America's Cup again - sail trim question.

[scotty123]

Watching this fantastic sailing spectacle, I noticed that the sails hardly changed position, whether going to windward or even gybing, even though the crew seem to be continually grinding.

Is this to do with the high speeds involved, so the apparent wind is on the nose almost continuously?

 

[savageseadog]

Watching this fantastic sailing spectacle, I noticed that the sails hardly changed position, whether going to windward or even gybing, even though the crew seem to be continually grinding.

Is this to do with the high speeds involved, so the apparent wind is on the nose almost continuously?

Apparent wind is always forward

 

[scotty123]

Apparent wind is always forward

really?

 

[Woodlouse]

At least some of the grinders are attached to hydraulic pumps and aren't directly geared to the winches. If they don't grind, they don't have hydraulic pressure and so can't use their systems.

Any that are geared straight to winches will have such a great power reduction that even small adjustments will mean a lot of winding.

 

[Melleman]

Read her it´s about this topic.

http://www.nauticed.org/sailing-blog/americas-cup-apparent-wind/

 

[Hambler Rambler]

The grinders are attached to hydraulic pumps and aren't directly geared to the winches. If they don't grind, they don't have hydraulic pressure and so can't use their systems.

Ah, that makes sense! I also noticed that occasionally you see one of them produce a winch handle (retro!?) and start grinding one of the winches directly, I think the the jib, although it looks like hard work. Can anyone shed any light here?

 

[stevebrassett]

really?

Yes - these catamarans are sailing faster than the wind - mostly a lot faster. This means that the apparent wind is always forward of the beam.

 

[skip50]

I think I read/heard somewhere, that the apparent wind when beating and when off the wind, changes by only 4 degrees!

 

[Woodlouse]

Ah, that makes sense! I also noticed that occasionally you see one of them produce a winch handle (retro!?) and start grinding one of the winches directly, I think the the jib, although it looks like hard work. Can anyone shed any light here?

Just done a bit of research, the pedestals can be linked either to the hydraulics or to the winches as required.

 

[Tempus]

Yes - these catamarans are sailing faster than the wind - mostly a lot faster. This means that the apparent wind is always forward of the beam.

In actual fact given the high speeds, and the fact that they never run dead downwind the AC72's have an apparent wind of 16deg upwind, and 19deg downwind - so only a 3deg shift, when moving fast. Compare that to most cruising boats who easily go from around 40deg upwind to ca 120deg apparrent downwind and it explains why the sails don't appear to move.

Like any high performance sail boat, the problem is when you slow down to gybe, or come off the plane/ foils, the apparent wind shifts backwards very fast. Hence it's a lot trickier than simply trimming the sails for a 3deg variation!

Loving it though!

ps - Ref http://www.nauticed.org/sailing-blog/americas-cup-apparent-wind/ for where the numbers come from - my trigonometry is too rusty!

 

[SailorPete]

Whats all this about gybing - I've noticed the commentators keep using it too? I always took that to mean putting the stern through the wind? Putting the bow through the wind is 'going about' surely? The apparent wing trig can't explain that surely? Maybe its just American vs English?

 

[Topcat47]

Wind conditions are promising for two races today. Off down to Marina Green.

ETNZ have a self tacking Jib, OTUSA have to trim theirs. This is why you occasionally see their jib trimmer with a winch handle. neither team trims the wing with a winch handle, the loads are too great.

 

[Woodlouse]

Whats all this about gybing - I've noticed the commentators keep using it too? I always took that to mean putting the stern through the wind? Putting the bow through the wind is 'going about' surely? The apparent wing trig can't explain that surely? Maybe its just American vs English?

Well, when going down wind they are technically gybing since the stern is going through the true wind. It might feel those on board like they're tacking but that's rather immaterial when your commentating on it.

 

[Tempus]

Whats all this about gybing - I've noticed the commentators keep using it too? I always took that to mean putting the stern through the wind? Putting the bow through the wind is 'going about' surely? The apparent wing trig can't explain that surely? Maybe its just American vs English?

It's totally correct they are still gybing and the stern goes through the wind, the apparent wind swings round the back, it then races forwards very fast as they accelerate.

Have a look at the website on my previous post, and mentioned earlier, very interesting.

 

[Topcat47]

These boats tack and gybe like ordinary boats. The downwind leg is all Gybes, the upwind Tacks. f you look at the ETNZ near capsize you can see the wing is set for the wind on the "wrong" side of the boat. the AC website has a good explanation of the manoeuvres on it's website, if the video feeds are not blocked in the UK.

 

[vyv_cox]

Even on much lesser catamarans such as the Hobies and Prindles I used to race, the apparent wind is far further forward than it would be on a monohull. Sail angle on a beam reach and a beat were pretty much exactly the same and on a broad reach the mainsail would be travelled well out but sheeted quite hard.

 

[savageseadog]

The apparent wind and many other things are quite well explained on the various race videos on youtube, link to them via the americas cup site---TV schedule