Fin Brainstorming

General Discussion
1

I have three fin ideas that I don’t have time to implement and test so I am throwing them out there. They probably aren’t all novel, but they are novel to me. Any DIYer can use them and any small volume on-site manufacturer for free (if they actually amount to something) but if Rainbow starts doing one I’ll take action.

I have a Ph.D. in Mechanical Engineering but I am more of a machine design guy than a fluids guy so these are all highly speculative.

  1. Twinline fins. Larger flex fin in front and smaller trailer. That is, two tandem longboard fin boxen (or a longboard box in front and a fixed mount like FCS in back). Might be loose for gentle turns but grip tighter for harder turns. Flex fin in front might give some of the thruster feel.

  2. Reflex fin (see attachment). If there are no flutter or other problems, should pull the tail down in a turn but allow flatter trim going straight.

  3. Swiveling single fin with spring preload. Only swivels/breaks away when the preload is met and then responds in a roughly linear fashion to torque on fin. Obviously, a rake fin will be required for this idea. The reasoning behind this is that gentle longboard turns look very smooth and arclike but harder turns look forced. It would be good to have a point at which the fin can break a bit to permit a tight, albeit somewhat slipped or slidden turn. Of course, flex fins permit this but the thing I don’t like about that idea is that the flex is always there, even going down the line and thus always permits some side slip. The preload would of course be adjustable by a knob or screw.

Note that I mean swiveling about an axis perpendicular to the board (the yaw axis) not about the roll asix.

2

I like idea number 3. I started to work on it a few years ago, but I conceptualized the pre-load as necessary to stop oscillations.

There’ve been a few regular posters here who’ve made dual in-line fin set-ups.

3

Yeah, same idea but it looks as though the preload on those movies is a bit low. I can see the board pivoting about a somewhat more forward point. I was envisioning setting it so that the rider could break it loose with a little extra pressure for an extra tight turn. I wouldn’t want it to break during ordinary pumping.

Thanks. I’ll look for the twin threads.

4

Lots of different pre-loads have been tried, by a substantial number of riders. The fin breaking away loosens up the rear, and lets the rider push off against an angled fin for drive. The more preload, the more it behaves like a classic single, the less preload, the looser it gets. Weight back you can turn quite tightly, but of course you cannot turn off the rail.

Anyway, as to the two in-line fins, check this

http://www.swaylocks.com/forum/gforum.cgi?post=152338;search_string=in-line%20fin;#152338

Good surfing to you.

5

I actually took the time to read this site. OK, yup, you are all done with that one

and it’s all yours!

Sorry to step on your turf…it’s the not idea so much as the implementation and

you have done it all. Nice work. I’ll scratch a line through that idea now.

BTW, I do travel to SF (to see friends) from time to time…I’ll try to remember to inform you in case you’d like to hook up, aren’t too busy, are amenable, don’t hate Floridians, etc. etc.

6

Hey TeeBird,

Glad to hear someone else is thinking alternatives. When I played with mine many years ago I had no clues as to whether it had been done before, I just had to try everything.

And that I think was an advantage. I just did my own thing, trying everything, learning what was good, and getting rid of the things that didn’t work for me, without being overly influenced by outside theories.

Don’t let my comments, or anyone elses, stop you from getting out and trying your own thing, even if it’s been done before.

It’s the self-exploration that’s the most fun, and going surfing and board design and manufacture are possibly the best combination to allow us to do that.

Take your own direction and enjoy every minute.

7
Quote:
I actually took the time to read this site. OK, yup, you are all done with that one

and it’s all yours!

Sorry to step on your turf…it’s the not idea so much as the implementation and

you have done it all. Nice work. I’ll scratch a line through that idea now.

BTW, I do travel to SF (to see friends) from time to time…I’ll try to remember to inform you in case you’d like to hook up, aren’t too busy, are amenable, don’t hate Floridians, etc. etc.

I have to warn you, if you look me up and come to SF I will be inclined to

  1. drag you out to surf

  2. equip you with a rotating fin board for that surf.

You have been warned…

I agree with Wildy - I’ve learned an enormous amount about boards and fins from my experiments, and the journey was worth as much to me as the knowledge gained.

8

Here is a fin I made that kind of combines all three of your ideas. The fin has a small amount of flex at the tip that causes the rear foil to pivot on a small pin at the base. The trailing edge of the fin moves on an axis perpendicular to the bottom of the board when the rear foil is pivoting.

The fin worked best on long walls where you could drive hard off the bottom. The more power the better. The small slot between the foils also decreased cavitation. The fin would not side slip very well when compared to a fin of same dimension but without the twin foils, slot etc. Also the down the line drive was decreased. The fin to my knowledge was never used on long boards.

The fin was produced by the Fiber Glass Fin Company in the late 70’s. Production was stopped because the fin was very difficult to produce.

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10

i’ve used a trailer on a few different single fins to prevent sliding. my theory is that a low profiled fin at the very tip of the tail will keep the board loose but will prevent sliding a little by keeping some more fin in the water when on rail.

11
Quote:
"I have three fin ideas that I don't have time to implement and test so I am throwing them out there. They probably aren't all novel, but they are novel to me. Any DIYer can use them and any small volume on-site manufacturer for free (if they actually amount to something) but if Rainbow starts doing one I'll take action".

What sort of ‘action’ were you considering? I strongly urge anyone who feels that they have a valid claim to a new invention to register that invention first. Is there a true ‘inventive’ step involved? Just talking about it here can invalidate any future claim to patent protection…

“I have a Ph.D. in Mechanical Engineering but I am more of a machine design guy than a fluids guy so these are all highly speculative”.

With all due respect, I have never seen anyone who is not a working pro board manufacturer contribute to practical board design. If one has the resources, it is much easier to experiment with the different combinations of template/rocker, fins etc. and then if one works better than the rest, work backwards and consider why?

  1. Twinline fins. Larger flex fin in front and smaller trailer. That is, two tandem longboard fin boxen (or a longboard box in front and a fixed mount like FCS in back). Might be loose for gentle turns but grip tighter for harder turns. Flex fin in front might give some of the thruster feel.

  2. Reflex fin (see attachment). If there are no flutter or other problems, should pull the tail down in a turn but allow flatter trim going straight.

“3. Swiveling single fin with spring preload. Only swivels/breaks away when the preload is met and then responds in a roughly linear fashion to torque on fin. Obviously, a rake fin will be required for this idea. The reasoning behind this is that gentle longboard turns look very smooth and arclike but harder turns look forced. It would be good to have a point at which the fin can break a bit to permit a tight, albeit somewhat slipped or slidden turn. Of course, flex fins permit this but the thing I don’t like about that idea is that the flex is always there, even going down the line and thus always permits some side slip. The preload would of course be adjustable by a knob or screw”.

I consider rail shape to be a factor in the ‘slip’ you are talking about. Hard edges can slip…

12
Quote:
Quote:

With all due respect, I have never seen anyone who is not a working pro board manufacturer contribute to practical board design. If one has the resources, it is much easier to experiment with the different combinations of template/rocker, fins etc. and then if one works better than the rest, work backwards and consider why?

really? you might wanna research that statement. pro shapers become pro shapers based on their innovations they made as a backyarder working in the shed at night. once they get rich they cant aford to deviate from their designs.

rails do effect slippage too, but ive found that the trailer fin coupled with hard edges and a concave does wonders for a single fin.

13
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With all due respect, I have never seen anyone who is not a working pro board manufacturer contribute to practical board design. If one has the resources, it is much easier to experiment with the different combinations of template/rocker, fins etc. and then if one works better than the rest, work backwards and consider why?

“really? you might wanna research that statement. pro shapers become pro shapers based on their innovations they made as a backyarder working in the shed at night. once they get rich they cant aford to deviate from their designs”.

Well, I grew up working in the factories a long time ago, before backyarders became popular. I worked alongside the guys that were shortening the boards and introducing Vs. However, I am always ready to stand corrected if you can state an example of a backyarder’s work entering mainstream design.

14

Steve Lis

15

Almady. That is awesome. Looks very close to the reflex fin idea. There’s nothing new under the sun, I guess.

CB - What part of “highly speculative” do you not understand? What part of “brainstorming”? How about a fin comment instead of a condescending remark? I said I don’t have the time to work on these. I also imply they might be worthless. If I have to have tested something to post here, what good is this forum?

“The mainstream.” Who says the mainstream is where it’s at?

Also, if I have no future basis to “take action” I really don’t care

that much. It looks like others have already had my ideas anyway.

16

Hey TeeBird,

That’s what I mean about not taking any notice of others comments. If I took everyones advice and comments on the fins I made seriously, I would have ended up a sad introvert living like a hermit.

Instead I went surfing and had a ball.

There are no ill effects from doing your own thing, as long as you live and learn. Move on and let the others squabble in your tracks.

17

You are dead right. Thanks for the attitude adjustment.

18

The Bonzer!

19

“With all due respect, I have never seen anyone who is not a working pro board manufacturer contribute to practical board design . . . . however, I am always ready to stand corrected if you can state an example of a backyarder’s work entering mainstream design.” (cb) Roy asked me to post this: “Assuming that a board design innovation is only practical if it enters mainstream design is silly.The practicality of a design depends upon what one wants from the design and whether or not it does that job. Entering the mainstream is possibly evidence that a particular design is practical, but it doesn’t follow that a design has to enter the mainstream to be practical. Laird’s foilboards are possibly an example of a backyard(?) builder producing a practical (in terms of the goal) innovation that isn’t mainstream” I wanted to say something along these lines but Roy said it more clearly.

20

I seem to have touched a nerve here…

“CB - What part of “highly speculative” do you not understand? What part of “brainstorming”? How about a fin comment instead of a condescending remark? I said I don’t have the time to work on these. I also imply they might be worthless. If I have to have tested something to post here, what good is this forum?”

Teebird, Like other experienced manufacters here, I am offering possible assistance to guys who wish to make themselves a surfboard. You may take from my comments what you wish, but they are made in good faith with the same attitude I would respond to anyone here.

“Also, if I have no future basis to “take action” I really don’t care that much. It looks like others have already had my ideas anyway”.

Patent advice can cost you 100’s of dollars an hour, and if you can learn from some else’s experience, good for you…

amaldy: “The Bonzer!”

Perhaps you are correct. I don’t know.

Dragon: “With all due respect, I have never seen anyone who is not a working pro board manufacturer contribute to practical board design . . . . however, I am always ready to stand corrected if you can state an example of a backyarder’s work entering mainstream design.” (cb) Roy asked me to post this: “Assuming that a board design innovation is only practical if it enters mainstream design is silly”.

I never said that mainstream design was necessarily where it is at. It’s just where I can see it.

“The practicality of a design depends upon what one wants from the design and whether or not it does that job”.

Enter surf conditions…

" Entering the mainstream is possibly evidence that a particular design is practical, but it doesn’t follow that a design has to enter the mainstream to be practical".

Entering the mainstream as a manufacturer however is a different matter altogether. Boards MUST work… I for one give little credence to talk. It is a huge challenge for an amateur builder to make himself a nice clean stick. It mightn’t get much attention as something radical, but to my thinking is a much harder challenge.

" Laird’s foilboards are possibly an example of a backyard(?) builder producing a practical (in terms of the goal) innovation that isn’t mainstream" I wanted to say something along these lines but Roy said it more clearly".

Hi Roy, they still don’t want to talk to you here :frowning:

I hardly consider needing a speed boat to catch a wave as practical, but great Laird footage anyway…!