Fin variable question for Bill Barnfield...

Hi Bill -

I know you’ve done lots of experimenting with fins and fin placement. You probably know exactly where to put them when installed on one of your boards.

For many of us who aren’t sure, the adjustable boxes maybe look like a good option. I notice Robin Mair’s system allows for inserts that alter the tilt. Another system allows a pivot which changes the toe-in. I think it’s the “4 way fin co.” that features a box that allows for multiple variables to be adjusted. I think they all allow fin changes and fore and aft postioning changes.

In your opinion, which would be the one thing that you would want to be able to change in a fin set up aside from the fins themselves? (I.E. toe-in, cant or fore and aft postioning)

John,

I know you’ve addressed the question to a different Bill, but thought I’d contribute. For me the most important feature of a box system is the fore/aft adjustability, and ability to change fin size and shape.

Hi Bill -

Yes, but aren’t you one of those crusty old bisquits still riding a single fin?

Nope,

Twin Fin. Chip posted a photo of the setup some time back. Yep, crusty.

OK, sorry - I thought maybe this beauty was your daily rider…

John,

That board is a near exact copy of my 1959, 9’ 10" Windansea gun. The only time that board has been in the water was for the Velzy Memorial. The hollow stringer twin fin next to it is the daily rider, when I do go out.

You mean this one? I was only kidding about the balsa board!

John,

Yep, that’s the one. 8’ 10" X 23", to an 8" square tail.

I feel a hijack coming on! Bill, what the…

What is that hollow stringer twin? I am very courious. I was thinking when you said you preferred twins that I knew what you were talking about. But no.

Tell us more.

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Hi Bill -

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In your opinion, which would be the one thing that you would want to be able to change in a fin set up aside from the fins themselves? (I.E. toe-in, cant or fore and aft postioning)

Aloha John

1st preference in removable fin systems would be for the tilt or cant to be infinately adjustable (not common in common systems)

2nd would be the toe in (not common in common systems)

3rd would be the position. (Some smaller adjustments are currently available)

4th would be the fin size and foils. (commonly available)

We can talk about why if you like.

We can talk about why if you like.

Please… I honestly would have thought that toe-in would have been the most critical variable. Seems like if that’s off too much one way or the other that it would create a lot of drag. I couldn’t really see how cant would have as much effect but that’s why I asked.

Aloha John

There is a huge amount of interplay between all the parts, but not enough time to disect them all and it is hard to do in print no matter how fast I can type! Ha! So… We gotta assume some likely agreed details and stay on point as much as possible otherwise as is typical of swaylocks…this will quickly drift into a political discussion of where the fins are made and an environmental discussion of how those materials are made. So please everyone, lets all agree to stay on point here.

It is my opinion that he most misunderstood and under valued part of why a tri fin thruster works so well is the fact that it is flying (hydroplaning) on the fins.

In my world, a surfboard fin is primarily a keel to keep the board from sliding sideways. The amount of surface area needed to resist a particular surfers turning force will depend on many factors. Too many to detail here so again lets not go there yet.

The most important ones are how much force a surfer can exert and therefore how much fin area is needed to resist it.

Yes, I agree that different foils can effect this but lets not go there and complicate the simple dynamics until they are well laid out.

Assuming an average turn, the laying up of the board on the rail will put the inside fin at a particular angle to the horizon. (horizon is just a base line for discussion, the fin doesn’t recognize horizon it just recognizes water flowing around it) If the fin has too much tilt then it can’t “catch” against the water as effectively and won’t have as much side drift resistence as a fin with no tilt.

So we have 2 important and conflicting issues. More Tilt allows hydroplaning on the fins, creating more lift without increasing wetted surface, thereby creating more thrust and speed. But more tilt also allows the board to drift sideways losing holding power in the turns and sacrifices the thrust and speed normally generated from turns. More of one creates less of the other and visa versa. Assuming normal fins and boards, then the solution is to find the best balance between them.

The reason I would like to infinately adjust the tilt, is because for every surfer, wave, fin, and board. There will be an optimum tilt that will create the highest amount of lift from the fins and the greatest amount of thrust from the turns. All with the least amount of drag and mass from the board.

It would be so cool to catch a wave, ride it, flip the board over and click the, yet to be invented “tilt clicker”, on the finbox one click for each .5 degree of fin tilt. Within couple of waves we would be riding the ultimate tilt angle for any circumstance.

Toe in is important but 1 degree of toe in on a 6’ board is less then 1" at the nose. Someone can check this. I didn’t run the numbers on my Cray Supercomputer! Ha! But I know someone on swaylocks will and please do.

1 " of toe in is less significant then 1 degree of tilt and… I hate to go there …but the template of the board matters more than the amount of Toe in. For example if the toe in is at the nose and the board is 19" wide the effect of the toe in will be much different if the board is 20" wide which creates a much bigger fulcrum point for the board to rotate on, while the effect of the tilt will be the same. Additionally, if the tail is super wide, the Toe In angle is now increased and you may begin dragging the fin too much sideways through the water. Like I said there are so many interacting factors we have to be carefull not to stray too far off course just to say, HEY. Look!! I thought of another one!!

So assuming a reasonable template and toe in of within 1" of the nose. The board won’t drag too much and will turn easily. But too little tilt and the board will not be fast and lively. Or too much tilt and it will drift and lose power in turns.

I should note here that if you tilt the fins far enough, toe in is eliminated as it is a vertical issue that exists less and less the more toward horizontal the tilt becomes.

These problems are often “sort of” corrected by different fin templates which surely can help, but imagine if you could get the tilt right for any fin template. Then you could begin to reduce the fin sizes until you were riding on the least amount of fin but getting maximum holding power and fin lift.

Then, if you could also adjust the Toe in angle on the fly, you could get that right also.

And now, we could effectively design fin foils that might enhance all the above and we would really be on top of our game.

The 4way system could do this, though not on the fly and they only advertise a 0 degree and 4 degree disc to adjust tilt. This is not sufficient.

The ProBox only adjusts tilt in 2 degree increments. This is still not enough but much better and their system doesn’t allow adjustment of the Toe In. And you can’t adjust any of this on the fly. But their routing system is very trick and way ahead of FCS and Futures which require too much pissing around.

I didn’t rate fin placement high on my list nor fin templates because we have those adjustments already. It is not that they aren’t super important, just that we have those options in some boxes now. And where you get the tabs located on your fin sets is another way of moving the fins around. So it shouldn’t be too hard to determine where the best location is. But Tilt and Toe In. That is a real problem. And adjusting tilt or toe within the construction of the fins is a big hassle.

thanks Bill !

it’s very refreshing to see a thread on fins not containing "mumbo- jumbo , blinded me with pseudo-scientific- bullshit " stuff , at last ! One that we plebs and tinkerers can get our heads around , finally . [Hip hip hooray for written simplicity !]

keep it coming …I’m all ears ! [well, eyes , actually , on / in this mediun , eh ?!]

cheers !

ben

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Toe in is important but 1 degree of toe in on a 6’ board is less then 1" at the nose. Someone can check this. I didn’t run the numbers on my Cray Supercomputer! Ha! But I know someone on swaylocks will and please do.

1 " of toe in is less significant then 1 degree of tilt and… I hate to go there …but the template of the board matters more than the amount of Toe in.

One inch of toe-in, measured a la Barnfield, on a 72 inch long board, is just under a degree.

If set optimally, changes in toe-in of 0.5 degrees, either way, have a noticeable, but not huge, impact.

To me it is roughly equivalent to 2 degree changes in cant.

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However, for any given board, I’d prefer to be able to change the cant for wave conditions, and use the same toe-in always.

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hth.

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Yo,

And then there are fins that are twisted. The cant and toe-in changes with the fin depth. On the fins I foil the cant increases with fin depth while the toe-in decreases. Yikes! As the fin is loaded (depending fin flexibility and a surfer’s power) the cant and toe in will both increase at the tip. When I consider that it all might be expressed in numbers I project myself into an process that is far beyond me. Help!

Off to the fin shop, Rich

Right you are, Halcyon. Fins and everything involved with them are some of the least understood aspects of surfboards. Surfboards and their fins look simple, but they are not. They are complex in their own right.

Maybe not as complex as space craft that surf gravitational waves of large moving bodies moving around the universe like a sun, planets, and moons. Not to mention withstanding the temperatures encountered upon re-entry. But even there they start with a design concept, draw it, build a model, and test it. But they start with a good understanding of physics and of design. I had to say that, because I know how much Ben really appreciates it.

Here is some info on the twisted wing, reasons for it, and the effect on washout.

http://www.aerospaceweb.org/question/dynamics/q0055.shtml

Some nice answers re: toe-in and fin tilt.

Many years ago when I designed my first fin system (Surfin Systems) I was suprised by the relationship between toe in, tilt and the board’s V. I designed the toe in and tilt to be inbuilt into the flanged base of the fin itself, and what I found after experimentation was that as the fin was toed in (up across the board’s V), the tilt leant out further. In other words I was adjusting both at the same time. Interesting…