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What force turns a twintip?

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sergei Scotland
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What force turns a twintip?

Postby sergei Scotland » Mon Jun 03, 2019 8:56 am

Question for someone who knows physics of TT planing:
there is not an obvious force turning TT downwind. Upwind is easy as kite rotates you upwind all the time through the hook plus any rocker does the same. On the other hand it is not obvious which physical force actually rotates board to go downwind especially during waterstart and transitions but also simple changing directions for example a carving turn downwind into toeside.
Anyone can explain? Ta!

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Re: What force turns a twintip?

Postby CaptainCore » Mon Jun 03, 2019 9:36 am

It's a simple force induced by more drag caused by foot pressure on one side of the board as the board planes over the surface of the water (which is static to all intents and purposes) Exactly the same as most board sports, snowboards on snow, windsurf boards, surf boards etc.
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Re: What force turns a twintip?

Postby sergei Scotland » Mon Jun 03, 2019 11:47 am

CaptainCore wrote:
Mon Jun 03, 2019 9:36 am
It's a simple force induced by more drag caused by foot pressure on one side of the board as the board planes over the surface of the water (which is static to all intents and purposes) Exactly the same as most board sports, snowboards on snow, windsurf boards, surf boards etc.
So to turn downwind while riding normally I need this force/drug at the back of the board, correct? More weight on the back foot to increase drag at the back of the board? Correct or wrong?

I think on a snowboard on hard snow it is opposite as to go downhill one needs more foot pressure at the front foot to allow /push front of the board to slide downhill?
May be similar to snowboard riding on powder snow - which I haven't really done. Probably different to snowboard on hard snow? May be this is what throws my TT learning off - wrong reflexes?

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Re: What force turns a twintip?

Postby rynhardt » Mon Jun 03, 2019 12:06 pm

The Force.. depends on your midichlorian count
:rollgrin:
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Re: What force turns a twintip?

Postby CaptainCore » Mon Jun 03, 2019 2:32 pm

Yes, the sidecut on snowboards is such that both front and back foot work whereas on water things, like monoski, wake and kite you tend to weight the front to increase wetted area to slow down. But it's not so much weight as angle toe pressure to bear off, heel to harden up.

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Re: What force turns a twintip?

Postby sergei Scotland » Mon Jun 03, 2019 2:55 pm

CaptainCore wrote:
Mon Jun 03, 2019 2:32 pm
on water things, like monoski, wake and kite you tend to weight the front to increase wetted area to slow down. But it's not so much weight as angle toe pressure to bear off, heel to harden up.
Weight front to slow down by going upwind, correct?
Toe pressure to flatten the board rotates it downwind? How? By removing the rocker 's push upwind?
Basically my question is : both hook pull and rocker are trying to rotate me and my board to go upwind (too much).
Which force I need to harness to counteract that?
My guess it has something to do with Fins, actually. And obviously with the fact that we always slide sidewise on the water because of the kite pull. Is it simply that front Fins are out of water when back is weighted. Or one of them anyway? May be as a beginner I could do with bigger Fins then!?

Also - loading front will increase wetted area and move the center of the lift forward. This looks like creating a rotation moment upwind, not downwind? Where do I go wrong?

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Re: What force turns a twintip?

Postby tkaraszewski » Mon Jun 03, 2019 3:57 pm

You can ignore the kite, really. A twintip turns for the same reasons a snowboard or surfboard (non-kite-powered) turns.

Essentially, when you lean into a turn and push harder on your back foot than your front foot, it pushes the back of your board farther away from you than your front foot. If you move one end of the board farther than the other end, the board will have rotated to a new direction - it turned.

To do a carving turn in most board sports you put weight and pressure over the back foot and thus it moves farther to the outside of the turn.

So to turn downwind you push the tail of the board to the upwind direction, and now the board is pointing. More downwind.
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Re: What force turns a twintip?

Postby rynhardt » Mon Jun 03, 2019 5:08 pm

sergei Scotland wrote:
Mon Jun 03, 2019 2:55 pm
Basically my question is : both hook pull and rocker are trying to rotate me and my board to go upwind (too much).
It sounds like you are fighting the fins. The further the footpad is from the fin, the more leverage the fin will have. Try widening your stance width or moving the fins closer to the footpads. Or use smaller or no fins.
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Re: What force turns a twintip?

Postby Matteo V » Mon Jun 03, 2019 5:14 pm

There 3 components to why a TT turns:

1. The moment (rotating force) applied by your body to the water AND the pull of the kite
2. Rail engagement with relationship to primarily sidecut shape (rail), and secondarily, the amount of rocker.
3. Forces from the fins via the rider induced moment, and/or the turn induced by engaging the sidecut


For #1, think about kiting along and then suddenly throwing the board sideways. This is the moment that you can apply without utilizing the sidecut/bottom shape, or the fins. This is the primary evidence for this being a distinguishable force.


For #2, a diagram of standard wakeboard sidecut vs reverse/snowboard sidecut.
Sidecut.jpg
So you can see that when you engage a rail that is curved, the average of that curve acts as a keel (not foiled). This is the primary turning force you can feel even when you do not try to induce a moment (by twisting your body), but rather lean back and to one side (don't lean back as much on a reverse/snowboard sidecut - you stay more centered).


And for #3, as a TT is turned by either #1 or #2, the fins engage at a higher and higher angle of attack (AOA) to the wind, generating more force until stall (spin out/ventilation). This helps reduce sideslip and actually adds to the turning forces which you can apply via your body or with rail engagement. Surboards rely heavily on this with larger fins as a means of turning. Smaller fins would be overpowered with the rear foot all the way back on the board, and thus the weight further back than you could achieve with a centered stance TT.

Drag, is not a primary means of turning. Though thinking of it as such does not hurt the mental approach to the issue at hand.

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Re: What force turns a twintip?

Postby Matteo V » Mon Jun 03, 2019 5:23 pm

CaptainCore wrote:
Mon Jun 03, 2019 2:32 pm
Yes, the sidecut on snowboards is such that both front and back foot work whereas on water things, like monoski, wake and kite you tend to weight the front to increase wetted area to slow down. But it's not so much weight as angle toe pressure to bear off, heel to harden up.
If this works, I definitely do not do it. Slowing down is done by heading upwind hard by engaging the rail and turning the board sideways. Front foot pressure is fun in perfectly flat water, but it is extremely stupid in chop without a highly rockered board.

Cappy, do you actually attempt to slow down in chop by weighting the front foot when the chop is more than 15cm?

In half meter waves with anything from a highly rockered wakeboard (used with a kite), to a flat surfboard with a good nose kick, is "kookicide" if you have more front foot pressure than back foot pressure.
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