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#1
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Sail Aerodynamics
This link was posted recently to a racing discussion
http://www.wb-sails.fi/news/470StreamAnim/index.htm# Not sure how useful this is, but the pictures are cool. One of the things I found interesting was the vertical difference in air flow, and the difference in pressure distribution between the main & jib. On the jib, the max pressure differential is much further forward. Also if you look at the photos of the sail, they are much flatter than often said to be ideal (there is no reference to wind speed, it might be light air) and the drafts are aft. Also it shows a vortex off the head of the jib.... now the question is, does a frac rig benefit because the mainsail supresses the jib's tip vortex, or does the jib vortex hurt the drive of the mainsail? This is kind of theoretical, I wich I could actually go sailing but right now everything is covered in snow & ice. Maybe later this week..... Fresh Breezes- Doug King |
#2
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Sail Aerodynamics
DSK wrote:
This link was posted recently to a racing discussion http://www.wb-sails.fi/news/470StreamAnim/index.htm# Not sure how useful this is, but the pictures are cool. One of the things I found interesting was the vertical difference in air flow, and the difference in pressure distribution between the main & jib. On the jib, the max pressure differential is much further forward. I would have thought you would have known that. Never seen the main luff rising to windward? It's due to the slot and the mast. Also if you look at the photos of the sail, they are much flatter than often said to be ideal (there is no reference to wind speed, it might be light air) and the drafts are aft. Yes they are flat, but these sails are trimmed for very very close sailing -probably much closer than most of the nags sailed here could achieve. Note the relative narrowness of the slot and the shape of the battens. Note also that the apparent wind is 22 degrees whereas at 33 degrees we used a slightly fuller set (in even lighter air). The draft is exaggerated by the camera angle in our shot whose purpose was to identify the max draft position. Note that this moves forward up the main as the CFD suggest it should). (Can you see the similar lower batten wrinkes low down that Booby (and you?) complained about). http://community.webshots.com/photo/...56514380nkBEsE http://www.wb-sails.fi/news/470StreamAnim/index.htm# Also it shows a vortex off the head of the jib.... now the question is, does a frac rig benefit because the mainsail supresses the jib's tip vortex, or does the jib vortex hurt the drive of the mainsail? Yes, the benefit is from the greater adjustability of the frac. rig. Cheers |
#3
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Sail Aerodynamics
MC wrote:
....Never seen the main luff rising to windward? It's due to the slot and the mast. Why, no, Navvie, I never have! Are you *sure* that a luff (or 'bubble' as it's often called) along the main luff is due to the slot & the mast? Who'd a thunk it? Also if you look at the photos of the sail, they are much flatter than often said to be ideal (there is no reference to wind speed, it might be light air) and the drafts are aft. Yes they are flat, but these sails are trimmed for very very close sailing -probably much closer than most of the nags sailed here could achieve. If that's true, then why are the photos of your mainsail, that you're so proud of, not shaped at all like the ones in the sailmakers web site? ...Note also that the apparent wind is 22 degrees Gee, Navvie, do you hold a protractor up to your computer screen? ....Also it shows a vortex off the head of the jib.... now the question is, does a frac rig benefit because the mainsail supresses the jib's tip vortex, or does the jib vortex hurt the drive of the mainsail? Yes, the benefit is from the greater adjustability of the frac. rig. And the adjustability has *what* to do with the vortex? I was hoping that somebody might like to discuss rig tuning & sail trim. Navvie, you are a font of meaningless, self-congratulatory prattle. And you're not as funny as Boobsie. DSK |
#4
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Sail Aerodynamics
does a frac rig benefit
because the mainsail supresses the jib's tip vortex, no. or does the jib vortex hurt the drive of the mainsail? yes. Yes, the benefit is from the greater adjustability of the frac. rig. lots of advantages to a frac rig, but suppression of the tip vortex of the jib is not one of them. |
#5
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Sail Aerodynamics
JAXAshby wrote: does a frac rig benefit because the mainsail supresses the jib's tip vortex, no. or does the jib vortex hurt the drive of the mainsail? yes. Yes, the benefit is from the greater adjustability of the frac. rig. lots of advantages to a frac rig, but suppression of the tip vortex of the jib is not one of them. Shh, it'll take Doug quite some time to figure this all out. Cheers |
#6
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Sail Aerodynamics
DSK wrote: MC wrote: ....Never seen the main luff rising to windward? It's due to the slot and the mast. Why, no, Navvie, I never have! Are you *sure* that a luff (or 'bubble' as it's often called) along the main luff is due to the slot & the mast? Who'd a thunk it? Yep a bubble in the luff -if that's what you like to call it. Now do you realize what it is? Also if you look at the photos of the sail, they are much flatter than often said to be ideal (there is no reference to wind speed, it might be light air) and the drafts are aft. Yes they are flat, but these sails are trimmed for very very close sailing -probably much closer than most of the nags sailed here could achieve. If that's true, then why are the photos of your mainsail, that you're so proud of, not shaped at all like the ones in the sailmakers web site? Look at the picture legends. Mine 33 degrees 5k ap. Theirs 22 degrees 16 knots. Are you blind or just so desperate to score one point you drop the ball (again)? ...Note also that the apparent wind is 22 degrees Gee, Navvie, do you hold a protractor up to your computer screen? No but I can read the picture legend and understand what it says. You are a such clown when it comes to the fine points of sail trim Doug! Cheers MC |
#7
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Sail Aerodynamics
DSK wrote: Yes, the benefit is from the greater adjustability of the frac. rig. And the adjustability has *what* to do with the vortex? You mean you don't know? Good lord! I was hoping that somebody might like to discuss rig tuning & sail trim. Navvie, you are a font of meaningless, self-congratulatory prattle. And you're not as funny as Boobsie. Bwhahhahahaha. You are soooooooooooo jealous. Cheers |
#8
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Sail Aerodynamics
"MC" wrote in message ... JAXAshby wrote: does a frac rig benefit because the mainsail supresses the jib's tip vortex, no. or does the jib vortex hurt the drive of the mainsail? yes. Yes, the benefit is from the greater adjustability of the frac. rig. lots of advantages to a frac rig, but suppression of the tip vortex of the jib is not one of them. Shh, it'll take Doug quite some time to figure this all out. MC, I'm usually quite lost (at sea) during your discussions with Doug. However, I never expected to see you depend on Jax for support. Well, now I know! Regards Donal -- |
#9
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Sail Aerodynamics
Donal wrote: "MC" wrote in message ... JAXAshby wrote: does a frac rig benefit because the mainsail supresses the jib's tip vortex, no. or does the jib vortex hurt the drive of the mainsail? yes. Yes, the benefit is from the greater adjustability of the frac. rig. lots of advantages to a frac rig, but suppression of the tip vortex of the jib is not one of them. Shh, it'll take Doug quite some time to figure this all out. MC, I'm usually quite lost (at sea) during your discussions with Doug. However, I never expected to see you depend on Jax for support. Well, now I know! You miss the point. Jax is correct on this one and I am giving him credit for that. Just 'cos he's Jax doesn't mean he's always wrong! Cheers |
#10
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Sail Aerodynamics
Donal wrote:
I'm usually quite lost (at sea) during your discussions with Doug. However, I never expected to see you depend on Jax for support. He'll take whatever he can get, first it was Bubbles tremendous expertise he relied on, now it's Jax. MC wrote: You miss the point. Jax is correct on this one and I am giving him credit for that. Just 'cos he's Jax doesn't mean he's always wrong! But he did not answer either question meaningfully. DSK |
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