Author Topic: Foil effect on board stability..  (Read 1528 times)

Wetstuff

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Foil effect on board stability..
« on: January 06, 2020, 10:52:49 AM »
I hear it said 'a foil adds stability'.  My fingers are crossed it means: 'initial stability' when mounting the board*...  Is there a way to quantify that?  Is there a simile; 'a 28" board vs. 32"' in calm water?  A whole lot of foil boards lack liters and length generally discussed on the Zone.  This bystander feels (not unusual) uninformed.  Thanks.

Jim

*it seems generally true - anything moving as intended is more stable than stationary.
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SanoSlatchSup

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Re: Foil effect on board stability..
« Reply #1 on: January 06, 2020, 11:26:18 AM »
From a "feel" aspect, my 6'x28.5"x5" foil board "feels" more stable standing on it than my 7'8x30"x4.125" mini-simmons, or even my 9'6"x28.785"x4" Laird/Pearson Arrow board.

It's the "feeling" that because of having a huge 28 inch "fin" hanging under that board, that the side-to-side movements - that were typically the cause of most of my standing splashdowns - were dramatically slowed down in nature, and as a result, the ability to correct for them increased 10-fold.

Last time I went out on a regular ol' SUP (Infinity Phoenix 7'6"x30"x4.25"), the first time I stood up on it to paddle out through the whitewater, the thing felt so twitchy, and unstable that I immediately fell off the darn thing...three times!! :o 

Eventually got the ship righted, and made it out to the lineup...where I felt as though I was back to many years earlier when I stood up on a SUP for the very first time. I was on that board because I had sold my beloved, and "long in the tooth" Corran Retro mini-Simmons shape, and was thinking about wanting to foil and SUP. That was over a year ago, and I decided not to buy the board, and have not been on a SUP since...and don't regret or miss it one bit.
Me: 6'1"/185...6'0" Kings Foil Board...6'0" Chelu Foil Board...9'6" Bob Pearson "Laird Noserider"...9'6" Costa Azul Wide Body...14' Lahui Kai "Manta"...8'0" WaveStorm for when proning urges still hit, and 7'3" Chuck Glynn foil board backup.

Dwight (DW)

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Re: Foil effect on board stability..
« Reply #2 on: January 06, 2020, 12:32:23 PM »
Exact same answer as Sano...

Also, the foil under you matters a lot and the board shape matters a lot.

Stiffest mast and biggest front wing are massively more stable.

red_tx

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Re: Foil effect on board stability..
« Reply #3 on: January 06, 2020, 12:37:16 PM »
The foil and mast absolutely add stability and also help track better than even a huge longboard fin on a traditional standie. I used to ride this Naish 7'0 raptor for surfing. I could maybe get three strokes on each side before I was forced to switch sides(Unless I wanted to go in a circle).

On my 7'4 starboard(Very similar pringle potato chip shape) I can paddle 8-10 strokes on each side in flat water until I have to switch.

I also feel like the foil is faster paddling in the flat water. Like 1.5 times faster. Might be in my head as I would never imagine this before foiling. I have a made up theory that the wing is creating lift at any forward movement, ever so slightly unweighting the entire vessel.

-red

JEG

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Re: Foil effect on board stability..
« Reply #4 on: January 06, 2020, 01:06:50 PM »
I agree what SanoSlatchSup & Dwight (DW) said and make sure you get the right advise on which board to get and foil combine.

Wetstuff

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Re: Foil effect on board stability..
« Reply #5 on: January 06, 2020, 02:44:48 PM »
Copy - thanks.  ...ya, look at those old, bulb'ed high aspect keels of years ago.

"I also feel like the foil is faster paddling in the flat water. Like 1.5 times faster. Might be in my head as I would never imagine this before foiling. I have a made up theory that the wing is creating lift at any forward movement, ever so slightly unweighting the entire vessel."   

Red, I betcha your theory is more than a notion. It might be an interesting test to see how tightly you could space the boundary layers of each —hull and foil— to where you had that 'paddling assist' you describe.

This whole thing reminds me of the early days of kites.  Whoopee!

Jim
 
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jondrums

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Re: Foil effect on board stability..
« Reply #6 on: January 06, 2020, 03:32:52 PM »
Such an interesting topic.  I am partway through an engineering analysis of this exact topic.  I'm not ready to post conclusive numbers yet, but here is what I am finding:
1) Adding a foil slightly REDUCES the righting-moment of the craft
     -when the board tips to one side, the foil goes the other way, adding buoyancy to the high side that wouldn't have been there without the foil.
2) Adding a foil greatly REDUCES the reaction speed necessary to stabilize the craft
     -the mast and wings have a huge moment arm and lots of viscous drag which combine to slow down any tipping motions and give the human time to react.

I have a solid model of a board with and without a wing, and am working on deriving the righting-moment in both cases. 

805StandUp

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Re: Foil effect on board stability..
« Reply #7 on: January 06, 2020, 04:04:48 PM »
Such an interesting topic.  I am partway through an engineering analysis of this exact topic.  I'm not ready to post conclusive numbers yet, but here is what I am finding:
1) Adding a foil slightly REDUCES the righting-moment of the craft
     -when the board tips to one side, the foil goes the other way, adding buoyancy to the high side that wouldn't have been there without the foil.
2) Adding a foil greatly REDUCES the reaction speed necessary to stabilize the craft
     -the mast and wings have a huge moment arm and lots of viscous drag which combine to slow down any tipping motions and give the human time to react.

I have a solid model of a board with and without a wing, and am working on deriving the righting-moment in both cases.

You actually may be onto something here... I would add: 1) the chord of the mast does add some level of resistance towards the initial tip; 2) the reduced reaction speed required enables the user to ride a narrower board with the foil than without and 3) when moving back to a regular SUP after foiling for a long time, our timing is completely off given the reaction speed differences.

clay

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Re: Foil effect on board stability..
« Reply #8 on: January 06, 2020, 04:36:09 PM »
What Dave said.  Getting back on a regular sup feels so twitchy.

I remember the foil being disorienting in confused seas, as in the foil is being moved or held by different currents.swell than the board on the surface.  Took me a bit to get used to this.  And secondary stability - can recover from being dang near vertical, just hang there for a second or literally push oneself back up with the paddle.  I have found in really rough water the foil adds ridiculous amounts of stability, especially given we foilers are on much smaller boards.
Aloha, I welcome and appreciate all responses of positivity and good feeling.

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Wetstuff

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Re: Foil effect on board stability..
« Reply #9 on: January 07, 2020, 07:19:24 AM »
JD...

"when the board tips to one side, the foil goes the other way, adding buoyancy to the high side that wouldn't have been there without the foil."

So, that would say, perhaps: bigger, clunkier, heavier, foil rig would be better to learn on, i.e., more stable.  Maybe if I got a metal mast it might make sense, rather than foam it to keep water out, drill it top/bottom to gain temporary ballast.  (at 8lbs/gal. it's not that much..)

"the mast and wings have a huge moment arm and lots of viscous drag which combine to slow down any tipping motions and give the human time to react."

That's the one I like the best!  The longer the mast - the bigger the effect. 

Clay... Twitch-n-Pitch has killed me. Our local shorebreak typically offers a three-swell entre with wind for an appetizer.  The people who make actual-dawn-patrol are the winners around here. I don't think I heard of a single, manageable, reform wave session here this past summer.

Can't wait.

Jim



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frenchfoiler

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Re: Foil effect on board stability..
« Reply #10 on: January 07, 2020, 08:19:46 AM »
A stiff mast also makes a big difference, the stiffer the mast, the more stability you get.

JEG

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Re: Foil effect on board stability..
« Reply #11 on: January 07, 2020, 12:53:22 PM »
A stiff mast also makes a big difference, the stiffer the mast, the more stability you get.

and bigger wings also add stability but add some drag, some find a compromise 

Wetstuff

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Re: Foil effect on board stability..
« Reply #12 on: January 08, 2020, 09:46:09 AM »
Back to red's point about; "faster in flat on the water"  ...here's a clip of a 'not-a-teenager' generating hull speed sufficient for takeoff - with a paddle. (not a 12M kite or windsurf sail in 20kts) He possesses strength and a great CV system.

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

Jim
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eastbound

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Re: Foil effect on board stability..
« Reply #13 on: January 08, 2020, 10:01:24 AM »
hey wet,

have you geared up with a foil/foilboard yet?

i think i recall youd bot a wing to eff around with on a sup--as a first step

have you taken additional plunges gear-wise?

i ask bc i might be a year behind you

still chronically thrilled with supsurfing, and little time to learn foiling--but might be i can arrange more time soon

so i watch your process with interest

and honestly, in not much more time, you and all the early adopters here will likely have many of the quirks sorted out---such that a starter kit for me and the conditions around me will be an obvious choice

fun to follow, even just as a voyeur----single-human-powered foil devices?? werent nil only like 5 years ago---amazing to see the speed with which it's developed--all grassroots hacker engineered--very cool


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JEG

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Re: Foil effect on board stability..
« Reply #14 on: January 08, 2020, 12:17:43 PM »
Back to red's point about; "faster in flat on the water"  ...here's a clip of a 'not-a-teenager' generating hull speed sufficient for takeoff - with a paddle. (not a 12M kite or windsurf sail in 20kts) He possesses strength and a great CV system.

 

Jim

thanks for posting the vid Wetstuff as my pump game not that good.

 


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