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Lightning mast blocking


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#1 cal40john

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Posted 10 April 2011 - 03:44 PM

For the tuning systems where you change mast block settings, why does it go from max prebend to minimal prebend for light to heavy air? In drifting conditions I know you want flatter sails, but the M5 tuning on North says this setting is good up to 6 knots of wind. And why the least amount of prebend for heavy air conditions? Does this have something to do with jib sag?

I've been looking at the Shore and North Sails tuning guides.

#2 4girlsintow

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Posted 10 April 2011 - 10:52 PM

You need max bend for light air to flatten main and sag jib. As the breeze increases you straighten the mast to add power to the main and straighten the jib luff for better point. As it gets to depower mode you max straighten the mast to keep the main from inverting when you apply backstay. It also stands the mast up straighter to take the sag out of the jib.

Hope it helps.

If this is confusing or too much work you should buy the Quantums or the North Fishers for minimal adjustments.

#3 cal40john

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Posted 11 April 2011 - 06:25 AM

You need max bend for light air to flatten main and sag jib. As the breeze increases you straighten the mast to add power to the main and straighten the jib luff for better point. As it gets to depower mode you max straighten the mast to keep the main from inverting when you apply backstay. It also stands the mast up straighter to take the sag out of the jib.

Hope it helps.

If this is confusing or too much work you should buy the Quantums or the North Fishers for minimal adjustments.



I'm trying to figure out the logic to this. This is how it appears to me. The light air setting sagging the jib increases draft and moves it forward, mast prebend moves the draft aft and flattens the main. This appears to be opposite tuning to me. North says the light air setting is for up to 6 knots. I would think that you want to go from a flat main for drifter conditions to a deeper shape much earlier than 6 knots. What am I mis-understanding?

Thanks

#4 4girlsintow

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Posted 11 April 2011 - 03:27 PM


You need max bend for light air to flatten main and sag jib. As the breeze increases you straighten the mast to add power to the main and straighten the jib luff for better point. As it gets to depower mode you max straighten the mast to keep the main from inverting when you apply backstay. It also stands the mast up straighter to take the sag out of the jib.

Hope it helps.

If this is confusing or too much work you should buy the Quantums or the North Fishers for minimal adjustments.



I'm trying to figure out the logic to this. This is how it appears to me. The light air setting sagging the jib increases draft and moves it forward, mast prebend moves the draft aft and flattens the main. This appears to be opposite tuning to me. North says the light air setting is for up to 6 knots. I would think that you want to go from a flat main for drifter conditions to a deeper shape much earlier than 6 knots. What am I mis-understanding?

Thanks


6 knots is considered light air. You can't really race until 4 knots. The lightning needs a very powerful jib. The M5 main is built so that it can be flattened for less drag in light air (max prebend). Many very successful Lightning sailors use a lot of cunningham in light air to keep the draft from going too far aft. Then at about 6-7 knots you can put a block in front and take up a turn or two on the lowers to power up the main while the jib luff tension is slightly increased to keep pointing ablility. The jib is still pretty powerful at this point to help the boat move. Then as you get all 3 up on the rail and hiking you can do more mast straightening then max straight to keep the main from inverting when a lot of backstay is used. The mast will still bend and flatten out the main in heavy air with proper backstay, cunningham and vang. This is pretty common is most every boat, bent mast in light air, straight mast in heavy air.

So in light air you want a "knuckle forward" shape. This helps with keeping the boat in a groove, easy steering. The main needs a flatter entry to help keep the air coming off the jib moving around the main. A closed "slot" (full main entry)is slow in light air and in heavy air.

This confusion is why there are sails out there that do not need this much attention and are just as fast.




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