Not surfing, but quite cool.

[Jimi]

For those who don't sail, the America's Cup might not mean much... and in recent years it went through a significant rules change to allow multihulls and hydrofoils... Now these boats sit on 43knots downwind, with an average speed AND vmg faster than the wind.

Anyway, the Kiwis look like winning at this stage, but there's still at least another 6 races.

[jaffa1949]

Holy Flying Cats Jimi,

[Jimi]

the bit that I find totally insane (and awesome) is that if you released a balloon at the same time as these boats went around the upwind mark, the boats would get to the downwind mark faster than the balloon in the wind - i.e. travelling with the wind at a speed faster than the wind by travelling at angles to the wind.

if that makes sense.

[kitesurfer]

Whilst i agree the new format is more exciting to watch than the old mono hulls, having worked with more than 6 different teams over the past 10 years i can safely say the America's cup is one massive d4ck p4ssing contest between Larry Ellison and Grant Dalton. Its more about who has the biggest ego rather than the sailing.

KS

[kitesurfer]

the bit that I find totally insane (and awesome) is that if you released a balloon at the same time as these boats went around the upwind mark, the boats would get to the downwind mark faster than the balloon in the wind - i.e. travelling with the wind at a speed faster than the wind by travelling at angles to the wind.

if that makes sense.

A balloon released into a 40 knot wind will not travell downwind at 40 knots. A sphere is not an efficent sail shape at all.

KS

[Jimi]

A balloon released into a 40 knot wind will not travell downwind at 40 knots. A sphere is not an efficent sail shape at all.

KS

Point is, that you can travel dead downwind at a speed faster than the wind!

[Jimi]

Whilst i agree the new format is more exciting to watch than the old mono hulls, having worked with more than 6 different teams over the past 10 years i can safely say the America's cup is one massive d4ck p4ssing contest between Larry Ellison and Grant Dalton. Its more about who has the biggest ego rather than the sailing.

KS

Fair call, however I have to say there is no other spectacle like seeing 75ft hydrofoils matchracing, no matter how big the egos of those who are involved.

[kitesurfer]

A balloon released into a 40 knot wind will not travell downwind at 40 knots. A sphere is not an efficent sail shape at all.

KS

Point is, that you can travel dead downwind at a speed faster than the wind!

Actually they can't. They can do speeds faster than the wind but not directly downwind. That is impossible. Sailing across the wind aloows the sails/kites or whatever to generate apparent wind. The faster you travel the more apparent wind you generate, hence the faster you go. However the closer you get to sailing dead downwind the smaller this effect becomes until it reaches 0 at dead downwind. At which point you cna only go at the speed the wind is pushing minus any other effects from drag.

KS

[kitesurfer]

P.S. I hope the kiwi's win as there's a bigger chance that they will return the cup to the boring old slow monhull format which will mean loads more work for me which means bigger Xmas bonus and more

KS

[Jimi]

A balloon released into a 40 knot wind will not travell downwind at 40 knots. A sphere is not an efficent sail shape at all.

KS

Point is, that you can travel dead downwind at a speed faster than the wind!

Actually they can't. They can do speeds faster than the wind but not directly downwind. That is impossible. Sailing across the wind aloows the sails/kites or whatever to generate apparent wind. The faster you travel the more apparent wind you generate, hence the faster you go. However the closer you get to sailing dead downwind the smaller this effect becomes until it reaches 0 at dead downwind. At which point you cna only go at the speed the wind is pushing minus any other effects from drag.

KS

Actually they can.

One of those unbelievable physics situations where the apparent wind allows the boats to sail deeper and faster until limited by the angle of travel and apparent wind converging to an angle approaching 0. Plenty of land yachts and ice yachts have been exploiting this for years but the drag on water has always been too great relative to the power of the sail. Not so in these or moths or other foiling boats.

[Jimi]

I could draw a really complicated vector diagram, but basically because you are never pointing dead downwind but tacking downwind, your apparent wind angle never reaches 0.

[Jimi]

http://m.instructables.com/id/Downwind-Faster-Than-The-Wind-Cart/

This is the instructible from the guys who conclusively proved dead downwind faster than the wind was possible. Done on land, but proof that there is no problem with the very counter intuitive physics. As said above, it relies on the changing direction of apparent wind relative to speed.

Make your own model and prove it to yourself if you don't believe.

[kitesurfer]

I could draw a really complicated vector diagram, but basically because you are never pointing dead downwind but tacking downwind, your apparent wind angle never reaches 0.

I appreciate the physics of the vector diagram and the tacking close to the wind to achieve speeds greater than the wind to do the course faster than the wind.
However a sailing boat with a sail can not travel directly downwind faster than the wind.

KS

[Jimi]

Sounds like we were at the same end point in that argument then. I thought you meant it was impossible to maintain aVMG faster than windspeed to a Mark placed directly downwind, rather than specifically referring to a boat that is traveling a course of the same heading as the wind without deviation.

P.S. kiwis are slaying the yanks, so looks like the cup will be in Auckland in a few years time.

[Jimi]

Incidentally KS what work were you doing on the 12m boats?