Author Topic: Go foil kai, Iwa, M200 kits with 29" mast now available  (Read 7204 times)

toolate

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #15 on: August 11, 2018, 12:34:07 AM »
what would you advise for a newbie 155 lb person looking for small waves 9once it gets over head high I will be on my regular sup for sure)

While this is exciting the lack of interchangeability from GoFoil is unacceptable.  And I am one of GoFoil / foilings biggest advocates.

Each iteration of the foil alone is costing $1,500 to $2,000.

Meanwhile the boards are changing EVEN Faster than the foils.

That said if any of your are thinking about it for SUP:

#1 Choice is the GoFoil IWA.  It will work for you in anything from 4 to 10 feet. 

#2 Maliko 200 - Great for 2 to 5 ft waves for people from 150 to 240 lbs.

jondrums

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #16 on: August 11, 2018, 01:26:09 AM »
longer chord doesn't necessarily do anything for stiffness.
...
 If their mast has the same camber as before it won't be stiffer due to longer chord alone.

I will politely disagree.  The stiffness of the mast should go up roughly linearly with the chord length.  So if it is 20% longer chord, than it will be approximately 20% stiffer assuming the same camber sectional shape.  Now, if the camber gets thicker, the stiffness can go up profoundly - something like the cube of the increase (20% more camber could equal 1.2^3 = 1.73 = 73% stiffer).

However, since the mast is longer, the overall stiffness goes down dramatically - roughly inversely proportional to the cube of the length.  So 29" is 11.5% longer than 26" and the stiffness will go down by about 28% because of that.

Did I lose you all yet? sorry about the geekfest.

jondrums

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #17 on: August 11, 2018, 01:28:14 AM »
oh - forgot to mention that all those numbers are for bending stiffness.  Torsional stiffness matters too, and that'll go up by the cube of EITHER the chord or the camber increase.  And it only goes down linearly with length.  So it is possible that for torsion about the axis of the mast, the new masts are significantly stiffer.

LM

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #18 on: August 11, 2018, 02:53:54 AM »
oh - forgot to mention that all those numbers are for bending stiffness.  Torsional stiffness matters too, and that'll go up by the cube of EITHER the chord or the camber increase.  And it only goes down linearly with length.  So it is possible that for torsion about the axis of the mast, the new masts are significantly stiffer.

Good point about the torsional stiffness, that's actually what I was referring to. My education is in aviation but I'm not an aeronautical engineer BUT I actually did have this exact conversation with an aeronautical engineer a couple of weeks ago & he explained that it's a common misconception that chord length affects stiffness. He showed me (with equations) why. I don't remember the exact details but I believed him, he's done design work for military drones, etc. & he's also owned a composites company for over 30 years so I figured he knew better than I. So I can't provide details & it's a topic difficult to find through Google searches but that's what I was told. We're currently trying to achieve more torsional stiffness with our masts & that's what lead to the conversation.

Beasho

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #19 on: August 11, 2018, 04:54:34 AM »
what would you advise for a newbie 155 lb person looking for small waves 9once it gets over head high I will be on my regular sup for sure)

IWA - One stop shop

PonoBill

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #20 on: August 11, 2018, 09:04:42 AM »
longer chord doesn't necessarily do anything for stiffness.
...
 If their mast has the same camber as before it won't be stiffer due to longer chord alone.

I will politely disagree.  The stiffness of the mast should go up roughly linearly with the chord length.  So if it is 20% longer chord, than it will be approximately 20% stiffer assuming the same camber sectional shape.  Now, if the camber gets thicker, the stiffness can go up profoundly - something like the cube of the increase (20% more camber could equal 1.2^3 = 1.73 = 73% stiffer).

However, since the mast is longer, the overall stiffness goes down dramatically - roughly inversely proportional to the cube of the length.  So 29" is 11.5% longer than 26" and the stiffness will go down by about 28% because of that.

Did I lose you all yet? sorry about the geekfest.

I didn't think that sounded correct for anything much thicker than paper either. If nothing else, it's just more material, and viewing it as a set of polygons--more polygons--each of which resists bending. If you consider the center of force to be the middle of the mast then there is also more leverage to the longer chord, both for the force and for the resistance, so those cancel each other somewhat.  So I could see the numbers going either way. I happen to have some mast shapes drawn in Fusion 360, so I blew up the chord length and let the software do the engineering analysis. Holding the thickness to the same value, the torsional and lateral stiffness increases a little less than linearly. Keeping the camber shape the same (which makes the mast thicker) increases both torsional and lateral stiffness quite a bit more. I don't know the mathematical relationship since I only did a couple of tries and didn't try to fit a formula, but I'd expect it to be some exponential value.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

frenchfoiler

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #21 on: August 11, 2018, 12:52:54 PM »
what would you advise for a newbie 155 lb person looking for small waves 9once it gets over head high I will be on my regular sup for sure)


Combo IWA/M200.

jondrums

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #22 on: August 11, 2018, 05:22:02 PM »
Deriving the torsional stiffness of a beam is a somewhat complicated undertaking.   Here is a good write-up:
https://en.wikipedia.org/wiki/Torsion_constant

The hard part is to derive the torsion constant for the foil shape of the mast cross section.   Below is an image which shows how to do this (note that K in the image below is the same as J in the wikipedia article = the torsion constant).



Does anyone know the exact dimensions of the old and new cross section?  I'm happy to do the math - this is fun for me. (chord length and thickness would be all I need)

PonoBill

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Re: Go foil kai, Iwa, M200 kits with 29" mast now available
« Reply #23 on: August 12, 2018, 11:48:11 AM »
I'll find out. Rod has one.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

 


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