[DDW]

Those of you who scoffed at my claim that a windmill powered boat could be capable of sailing dead downwind faster than the wind will find a good discussion of exactly that in Max Ebb's column in this month's (March) Latitude 38.

[Mid]

DDW, on Mar 13 2006, 04:51 AM, said:

Those of you who scoffed at my claim that a windmill powered boat could be capable of sailing dead downwind faster than the wind will find a good discussion of exactly that in Max Ebb's column in this month's (March) Latitude 38.

link pls ???

[DDW]

Mid, on Mar 12 2006, 09:24 PM, said:

link pls ???

No on line. You will have to buy the magazine. Fortunately, its free. But is is only widely distributed on the west coast of the USA, based out of San Francisco (hence the name).

[LittleManInABoat]

Yawn

[sailman]

For those who could give a crap less about Lat 38 how about a Reader's Digest version of how this works?

[The Winner]

It's in a code only Mac 26 owners cypher

[Blackadder]

http://www.infoasis.com/~latitude38/

[B30]

I call total BS on this. I can see it going faster downwind than the the wind at an angle, but not ddw. As bs approaches tws, aws drops to 0. No aws, no drive. Dead upwind faster than the tws I can believe though.

[Flip Rigsby]

You can go fatser than the wind DDW on many boats. That is faster than the wind DDW TWD. To go faster than the wind DDW your AWA will be forward of DDW TWD. So yes it is possible for a Windmill to go faster than the wind DDW TWD...

[Guitar]

I read the article this weekend. Interesting, water impeller powering a windmill, drag of water applying enough force to generate power for the windmill sort of thing.

Try http://www.well.com/~pk/fishmeal.html. He may have it somewhere on his site.

[B30]

Flip Rigsby, on Mar 13 2006, 09:47 AM, said:

You can go fatser than the wind DDW on many boats. That is faster than the wind DDW TWD. To go faster than the wind DDW your AWA will be forward of DDW TWD. So yes it is possible for a Windmill to go faster than the wind DDW TWD...

Flip, you are wrong!

DDW = Dead Down Wind. That means in the SAME direction as the wind. I do not know of any sail craft (water, land, ice) that can go faster than the wind pointing in the exact same direction as the wind. Of course I know that many boats go faster than the wind speed on an angle, and thats what I wrote if you read my last post more carefully. There are some, but very few boats that can beat the winds VMG by sailing angles. It's the "old can it beat a balloon downwind" test. Land yachts and ice boats do this easily, but on water it is very tough.

This thread says a windmill powered craft going DDW (in the same direction as the wind) can go faster than the wind. No fucking way. Can one pass the balloon test by saing angles? Why not, But never DDW.

[Emu]

DDW, on Mar 12 2006, 01:51 PM, said:

... find a good discussion ... in Max Ebb's column in this month's (March) Latitude 38.

My latitude is pretty close, but apparently my longitude is off. Can someone post a link or a coherent summary of the article?

I can picture how linked air and water props might accelerate you until BS = TWS, but then I'm a little mystified how you get to BS > TWS.

[Flip Rigsby]

B30, on Mar 13 2006, 01:04 PM, said:

Flip Rigsby, on Mar 13 2006, 09:47 AM, said:

You can go fatser than the wind DDW on many boats. That is faster than the wind DDW TWD. To go faster than the wind DDW your AWA will be forward of DDW TWD. So yes it is possible for a Windmill to go faster than the wind DDW TWD...

Flip, you are wrong!

DDW = Dead Down Wind. That means in the SAME direction as the wind. I do not know of any sail craft (water, land, ice) that can go faster than the wind pointing in the exact same direction as the wind. Of course I know that many boats go faster than the wind speed on an angle, and thats what I wrote if you read my last post more carefully. There are some, but very few boats that can beat the winds VMG by sailing angles. It's the "old can it beat a balloon downwind" test. Land yachts and ice boats do this easily, but on water it is very tough.

This thread says a windmill powered craft going DDW (in the same direction as the wind) can go faster than the wind. No fucking way. Can one pass the balloon test by saing angles? Why not, But never DDW.

I'm not even going to bother trying to explain True Wind Direction and Aparent Wind Angle to you.

Carry On...

[nroose]

The gist is that it is upside down from what you would think.

Apparently some guy built a landsailer that did this in the 70s.

Pretty convincing.

Quote

"First you have to understand the basic energy relationship for propellers and windmills," she explained, "Power in or out is proportional to thrust or drag on the propeller, times the speed of the fluid moving through the propeller."
'"That's just the same as saying power equals force times speed, right?"
"Exactly," she confirmed, "You actually remember something from school. Now imagine this boat is going downwind at 15 knots in a 10-knot breeze."
"Okay, but the windmill will only see 5 knots of apparent wind, and the force on it would be pushing backwards."
"No way! The propeller is pulling forwards. There's power going into the propeller. The windmill part is underwater, that's where the power is coming from. Like, the key to this is that the power is coming from the water turbine, and the thrust is coming from the big air propeller."
I stared at the diagram while Lee wrote in some numbers for speed, drag, thrust, and power.
"Remember," she continued, "power is force times speed. The water turbine can make more power than the air propeller needs, and do it with less drag in the water than the thrust of the air propeller, because the water is moving three times faster than the air."
"Well, maybe," I allowed. "Has anyone actually built one of these?"
"Not that I know of. They've made one that works on land, but not on water. The efficiencies have to be, like, really up there. in a real-world kindaway.

Attached File(s)

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[DDW]

B30, on Mar 13 2006, 10:04 AM, said:

This thread says a windmill powered craft going DDW (in the same direction as the wind) can go faster than the wind. No fucking way. Can one pass the balloon test by saing angles? Why not, But never DDW.

It is theoretically possible, it can be done, and it has been done. My attempts to explain it are all here. I'm not going to go through them again.

Warning: you are not going to begin to understand the physics of this until you consider the relative fluid flow on the foils themselves - which are rotating and therefore seeing very different conditions than the hull. Those claiming that as you approach true wind speed energy extraction goes to zero are merely admitting they don't understand the physics of energy extraction in this case. A very simple minded view is that the rotating foils are doing the tacking for you.

[B30]

Flip Rigsby, on Mar 13 2006, 10:32 AM, said:

B30, on Mar 13 2006, 01:04 PM, said:

Flip Rigsby, on Mar 13 2006, 09:47 AM, said:

You can go fatser than the wind DDW on many boats. That is faster than the wind DDW TWD. To go faster than the wind DDW your AWA will be forward of DDW TWD. So yes it is possible for a Windmill to go faster than the wind DDW TWD...

Flip, you are wrong!

DDW = Dead Down Wind. That means in the SAME direction as the wind. I do not know of any sail craft (water, land, ice) that can go faster than the wind pointing in the exact same direction as the wind. Of course I know that many boats go faster than the wind speed on an angle, and thats what I wrote if you read my last post more carefully. There are some, but very few boats that can beat the winds VMG by sailing angles. It's the "old can it beat a balloon downwind" test. Land yachts and ice boats do this easily, but on water it is very tough.

This thread says a windmill powered craft going DDW (in the same direction as the wind) can go faster than the wind. No fucking way. Can one pass the balloon test by saing angles? Why not, But never DDW.

I'm not even going to bother trying to explain True Wind Direction and Aparent Wind Angle to you.

Carry On...

Apparently Flip, you have the reading compression of a first grader. Do you even understand what this thread is talking about? Listen up. When you are going DDW the apparent wind angle DOES NOT CHANGE until you exceed the wind speed, then it switches 180 degrees. We are not talking about sailing angles and bringing the AWD forward you moron. That’s what made this thread interesting. Show me any wind-powered vehicle traveling THE SAME DIRECTION AS THE WIND that can go faster than the wind. Get with the program!

[kiwi4shore]

Surely once the windmill is turning(blown around by the wind)and the craft reaches tws,then goes faster than windspeed?,the apparant wind is now from the front and the windmill will start to turn in reverse thus slowing the craft down,unless the pitch of the blades is reversed of course.

[The Winner]

DDW

Dude your killing my buzz

[rotten dog]

Blatant BS - pics or it didn't happen

[B30]

Forget being on a boat. Lets use the landsailer example above. It is much more efficient than any boat. I think this too is BS. I searched Google for anything on this Sir Isaac Helm and the Baby Stroller and found nothing. I believe that if you can make a wind turbine craft (water, land, ice) exceed the TWS in the same direction as the wind, you have created a perpetual motion machine. Lets use the example of 0 TWS. Now give it a push to get it going and build some AWS. According to this the AWS should be enough to keep to craft moving! We have just solved all of our energy problems!

Now of course I could be wrong. The spinning blades do bring their individual AWD's forward, but I bet if you add up all of the vectors for the spinning blades AWD's they would equal 0 as long as you are traveling in the same direction as the wind no matter what the TWS is.

Now, if you took the same craft, added some wind and "heated it up" a few degrees from the TWD, then the sum of the vectors of the AWD's of the spinning blades would not equal 0 and you would move forward possibly even faster than the wind. BUT that is not what we talking about here.

[JeffR]

what's it rate?

[DDW]

kiwi4shore, on Mar 13 2006, 11:32 AM, said:

Surely once the windmill is turning(blown around by the wind)and the craft reaches tws,then goes faster than windspeed?,the apparant wind is now from the front and the windmill will start to turn in reverse thus slowing the craft down,unless the pitch of the blades is reversed of course.

Again, you must look at it from the point of view of the windmill blade. Unlike a boat (where the hull and sails are always seeing the same relative wind) the windmill blade does not see a dramatic change in relative wind direction when the boat passes the wind speed. Prior to achieving wind speed, the relative pitch is slightly negative (windmill powers propeller, propeller pushes boat). After exceeding wind speed, the relative pitch is slightly positive (propeller powers windmill, windmill pushes boat). The physical pitch need not change. The energy flow through the drivetrain changes direction but the rotation does not.

And Lee Helm is wrong about it not having been done. Scale models have been built and perform as claimed.

[Flip Rigsby]

Damnit! I thought we were talking sail boats here on Sailing Anarchy.

Now that compression has set in, I guess I am a moron... Back to first grade.

Again carry on...

[B30]

DDW, your math is fucked. It cannot work and has never worked. As long as the direction of motion of the craft, and the TWD are the same, you will never even equal the windspeed let alone surpass it. What ever school you gaduated from should ask for you degree back. I don't care if it is a kite doing figure eights or the most efficient blades ever created spinning a frictionless hub. Once you add up the vectors you come up short every time my friend.



Thanks for the spelling tips BB. :rolleyes: