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Lift 170 vs 170 fish
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Post new topic   Reply to topic    Northwest Kiteboarding -> Gorge / Portland / Oregon Coast
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apctjb

Since 19 Aug 2007
267 Posts

Obsessed



PostMon Sep 03, 18 6:49 am     Reply with quote

Just got a GW 91 with 633 wing which I will use with Alien Air 4'-8" and had heard that some modification is needed to reduce front foot pressure. Some riders are drilling additional mounting holes in the mast base to allow the mast to be mounted ~1" further back, and some suggest shimming (1/8" shim) where the mast attaches to the fuselage to move the center of lift backward.

I was curious about the shim thing so did a quick CAD drawing to determine how thick a shim would be required to move the center of lift ~1" aft and came up with .2" if the shim was placed as far forward as possible in the slot for mounting the mast in the fuselage.

So on paper it appears that shimming could work.

Curious to hear what others are saying about the pros/cons of shimming vs drilling additional holes in the mast base. Has anyone talked with Slingshot to see what they recommend???

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eric

Since 13 Jan 2006
1312 Posts

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PostMon Sep 03, 18 7:38 am     Reply with quote

<<move the center of lift ~1" aft and came up with .2" if the shim was placed as far forward as possible >>

You've got the backwards. The shim needs to be in the rear of the mast-fuse union if you want to move the center of effort back relative to your foot position. See photo on previous page posted by LDHR.

If you have not watched it already, how to shim mast video below is great:


https://www.youtube.com/watch?v=mVdSx5eNdUA

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apctjb

Since 19 Aug 2007
267 Posts

Obsessed



PostMon Sep 03, 18 8:18 am     Reply with quote

Quote:
You've got the backwards. The shim needs to be in the rear of the mast-fuse union if you want to move the center of effort back relative to your foot position. See photo on previous page posted by LDHR.



Got it, thanks

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ldhr

Since 21 Jul 2009
1073 Posts
Hood River
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PostMon Sep 03, 18 8:31 am     Reply with quote

apctjb wrote:


Curious to hear what others are saying about the pros/cons of shimming vs drilling additional holes in the mast base. Has anyone talked with Slingshot to see what they recommend???


Slingshot team riders are using popsicle sticks as shims.... don't over think it.

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apctjb

Since 19 Aug 2007
267 Posts

Obsessed



PostMon Sep 03, 18 9:44 am     Reply with quote

Quote:
Slingshot team riders are using popsicle sticks as shims.... don't over think it.


Part of the attraction of foiling is jumping on a new learning curve, not just riding but understanding how it all works. Thanks

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underwood

Since 26 May 2018
12 Posts

 



PostMon Sep 03, 18 2:27 pm     Reply with quote

The Ghost Whisper 91 mounting plate is not perpendicular to the mast so when the foil is level the mounting plate slopes upward about 2 degrees facing forward.

Anyone know the purpose of the upward slope in the mounting plate and does this add to the problem? (shimming the rear has the net effect of bringing the mounting plate back to level.)

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ldhr

Since 21 Jul 2009
1073 Posts
Hood River
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PostMon Sep 03, 18 4:50 pm     Reply with quote

underwood wrote:
The Ghost Whisper 91 mounting plate is not perpendicular to the mast so when the foil is level the mounting plate slopes upward about 2 degrees facing forward.

Anyone know the purpose of the upward slope in the mounting plate and does this add to the problem? (shimming the rear has the net effect of bringing the mounting plate back to level.)


If you're talking about the mounting plate for the mast to the board - I'm not so sure about your observation.
Did you watch the video?
The guy explains why the angle of the board to the mast is kinda irrelevant. I don't think 2 degrees would have any effect. 10 degrees maybe, but not 2.
Explanation comes at 2:38 in the video.

It might explain why people who ride SS GW foils always look like the nose of their boards are pointing up.


https://www.youtube.com/watch?v=mVdSx5eNdUA

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caps

Since 23 Dec 2010
302 Posts

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PostMon Sep 03, 18 7:22 pm     Reply with quote

underwood wrote:
The Ghost Whisper 91 mounting plate is not perpendicular to the mast so when the foil is level the mounting plate slopes upward about 2 degrees facing forward.

Anyone know the purpose of the upward slope in the mounting plate and does this add to the problem? (shimming the rear has the net effect of bringing the mounting plate back to level.)


Maybe it's for better touch down success. It may produce the same effect as rocker on a board.

And my other thought is that it probably doesn't matter.

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