Fin angle

[Merman Storm]

I got a fin fun tail. When I tried it, I found the fin was rather flexible. It was still quite useable, but I would prefer a stiffer fin. Fortunately, the Fin Fun tail allows removal of the fin, and the plastic inset inside the neoprene sleeve. I had some quarter inch plastic in the scrap pile, so I traced out the fin shape, cut, and sanded a new insert.
The result was useless. The neoprene cover, which is what holds my feet to the fin, was not strong enough to keep my feet in contact with the fin.
I happened to have some swim fin pockets that I rigged to attach to my Lunocet fin. I decided to see what would happen if I bolted those pockets to the quarter inch fin I had just made.
Again: useless. The fin provided some propulsion on the backstroke (fin moving from my front to my back, or upward in a normal face down swimming position), but on the forward stroke, the fin actually pulled to the rear.
The fin sits at the same angle as the soles of my feet, which is not good for propulsion. Even if I point my toes as much as I can, the soles are still at an angle of 40 degrees to horizontal while I swim. So, I decided to bend the plastic.
I clamped the front part to the worktable, heated the fold line with a torch, and made a 10 degree bend. This helped; I was actually able to swim. But it was clearly not enough. I bent it to 20 degrees, and that was quite a bit better. 30 degrees was the best of all. The picture shows the result. Also shown in the picture are the fasteners I used, the nut plate, and the flat head bolt. The nut plate goes in the fin, such that my foot touches it.
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Although I found something that worked, I’m left wondering what’s going on. Most monofins do not have a 20 to 30 degree bend, nor do mer-tails. My Lunocet fin does have a 20 degree angle built into it, between the feet and the fin. The Leaderfin Hyperfin has a 22 degree angle. But I’ve not seen that in other monofins, or in mer-tails. Most have the fin mounted parallel to the sole of the foot. Even with a flexible fin, it seems to me that you would want the fin to naturally rest at an angle parallel to the water flow when you are costing along. What am I missing here?

[MermanOliver]

The angled blades seem to be quite a recent development in high-performance monofins, at least according to the teacher who gave the monofin course last week.
You are right, keeping the blade in a straight line reduces drag enormously, but at the same time an angled blade is more difficult to manufacture. Leaderfins (I guess that was them) for example build a somewhat straight blade and give the angle by tilting the foot inside the footpocket, so the fin is literally a straight extension of the leg. But the fin costs about double the price of a Competitor, if I am right.
Furthermore an angled blade might be harder to build into a tail, and the increased performance is more than countered by the drag introduced by the rest of the tail.
And maybe the reason why there are just straight fins in tails is because no one has tried otherwise? ;) So feel free to experiment!
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[Rett]

This could solve the issue of the flukes of tails occasionally sticking up in an unrealistic fashion :D I have been eyeing the Leaderfins actually because of this, but I cant even afford a competitor really, so the Leaderfin is out of the question for the time being. Cool experiment though :D

[Dame Melusine]

Thats awesome Storm!
I was considering disassembling and bending mine, but not sure what temperature I would need...Do you think a heat gun would be enough? Also, you are using Lexan, right?

[Mermaid Aria]

After swimming with my wave monofin for almost a week straight (i just bought it last week) I noticed the plastic blade has a significant curve downwards and if i remember correctly it was pretty straight when i got it. I assume it bent that way from the water pushing it. Maybe yours had an issue because its not as flexible of a plastic?

[Merman Storm]

I tried a heat gun, and it was not enough. Maybe with more time, some insulation, and patience, it would have worked. I considered what I was doing to be a throw-away experiment, so I just used a propane torch. You can see the white blemish on the plastic from there it got a little too hot.
It was polycarbonate (Lexan is a trade name for polycarbonate). It requires about 140c to bend easily. For the next trial, I'll use a metal pipe, let it heat up with the heat gun, then bend the plastic in a gentle curve. I'm getting some thinner plastic so it has some flex, but not as much as the Fin Fun fin.
As far as disassembling the Fin Fun fin and bending the plastic insert: I'm not sure what kind of plastic they used. So I left it alone, and made a new fin.

More testing: I tried putting my bent fin back into the Fin Fun neoprene cover. It works better than when the original Fin Fun fin is in there, but still has issues. The neoprene cover still does not hold my feet to the fin very well. At least the cover did not look odd when it was on the bent fin. i would like to use the cover, as it provides padding between the fin and the cloth. That padding helps prevent holes if and when I have stand. I'm considering adding additional straps to better hold my feet to the fin.

[Dame Melusine]

Thanks for sharing Storm! I thin you've got the next evolution of monofins there!
Mine is actually homemade with o.o93 inch lexan x 2 where I want to bend it. Its "double ply" with ridges for strenght with trimmed flippers riveted in. How thick is yours? I might try with a heat gun even if it takes longer. BTW a friend of mine who is a mutimedia artist recommends popping it right in the oven at lowest temperature. Mine is too long, but maybe for my next one... Have fun with the experimentation!

[Merman Storm]

Dame Melusine, I'm confused. When you say "double ply", did you glue the two layers together? If you did connect them together, did you do it over the entire fin, basically making one sheet that is 0.196 inches thick?
Where did the ridges come from? Did you glue them on, mold them, or what?
I used 0.25 inch plastic, as I happen to have alot sitting in my scrap pile, It is far too thick. I'm getting some thinner material.
About using an oven: Mine is far too small for a 2 foot span tail. Also: you would have to be careful to not get a bend someplace else as the fin was handled. If you lay it on a mold as it heated up, you would have to be careful that the soft plastic did not stick.

[Dame Melusine]

Merman Storm,
Thank you for the info! if yours is o.25, I may be able to manage the 0.196 with a heat gun. BTW I highly recommend the combination of 2 layers of 0.09 in at the base with a single at the end, it is strong enough for fighting waves but flexible enough for a nice tail flip! The spot where I would bend would be about 3-4 inches past the end of the foot pocket and has 2 layers of lexan glued with marine epoxy. Not sure how the epoxy would react to heat?!? I will cut the rivets out of the "ridges" of the original bifins and punch new holes in their plastic once I see how they align with the original holes in the lexan after the bend. Here is a pic of it, the white stuff is epoxy to fill in the dents in the rubber layer I made to secure the rivets to the plastic layer of the bifin ridges.
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[Merman Storm]

Thanks for the explanation.
Epoxy does not like heat, and is in fact destroyed by it. You can remove epoxy from clothing by heating it up with an iron and scraping it off. I recommend bending the plastic before gluing it together.
As for progressive flexibility: It may be the way to go, but I've been thinking about it. I think that people put that sort of flexibility into swim fins and monofins because, without the built in bend, alot of flexing is needed to get at least some part of the fin at an angle that results in propulsion. Once its bent, I think a stiffer blade will work better. When I tried my completely stiff fin, I had no propulsion until I bent it. After it had that 30 degree bend, it worked quite well, despite having virtually no flex at all. It feels quite different. The stiffness makes it move differently. An experienced monofin user might be driven nuts by it. But I'm still learning, so I'm not fighting long term muscle memory.

What I'm going to try: Place the bend right at the toes, so the fin lines up with the top of my foot. That will look nice and clean. The part of the fin just aft of the bend will be where most of the flexing takes place. The blade itself Will have little flex.

[Merman Storm]

Update: I made a new bent fin from 0.125" polycarbonate, and it worked very well. Just about the right amount of flex, maybe a bit too too much. The extra flex may actually be because I put the polycarb fin in the Fin Fun neoprene sock, the one that also holds your feet. It's stretch on the front stroke feels sort of like excessive fin flex. I'll see what I can do about that.
When I ordered the 0.125" material, I also ordered some 0.091" material, as many said that was the thickness to use for homemade monofins. But, if 0.125" is a little too flexible, 0.091 would have been way to flexible. Now I have a 2 foot square sheet of polycarb with no purpose in life.....
Why do others find 0.091" is the right thickness? I think it's because they do not put in the bend I have been using. As a result, a large amount of flex is needed to get the fin to the right angle for propulsion.

[Dame Melusine]

Thank you for sharing the info about your trials, good info for better planning such projects. Maybe stick the 0.091 to the 0.125 with di-clo or epoxy to reduce the flex a bit?

[Merman Storm]

Thank you for sharing the info about your trials, good info for better planning such projects. Maybe stick the 0.091 to the 0.125 with di-clo or epoxy to reduce the flex a bit?

Maybe, its surely a way to go. I did add an extra neoprene strap to the fin, to better hold my feet in place. It does seem to help, but I need to go to the gym to test it out in a good size pool. Tomorrow!

[Merman Storm]

The extra neoprene strap does help, but there is still a little more flex than I want. But the result is quite swim-able. I also think it looks a bit better. I don't look like I have a cookie platter stuck to my feet. The look of the tail, with the bent fin, when I wear it:
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And with the original flat fin:
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In both cases I am pointing my toes as much as I can (I'm not very flexible.)

[Dame Melusine]

Awesome!

[Sabrina the Selkie]

That looks quite nice, actually!

[Merman Andrew]

As others have said, having angled monofins is a relatively new development and therefore still catching on, some high end free diving/fin swimming monofins have started to introduce the exact angle you described (20-30 degrees), as it provides better streamlining in the water as you say. I've asked some free divers about what the difference is between a typical 0 angle monofin and an angled monofin, and they said that less angle gives more speed, greater angle gives more streamlining. Though they also think that 20-30 degrees is a good sweet spot where you still get good power and streamlining as well. Some free divers have been winning records at competitions with these new angled monofins.

[moniee]

Storm, I just found your thread after you kindly helped me out in the other thread (thanks for that!). I have to say this is a genius idea! It even looks so much better around your heels. I laughed at the cookie platter bit :D I'll study your thread a little bit more as I may just bend my 4mm lexan too!

[moniee]

I'm sorry to getting on your nerves guys - I've gotten myself into the preparations of tailmaking and I'm just trying to research as much as I can so please excuse me!

The thing I was wondering about was that how do you bolt the Lexan and the foot pockets together in a way that the end of the bolt/nut is not sticking out either way?
As I imagine, that roughly ~5mm that is the nut's height, or the bolt's head, would stick out either on the inside of the foot pockets - hurting your feet - or on the outside, at the bottom of the foot pockets - potentially piercing the silicone.

Could someone please help me with this? I do keep researching but I seem to not fulyl able to find this out.
Thank you so so so much!!!

[Delphin]

Monlee, Here's the hardware stack I'm trying:

#8 by 1 inch long flat head screw - cut to length afterward
1/4 inch flat washer
plastic
foot pocket
3/16 inch x 1 inch OD fender washer
#8 thin nut

Sorry about the english units, I'm guessing metric has better availability for you.

The screw's head nestles into the over-sized washer hole to make a very flat surface for one side. I've got 1.5 mm of screw head and washer sticking above my plastic, and 4mm of nut and washer on the foot pocket side.

Keep in mind though that I haven't done any swimming with it yet. Until proven otherwise, I'm going to keep an eye out for locally overloading my plastic or foot pocket at the screw locations.

[Merman Storm]

Go back and look at the picture of my fin and the T-nut and bolt.
The hole I drilled in the fin is big enough that the nut can fit into the hole. The T-nut sits in the fin with the nut side down, away from your foot. All you feel is the flat plate. The bolt length is chosen so it does not protrude through the nut. I got several different lengths so I could get this result. Also, some bolts I had to grind a little shorter.
On the fin side, the bolt is countersunk, so it does not protrude there either.
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[moniee]

I've just cut and sanded my lexan monofin, so I will start experimenting with your helpful ideas - thank you so much all!

[moniee]

My friend actually just got me a surprise!

http://i.ebayimg.com/00/s/NTAwWDUwMA==/$(KGrHqZ,!joFCfd+lDwkBQyLIEDRZQ~~60_12.JPG
He's ordered me these! I'll try and see if they work :)

[Dame Melusine]

Moniee, pop rivets and washers worked for me. You can see my monofin in the first page of this thread. Dont mind the white goop, i just added some epoxy where I had to dig into the fin ridge's sillicone. I would suggest you add a little drop of clear sillicone right where your screws come out to reduce metal on neoprene friction and wear and tear.

[moniee]

Thank you Dame Melusine! Your monofin looks super professional!
Unfortunately we ordered too long screws and I was told you can't cut it shorter without damaging the threading... so I got some countersunk bolts and nuts too just in case. I really need to complete the monofin so I can test it in a lake this weekend!!
Thanks so much all for your help :) :)

[Dame Melusine]

You are welcome Moniee. Good luck for the rest of your project!

[moniee]

Hey guys

So I went ahead and tried my monofin out in the pool. Bad news, it really didn't help me to swim that much - it was fine when I was stroking my legs backwards (knee bending) but when I was trying to propel forward, it would. not. doit. I could feel the material was so stiff there was not going to be any force to bend it and so I really struggled swimming in it, and had foot cramps all the way through. It basically felt I have a wooden tabletop attached to my feet.

I had the wonderful Mortisha and her partner with me though so they kindly let me swim in their Hydra monofin so I could compare the two togerher on site.

What I noticed was that the hydra was so much more flexible, when I stroked from the back to forward, it would flex soooo much, it would acrually bend and propel me in the water.

I'm thinking, have I gone for a too stiff Lexan (4mm) here? As my fluke design is fairly tiny, should I have gone for a thinner one, is it gonna solve this problem?

I'm thinking about getting either a 2mm or 3mm sheet and try again but I'm torn which one to go for. I'm also unsure on how the thin Lexan will handle holes pierced in it for the screws.

I'm not sure I should go for the heating and bending method, because it's gonna be still too stiff and I also have no access to these tools (it was a whole journey getting a jigsaw from a friend for a little while).

Any tips? :(

[Merman Storm]

4 mm is somewhat thick. My trick of bending it will give you a working monofin. Your description of that it felt like while swimming is just what I felt when I made a monofin out of 6 mm polycarbonate. I put in a 30 degree bend, and it worked. I also made a monofin for my Fin Fun tail out of 3 mm polycarbonate. It worked without the bend, but it worked much better with the bend.

[moniee]

Thank you storm. I guessed it was too thick for my design - I will try and use your method in the future -thank you so much for sharing it - but there is no chance I can get access to such tools as a flame torch or anything like that at the moment.
I went ahead and ordered 2mm polycarbonate and I'll try again with that. Since the Fin Fun is made of 2mm, and my fluke shape is even smaller than a Fin fun I have high hopes it will work...

[Dame Melusine]

Hi Moniee,
im sorry you are having a hard time. Togo with Merman Storm's suggestion, it may be worth checking at your local hardware stores if they rent the tools. Many do. Also, my fin is mostly 0.093inches or 2.36mm, and I doubled it under the foot pockets to give more strenght where the rivets are and where it would bend in the water. You can use diclo with proper instructions and safety precautions or just some epoxy glue to stick the sheets together.

[Dame Melusine]

I finally got the guts to try bending my monofin with a heat gun! This is my set-up, now letting it cool. I hope it sticks....
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[PearlieMae]

Quick answer to your question about the popularity of .093" polycarbonate is that it's the thickness readily available at Home Depot or Lowe's.

Also, be careful heating polycarbonate, it gives off cyanide gas if overheated.

[moniee]

Yeah I know they rent the tools however the cheapest rent price would be equivalent to a new monofin's price :(

I went ahead and remade the monofin from 2mm, doubling it below the footpockets and now it works like a charm, I'm so happy!

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