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Minute drag reduction #227746
01/29/11 04:57 AM
01/29/11 04:57 AM
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West coast of Norway
Rolf_Nilsen Offline OP

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Following yesterdays excellent ideas thrown around on how to simplify setting/dousing spis.

Here is another topic thrown around. Drag reduction from cables. The drag from the cables in the rigging is not large, so this is a minor component on speed compared to the loose nut on the tiller. Still, here is a small discussion on drag reduction in rigging as posted by Tom Speer on the landyacht forum.

Quote
Freely rotating cable fairings have been tried many times in the past, without much success. There are several physical constraints on the problem that make it very difficult.

The aerodynamic center must be behind the axis of rotation for the fairing to be statically stable. The distance between the axis of rotation and the aerodynamic center must be great enough to overcome friction and to provide a natural frequency high enough to track wind gusts. The center mass of the fairing must be ahead of the axis of rotation to be dynamically stable against flutter. One would like the cable to be located near the thickest part of the section, or else the fairing will have excessively large frontal area. Different parts of the fairing must be able to rotate independently because of the change in apparent wind angle with height.

I suspect the fairings need to have tails attached in order to meet all these requirements. This makes the fairings heavier and more fragile. Not to mention adding additional wetted area.

A simple flat plate with its leading edge against the cable, possibly with ballast extending ahead of the cable, may prove to be the best design. Simply preventing the formation of the Karman vortex street using the splitter plate can result in a significant reduction in drag.



Landyachts operate at far higher speeds than F16s so drag is much more critical. But I thought I would throw this idea out here and see what happened.

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Re: Minute drag reduction [Re: Rolf_Nilsen] #227748
01/29/11 06:03 AM
01/29/11 06:03 AM
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Essex, UK
Jalani Offline
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I've wondered about a thin, flat' stiffener' inside of the weave of dyneema several times in order to keep it flat. If such a line were then used for rigging, would it automatically orient itself for least drag?

It'd not be perfect, but it might be less drag than 'round' rigging?

As I said, I've wondered - but I've not explored it at all......


John Alani
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Re: Minute drag reduction [Re: Jalani] #227753
01/29/11 10:07 AM
01/29/11 10:07 AM
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West coast of Norway
Rolf_Nilsen Offline OP

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I think you need pretty large surface areas to make it self-orienting. A "foil" not properly aligned is far worse than the round wire/line.

Re: Minute drag reduction [Re: Rolf_Nilsen] #227756
01/29/11 10:44 AM
01/29/11 10:44 AM
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pgp Offline
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Attach rigid sails directly to the rigging?


Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: Minute drag reduction [Re: pgp] #227766
01/29/11 06:11 PM
01/29/11 06:11 PM
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France
pepin Offline
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I can't wait for the first protest against these illegal sails smile

Re: Minute drag reduction [Re: pepin] #227769
01/29/11 06:38 PM
01/29/11 06:38 PM
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pgp Offline
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yeh...forgot about that. blush


Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: Minute drag reduction [Re: pgp] #227774
01/29/11 07:31 PM
01/29/11 07:31 PM
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Essex, UK
Jalani Offline
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You can already (for quite some time now) get aerofoil cross-section rod rigging and, naturally, it's expensive. The area is no greater than round s/s rigging - I'd always assumed that it must reduce drag and must also self-orient (twist) to some extent. I havn't seen it in use for ages now though so it may have been discontinued.
Looking around though, I cme across this: Hall SCR

Last edited by Jalani; 01/29/11 07:37 PM.

John Alani
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Stealth F16s GBR527 and GBR538
Re: Minute drag reduction [Re: pgp] #227775
01/29/11 07:36 PM
01/29/11 07:36 PM
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waynemarlow Offline
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At the speed we travel, the drag of say 1mm larger wire is insignificant, what is not insignificant is the spinnaker snuffers and all the weavers loom up front. But any reduction is a reduction, the A class seem to have all gone over to 2.5mm ???? wire ( someone will fillin that blank please ) which is about 25% stronger than the normal wire we use.

Now if only we could stop the creep of synthetic cord we certainly could have both lighter and smaller diameter. confused

Re: Minute drag reduction [Re: waynemarlow] #227807
01/31/11 03:14 AM
01/31/11 03:14 AM
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Netherlands
Hans_Ned_111 Offline
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Hey Wayne,

I use from the beginning 3 mm as main stay and 2,5 mm as front stays and this is more than enough to absorbe the load ( also in 2 up ) on the A-class i do use 2,5 mm mainstays and 2 mm front stays for about 8 years already and also this is more then enough to have no trouble. You are right that the spinaker kit in front is the biggest problem of drag on the F16, it is enormous and i do try to make a workable solution to get it reduced but not really found a good solution for it yet. In long distance races like Texel it would be better to have the spin in a bag on the trampoline because this saves a lot of drag and you never use the spin as much as in course racing where time of hoisting in more an issue.

Regards,
Hans

http://www.catamaranparts.nl
http://catamaranparts.blogspot.com


Re: Minute drag reduction [Re: Hans_Ned_111] #227808
01/31/11 04:55 AM
01/31/11 04:55 AM
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waynemarlow Offline
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Originally Posted by Hans_Ned_111
You are right that the spinaker kit in front is the biggest problem of drag on the F16, it is enormous and i do try to make a workable solution to get it reduced but not really found a good solution for it yet.


I think the integrated front beam and centre snuffer [Linked Image]
goes a long way toward solving this problem, it seems to work better than expected. With a bit more thought such as making the snuffer also the front stay mount, we get other benefits such as tight jibs and less weight in the hulls ( less reinforcing to take the inward stay loads needed )Bitsa is in the process folks to um shall we say take a further step in this direction, this summer.

Re: Minute drag reduction [Re: waynemarlow] #227809
01/31/11 06:39 AM
01/31/11 06:39 AM
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Looking for a Job, I got credi...
scooby_simon Offline
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Originally Posted by waynemarlow
Originally Posted by Hans_Ned_111
You are right that the spinaker kit in front is the biggest problem of drag on the F16, it is enormous and i do try to make a workable solution to get it reduced but not really found a good solution for it yet.


I think the integrated front beam and centre snuffer [Linked Image]
goes a long way toward solving this problem, it seems to work better than expected. With a bit more thought such as making the snuffer also the front stay mount, we get other benefits such as tight jibs and less weight in the hulls ( less reinforcing to take the inward stay loads needed )Bitsa is in the process folks to um shall we say take a further step in this direction, this summer.


Wayne,

Does your under tramp box have the dolphin striker post thru the middle ?


F16 - GBR 553 - SOLD

I also talk sport here
Re: Minute drag reduction [Re: scooby_simon] #227811
01/31/11 07:27 AM
01/31/11 07:27 AM
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waynemarlow Offline
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No, the sides of the snuffer box are beefed up just at the point of the dolphin striker intersection and take the loads of what would have been the post at the central point. The location ball for the mast simply is bolted through the upper part of the box and the loading is taken by a nut on the top surface. To tighten the dolphin striker all I did was put a couple of " shimms " between the striker bar and the snuffer box.

As much as I used to hate the central beam, on going down that route a whole load of possibilities arise if we rethink things to make the central beam the main load bearing / snuffer structure and the hulls are just the floatation devices. Little things like the front beam could be moved way foward to strengthen and stiffen the hulls and yet the mast base could be moved about at will.

Perhaps the front beam could be radiused as per the front jib traveller, the mast base reset according to single or double handed, the front of the hulls lightened as they no longer take any loading other than from the bouyancy aspect, the cross beams lightened as the load from the mast is now spread fore and aft by the central beam, lots of possibilities here guys but it need to be rethought completely.

Weight would be probably be lighter overall and hull shapes would be better with less reinforcing ( weight ) and thus less hull volume needed in the front end. mmmmm would love to make a complete design change here. smile

Re: Minute drag reduction [Re: waynemarlow] #227812
01/31/11 07:33 AM
01/31/11 07:33 AM
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waynemarlow Offline
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What many haven't worked out is that the front spinny pole is also self supporting. [Linked Image]

Re: Minute drag reduction [Re: waynemarlow] #227825
01/31/11 10:21 AM
01/31/11 10:21 AM
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Ft. Pierce, Fl. USA
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Am I the only one that sees the Pink Elephant in the room?
Did I miss something? I thought the whole idea of this thread was drag reduction...how in the world does putting a huge square box under the tramp reduce drag? What happens when that thing chokes on a big piece of chop? All this tweaking and redesigning of hull shape to make for the least resistance forward...then put something under the tramp that looks like it would stop the boat dead when sailing into steep chop/waves. Maybe the picture makes it look bigger than it actually is ...but at first glance this system looks like it would create more problems than it solves.

Re: Minute drag reduction [Re: Jalani] #227827
01/31/11 10:38 AM
01/31/11 10:38 AM
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Hamburg
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Originally Posted by Jalani
I've wondered about a thin, flat' stiffener' inside of the weave of dyneema several times in order to keep it flat. If such a line were then used for rigging, would it automatically orient itself for least drag?

It'd not be perfect, but it might be less drag than 'round' rigging?

As I said, I've wondered - but I've not explored it at all......


No, it would put it squre to flow. That's because the aerodynamic forces act at about 25% chord from the leading edge, while the mass would be around 50% chord and the turning point (where the line is under highest tension) would be at 50% as well.

Cheers,

Klaus

Re: Minute drag reduction [Re: Seeker] #227828
01/31/11 10:41 AM
01/31/11 10:41 AM
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Hamburg
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Originally Posted by Seeker
Am I the only one that sees the Pink Elephant in the room?
Did I miss something? I thought the whole idea of this thread was drag reduction...how in the world does putting a huge square box under the tramp reduce drag? What happens when that thing chokes on a big piece of chop? All this tweaking and redesigning of hull shape to make for the least resistance forward...then put something under the tramp that looks like it would stop the boat dead when sailing into steep chop/waves. Maybe the picture makes it look bigger than it actually is ...but at first glance this system looks like it would create more problems than it solves.

True. And I may add that I still think that my furled hooter produce only insignificantly more or less drag than a conventional mid pole snuffer and all its wiring. Still the spi has more area than a hooter of same stay length though...

Re: Minute drag reduction [Re: Seeker] #227839
01/31/11 12:45 PM
01/31/11 12:45 PM
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waynemarlow Offline
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Originally Posted by Seeker
Am I the only one that sees the Pink Elephant in the room?
Did I miss something? I thought the whole idea of this thread was drag reduction...how in the world does putting a huge square box under the tramp reduce drag? What happens when that thing chokes on a big piece of chop? All this tweaking and redesigning of hull shape to make for the least resistance forward...then put something under the tramp that looks like it would stop the boat dead when sailing into steep chop/waves. Maybe the picture makes it look bigger than it actually is ...but at first glance this system looks like it would create more problems than it solves.

Mmm a naysayer, can I ask a question, how much of the time does your front beam and striker hit the water at the moment. I tend to fly a hull all of the time I can including downwind for the very purpose of making sure the front beam doesn't hit the water, about the only time I see water any where near the striker is when tacking or gybing and thats when the boat is almost stopped anyway.

Anyway fully accept your comments and acknowledge that there could be a possibility of being hit by the waves. This was just a quick knock up to prove a concept ( will the spinny fold in through the twin forestays ) but would comment that the Mk2 version has a fully enclosed underneath and there is no real opening beneath the beam as per the current setup for the water to get in.

Re: Minute drag reduction [Re: waynemarlow] #227872
01/31/11 04:46 PM
01/31/11 04:46 PM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline OP

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Midpole snuffers are known to scoop decent amounts of water at times. Going downwind in strong winds and the mainbeam is often quite.. Wet.. Especially when punching through waves downwind. As the spi hopefully will be set at that time and there is sufficient drainage, I would not worry until I caught something big and bad in there like a tiger shark or man o' war.

BUT, nobody knows until it has been tried. Wayne, I cheer you on! smile

Re: Minute drag reduction [Re: Rolf_Nilsen] #227911
02/01/11 03:51 AM
02/01/11 03:51 AM
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What you wear has more of an impact than anything else. And especially if you are 2-up, if one is sticking up higher/lower than the other on trapeze, you are increasing area of drag.

Re: Minute drag reduction [Re: taipanfc] #227912
02/01/11 05:34 AM
02/01/11 05:34 AM
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Having a big steel box underneath your boat is a very bad idea for several reasons.
-It basically is just a giant scoop and that will completely stop you when the frontbeam hits a wave.
If the sail flushes out while a wave hits you have no wat to retrieve the sail without destroying it.
But what are the odds? One in a million? wink
-In a normal pole-mounted snuffer the sail has an opportunity to dry whilst sailing upwind.

[Linked Image]

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