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Faster than the wind!

PostPosted: Tue Jul 16, 2013 7:59 pm
by Breakin Wind
I'm having dinner with a friend, and he commented that a sailboat can actually achieve speeds greater than the current wind-speed.

True? False? Wives-tale? Too many beers?

Thanks

Re: Faster than the wind!

PostPosted: Tue Jul 16, 2013 9:04 pm
by K.C. Walker
Definitely true! Mostly with catamarans, the America's Cup boats are sailing as much as 1.7 times the speed of the wind. Ice boats can sail 4 to 5 times the speed of wind!

It's tricky with the DaySailer, though lately I think I've been able to sail at or above true wind speed! It's hard to get the true wind speed while sailing because of the apparent wind. Also, a GPS isn't truly accurate for speed measurement. However, with the UPS sail, in about 3-4 kn of breeze I was sailing 4.3-4.7 kn of boat speed. This was in super flat water, actually pretty shiny, with very small wavelets.

If your hull is very smooth and fair (mine is) and the hull shape is good (the DaySailer is) there's relatively little resistance up to hull speed. With enough efficient sail area (I have approximately 220 ft.² of upwind sail area with the UPS) at about 5 kn apparent I can feel the sails really start pulling. I think pretty much anything above 5-6 kn true wind I'm sailing slower than the wind.

Re: Faster than the wind!

PostPosted: Tue Jul 16, 2013 10:24 pm
by Salty Dog
I think a beam reach is the fastest point of sail.

Re: Faster than the wind!

PostPosted: Tue Jul 16, 2013 11:12 pm
by jdoorly
How do those AC race committee genious's lay out a race with no downwind legs???

Re: Faster than the wind!

PostPosted: Wed Jul 17, 2013 1:37 am
by GreenLake
jdoorly wrote:How do those AC race committee genious's lay out a race with no downwind legs???

On our lake that takes no genius :) Had plenty "all upwind" races there - just a quirk of the topography and timing of the race. :D :D

Re: Faster than the wind!

PostPosted: Wed Jul 17, 2013 7:37 am
by rnlivingston
My iceboat hit a speed of 62 mph in about 15 mph wind last winter. The fully battened sail acts like the wing of a plane, but instead of lift it produces forward motion. The faster you go, the more wind travels over the sail and you go faster. If it wasn't for friction, I could hit warp one.

Roger Livingston

Re: Faster than the wind!

PostPosted: Wed Jul 17, 2013 8:41 pm
by Salty Dog
WoW that looks cool.

Re: Faster than the wind!

PostPosted: Thu Jul 18, 2013 9:36 pm
by jdoorly
Roger- can you tell me the true wind and apparent wind angles when your traveling at that speed?

Re: Faster than the wind!

PostPosted: Thu Jul 18, 2013 10:13 pm
by rnlivingston
The telltales on my shrouds give me the apparent wind. I have to look at flags flying on shore to see the true wind. We sail an iceboat sheeted in tight to maintain a good foil shape and present a proper angle to the wind. But like any sailboat, our best point of sail is a reach. Like a catamaran, we tack downwind.

Re: Faster than the wind!

PostPosted: Fri Jul 19, 2013 8:52 am
by rnlivingston
After rereading my answer to you, I don't think I answered your question. While there are people in the iceboating group who could give you an answer, I'm not sure. Since iceboats travel faster than the true wind all the time, the apparent wind angle does not seem to change on most points of sail. You would think you could sail straight into the true wind and on smooth ice, you can travel a long distance into the wind, but you eventually slow down. And downwind, when the speed of the boat matches the true wind, you almost come to a stop.

Roger

Re: Faster than the wind!

PostPosted: Sat Jul 20, 2013 5:56 pm
by GreenLake
There are ways to set up propulsion systems that deliver speeds downwind in excess of the true wind speed, but they are not simple drag devices. They usually involve windmills turning wheels, with the kicker that the windmill can operate even if the vehicle pulls away from the wind... (google and youtube will provide details / videos galore).