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Canting on fins?

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spacemonkey
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Canting on fins?

Postby spacemonkey » Fri Jun 15, 2012 10:54 am

Can someone explain the difference I should feel between racing with cant on the fins and no canting?

What does it exactly do?

ronnie
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Re: Canting on fins?

Postby ronnie » Fri Jun 15, 2012 5:24 pm

This guy can.


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ktouhey
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Re: Canting on fins?

Postby ktouhey » Fri Jun 15, 2012 5:35 pm

+1 for Paolo's explanations.

these days, I'm not sure anyone is using no-cant fins.
I think its not a matter of "do you need cant?" but more so "how much cant is right?"
You are playing in a 2degree-to-5degree range, depending on the board model and fin-maker's philosophy, to balance lift (and foiling)/drag and control, both upwind and downwind.

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Re: Canting on fins?

Postby Johnny Rotten » Sat Jun 16, 2012 5:39 am

The word LIFT as it refers to the wings on our boards (known as fins) is often times confusing and and can be misleading
Any wing has "lift" perpendicular to it's direction of travel.
a fin straight up and down moving in the water with 0 cant will produce a lifting force that acts towards the windward side of the board. To make matter less confusing Let's call this UPWIND DRIVE. This is what keeps you from sliding downwind with your board when riding it flat.
.
Add a few degrees of cant and a small component of what was your upwind drive is now acting vertically lifting the board out of the water Let's call this BOARDLIFT
BOARDLIFT = UPWIND_DRIVE@0cant x sin(cantangle). IE the two are related.
increasing cant angle increases boardlift at the expense of upwind drive.

Since you need the side fins for rotational stablity of the board, you may as well have them foil that fat board out of the water (BOARDLIFT) to reduce the HUGE drag of that big board at the expense of a small amount of upwind drive (which can easily be regained by making the fin a bit longer.)

Not enough cant and you'll be slugging that fat board through the water Too much and it'll try to fly out of the water and get blown downwind more for a given fin size at a given speed due to less upwind drive

spacemonkey
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Re: Canting on fins?

Postby spacemonkey » Sun Jun 17, 2012 10:16 am

Hey Johnny,

Really interesting...you seem to know alot about it.
So i can ask you the following: yesterday i was racing with one of the top pro from North.
I asked him about the canting, he said he compared the two and found out that the NON canted fins got him more speed, and most important that it is very much related to the rocker of the board.
He rides the north board, is this so different to other boards?

Can you explain?





Johnny Rotten wrote:The word LIFT as it refers to the wings on our boards (known as fins) is often times confusing and and can be misleading
Any wing has "lift" perpendicular to it's direction of travel.
a fin straight up and down moving in the water with 0 cant will produce a lifting force that acts towards the windward side of the board. To make matter less confusing Let's call this UPWIND DRIVE. This is what keeps you from sliding downwind with your board when riding it flat.
.
Add a few degrees of cant and a small component of what was your upwind drive is now acting vertically lifting the board out of the water Let's call this BOARDLIFT
BOARDLIFT = UPWIND_DRIVE@0cant x sin(cantangle). IE the two are related.
increasing cant angle increases boardlift at the expense of upwind drive.

Since you need the side fins for rotational stablity of the board, you may as well have them foil that fat board out of the water (BOARDLIFT) to reduce the HUGE drag of that big board at the expense of a small amount of upwind drive (which can easily be regained by making the fin a bit longer.)

Not enough cant and you'll be slugging that fat board through the water Too much and it'll try to fly out of the water and get blown downwind more for a given fin size at a given speed due to less upwind drive

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Re: Canting on fins?

Postby wdric » Sun Jun 17, 2012 11:18 am

ktouhey wrote:+1 for Paolo's explanations.
these days, I'm not sure anyone is using no-cant fins.
.


North 2012 green board with black fins dont have any cant!

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lobodomar
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Re: Canting on fins?

Postby lobodomar » Sun Jun 17, 2012 6:24 pm

According to a mail sent to me from Paolo Rista, the 2012 North board works best with 0 cant. I guess on some boards the "boardlift" is provided by just the rocker line, and in some others the bottom shape also provides all the necessary angle needed for the generation of "boardlift" through the fins without the need to cant them in the base.

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Re: Canting on fins?

Postby Johnny Rotten » Sun Jun 17, 2012 9:33 pm

Hey spacemonkey,

Super interesting, regarding the zero cant on the north board. In all honesty I have no F'n Idea...here are my thoughts....i will research more and respond with anything intelligent I find.

The rocker line will induce some board lift as does wind etc acting on the underside of the board. Depending on the amount and center of pressure of that lift (where it's located) adding some board lift from the fins may make the board quite unstable, with the likely result that the nose would want to fly up in the air. Unless you moved your foot (actually your ass...which usually requires some foot motion) farther forward than the original design intent.

In theory I would not want to use rockerline to generate much board lift in anything other than REALLY light winds as from watching videos the dynamic rocker line is all over the place in kite racing and never predictable where as the depth of fin due to it's location is much less influenced by chop etc.

There is always going to be lift associated with the rocker and maybe it's just that North has intentionally placed the center of pressure in an area to use it effectively and are then able to get away with more upwind drive from a smaller fin at zero cant with less drag. In reality I suspect they used a board design from their vast windsurfing experience and a fast windsurfing rockerline would not rely on any fin cant for lift and as a result the board behaves best with zero cant.

I have no idea if there is a drag advantage to using rocker line vs fin for board lift, only testing would tell. However I suspect a small thin aerofoil could do it more efficiently than a big fat board and with more predictability in choppy conditions.

Of course it's more the rider than the gear but an important question is ....anyone doing WELL on North race boards this year?.......

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Re: Canting on fins?

Postby Johnny Rotten » Sun Jun 17, 2012 10:03 pm

lobodomar wrote:and in some others the bottom shape also provides all the necessary angle needed for the generation of "boardlift" through the fins without the need to cant them in the base.



I think I'm missing something as I can't envison the flow/physics that make this possible....on a flat race board.

Some type of concave or funky bottom shape would have similar effect to cant but only in a small boundary layer of the board and base of the fin and would not have sufficient angles or depth(area) to generate any signicant forces through the fins. Is there a board (windsurf or other) where this an advertised design feature or known to work?

"He who knows not and knows he knows not, he is simple....teach him"

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lobodomar
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Re: Canting on fins?

Postby lobodomar » Sun Jun 17, 2012 10:52 pm

Wouldn't a 2dg (for example) V-shaped bottom at the front fins station have the same effect on the fins angle as canting them by 2dg at their base?

Regarding results, in the last pkra event 4 of the top ten used the North board (Dansin, Nocher, Ozog and Santoni).
But buyers beware, quality control at the factory in China has been :o
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