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Mast spanner setting for downwind under spinny #248643
05/21/12 04:39 AM
05/21/12 04:39 AM
Joined: Sep 2005
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waynemarlow Offline OP
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waynemarlow  Offline OP
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There is a slight contradiction in my understanding of the spanner ( mast rotation arm ) setting whilst downwind.

Whilst sailing the A it was very important to let the spanner off fully and if possible have it parallel or even beyond the front beam to get the main to really start to power up. Looking at most A sailors they all seem to have this setting with some of the top guys even having setups to lock the mast rotation arm some degrees in front of the beam.

Now if we did that with our F16's, technically we would have the mast in its weakest axis if we flew the kite, ie the smallest least stiff section would be supporting the spinny and could be prone to mast breakage.

Am I correct in thinking this and should we be ignoring the optimum mast setting and just aligning the strongest section of mast with the direction of most load ?

Comments please.

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Re: Mast spanner setting for downwind under spinny [Re: waynemarlow] #248644
05/21/12 05:17 AM
05/21/12 05:17 AM
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Posts: 1,669
Melbourne, Australia
Tornado_ALIVE Offline
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Melbourne, Australia
Let it of and find it's own rotation. Shold be just a little behind the front beam. Note, the A's run their traveller further out and their apparent is not as far forward as a spin cat. That is why they over rotate more.


Re: Mast spanner setting for downwind under spinny [Re: waynemarlow] #248645
05/21/12 06:14 AM
05/21/12 06:14 AM
Joined: Jan 2005
Posts: 6,044
Sebring, Florida.
Timbo Offline
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Timbo  Offline
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Sebring, Florida.
When I look up at my mast/mainsail under spin, I'm looking to see how the mainsail tell tales are flowing on the backside of the main.

As said above, the traveler is not out nearly as far as a non-spin boat, and the apparant wind is much more foreward of the main beam, so the mast doesn't need to be over-rotated.


Blade F16
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Re: Mast spanner setting for downwind under spinny [Re: Timbo] #248666
05/21/12 10:54 AM
05/21/12 10:54 AM
Joined: Oct 2002
Posts: 606
Maryland
Kris Hathaway Offline
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Kris Hathaway  Offline
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Maryland
No downhaul and let her rotate on its own to get good flow around the main with the wind mast. Remember the (nearly) centered and firm mainsail is also the backstay and you have the diamonds supporting most of the mast's lateral axis which is enough to support the chute with a rotated mast.

BTW, it is not a pretty sight if you forget the downhaul and there is a good wind. The pull from the chute and the downhaul induces a reverse mast bend. Yikes.



Kris Hathaway
Re: Mast spanner setting for downwind under spinny [Re: waynemarlow] #248671
05/21/12 11:34 AM
05/21/12 11:34 AM

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Mac m
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Did a clinic with REd Gear Racing before the Spring Fever Regatta and he suggested putting a mark on my downhaul scale on the mast that was actually more downhaul than the normal setting. My boat has a positive mast rotator setup, he suggested rotating all the way over in very light air.

Re: Mast spanner setting for downwind under spinny [Re: waynemarlow] #248769
05/23/12 02:42 AM
05/23/12 02:42 AM
Joined: Sep 2007
Posts: 571
Hamburg
Smiths_Cat Offline
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Smiths_Cat  Offline
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Hamburg
Originally Posted by waynemarlow
There is a slight contradiction in my understanding of the spanner ( mast rotation arm ) setting whilst downwind.

Whilst sailing the A it was very important to let the spanner off fully and if possible have it parallel or even beyond the front beam to get the main to really start to power up. Looking at most A sailors they all seem to have this setting with some of the top guys even having setups to lock the mast rotation arm some degrees in front of the beam.

Now if we did that with our F16's, technically we would have the mast in its weakest axis if we flew the kite, ie the smallest least stiff section would be supporting the spinny and could be prone to mast breakage.

Am I correct in thinking this and should we be ignoring the optimum mast setting and just aligning the strongest section of mast with the direction of most load ?

Comments please.


Wayne,

the mast is stiffer in the left - right direction than in the fore - aft one. Only the part above where the diamonds ends is stiffer in fore-aft direction. Hence for structural reason the mast should rotate to the beam (spreaders pointing in fore and aft direction). Anyway as long the mainsheet is reasonable tight, there is no risk of breaking. For aerodynamic reason you should watch the tell tales of the main.

Cheers,

Klaus


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