2.8 xFaster than the wind dead down wind !!!

[roger]

Thread from the merlin website. Not Classic Not boat but for you engineers out there.... I find it fascinating if a little confusing.

http://www.merlinrocket.co.uk/forum/mai ... =1&search=

[Steve Bailey]

There was a long and ultimately acrimonious thread on a well known boat design web site about this. It is perfectly possible for a "boat" to travel dead downwind faster than the wind (ddwfttw), without gybing like a high speed catamaran or ice yacht.
You need an underwater turbine that drives an air propellor and the correct gearing.
You also need to understand it is the water driving the vessel and not the wind, though the wind does start the motion initially.
It was this inability to understand the water as the driving force that led to the bust up on the boat design site.
It got so serious that the originators eventually said they were pulling everyone's leg, just to keep the peace, though really they were right and even had videos of a land version going ddwfttw.
I'm just wondering if I've lit the blue touchpaper and if so should retire to a safe distance . . .

[roger]

i have toadmit i thought it was a wind up and even the contributor on the merlin thread said some physicists wouldnt accept it.

It took me a while to get my head round it but it does make sense. (I think)

[Rupert]

Like most things (computers, brewing, telephones etc) I find it easier just to accept that someone knows how it works, so all I need to know is that it does...

[Garry R]

Once you have consumed the results of the brewing most things make sense but it essential to get the computers/brewing/telephones in the correct order!!

[Steve Bailey]

What made me smile about the whole thing is that such a craft has no use other than to travel directly downwind. The people who were getting so uptight - they were really slagging each other, and some of it was bang out of order - were upsetting themselves over something of no practical use whatsoever.
At least we have sufficient sense to disagree about really important things, like the best sort of badger hairs to make varnish brushes from, and whether a preposition is the right word to end a sentence with.

[JimC]

What made me smile about the whole thing is that such a craft has no use other than to travel directly downwind.

No reason why you shouldn't be able to have a rotating airscrew and go cross wind, and change the gearing and it will go directly upwind. But yes, basically its a toy and a neat demonstration of some very none-intuitive physics. However having said that what these carts demonstrate is a wind powered vehicle that can travel on ordinary roads because it will operate with the wind in any direction. Who knows, if the oil runs out before we get fusion power such things might be useful...

[Bill-Conner]

And if
"The wind doesn't blow
and the cart will not go"?

Just wondered.

[Garry R]

Seeing this thread about wind/propellors etc I have become increasingly concerned as to whether all these winfarms popping up will in time affect the orientation, rotation and orbit of the earth. Already there is severe snow here in November - could this be because the UK is now orientated a little more to where the North Pole used to be or possibly we are saving too much energy and the earth is cooling. I have it on good authority that Santa is busy packing sacks in a pair of Speedos wearing Raybans!!

[jpa_wfsc]

If sailing dead downwind means within 5 degrees of dead down wind then of course it is possible - its just extending the broad reach screamer a little bit.

But 0 degrees, dead downwind - no way - and was not claimed anyhow. The craft actually was sailing at 5 degrees to the true wind direction for most of the exercise. http://www.nalsa.org/BlackBirdDDWSR/Obs ... 032010.pdf

Which is still very impressive!! But is not 'dead downwind'.

[JimC]

But 0 degrees, dead downwind - no way - and was not claimed anyhow.

Yes dead downwind. Its possible, claimed and demonstrated. These guys - and they are not the first to create one of these things, just the first to get the demonstration ratified by an external body - started out by building a model and running it on a treadmill, which for anyone with a good handle on physics is all the proof you need. However it seems that too many people don't understand frames of reference, so they built the full size unit, which being in real wind is very difficult to maintain at exactly zero degrees.

But its been explained enough times on the net, no point in rehashing it here. Use a search engine.

[JB9]

In an attempt to bring this back to classic boats there is a Kestrel keelboat in the Classic Boat Museum with rotating blades which sailed early to mid 1900s I think.

http://picasaweb.google.com/tchanter/Cl ... 3586184162

[Michael Brigg]

I think you will find this is a Bembridge Redwing...but the boat is named"Kestrel" so you are correct.

http://www.classicboat.co.uk/classnotes/252860/redwing

Here it is in action!

http://www.google.co.uk/imgres?imgurl=h ... 20&bih=930

[neil]

I try and avoid standing dead down wind of a road kill badger when scrumping for brush hair, unless it's a very fresh, dead badger.

[Garry R]

The road kill badger - would that be due to a "brush with a roller" accident?!! (Thank goodness for the banter section!)