Hi guys
I'm trying to understand the dead downwind faster than the wind thing.
Can anyone on here say that they have definitely achieved any of these speeds?
at 110 degrees 2.92 times the speed of the wind
at 120 degrees 2 times the speed of the wind
at 130 degrees 1.55 times the speed of the wind
eg going 40 knots in 25.8 knots of wind at 130 would count
going 30 knots in 19.4 knots of wind at 130 would count
going 20 knots in 12.9 knots of wind at 130 would count
i'd back myself to do 20 knots at 130 off the wind on a formula board. it would be close but i think possible. maybe some of the guys with vmg data can confirm.
ok, I'm not convinced that it has been done on water but that's just a drag thing. It could be done because it definitely has been done on ice ...
Didn't BMW Oracle and Alinghi in the last Americas Cup sail both upwind and downwind faster than the wind. I remember the commentators saying that if you let a balloon go at the top mark, both boats would beat it to the bottom mark.
It is just a matter of the speed of the air flowing over the sail combined with low enough drag to do this isn't it?
GP, come to Sandy Point on a south-westerly... it can be blowing (only) 25kn, yet some guys will be getting 40kn on the dial. And we know its 25kn as we have taken a long walk with a wind meter...
Formula sailing can easily do 2x windspeed, ie: 12kn + flat water should result in 25kn peaks.
I would like to see more definitive work done as to just how strong the wind is at a given moment. eg the wind varies greatly at various heights say from 300 mm off ground level to 3 meters. Gusts are coming and going all the time.
IMHO it is very difficult to say how strong the wind was when a particular speed was achieved.
Herby
On numerous occasions sailing deep downwind on a Formula board in gusty conditions ( Northerlies at Green point) I have sailed out of the front of the gust, slowed down and then had the gust catch up to me and take off again.
You would have to be going faster than the wind to do this I would think!!!!
Thanks Slowboat....I've been hoping for some such info for years.
I have not heard of any other serious efforts to accurately measure the wind
and compare it to the speed of a passing sailor.
i think it's a moving target though because of drag. effiencies are higher at lower wind speeds because drag is less due to reduced speed.
when i had my formula gear and gps, ratios were always high from 10-15 knots and then decreased drastically as wind speed increased.
Simply not possible.
If the first post of the thread is adhered too.ie.Faster than the wind DEAD DOWNWIND,its easy to go faster than air speed both downwind and up,but everyone is talking about a degree off dead downwind.Going from a reach,at higher than windspeed to dead downwind may show a momentary over windspeed reading but this will disappear real quick.
By all means claim to go faster than the wind,it happens every day but going DEAD DOWNWIND faster than the wind for any extended period of time,doubt it.
If we apply some high school trigonometry to the Sandy Point example given by slowboat ie.
avg speed = 44.9 knots
avg angle = 132.5 degrees
The downwind sailing speed works out to be 30.3 knots. The actual wind measurements in the above example were between 29-31 knots, so it's... too close to call it a proof.
However, I do agree with Gestalt that the drag is much lower at lower speeds, so it will be much easier to beat the wind at sailing speeds of around 20 knots then at 45knots. Has anyone got any reliable wind/speed/angle measurements for lower winds?
Edit:
Even better, if you have some data you want to try, copy this formula into Excel spreadsheet:
=COS(RADIANS(180-132.5))*44.9
except substitute your own sailing speed and angle instead of Chris's. This will calculate the downwind component of your sailing speed, which you can then compare with your actual wind measurements and see if you went faster.
(for better accuracy avoid using instantenous speeds, just stick to some average like 500m).
