As I get better sailing this thing, I want to find out the nuances of all of the systems to squeeze every bit of speed out that I can. My current topic of study is the mast rotation. When rigging the boat, I usually run a line from an eye on the boom, through the block on the gooseneck, and back through the jam cleat on the boom. I usually cinch this as tight as it will go. My question is- in what circumstances would one wish to loosen the rotation line to allow more rotation. I know many larger aircraft have leading edge slats that are extended for take off and landings to allow the wing to be more efficient at lower speeds; I think allowing the mast to rotate more would accomplish something similar, but am not sure how and when to employ this. Any suggestions?
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Eric C
Force 5 project boat
Unnamed
Previous boat
1980 Nacra 5.2
"Double Vision"
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Nacra mast rotation
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- Rank: Lubber
- Registered: Aug 25, 2010
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- Posts: 94
Posted: Jul 26, 2011 - 07:07 AM
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- Rank: Lubber
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Posted: Jul 26, 2011 - 08:37 AM
The point of the mast rotation is to control mast bend. Your mast will bend more, much more, sideways to the mast section than it will front to back. When you set up the mast rotater tight like that you are preventing mast bend and keeping the sail full. Good for light to medium not so good for heavy winds. As a rough rule the rotater wants to point at the side stays, so allowing a touch more than 45 degrees of rotation on each side. As the mast rotates the thinner, bendier section points more forwards, the mainsheet tension pulls backwards, the mast bends and pulls excess fabric out of the middle of the sail. This changes it from full (like a glider, slow speed) to flatter (like a jet, higher speed) airfoil. If you have diamond wires they limit the amount of mast bend you get and so are set according to your weight. Lighter crews have slacker diamond wires to allow more bend to flatten the sail more and control the power. It looks "wrong" to allow more rotation and have the mast point more sideways in the boat. Look at the big picture. The sail is a lot bigger than the mast so the bend is more important than the angle of the mast.
When it is set up right it's like an automatic transmission. When the wind is light you sail with a soft mainsheet and the sail is full to push the boat through the water using all the available power. As the wind gets stronger you sheet harder, the mast rotates more, the mast bends more, the sail flattens, and the required righting force (you on the trapeze) is limited to what you can provide.
Cool, eh?
I can't help you with diamond wire tension on a NACRA but this guy probably can:
http://www.columbussailingclub.org/pdf/nacra_5.2_tuning_guide_by_R._McDonald.pdf -
- Rank: Mate
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Posted: Jul 27, 2011 - 02:38 AM
be aware that that tuning guide is for the later nacra 5.2 with swept spreaders
they made a few hundred of those
most of us have the 5.2 that nacra made in thousands, with straight spreaders...
i'd say forget the mast bend stuff about mast rotation on the older 5.2
to me it's all about aerodynamically smoothing the entry of the air to the sail
to do that, set your mast rotation so that the stainless rotator arm is pointing back to the shroud
then leave it along
if you want to tweak further against other 5.2's in 1 design racing set the wishbone to point slightly ahead of the shroud in light wind, slightly behind the shroud in strong wind, fully uncleated downwind and fully cleated in survival winds -
- Rank: Chief
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Posted: Jul 27, 2011 - 08:20 PM
Yurdle, can you descibe how you live linked to the website?
I've tried right clicking (Fuirefox) to try & find a "copy link locaton" or something, but no success.
Your link is always more convenient than copy/paste.
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Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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- Rank: Mate
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Posted: Jul 27, 2011 - 09:11 PM
In FF just highlight the entire address bar, copy/past into the reply window and use the URL button below.
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Rob
OKC
Pile of Nacra parts..
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