By Doug
Laser Cheat Sheet. Watching windsurfers has always fascinated me. I love the way they pull the rig to windward as shown on the left. They dig in when a gust hits and then take off. If the gust is really strong, it knocks them vertical but they're still under control.
Less experienced windsurfers sail with the rig straight up, as shown in the middle. When a gust hits, they're knocked over, out of control, and overpowered even through they're spilling wind.
Heeling to windward, trapping the wind, and going vertical in a gust all seemed to make sense, so of course I wanted to try it in a Laser. And this led me to another discovery from sailing at night. Here's what I learned:
· This only works in relatively flat water.
· You cannot go block-to-block and the boom appears to be higher in the air because of the windward heel.
· The feeling of speed only lasts for a few seconds and you then have to go vertical and bear off a little to keep your speed.
· But the best part: you can really feel the lift from your centerboard as it digs in.
Volumes have been written about getting more lift from sails, but how much has been written about getting more lift from your centerboard? Water is more than 800 times denser than air, so how the centerboard moves through water really should matter. Just hold a centerboard beside a motorboat moving even slowly and try different angles and you'll feel the lift.
Here's what I think is happening. The windsurfer in the middle diagram has the wind go across the sail, which is what we expect. The windsurfer on the right has the air go up the sail. Both are bad because of the vortex created at the top of the sail. Airplanes have this same problem with the vortex at the end of each wing, and they're refitted with winglets to reduce these vortexes and save about 5% in fuel costs.
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| Courtesy of Boeing |
The windsurfer on the left heeling to windward has the wind going down the sail and there is no vortex because the water is acting like a winglet. The air is trapped and not wasted. It's similar on a Laser when heeled to windward with the air trapped at the bottom of the sail, and it's fast. But that's not the best part!
Everything is the same below the water with the centerboard, except it's reversed: the push comes from the leeward side, the lift is on the windward side, the water flows up, and the winglet is the hull. And you can feel the centerboard dig in and lift, and this force can be significant as our motorboat test showed.
When we were in Sydney
And with the right touch, this trick is easy to learn. When Pam was brand new to Lasers, she lifted so much that I had to keep asking her to please put her foot in the water so that I could catch up!
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| Excellent form... and fast! |
I experimented with windward heel in club racing last summer, but it was inconclusive. However, I did seem to get the bursts of speed you describe, but it was not sustained and boats were creeping up on me while I lost height. The groove seems very narrow.
ReplyDeleteWindsurfers are also generating substantial vertical lift by the windward heel.
This is one of those topics that crops up on sailing forums from time to time. The general consensus seems to be that the effect is real but it's not easy to do it right. The discussion then usually moves on to some esoteric subject like how much advantage you would gain by filling the hull with helium.
ReplyDeleteThe groove is indeed narrow and the conditions have to be just right. For me, the trick is to stop trying if it does not work the first or second time. I made this mistake in race 9 at the Cork Worlds and lost a lot of ground. But this worked like a charm coming off the line in race 3 at the Halifax Worlds.
ReplyDeleteWhat I have learned is to not bother trying if the wind is over 10 or the waves are lumpy. When it does work, it's very fast and people will try to copy you.
I seem to recall seeing a picture of Glenn Bourke doing this in his book. The wind was under 10 and there was little wave movement.
The Rooster Boat Whisperer DVD has footage and discussion of this.
ReplyDeleteWe have not seen this and would be interested in your interpretation of what Stephen said. He's a great sailor.
DeleteOK. I took a look at it. He says that doing this is very tricky and there is a small window in which it works - light air and flat water. It may help to shape the sail for speed, rather than power. What happens is when you heel to weather, the boat wants to turn off the wind, which you counteract by pushing the tiller away. This creates a waterflow direction that pushes the centerboard to windward. The shape of the heeled to weather hull also generates "windward suck."
DeleteI did also read once that when it works, you will have positive rudder, but the boat tracks straight. Apparently, this has something to do with the board having "gybed", however I'm not all that convinced. Reason being is that if you are heeling to windward, the hull shape will steer you away from the wind so you would need positive rudder to counteract this. I think there's a PhD in this somewhere!
ReplyDeleteThanks MJ and Oztayls for your comments, I really appreciate them. Interesting explanations I had not thought of. Wish I could have discussed this subject in more detail with Frank Bethwaite when I last saw him.
ReplyDeleteInteresting observation on the windsurfers.
ReplyDeleteI can confirm that when we are sailing formula boards in high winds we sail with the rig to windward to keep things under control. The minute the rig comes up, you loose efficiency and speed and angle suffer.
However its just the opposite in light winds where we try to get the rig as vertical as possible to add more power. This is when you see racers sailing with their front hand on the uphaul and theirs rigs standing upright.
Thanks Steve for your comments. While I owned a windsurfer many years ago, I never raced one and marvel at the skill required to do so.
DeleteI can appreciate how you power up for light air and depower for heavier air, and how it's so different compared to boats like a Laser. I now understand why the RS-X sailors hold the uphaul in some of the lighter races.