Faster than the Wind

[Gary Wyngarden]

For those of you not following it, The Race is a non-stop around the world race among six maxi-cats ranging in size from 85 to 125 feet and capable of some pretty incredible speeds.Cam Lewis, skipper of the 110 foot, Team Adventure, wrote the other day of "driving the bus" for two straight hours at a speed of 28.5 knots in 15 knots of wind, travelling nearly 60 miles during his stint at the helm.I think I understand a little about sailing theory, but I'm struggling with the concept of travelling at a rate nearly twice that of the wind. I suspect it has something to do with "flying a hull", planing the other, and lift forces on the sail as well as drag. But this is hard to comprehend. Can anybody offer a simple explanation? Thanks

 

[david lewis]

Faster than wind

Like Einsteins theories wind is relative. In all seriousness, there is an actual wind speed and an apparent wind speed. When the boat is beating or close hauled the apparent wind is the speed of the wind actually moving over the face of the earth plus the speed of the boat through the water. So the wind the boat sees is a lot higher. Ice boats for instance can go say 60 to 100 miles an hour in like 25 knots of wind because there is little to no resistance to their forward motion. The opposite is true when the boat is running. The speed of the boat subtracts from the speed of the wind so the apparent wind is less, this is why in a severe weather storm boats will run with bare poles as the apparent wind reduces the effect of the storm.Hope this help, I tried to avoid a lot of vector mechanics in my explanation but if you are interested in the technical aspects there are a lot of great books oout there.regards,dave

 

[Rob Rich]

Stability of Cat

Lifting a hull is part of it, as there is less drag, but the actual vector of the leward hull pushing back against the force vector of the true wind allows a cat to convert wind speed to boat speed more efficiently.In short, the leeward hull generally acts like a foil, or wing, and produces lift that pushes the cat back against the wind. This eliminates a lot of the "slip" that monohulls are subject to. Without that slip, the cat converts the energy into forward movement. If you are interested in it, I can point you towards a few books on the subject.It's a weird concept, but I have done this on my 16 foot catamaran. 15 mph of wind will get me 20 on a reach. Lots of fun!!