DDW faster than windspeed !

[Breaking Waves]

in a pure deed of gift AC match - there are no design rules/requirements, except the deed does sail the vessel must be propelled by sails.

It would be fascinating to watch the NY supreme court try to decide if a vertical turbine was a sail or not. I guess they would conclude it was . . . but that having it drive a propellor was not allowed . . . but hard to pre-guess such a case.

[clakiep]

Exactly downwind it is not possible to go faster than the windspeed. You need a slight deviation from the wind direction to create an apparent wind wich is also not parallel to the movement of the craft.

Capt. Claus

[Dave_S]

Originally Posted by Dockhead

That's all true, but not an answer to the question I was asking. How do you sail directly against the apparent wind?

Answer: you can't. Not even an AC boat.

You asked where is the AW in your first post, a different question. I thought my explanation showed it is on the blades of the propeller.

The yacht (land yacht, like Blackbird with wheels on the ground that are connected to a propeller that has positive or negative gearing to the wheels and that the drive is drawn from a different plain relative to the restriction).

The drawing power from a different plain to the direction of travel removes wind speed and direction from being any sort of barrier. This makes it different to a boat with sails or wings like an AC boat or our boats. In theory with no drag, our boats could sail infinitely close to DDW or DUW but never exactly on it. You must be able to draw power from a different plain to do that and you must have a speed differential from at least 2 mediums that you can leverage against.

The AW exists and continues to exist at all times as far as the propeller blades are concerned because dynamically they are never travelling DDW. There may be no AW flowing over the yacht but there is always AW on the blades as they screw their way DW. The propeller blades are not only travelling longitudinally in the direction of the wind they are rotating. So the rotation of the blades ensures they are always have air speed flowing over them.

At no time ever do the blades not see an apparent wind except when the vehicle is stopped with no breeze at all and as stated above. It wont work if the is no ground wind.

[Dave_S]

Originally Posted by Dockhead

That's all true, but not an answer to the question I was asking. How do you sail directly against the apparent wind?

Answer: you can't. Not even an AC boat.

This question.

Assume you have very little drag.

You know all about propellers lift and drag.

If they are driving the wheels DUW or in DDW are being driven by the wheels at the most efficient drive ratio for that purpose then DDW the wheels are driving the propeller to apply a positive force on the yacht to accelerate it forwards. When this matches drag you have reached maximum speed.

The difference between them and us is the plain the power is drawn from. With our sails we are at the extent of useful drive generation with our sails pulled close hauled. Rotate the plain you draw power from 90° and these two extremes are right in the efficient zone.

[Dave_S]

Originally Posted by MartinR

I sail iceboats, and, like land yachts, DDW does not work. 30 degrees off and then you can make your own wind. Iceboats are always close-hauled.!

They must be exciting to sail. Not a lot of ice here 🙂

The ice boats have very little drag so can do amazing things when compared to a boat in the draggy water but you are still limited by the plain from where you draw your drive from so you can never sustain DDW or DUW. Unless you can apply drive to, or take drive from the ice with a spiked wheel or similar and rotate that drive at least some degrees. But if you did you would be able to do better than 2.8x DDW because you have less drag than the Blackbird Yacht.

[chrisr]

Originally Posted by clakiep

Exactly downwind it is not possible to go faster than the windspeed. You need a slight deviation from the wind direction to create an apparent wind wich is also not parallel to the movement of the craft.

Capt. Claus

this is true of a conventional sail driven vessel...but not universally true, as the experimental craft in the video shows

seems to me the key is the different angle of attack created by the propeller

cheers,

[44'cruisingcat]

Originally Posted by Dockhead

Explain the physics behind that?

DDW faster than wind speed, where is the apparent wind? Right on the nose is where. I never saw a sailboat which could daily directly into the wind. It's not possible.

There was a boat that had a wind turbine driving a propeller. It could " sail" directly into the wind. In fact IIRC dead upwind was actually it's best point of sail.

[StuM]

Originally Posted by cal40john

You can't with traditional sails, but you can with a propeller similar to DDWFTTW.

I guess it depends on your definition of "sail" and "sailing".
I'm in the DH camp. As far as I a concerned, wind turbines and propellors are not "sails" although the physics are very similar.

[TBear60]

Check out Sail GP videos on Youtube. Not DDW but close to it and EXTREMELY fast... 60mph+... interesting though, in practice faster DW and UW....50ft foiling cats!! Much fun, yeah?

[arsenelupiga]

Originally Posted by chrisr

super interesting video

https://interestingengineering.com/v...physics-debate

perhaps limited application to sailboats, but it does involve windpower...and may explain why some lagoons are so quick

anyway : enjoy !

cheers,

rumours on the streets are true, we can do 1/2 of wind speed.

[HappyGuy]

Originally Posted by Dockhead

That's all true, but not an answer to the question I was asking. How do you sail directly against the apparent wind?

Answer: you can't. Not even an AC boat.

When I lived in Whangarei NZ - somewhere between 1984 and 1986 I saw a catamaran about 35 feet long that had a 3 blade (if I remember correctly) windmill mounted on the mast that drove a propeller in the water.
I saw it "sailing" up Whangarei Harbour against a fresh SW breeze of about 25 knots. I would estimate it's speed at around 8 knots.

[Dave_S]

A new video on this.

https://youtu.be/yCsgoLc_fzI

[HappyGuy]

Thanks for the link.
I had a good laugh at seeing the physics professor get his backside kicked and proven wrong.
That was an expensive bet at 10 grand. I bet he thinks twice before making that kind of bet again!!

[seandepagnier]

Originally Posted by clakiep

Exactly downwind it is not possible to go faster than the windspeed. You need a slight deviation from the wind direction to create an apparent wind wich is also not parallel to the movement of the craft.

Capt. Claus

This is completely false and proven so, at least on land. Has anyone found an example of doing so in the water? I imagine it is a bit more difficult but not impossible.

Now interestingly, the craft that can do it would not work very well upwind because the air propeller would not be cambered to act as a turbine, and the water turbine would not be cambered to act as a propeller.