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PostPosted: Wed Sep 10, 2008 7:42 am 
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Location: Punta Gorda, FL
Sailing the other day in strong winds, I noticed that angling the board back seemed to help on every point of sail, including hard on the wind. I had previously found better performance hard upwind by reefing the sail and leaving the board vertical. With too much sail out, angling the board seemed to help.

Another important variable is the presence or absence of the Mirage Drive. I sail with mine installed almost all the time, only occasionally sailing with it on the bottom of the creek. Though the blades will tend to feather themselves, they still create some lift far forward. It could be that without the Mirage drive, the whole situation changes.

Anyway, I've taken to just leaving my board angled back almost all the time. It seems to help, but I do have to say that I'm usually sailing with my wife. She always rigs the bungee to hold her board down and vertical. She's also pretty sloppy about sail trim and not so great at steering a straight course. I'm usually (but not always) a bit faster than she is, but only a bit. The AI is a very forgiving boat. Needless to say, it really makes me nuts when she's actually going faster. Shouldn't be possible! ;)

I'd encourage you to read the wiki article, if nothing else in case some of your customers are pilots... ;)
Quote:
The swept-wing also has several more problems. One is that for any given length of wing, the actual span from tip-to-tip is shorter than the same wing that is not swept. Low speed drag is strongly correlated with the aspect ratio, the span compared to chord, so a swept wing always has more drag at lower speeds.


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PostPosted: Wed Sep 10, 2008 8:11 am 
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The important part of your citation with relation to drag and sweep.

Tom Ray wrote:
Quote:
at lower speeds.


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PostPosted: Wed Sep 10, 2008 8:20 am 
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I don't think that's the important part when it comes to AI's, Dog. By "slower speeds" they mean speeds of less than a few hundred knots, where shock waves from transonic airflow are not a problem. In the absence of those shock waves, the general rules of aspect ratio and drag apply, whether the wing is in the water or the air. Just how fast are you sailing? ;)


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PostPosted: Wed Sep 10, 2008 8:46 am 
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Tom Ray wrote:
I don't think that's the important part when it comes to AI's, Dog. By "slower speeds" they mean speeds of less than a few hundred knots, where shock waves from transonic airflow are not a problem. In the absence of those shock waves, the general rules of aspect ratio and drag apply, whether the wing is in the water or the air. Just how fast are you sailing? ;)


Mid to high 30's when dialed in.... High 20's to low 30's when I'm farking around.


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PostPosted: Wed Sep 10, 2008 10:23 am 
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Hmm...I must really be doing stuff wrong! My AI doesn't go anywhere near that fast! ;)

Seriously, I'm guessing you're on a windsurfer or something, since few sailboats approach 40 knots. Of those that do go those kinds of speeds, it seems like most have swept back daggerboards in the main hull, and curved (but not swept) daggerboards in the amas. It's not just the Oracle boat.

http://www.youtube.com/watch?v=CN7qNMWywSE

All but one in that video.

As Ike heads for you guys in Texas, it's dragging behind some nice sailing winds here in SW Florida. I'm going to go out for some more experiments this afternoon. Purely out of professional interest, of course. It's a tough job, but somebody's got to do it. ;)


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PostPosted: Wed Sep 10, 2008 12:53 pm 
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Tom Ray wrote:
Seriously, I'm guessing you're on a windsurfer or something, since few sailboats approach 40 knots.


You say that like it's a bad thing. :wink:

I started a long, long time ago in dinghies. I've done small boats, big boats and multihulls. I did my bareboat cert just around the corner from you. Among the boats I've owned was a wood Thistle and one of the first H-17's. I've sailed on more boats than I could hope to count. I started windsurfing in '82. I sold my last boat in '92. I was tired of going slow.

As long as the body is willing, I'll keep sailing windsurfers fast. When I get too old for the 40 knot club, maybe I'll get another sailboat. It would be nice to have a place to set a beer down again.

I've had an AI up to a shade over 11mph. Admittedly, it was terribly rough that day and I was trying to break it, not actually sail it fast.

I'll try to check out the tube video later... I've got boats coming and no room in the warehouse.


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PostPosted: Wed Sep 10, 2008 1:31 pm 
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It IS a bad thing! More sailboats should approach 40 knots! :D

(Or maybe that wasn't what you meant... ;))


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