Zero Cant & Toe Fins on a Sup

[supsurf-tw]

This has been beat to death for years and it comes back to having a fairly standard approach for fin toe\cant. This allows all other aspects of board design to be explored and fine tuned. You can put fins in backwards if you want and just design the rest of the board around the positive\negative aspects of doing so. You ultimately want to end up with a board that performs as intended via rocker, outline, fin setup, etc. It's the overall equation not the individual elements.

[Mungo]

So.... toe and cant equals more drag and JP boards are fast yet loose because of their fin setup.

Pish and twaddle.

[SuppaTime]

Some of the physics being tossed around here is way off base. Just an FYI.  Carry on....

[OUTSIDEWAVE]

So the question for is if this is   so good how come there aren't more manufactures and shapers doing it? I mean my custom board from King  got a greta deal of  skill in the shaping process and  the fins well  they know where they wanted them to be  and  the angle was just pointed towards the  nose which seemed fine to me  So. 
I h guess the next question will be when will we see fin box designs  with adjustable  toe  kinda similar to what  is done with snow boards   seems like it  might be very easy to do.. Think what  you could try  reverse toe?  neutral     crazy stuff.!!!!!

[PonoBill]

Cant probably doesn't generally increase drag, but toe does--at least sometimes, like when you're just going straight. When a board is turning the toe in of the outer fin reduces drag of that fin because the fin is more closely following the arc of the turn--more or less. The inside thruster drags some, but that might help quicken the turn and keep the tail planted by generating more lift towards the inside of the turn. The ideal might be to have continuously variable toe, or at least some simple turn radius compensation like ackerman in a car, but that kind of complexity isn't currently worth doing.

As with all things hydrodynamic, any reasonably accurate prediction of what a fin is doing and how to improve it for a given maneuver would require a lot of modeling. Dense medium, complex flow, lots of chaotic stuff happening. Simply saying that "an assymetric fin works this way, or a canted fin works that way" is not complete enough to even be wrong. 

Piros posits fin flex somehow driving a board forward at the end of a turn. I have a tough time with that. I can't imagine storing enough energy in a flexed fin to drive even a featherweight board and rider to any degree. I think flexing fins do things, but not that.

I've tried high aspect fins on race and downwind boards, they might reduce drag but also make the tail wag a lot, I don't think that's gaining much. they're also not much for stability. I have a modified drake fin on Little Jeeter, my 12'2" KuNalu. I left the base the stock width, narrowed the midsection and left the tip alone. It's good for stability, gives decent drive, and feels less draggy than a standard dolphin fin. I haven't measured anything, so I don't know fo0r sure, but it feels good.

[Dwight (DW)]

Lets not loose sight of lift (drag) being good and making more speed under certain conditions. Without lift from the fins in a hard turn, you won't be driving out with more speed. So lift can equal more speed at times.

Regarding swept fins, anyone who's windsurfed felt what they do instantly. Don't need tech to understand that one.

[SuppaTime]

The ideal might be to have continuously variable toe, or at least some simple turn radius compensation like ackerman in a car, but that kind of complexity isn't currently worth doing.

As with all things hydrodynamic, any reasonably accurate prediction of what a fin is doing and how to improve it for a given maneuver would require a lot of modeling. Dense medium, complex flow, lots of chaotic stuff happening. Simply saying that "an assymetric fin works this way, or a canted fin works that way" is not complete enough to even be wrong. 

Yup, I agree on that.

We need someone with the budget of an America's Cup yacht. They do some pretty impressive computational fluid dynamics and tank testing to come up with the improvements that have happened the last 20 years or so. I think the surfing problem is much harder because of the need to support a wide variety of situations. Optimizing for turning is one thing but what effect will that have on straight pocket riding? It is hard for me to imagine that any one fin configuration can work in all situations - rights, lefts, bottom turns, cut backs, pocket riding, 360's, etc.  I think JP realized the difficulty and just decided that zero toe-in is as good as some other arbitrary choice.

[Beasho]

Cant probably doesn't generally increase drag, but toe does--at least sometimes, like when you're just going straight.

Let's deal with one thing at a time.  Toe will increase drag 100% of the time no matter which direction you chose to go:  Forward, backward, Left or Right. 

Think of a race car, short of lifting up a tire toe will ADD DRAG and eventually wear off the tires.

Add Cant to Toe and you add more drag.  I ask again:  Why is drag good?

Look at the snapshot taken from above as though the board were transparent.  At the extreme you can now see what is going on:  DOWNFORCE

This starts to make sense.  The Cant is NOT LIFTING THE BOARD rather it is being used to HOLD THE BOARD TO THE WATER. 

This has been widely applied with (back to) race cars wings using more $$$ than even Larry Ellison could throw at the problem.  The benefit to race cars is tighter turns at the expense of drag.  But when you are trying to turn, and turn fast, and have 1,000 horsepower at your disposal – WHO CARES!
 
When surfing on a wave we essentially have unlimited power because we are riding downhill.  The Downforce ensures that the tail end of the board doesn't pop out of the water and essentially cause spin-out.

These influences and the drag caused are not arbitrary.  You might try adding toe and cant to your racebards to see if things get better?  Why not add a Christmas ornament to the bottom of the board, or heck a small dog.  It might work better.

Apparently JP has found something that challenges conventional (read convenient) wisdom but they claim works better.

To Piros' question "What happened when you tried it?"

[Beasho]

This reminds me of one of my favorite quotes on Scientific progress (below).

Add to Feynman's observation the benefit of crowd sourced feedback and we may not need Ellison's budget to gain meaningful insights rather a collection of people willing to try something new and report back.  Without this type of perseverance our stoke for SUP would have been similarly lost in a cacophony of naysayers and we left struggling with short boarders or angry old longboarders with ponytails.

As Richard Feynman has said, "One of the ways of stopping science would be only to do experiments where you know the law."  Physics is about probing into the unknown, and:

"what we need is imagination, but imagination in a terrible strait-jacket.  We have to find a new view of the world that has to agree with everything that is known but disagrees in its predictions somewhere, other wise it is not interesting.  And in that disagreement it must agree with nature.  If you can find any other view of the world which agrees over the entire range where things have already been observed, but disagrees somewhere else, you may have made a great discovery.  It is very nearly impossible, but not quite. . . . "

Conclusion- In Search of Schrodinger's Cat

[Beasho]

PS:  The Downforce theory should support DW's observations:

1) The fins stay in the water so that in a turn they can all be effectively 'lifting' against the turn and not letting the tail slide like an Alaia board

2) The Cant acts like a dihedral on an airplane that would result in stabilizing the board similar to a V-Hull.

[standuped]

I look at it like the wave actually has a finite amount of power and the more drag a board has the slower the board is down the line.  You can "induce" all the turning drag you need with the paddle.  It gives you the ability to configure the board for each wave, each turn, manage your energy and make the next section, avoid a close out etc. Energy management system EMS.   very similar to the Sham-Wow.

[Mungo]

There's been a fair bit written about toe and cant on various different websites/forums. I can't claim to be an expert but I understand the basics. Here's a few points to consider.

Water doesn't flow in a straight line directly underneath the board.
The direction of flow directly underneath the board is influenced by the bottom shape and the speed at which the board is travelling. The faster the board, the straighter the flow, hence why windsurf boards have minimal or zero toe (and indeed big wave guns). The claim that JPs are fast because of their fin configuration is marketing bullsh*t.
Why do I say this?
Because the biggest factor in board speed (imho) is rocker.
Because the optimal (read least drag) angle of attack for an asymmetrical fin is not 0° to the water flow (it's slightly toed in) so even if the flow was dead straight the fin angle would still be off.

My guess is that most board manufacturers do not attempt to optimise fin toe for each board. Probably because the gains are minimal over the 'educated guess' configuration.

It's generally accepted that fin setups with more toe turn better. This is true up to a point, but too much toe will slow a board down (as will not enough).
I've ridden a JP (8'10) with zero toe and found it pretty stiff in the top turn, but how much this down to the fin setup I don't know because I didn't get the opportunity to try it with toed-in fins. Bear in mind that the rocker on this board is fairly flat (it glides beautifully) and this will also affect it's ability to perform tight turns in comparison to more rockered boards.
Please don't misunderstand me. I'm not saying that the no toe-in setup can't be made to turn quickly, you only have to watch the videos above to see this is not the case. Just that initiating the turns takes a bit more effort and technique.

[standuped]

The claim that JPs are fast because of their fin configuration is marketing bullsh*t.

That's the power of the Sham-Wow.

[Sup-position]

Ok then might be worth a try.
Double Foils all around on a Thruster.
Any way you turn you will create lift..
Talk about loose...
This might be the next configuration for doing spins...

[Mungo]

Toe will increase drag 100% of the time no matter which direction you chose to go:  Forward, backward, Left or Right. 

Not really true this. It depends on the direction of water flow under the board, which as we know is not straight. Fins which have no toe-in (to the board) will actually cause more drag because they are effectively toed-out to the direction of flow.

Think of a race car, short of lifting up a tire toe will ADD DRAG and eventually wear off the tires.

Not a good example. The road is not affected by the car going over it.

Add Cant to Toe and you add more drag.  I ask again:  Why is drag good?

And cant increases drag how?

Look at the snapshot taken from above as though the board were transparent.  At the extreme you can now see what is going on:  DOWNFORCE

This starts to make sense.  The Cant is NOT LIFTING THE BOARD rather it is being used to HOLD THE BOARD TO THE WATER. 

Are you suggesting that cant increases downforce?
Downforce due to cant would only exist if there was too much toe-in, but if the toe-in was optimised to the flow of the water it wouldn't make an ounce of difference. Given the amount of cant on most boards, I doubt it would make any significant difference anyway.

This has been widely applied with (back to) race cars wings using more $$$ than even Larry Ellison could throw at the problem.  The benefit to race cars is tighter turns at the expense of drag.  But when you are trying to turn, and turn fast, and have 1,000 horsepower at your disposal – WHO CARES!
 
When surfing on a wave we essentially have unlimited power because we are riding downhill.  The Downforce ensures that the tail end of the board doesn't pop out of the water and essentially cause spin-out.

These influences and the drag caused are not arbitrary.  You might try adding toe and cant to your racebards to see if things get better?  Why not add a Christmas ornament to the bottom of the board, or heck a small dog.  It might work better.

The water flow under a displacement hulled race board is quite different from a planing hulled surf board, I would imagine. I don't think toe-in would improve performance, but who knows?. I guess is depends where the fins are placed. I can't see cant being much use in this application.

Apparently JP has found something that challenges conventional (read convenient) wisdom but they claim works better.

Maybe I'm just too cynical, but I've heard so many "claims" from the JP marketing team over the years that I've stopped listening. It would be awesome if a major player like JP were to do some significant research (signifiCANT, geddit?  ) into the effects of toe and cant, but I suspect that it's not economically viable for them to do so. There are others out there who are, though. Just not specifically for SUPs.