Lexan Monofin question

[Lyretail]

Does my (lexan) monofin have to be all one solid board, or can I make a custom (lexan) monofin made up of multiple sections???
(For example instead of just one large panel, make four smaller panels that would roughly be the same size of a monofin that isn't divided by sections.)

Would it work or break? (I might just end up making one ((or more versions)) to test this out myself. )

How well do solid panel mono fins hold up during spinning/twirling motions? (cork screw)
^This is mainly why I'm considering dividing the monofin into sections, I want a dramatic effect when I spin underwater.
The way I picture it in my head, if the fins are divided, instead of one big chunk, they will have more of a realistic look.
Some water currents would be pressing on a left panel, while other would be pressing on a right panel-- and if the panels aren't one big attached panel, they would extend in their respective directions better?


http://i259.photobucket.com/albums/hh298/Luna_Imbaasu/example-1.png

Any help or advice would be appreciated. (Things I know so far; Use 'u' instead of 'v' as a stress point for full panels, support at the top is required through the use of layers.)

[MerAnthony]

That would work but to start I would make the base one piece then layer the pieces on. That way there will not be a chance of the monofin breaking. When you layer with out a base you are creating weak points an you really don't want weak points.

[PearlieMae]

I've been messing with the scraps I've cut off my lexan fluke (it's ome big piece), and it is SO hard to break! I've folded long narrow pieces all the way back and forth until it breaks - and I mean completely folded! - and it takes a lot to break it! It isn't like plexiglas, it does not fracture, and I think the even if you put an acute V cut into it, I don't think it will break. I could be wrong, but a small, rounded curve could be enough.

That being said, pieces of Lexan could make a dramatic, flowing fluke, but you will be sacrificing propulsion you would get with one solid piece. If you are going to be swimming in pools or still waters like lakes, it shouldn't be an issue. Ocean swimming might be different.

I am going to use one of my cut off pieces to strengthen the center of my fluke, it's a U shaped piece, and should augment my push through the water. I am using nylon wire ties through drilled holes and PolyZap CA glue to attach the pieces.

Hope this helps!

[Lyretail]

Thank you both for the responses!



That would work but to start I would make the base one piece then layer the pieces on.

A base piece, eh? Thank you for the heads up! Do you think a half sized base could work, or would it have to be a full length base? (in comparison to the rest of the layers being used)

http://i259.photobucket.com/albums/hh298/Luna_Imbaasu/base-1.png
... I like the half sized crescent shaped base, but if that wouldn't work, it's probably just not meant to be.



That being said, pieces of Lexan could make a dramatic, flowing fluke, but you will be sacrificing propulsion you would get with one solid piece. If you are going to be swimming in pools or still waters like lakes, it shouldn't be an issue. Ocean swimming might be different.

I am going to use one of my cut off pieces to strengthen the center of my fluke, it's a U shaped piece, and should augment my push through the water. I am using nylon wire ties through drilled holes and PolyZap CA glue to attach the pieces.
That's good to know, thank you for telling me. Yes, unfortunately I wont be getting to the ocean very often; if at all. (Plenty of shallow creeks, pools and vast lakes to float around in though. Huh. There are even at least 3 different waterfalls near by too, come to think of it, Kind of makes up for the lack of ocean I guess. )

Oh really? I'd love it if you shared some progress images here. If not; that's fine too. :D

[malinghi]

I'm not sure if I understand the drawings you posted. In my experience predicting how flexible materials will deform due to their motion in the water can be pretty hard to do.

When you say you want it to bend while you're spinning, how do you want it to bend?
Here's an image to use as a reference for the monofin not under any loads to make the other drawings easier to recognize. I tried to make it look like a competitor monofin since its easier to draw.
18485

The figure below is looking at the monofin from the same perspective as figure 1c. The lines show the distribution of force while you're spinning. This is a huge oversimplification, since the drawing is 2D, and because it assumes the forces are steady, when in real life they flow over the monofin is probably changing at every moment in time, especially since the monofin is changing shape as you move through the water.
18486

Figures 3a and 3b show how I think the monofin will deflect under the loads in figure 2. Since they aren't connected in the middle, they each deflect mostly in the z direction. This is again a simplification and a guess on my part. The flow over the monofin is unsteady, the monofin is changing shape, and the whole flow is 3D, so there's a lot going on here.
18487
In 3c and 3d it shows my best guess as to what would happen if it were not split down the middle. Mostly the two flukes wouldn't bend apart so much. I'm not sure but I assumed this is the kind of bending you want the monofin to do when you spin.

If that is the way you want it to bend, I think you would want it to be stiffened in the middle and become less rigid on the sides, as depicted in figure 4a. For comparison, figure 4b shows the way monofins are typically designed to bend. I think its something like this. I'm not certain whether any of this is correct, this is just the best of my reasoning.
18488
Figure 4c shows another possible problem that could arise from this. If it was stiffened at the center and less stiff near the sides like in 4a, the monofin would bend on the sides while not swimming, giving you less power, and possibly looking weird.

Perhaps it might look better if it was stiffest near your feet, and had the stiffness decrease as shown in figure 5. Although I really don't feel very certain about any of this. What you're describing may be a pretty complicated problem.
18489

[PearlieMae]

^ :hail:

[PearlieMae]

Wow Malinghi! You are making my brain smoke!

Lyretail, I think that the way you want your fluke to flow in the water, you would be better off making a short, sturdy lexan fin and having your fluke flow long off the end of it. Know what I mean? You might be going at it the hard way.

[Miyu]

Malinghi, that last drawing you posted looks quite like a Hydra monofin - It's thicker near the footpockets, and tapers with "steps" to the end of the monofin (where it's thinnest). It's one of the two monofins I've been able to test so far (still only two monofin swim sessions under my belt, LOL), and I prefer it over the Finis I was using... neither of which were mine, just borrowed :P

[MerAnthony]

Layering your lexan to much will make the monofin stiff an not flex to well. You basicly want it to be on the thinner side towards the bottom of the fin so it will have flex an give you movement. I understand on what you are tring to do , but undstand this. To much maybe to much. It still has to flex alittle bit. You add to much an it will get heavy an not work very well.

[Lyretail]

Figures 3a and 3b show how I think the monofin will deflect under the loads in figure 2. Since they aren't connected in the middle, they each deflect mostly in the z direction. This is again a simplification and a guess on my part. The flow over the monofin is unsteady, the monofin is changing shape, and the whole flow is 3D, so there's a lot going on here.
18487
In 3c and 3d it shows my best guess as to what would happen if it were not split down the middle. Mostly the two flukes wouldn't bend apart so much. I'm not sure but I assumed this is the kind of bending you want the monofin to do when you spin.


If that is the way you want it to bend, I think you would want it to be stiffened in the middle and become less rigid on the sides, as depicted in figure 4a. For comparison, figure 4b shows the way monofins are typically designed to bend. I think its something like this. I'm not certain whether any of this is correct, this is just the best of my reasoning.
18488
Figure 4c shows another possible problem that could arise from this. If it was stiffened at the center and less stiff near the sides like in 4a, the monofin would bend on the sides while not swimming, giving you less power, and possibly looking weird.


18489
"When you say you want it to bend while you're spinning, how do you want it to bend?" ---Yes, Pretty much like how you've got it down in figure C3/3D


Wow! Thank you so much for taking the time to provide these visual aids. Your calculations look pretty good~
Also it hadn't occurred to me until I was looking at your works that, if I were to use the sectioned fins, I would basically look like a person wearing flippers with their ankles held together! :$
I much prefer the solid panel fin when you put it in this light.








Lyretail, I think that the way you want your fluke to flow in the water, you would be better off making a short, sturdy lexan fin and having your fluke flow long off the end of it. Know what I mean? You might be going at it the hard way.
You're right. I think I've been over analyzing the whole thing.
What you say makes pretty good sense!



Layering your lexan to much will make the monofin stiff an not flex to well. It still has to flex alittle bit. You add to much an it will get heavy an not work very well.
Fair points, thank you, I'll totally cut back on the layers!

[Lyretail]

Thank you, again, to everyone who has contributed so far. I appreciate the insights provided!



In light of what's been said;
I think I will scrap the sectioned layers/split-rudder concept.
I'll stick to a full one piece panel!
^-^
I'll try to cut down on my layers. (remove four of the seven)
And I'll try to keep the support/density towards the upper middle of the tail.
(So the sides and bottom are lighter)

Also ...I don't know if I fully get what a 'fluke' is... (I think it's the 'skin' you put over the monofin when its done?)
But I'll try to keep my monofin short and sturdy, with a longer fluke!

[PearlieMae]

Excellent! you're right, when I said fluke I meant the "skin" that will be going over your monofin.

[MerAnthony]

fluke 2 (flo̅o̅k)n.1. Nautical The triangular blade at the end of an arm of an anchor, designed to catch in the ground.
2. A barb or barbed head, as on an arrow or a harpoon.
3. Either of the two horizontally flattened divisions of the tail of a whale.

Thi is what a fluke is. Just to give you an idea.

[PearlieMae]

MerAnthony, you are correct!

In this instance, however, and so often in tailmaker nomenclature (vernacular?), FLUKE is used to indicate the external/ornamental tail fin, as opposed to the internal/structural monoFIN.
:rollover: