Making a monofin

[Scrounger]

Hi, new to the hobby and want to make a monofin. I have a pair of swimfins I want to turn into monofin but need advice. Im going for more of a dolphin shaped fin rather than fish. But to accomplish that i would need to pad it out a bit. I have the fins for propulsion but what material would be good for a more 3d dolphin fin shape? I have eva foam on hand as well as a few foam pool toys. Would that work or should i find something else?

[OrcaMatt]

Foam like that it's going to be way too floaty to use as a monofin. A lot of times what people end up doing with swimfins is just using the foot pocket, and making a new monofin blade with lexan.

[Merman Storm]

To give it an airfoil shape, your only real options are to make a mold and cast it in polyurethane or silicone. I would go with silicone as that will lead to making full tails.

As for the airfoil shape, I recommend the S8025 (http://airfoiltools.com/airfoil/details?airfoil=s8025-il).

[Sarah Rose]

Hey all, I have a Mahina monofin and a Mertailor Whimsy Three. I'd like to make my own vinyl insert to fill out the shape of the fluke. I saw a good how-to video, but I think the PVC plastic she uses in the video would be too flimsy to fill out the corners and edges.

Anyone have a recommendation or idea for what type / thickness of vinyl to use?

Thank you in advance!!

[Merman Storm]

I like 1/8" Polypropylene.
https://www.mcmaster.com/sheets/polypropylene-sheets-and-bars/

[Sarah Rose]

I like 1/8" Polypropylene.
https://www.mcmaster.com/sheets/polypropylene-sheets-and-bars/

@Merman Storm - And that's for a supplementary insert, right? (Since this will be used in tandem with an actual monofin.)

Thanks!

[Merman Storm]

i make complete monofins out of it. I get bi-fins, cut off the fin part to get the foot pockets, and bolt them to the polypropylene sheet. I have to use bolts as nothing glues to polypropylene well.
But you could use it as an add-on. you still need bolts, or some sort of fastener.

[Sarah Rose]

Ah. I'm looking for something that doesn't need to be bolted on. Along the lines of what's in the video below, but I'm thinking it would need to be just a little bit more sturdy than what she uses.

https://youtu.be/qGleaigUVrs

[Merman Storm]

You can always try gluing layers of vinyl together. 2 layers increases the stiffness by 8. Three layers: 27 times stiffer.
That is almost sufficiently interesting I may try it.

[Sarah Rose]

That could be worth a try, for sure. Thanks!

[Merman Storm]

One thing to consider: Vinyl is heat sensitive, and can take a set. Leave it bent in a warm environment, even a garage, and it will keep the bend. It can even slowly take a set at room temperature, given a few days.