Selfmade fiberglass fins

[azapa]

here is something very non-technical and therefore aesthetic and subjective. I was recently in the water at a big event with 50 top level freedivers, only bifins were allowed. We were practicing depth and style, constant weight, to about 30m.

Looking at the plastic fin users (Cressi 3000Ld's were popular) and you really could see a stiffer, less fluid style. I have a video of nearly all 50 divers (instructors and would-be's) and watching it with my eyes half closed (standard dopey state) you can pick out the plastic fin pilots a mile away.

Between fibre and carbon, no idea. But fibre to plastic: big style and smoothness difference.

ZMagoj, if you ever do the PHD I can offer the film as material for your study

 

[Zmagoj]

ZMagoj, if you ever do the PHD I can offer the film as material for your study

Thanks, but I already work on too many projects for school and business. I got this idea after a small research through articles with SCI index. I just couldn't find a direct research about this subject.

 

[settingsteel]

Excellent thread and superb work Zmagoj...thanks for posting!

 

[spaghetti]

Excellent thread and superb work Zmagoj...thanks for posting!

Tone, amigo, any fancy to start making fins from your side? After I saw the guns and that wonderful hawaiian sling you made, I think I can expect anything from you!

 

[Zmagoj]

Excellent thread and superb work Zmagoj...thanks for posting!

Thanx.

It was a team work.
I have to thank you all who helped me with comments or encouragement thoughts. I hope you will find it useful.

 

[Zmagoj]

So here it is, the second "part 5" blade:

[ame=http://www.youtube.com/watch?v=OhR4jvB3G8k]YouTube - Making a fiberglass freediving fin -part 5_2[/ame]

And the tests:
[ame=http://www.youtube.com/watch?v=msFMqgB_fpE&feature=channel]YouTube - Testing the part 5 freediving fin[/ame]

The fin is pretty soft. Perfect for my needs/weight (60 kg), but maybe too soft for heavier divers. I would range it as a very soft (bluetec standard).

So I came to an end, I've got myself a nice pair. There are still some flaws, but aren't there always?


I will soon start another thread about monofin design, where I would also appreciate your help.

 

[settingsteel]

Tone, amigo, any fancy to start making fins from your side? After I saw the guns and that wonderful hawaiian sling you made, I think I can expect anything from you!

aha well my distant friend indeed I have been throwing the thought around for some time.....but for now stay tuned for a few guns like never seen before...yes work has slowed down so time to play again:t

 

[settingsteel]

and Zamagoj I hope never to contact you as then that would mean I'm starting to build some fins:head...anyways great job and looking forward to seeing those mono's keep us in the loop

 

[Zmagoj]

On the Slovenian forum we made some progress.

The tests of the 5-th fin show bending near the foot pocket. A friend on the forum explained that round would be the optimum curve.

I made some calculations, from which the shape of the layers could be easily extracted.

In the water, the blade is a subject to uniform load q. The blade thickness function h(x) for the round curve is h(x) = x^(2/3) as shown bellow.
From the analytic result we can extract the blueprint for laminate (eg. for 10 layers of equal thickness).

I would like to hear your comments on this!

And just to make you wander...

 

[Zmagoj]

The link to the Slovenian forum:
Fiberglass plavuti : apnea oprema - Page 2

with google translation:
Google Prevajalnik

 

[bobdonny]

Wow very impressive, I was thinking of doing some repair jobs on my fins and this gives me some great idea's Thanks!

 

[Zmagoj]

Well, I haven't heard any reply on my calculation.

There is hidden a huge simplification/mistake.

The calculation is knowna as Euler-Bernoulli equation:
[ame="http://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_equation"]Euler–Bernoulli beam equation - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Question_book-new.svg" class="image"><img alt="Question book-new.svg" src="http://upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png"@@AMEPARAM@@en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png[/ame]

the mistake is hidden in I(x), where the width of the fin (a) is assumed as to be constant, but it is not.

So it needs a minor correction. The curve a(x) can be aproximated with a root function or 2nd order polynome...when I will have time and will...

ps.
I've started a new thread in monofin section. I hope you'll find it useful.

Regards,
Zmago

 

[higiff]

Thanks Zmago you have inspired me so I have just ordered all the materials, borrowed my friends vacuum pump and have created a mold.
Once i get them i am gonna try and make a pair of bi fins, when there completed I'll upload some photos and a test report.
(materials are expected to come in next week some time, so it might be a while before i post my creations.

 

[cid]

Amazing work Zmagoj! Adding the footpocket angle, variable thickness, etc... really makes your blades identical to the current professional blades.
Now I understand how manufacturers make composite fins. It's not easy but maybe I'll experiment in a couple of months.

 

[settingsteel]

indeed quite interesting!!!! Various manufacturers use different methods of fin construction patterns to achieve the "optimal flex" and thus optimal performance per kick.

-Tapering pattern (I think easiest and most common) starts with a thicker blade at the foot pocket and gradually gets thinner towards the tip
-CrissCross pattern crosses strands of material to obtain the correct flex, probably most complicated thus most chance of error
-Computer generated Design, seems alot of manuf. are heading this way, based on lengthy data, a computer generates the ideal (that is most efficient) design for a fin to flex, thus provide optimal thrust per kick.

you can see alot of these patterns by holding the fin up to a light source

I heard of a greek manufacturer that has come up with the "perfect designed" fin his name slips my mind, I'll rack my brain to see if I come up with his name:head

Another influencing factor is the angle of the blade 20-25 degrees seems to be the "magic" range for most applications

 

[Zmagoj]

Thank you all for support.

If anyone tries it, can post an image before the actual resin infusion, so I can check if there is anything missing and maybe add some comments I forgot to mention.

It is not really important which fiberglass to chose, but if I were you I would buy
cca 280g/m2 twill cloth just for top and bottom layers, for the inner layers I would use 200g/m2 unidirectional aero glass from R&G (or similar, could be ticker - I've used 600g/m2)

If you've bought anything, as I said, it is OK.
Really looking forward.


About the blade curve
The round cure was suggested by my Slovenian spearo friend.
It doesn't mean, that the blade bends for 90° at the tip, but that it bends equally over the whole length.
If anyone has his own idea/opinion about this please share. I am moving in dark here.
The h(x) equation can be modified for any curve.

I

heard of a greek manufacturer that has come up with the "perfect designed" fin his name slips my mind, I'll rack my brain to see if I come up with his name

Please share if you find anything!

I have to say that I am really happy to see how the things are moving here.

 

[higiff]

The materials you have stated are the ones i have bought, plus i am adding a 200mg plain weave to make them a little stiffer and using one extra 200mg layer of UD to also make them stiffer and have more spring. I will be trying the distances, but not as much as you have you in your post. Only a few of the lengths will be altered with the UD in the center.
And i have got resin colour, so my fins will be red

 

[Predator_Team]

Zmagoj my friend have "Max invisible" fins made in Croatia maybe u can ask them if u have any problems about makeing your blades i`ll try to make one for me it looks very simple keep up good work

 

[Zmagoj]

Zmagoj my friend have "Max invisible" fins made in Croatia maybe u can ask them if u have any problems about makeing your blades i`ll try to make one for me it looks very simple keep up good work

Thanks for the link to the "neighbor". I checked the site located here (very interesting):
http://www.maxinvisible.com/
This is a spearo fin. Probably compression molded polycarbonate. It sufferes the same problem as my blade - uniform thickness. You can see that on the bottom image, where the blade bends near the footpocket.

I assume, the blade is good for hunters, but for energy efficient diving, the calculation I posted should be considered.

 

[cid]

hey Zmagoj,

Do you think one can make fins with only unidirectional fabric?
Or will the fin twist too much because the width of the fin is more flexible than the length of the fin?
If unidirectional fabric is more 'springy' that twill fabric, why aren't more manufacturers using unidirectional fabric?

I'm getting closer to want to start experimenting... :blackeye

Edit: I found one manufacturer that uses unidirectional fibers in their fins. Check out these HST fins at http://www.hst.gr/?page=subcategory&id=3