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Gaastra Nitro IV 11.0 Tuning

 
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d0uglass



Joined: 28 May 2004
Posts: 1049
Location: Bonita Springs, Florida

PostPosted: Wed Aug 07, 2013 6:54 am    Post subject: Gaastra Nitro IV 11.0 Tuning Reply with quote

I just picked up a used Gaastra Nitro IV 11.0 and 550 Fiberspar mast. I'm using it on a wide-tailed formula board. I've only had one session on the sail so far. The power is there, but I felt pretty out of tune and had a tough time getting dialed in the squally 7-17 knot conditions.

http://www.jimbodouglass.blogspot.com/2013/08/this-quiver-goes-to-11.html

Maybe someone on this forum is familar with Nitro IV tuning and could help me with my tuning questions?

Question 1- Downhaul: How much? The sail luff is 554, which I have assumed means having the mast extension set as short as possible. (On my chinook extension, the lowest exposed hole is around 6 or 8.) With the extension all the way low, I downhauled until the leech was loose through all the batten intervals that had mini-battens, and the entry to the belly of the sail was quite lean. At this point there were still a few centimeters of line between the pulleys on the sail and the pulleys on the extension, but I was afraid to downhaul more for fear of making the sail too flat and interfering with cam rotation.

Question 2- Boom height. With the boom a little shy of the center of the boom cutout, it was at my eye height. (I'm 5'10") On my other sails I usually have the boom up to at least the middle of the cutout, but that felt too high on this Gaastra, which made me wonder if the cutout was higher than typical or if I was really missing that last ~5 cm of downhaul that would have slightly lowered the cutout relative to where the boom was attached.

Question 3- Mast base. With my 9.5 Ezzy cheetah I had been running the mast base about 1/3 from the back of the track. I moved it forward to nearly the center of the track for the 11.0, but I still felt like the mast was raked too far forward when I was sailing and I had trouble closing the gap. I wonder if I should move the mast track forward, or if messing with the boom height and downhaul will take care of things. I'm hesitant to move the base much forward of center, because I don't want to overweight the board ahead of the flat part of the rocker, which I reckon would make things slow and sticky.

Question 4- Outhaul. When pumping to plane, should the outhaul be slack or tight? On my camless Ezzy cheetah slacking the outhaul is good for going downwind but seems counterproductive when pumping to plane. But with the Nitro IV I seemed to get planing better with a pretty slack outhaul. Could have something to do with that "lean entry" on the Gaastra relative to the Ezzy.

Anyway, I appreciate any help or hints folks can give.

Thanks,
James Douglass

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http://jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html
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lucashurt



Joined: 06 Oct 2010
Posts: 9

PostPosted: Thu Aug 08, 2013 10:50 am    Post subject: Reply with quote

Hi James,

I've enjoyed you blog over the years, so thanks! I have a Nitro III 11.00 also with a 550 Fiberspar. I think I only ever rigged it once, but I'm getting more keen to try it again as I've spend a few sessions on a formula board recently and liked it. I hope you get some good tips here. I'll try to post up my experiences as they come.

Luke
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zirtaeb



Joined: 03 Jul 2009
Posts: 2281

PostPosted: Thu Aug 08, 2013 4:12 pm    Post subject: Reply with quote

More downhaul, to batten below the mini battens.
Cutout is high, because short people aren't supposed to use 11 meters. At least according to design.
Use the sail with higher booms, since it's so tall, to give yourself some leverage over the tall sail. Most short guys run it at the top of their head. Some shorter Formula guys run the boom height near 60", and a couple more when experimenting around.
Measure center of front straps to mast base. For an 11, depending on what exact board, you should get close to 25".
You didn't specify fin or exact board.
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d0uglass



Joined: 28 May 2004
Posts: 1049
Location: Bonita Springs, Florida

PostPosted: Fri Aug 09, 2013 8:09 am    Post subject: Reply with quote

Board is a Don Wagner custom with lots of tail width (almost 92 cm at the back footstraps) but thin rails and footstraps set more inboard than typical because that's the stance that Don likes.

http://www.jimbodouglass.blogspot.com/2013/06/dons-lab-home-built-formula-board.html

Fin is an old 85 cm Curtis cut down to 70 cm. Stiff and straight.

I haven't measured distance to mast base but I'll give that a try. The board is quite short and the mast track definitely spans the area where the rocker transitions from flat to curving up towards the nose. There may be a narrow sweet spot between where the mast base is too far back to get good leverage on the 11.0, and where the mast track is too forward to let the board unwet efficiently.

Afternoon thunderstorms keep getting in the way of my attempts to sail after work, but I'll hopefully get another tuning session this weekend.

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http://jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html
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