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tech99
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There is a video of a model windmill boat going directly into the wind at this URL:-
Jacques Cousteau implemented a not-especially-dissimilar concept on his supplementally-wind-powered (primarily diesel powered) vessel Alcyone.tech99 said:However, if you have a windmill on a boat, driving a water propeller, it can push the boat against the wind.
He probably wasn't the first. The optician Bernhard Schmidt actually build such boats in the 1920s:sysprog said:Jacques Cousteau dreamed up a way to make a wind turbine that could drive a propeller so that a vessel could go directly into a headwind
Apparently, you missed the point.Catsailor said:Apparently, none of you are multi-hull sailors.
Sure, but not directly upwind or downwind.Catsailor said:On a reaching course,...
We tack upwind , and even downwind. It's faster than the wind on either point of sail.. My point is, postulating a motor facing the wrong way on boats that have been perfected over the centuries for their speed, economy and versatility is beyond silly I have gone 30 MPH on the ocean on my 18'. Physics puzzles are fine. But boats were Man's first vehicles. The engineering, banking, insurance and investing industries all relate back to historic water transport. The boat I currently sail used Formula One computer aided design with millions of data points. Then there are cartoon boats with fans on them. Then there is the difference between beating a dead horse, or in some cases, riding one.A.T. said:Apparently, you missed the point.Sure, but not directly upwind or downwind.
And physics forums are for physics puzzles.Catsailor said:Physics puzzles are fine.
A.T. said:And physics forums are for physics puzzles.
Wait, isn't Utah a desert?Catsailor said:Three times Utah Catamaran State Champion here.
That "apparent wind" is the vector sum of the wind and the boat velocity. There is no new or faster wind generated on the boat. It is still impossible to continue sailing a conventional sail cat directly into the wind, or when there is no wind.Catsailor said:On a reaching course, the side-force pushed on the boat and via the centerboards, are converted into forward motion. As the air accelerates over the wing shaped sails, it creates apparent wind.
Just a plain ol sailor here with no prizes.Catsailor said:As pertains to the title of the thread, yes sailboats can provide their own wind. Apparent wind. Three times Utah Catamaran State Champion here.
Try reading the actual question, not just the title. This is not what the OP means by "provide their own wind".Catsailor said:As pertains to the title of the thread, yes sailboats can provide their own wind. Apparent wind.
Uh, 40 large high altitude reservoirs, One Pleistocene lake at 6000'that is 104 square miles, 400,000 years old. Three high volume whitewater rivers, Colorado, San Juan, and the Green, Lake Powell, 162,000 acres, 1900 miles of shoreline. We do ok.berkeman said:Wait, isn't Utah a desert?
Dale said:Myth busters did this:
I don't think a sideways force can push a boat forward.Catsailor said:On a reaching course, the side-force pushed on the boat and via the centerboards, are converted into forward motion.
I suggest defining "sideways" and "forward" precisely, to avoid endless talking pass each other.tech99 said:I don't think a sideways force can push a boat forward.
A.T. said:The vectors are explained nicely here:
http://www.onemetre.net/design/CourseTheorem/CourseTheorem.htm
The relative water flow is the same in all diagrams, and as you see the force balance works out that way. If you think that you can balance the forces with the water flow from the other side, then I would be interested to see your vector diagram.tech99 said:The first diagram of the link does not look correct to me, because the water should be hitting the centreboard on the leeward side, to provide lift, and not as shown.
So, assuming you have ice skated or roller skated. Do you put the skate behind you and push forward? Or do you push out to the side? Pushing from Behind will get you about ten miles per hour. So how come speed skaters hit 37 mph? Vectors, as explained below.tech99 said:I don't think a sideways force can push a boat forward.
My understanding is that a sail has two components of force created by the air flow: one, at right angles to the wind, called lift, and another in line with the wind, called drag. When sailing close to the wind, the lift is, by geometry, at a small angle abaft the beam, and so has a component in a direction to propel the boat.
The drag has a component slowing the boat. Both have sideways components arising from the angle of the lift and drag vectors, and these components are canceled by the centreboard. To do this, it operates at a small angle of attack to the water and generates lift to cancel the sideways forces.
The boat points at a small angle upwind of its track in order to give the centreboard the required angle of attack. Those on board see this effect as leeway.
A.T. said:The key word here being "roughly". Depending on how the sail is shaped the boat can go forward, but it's not as efficient, as just using the propeller.
When I think about this: is the affected air is carrying air next to it along for the ride, I would assume that this transfer of force to adjacent air molecules comes in response to slowing down the directly affected molecules. Basically slowed down by friction with other air molecules, and then that friction imparts momentum to its neighbors...DaveC426913 said:It can be done in theory, using a principle known as entrainment.
Even though the fan is attached to the boat, and pushes back with equal force, the air is viscous, and carries some air next to it along for the ride. You can get a little forward motion (if you angle the sail right), but its very inefficient.
It does not violate conservation of energy, since, after all, you are adding energy into the system, by whatever powers the fan. And it doesn't violate Newton;s Laws of motion because it's not a closed system.
This has been demonstrated.
What is the end effect you're saying will happen here? Forward movement, zero movement or no movement?A.T. said:Replace the sail with a board, and let the passenger collect balls from the ground and throw them at the board, so they bounce off and leave with backwards momentum.
The boat gets the opposite forward momentum.
I'm not sure though, as this TV series is aimed at children, and I'm not sure they would actually recognize how impossible this would be in real life, sort of like they probably don't grasp the difficulty of hanging 1-handed from a rope while a pair of friends dangle from your legs, as characters not stereotyped as super-strong still manage to pull off.Cutter Ketch said:I think you may be missing the point. It is supposed to be instantly recognizable as impossible. That’s why it’s funny when it works. It’s exactly like a cartoon character picking themselves up by their bootstraps.
Dale said:Myth busters did this:
I have no idea what you would call it, but yes, it is a thing. Jet aircraft use that idea to go in reverse. They just bounce their backward facing jet exhaust into the forward facing direction so that they can go in reverse. They use metal ducts instead of a sail, but it is the same principle.fleeker said:they got an effect like a weak fan aimed backward because the sail "bounces" a small amount of the forward-facing air backward...
Is that a thing? What would you call that?
...but this design is considerably more efficient than a fan and sail!Dale said:They use metal ducts instead of a sail, but it is the same principle.
“Vector thrust”.DaveC426913 said:Wouldn't it simply be "directed air flow"?
Agree. But I was looking for a general term.Baluncore said:“Vector thrust”.
“Reverse Thrust” brakes on jet aircraft, also VTOL.
Also used on jet boats (water) for steering and reverse.
Did you watch die video starting at 4:00? There is a diagram at 4:34.fleeker said:I'm not sure I understand how the shape of the sail could manage to generate more forward force than the backward force created by sucking the air behind the propeller forward, could you explain?
Are you familiar with momentum conservation? If the balls (initially at rest) end up with negative momentum after bouncing from the board, the boat will get the opposite forward momentum.fleeker said:I imagine if you threw a ball forward there would also be backward movement. Albeit very hard to perceive since it would be so minor.
Yes, the "go faster and create more wind" part omits that at higher speed the apparent wind also comes more from the front.rcgldr said:The "apparent wind" explanation is also mis-leading.
I created a new thread for this and deleted my posts related to apparent wind.A.T. said:Yes, the "go faster and create more wind" part omits that at higher speed the apparent wind also comes more from the front.
But as you note, this not at all what the OP means by "own wind", and the mods already had to delete this derail from this thread once.
Most commercial airliners can do this, but this can only be done at airports where the terminals are built / designed to handle the reverse thrust used to backup.A.T. said:video - "some planes can back up on their own"
Ironically airliners were using thrust reversal even back then. Yet apparently the myth about its impossibility persists even today.Mister T said:Robert Beck Clark wrote an article on this in either TPT or AJP, back in, maybe, the 1980's.