false !

 

Well, all of this is very very interessant ! I wonder if someone is able to make a power balance of the proposed solution, meant to "extract", "convert","transform","use" every kind of "energy" from "movements", "gradients","potentials"... And how much of these solutions have true and proven application. Below is not an example taken out of the water, but still, it is a very elegant INDUSTRIAL system that converts the gravity potential energy (in mechanical terms) into a usefull movement. Beware ! The title containing the expression "[...] uses no power..[...]" may be troublesome, as there is indeed a consummed power that allows the system to operate.
I let you guess what power it is, and by the way, discover that the idea behind energy convertion or extraction is indeed the idea of energy consumption minimizations, unless you violate - or invent- new thermodynamic laws. Have a nice watching !

 

Since this assumption is exactly what's need to be verified, I have some doubts about this particular reasonning .

 

Without watching the video, they are using the potential energy in stuff mined on a higher level to pull the empty carts back up.

This has hardly anything to do with making use of the energy in moving masses of air and water except that energy, in the end, also come from what happened in (the) sun(s <- to be more exact).