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Re: Mast theory [Re: Darryn] #145256
06/16/08 08:00 AM
06/16/08 08:00 AM

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to much pre-bend causing the draft to move forward?

-- Have You Seen This? --
Re: Mast theory [Re: Darryn] #145257
06/16/08 09:35 AM
06/16/08 09:35 AM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
Carpal Tunnel
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Quote
Good sail, but not setup right.

Whats wrong?

Darryn
Mozzie
1782


Looks like the top is closed. Maybe a lot of prebend and no rotation?

Regardless of what I think, I believe the direction we're going in on this thread (photos with answers) is GENIOUS.

Keep it up!


Jay

Re: Mast theory [Re: Darryn] #145258
06/16/08 10:02 AM
06/16/08 10:02 AM
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Posts: 160
claus Offline
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Quote
Good sail, but not setup right.

Whats wrong?

Darryn
Mozzie
1782


Lot of cunningham tension and slack diamond wires (or is this an optical effect?). Very little rotation.

Last edited by claus; 06/16/08 10:02 AM.
Re: Mast theory [Re: claus] #145259
06/16/08 10:33 AM
06/16/08 10:33 AM
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Klaus, does the sail stall first above the boom on the windward side when pointing or on the leeward side when footing?

Re: Mast theory [Re: claus] #145260
06/16/08 10:45 AM
06/16/08 10:45 AM
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Hamburg
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On the leeward side when footing. For light wind sailing I woule like to stall the whole sail, not only the lower part.

Cheers,

Klaus

Re: Mast theory [Re: Smiths_Cat] #145261
06/16/08 11:47 AM
06/16/08 11:47 AM
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Posts: 160
claus Offline
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So if we are talking about 5knts+ (no laminar boundary layer) you want a fuller sail downstairs and a flatter sail upstairs. I would begin loosening a bit of outhaul (which gives you the lower part) and maybe try with a little more of rotation (which combined with sheet tension gives you the upper part). If the diamond wires are almost slack, maybe you want to try a little bit more of prebend by applying diamond tension, so the mast follows the luff curve better (I think a little of prebend is necessary in all winds). Cheers, Claus <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

By the way, a nice discussion about under/over rotation and wingmasts can be found here: http://www.tspeer.com/Wingmasts/teardropPaper.htm

Last edited by claus; 06/16/08 12:03 PM.
Re: Mast theory [Re: claus] #145262
06/16/08 01:39 PM
06/16/08 01:39 PM
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Hamburg
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that's a good link. Actually my problem is not how the best trim would look like in theory, but how can I close my leech in reality.
For strong wind my sail looks like I wish. In light winds I couldn't close my leech as much as I wished (with tight main sheet and open downhaul). Maybe my wish of a closed leech is not realistic at all, but with your suggestions it could be that the battens in the top are too stiff or I still have too much pre-bend or the sail cut is not ok. Hopefully I will have better wind next week end, so I can figure it out and make some more pictures. So far thanks for your comments.

Cheers,

Klaus

Re: Mast theory [Re: Smiths_Cat] #145263
06/16/08 02:09 PM
06/16/08 02:09 PM
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Posts: 4,451
West coast of Norway
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I spent 1 minute with accumeasure (download on the Uk Halsey site), result attached. No significant twist in that mainsail, but you really should flip the boat over when taking photos like this, so you can get some force pulling on the leech.

Lots of gotchas to look out for in that analyzis, especially the top one where I dont know the angle of the batten! I would say the sail is a bit deep for my taste all over, but the twist profile is where I would expect it to be with no kind of force pulling on the leech.

Attached Files
148411-klaus-mainsail.jpg (105 downloads)
Re: Mast theory [Re: Rolf_Nilsen] #145264
06/16/08 04:40 PM
06/16/08 04:40 PM
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Posts: 160
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I think your problem is not the leech but the sail shape in the lower part, i.e. chamber too much aft and too flat close to the boom.

Re: Mast theory [Re: Darryn] #145265
06/16/08 05:36 PM
06/16/08 05:36 PM
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Posts: 502
Port Noarlunga, SA, Australia
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Quote
Good sail, but not setup right.

Whats wrong?

Darryn
Mozzie
1782


In this photo downhaul and mainsheet are cranked on as hard as possible, much more then sailing setting, still cannot pull the depth out of the lower part of the sail. We decided the mast wasn't bending enough below hound fitting to suit the luff curve so Gordon (former owner in pictured) recut the luff curve in that area. The sail is now competitive and has won races against other Mozzies, last by a long way before recut.


Darryn
Mozzie
1782

Attached Files
148437-MastBend.jpg (86 downloads)
Last edited by Darryn; 06/16/08 05:41 PM.
Re: Mast theory [Re: Darryn] #145266
06/16/08 07:41 PM
06/16/08 07:41 PM
Joined: Mar 2005
Posts: 322
South Australia
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Darryn,

Do you by chance have a photo before the recut?

The mozzie mast is quiet a different animal to the F16 mast.!

Marcus


Marcus Towell

Formula Catamarans Aust Pty Ltd
Re: Mast theory [Re: Rolf_Nilsen] #145267
06/17/08 01:23 AM
06/17/08 01:23 AM
Joined: Sep 2007
Posts: 571
Hamburg
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Thanks Rolf,

as I said, I don't how to use this numbers. But I have found a pictures of Gilos Blade Sail with open downhaul and it looks pretty much like my sail, at least in my eyes.
I agree with the excessive camber, but with the downhaul I can reduce it quite efficient. No pics in the moment, sorry.
I will continue with on the water testing, because I can understand what tell-tales tell to me.

Quote
I think your problem is not the leech but the sail shape in the lower part, i.e. chamber too much aft and too flat close to the boom


Claus,

I tried various outhaul tension (on the water) and I am pretty sure that neither the sail is to flat there nor is the camber to much aft. Both more camber and more forward position of camber let the bottom stall earlier.

Thanks again for your input.

Cheers,

Klaus

Re: Mast theory [Re: Smiths_Cat] #145268
06/17/08 01:52 AM
06/17/08 01:52 AM
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Posts: 9,582
North-West Europe
Wouter Offline
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From the pics I think your leech is too tight.

The larger the squaretop is the more leech twist you want "see".

I write "see" as in this case it is different from actually having more leech twist. Basically the twist angle is the same but the large head shows more falling away to leeward at its tip.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Mast theory [Re: Smiths_Cat] #145269
06/17/08 04:06 AM
06/17/08 04:06 AM
Joined: Nov 2005
Posts: 246
Kiel, Germany
Baltic Offline
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Kiel, Germany
Klaus, where are you sailing? I'd like to have a look at your sail in flesh since I believe my A-Kat sail has the same problem.


F18: C2 / A-Cat: Minelli
Re: Mast theory [Re: Baltic] #145270
06/17/08 12:05 PM
06/17/08 12:05 PM
Joined: Sep 2007
Posts: 571
Hamburg
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Baltic,

Very good idea. I will give you a call later.

Wouter,

I agree with you for upwind courses. But if I am on a reach, drag doesn't matter, only lift until you can't hold the heeling moment any more. And you get the maximum lift out of a sail or wing, if you bring all parts of it close to stall at the same time. And exactly for this condition I want (or I hope at least) to set up the sail as well. I can always open my leech with the downhaul for the upwind leg.
Maybe it is not possible to stall the top with a square head sail + wing mast and without jib (which protects the lower and middle part of th emain from stalling) <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />, but before I make early assumptions I will listen if you guys can stall the top of a cat rigged square headed and wing masted boat.

Cheers,

Klaus

Re: Mast theory [Re: Marcus F16] #145271
06/17/08 04:47 PM
06/17/08 04:47 PM
Joined: Jun 2004
Posts: 502
Port Noarlunga, SA, Australia
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Quote
Darryn,

Do you by chance have a photo before the recut?

The mozzie mast is quiet a different animal to the F16 mast.!

Marcus


Hi Marcus, that is the photo before the recut. Looking for the ability to flatten the sail completely, a small pocket down low is Ok but the depth extending all the way up to the hound fitting with all adjustments maxed means that when downhaul and mainsheet are eased to normal sailing positions you cannot point. Fast downwind but low VMG upwind. I'm sure you know this already with your sailmaking skills, I'm putting this on here for those who might not.

Mozzie pear shape mast and pin head sail is very different to F16 wing mast and square top which this topic is refocusing on, a cue for a timely exit I think <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Darryn
Mozzie
1782

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