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 Post subject: Twisted Fins (was Progressive toein Fins)....... experiment.
PostPosted: Wed Sep 23, 2009 7:22 pm 
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So this is one for the surfboard/fin techies out there.

I have been giving waterflow under my surfboards some thought.

The waterflow as you ride tends to run seperating somewhat as it goes from the tip towards the tail of the board due to the displacement as you ride when on the plane.

For this reason surfboard have more toe-in on the side fins.

This also increases turning reactivity and stability, but it increases drag.

Now lets think of the waterflow under the board in depth.

I am convinced that an inch or just a bit more the waterflow is more parralel to the centerline.

So..... for this I have heat deformmed a set of fins so that the deeper (in the water) part of the fins run almost parrallel to the centerline of the board, while the less deep part runs more parrallel to the fin box.

The result is a fin that has less toe-in on the tips of the fins that are deeper in the water.

My theory on this is that I will get a fin setup with less drag like a twin tip fin setup, but with the same turning ability of traditional toe-in fin setup.

Any thoughts anyone.......

This weekend I'll get to try them out.

Cheers

Fred


Last edited by FredBGG on Thu Oct 01, 2009 12:08 am, edited 1 time in total.

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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Wed Sep 23, 2009 9:36 pm 
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Cool!
How did you heat them?
I have a pair of molded plastic fins I don't use that might become candidates for an experiment,,,


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Wed Sep 23, 2009 10:02 pm 
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BWD wrote:
Cool!
How did you heat them?
I have a pair of molded plastic fins I don't use that might become candidates for an experiment,,,


I used a proffesional hairdryer. paint removing heat gun would also work.

I put the fin insert into a vice and then made a sort of splint for the tip of the fin. Then using a couple of ratchet straps attached to the splint I twisted the tip around to an exact amount.
I also used a second splint half way down the fin to push the middle out just a bit so as to create a little bit of foil concave on the inside of the fin.

I'll take some photos next time I "cook" a fin.


Last edited by FredBGG on Thu Sep 24, 2009 6:11 am, edited 1 time in total.

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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Wed Sep 23, 2009 11:10 pm 
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I am not a surfer and haven't asked (yet) a surfer the purpose of the "toe-in", or if I did I didn't receive a satisfactory answer.
My theory is that when you edge (whilst surfing the wave), one of the fins is partially out of the water, so the other "deep" fin has more effect, preventing somewhat the board going away from (do you say down?) the wave. Similarly, going upwind (toe-side!) is made easier for the same reason.
Like Fred, the drag of non parallel fins bugs me. My theoretical solution :idea: to the drag problem was fins that would be allowed to self-rotate to some extent. The movement should be damped as well as limited. The direction of the water pressure would make them rotate in the right direction, whilst they always remain both (or all three for the purpose) aligned with the water flow.
Flexible fins could do just as well.
My cent. :bye:
Alex


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 12:01 am 
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Location: PASA Level III Instructor FL- OBX - MI - the world
I've been giving this some thought as well. I am by no means an expert on surfboard design and fin placement, but it's obvious that they toe in the fins for a reason.

My 5-8 rnf Lost has tri-fin with toe-in. I like the way this seems to make the board pivot. I also feel like I can sometimes get better upwind performance in light wind/marginal power by "scalloping" or doing mini "s-turns" to build board speed/apparent wind...carve up.. burn down...carve up..etc. The fins seem to propel me upwind very fast on the "carve up" phase. If I hold a straight line going upwind the board seems to bog down a little if I am not more active with it. Maybe that's just lack of experience?

When kiting many people tend to ride in a straight line more often and perhaps the toe-in is not optimal, but for turning and reaction on waves I wonder if straight fins will be a disadvantage.

I've also thought about putting a rather large swept fin in the middle and smaller fins in on the sides.

I'll be interested to hear about Freds experiments.

I imagine the answer to this dilemma is like many other things, such as a sailboat: there is not one boat design that will do everything well.

...that's why we have to have lot and lots of boards....hehehehehe 8)


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 12:22 am 
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FredBGG wrote:
So this is one for the surfboard/fin techies out there.

I have been giving waterflow under my surfboards some thought.

The waterflow as you ride tends to run seperating somewhat as it goes from the tip towards the tail of the board due to the displacement as you ride when on the plane.

For this reason surfboard have more toe-in on the side fins.

This also increases turning reactivity and stability, but it increases drag.

Now lets think of the waterflow under the board in depth.

I am convinced that an inch or just a bit more the waterflow is more parralel to the centerline.

So..... for this I have heat deformmed a set of fins so that the deeper (in the water) part of the fins run almost parrallel to the centerline of the board, while the less deep part runs more parrallel to the fin box.

The result is a fin that has less toe-in on the tips of the fins that are deeper in the water.

My theory on this is that I will get a fin setup with less drag like a twin tip fin setup, but with the same turning ability of traditional toe-in fin setup.

Any thoughts anyone.......

This weekend I'll get to try them out.

Cheers

Fred


wouldn't this make the fins have a tendency to cavitate in higher speeds and thus lose any effect of having fins?

I'd say if you want to work with movable fins check out this:
http://www.blakestah.com/fins/truckexplain.html (you might have seen it already)

For surfing smaller wave the drag definitely has a purpose. It slows you down a little on the wave. As long as it isn't too much I think it is fine....or just get a quad board. They seem to have a lot less drag. I noticed quite a big difference between different boards. :-)

Of course experimenting is fun anyway so report back.


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 2:15 am 
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tautologies wrote:
I'd say if you want to work with movable fins check out this:
http://www.blakestah.com/fins/truckexplain.html (you might have seen it already)


That looks interesting. Too bad it cannot be inserted into a standard fin box.
Know anyone who has tried it?


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 2:20 am 
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I don't know anyone who has tried them no. I am not sure of the actual benefits, but trying out new things is fun regardless :-)


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 4:23 am 
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Hein used to toe the fins in a bit on his twin tips.

He would be a great person to discuss this topic. I hope he's still here and chimes in.

Ed


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 Post subject: Re: Progressive toe-in fins....... experiment.
PostPosted: Thu Sep 24, 2009 5:02 am 
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I think thats a really sharp idea. Its like twisting a sail to have a lower AOA as it gets farther from the mast. But I also wonder if the toe is needed to make a board more lively. Very interesting to think about indeed. I'm really glad you posted the idea here so it is public domain. Hopefully you get credit if this is the next big thing.

P.S. - what ever happened to the bannana board? I'm still thinking about putting a wide round nose on one side of a spleen session. And are you still riding Zone type boards or are you gravitating more toward flotation now?


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