Making a mermaid tail that can be used to swim
Care must be taken when swimming with a monofin or the complete tail. With it on, you cannot quickly remove your feet if there is an issue. I prepared by watching lots of videos, and with practice. I started by first swimming without it, and just holding my legs together pretending. This built confidence in being ok with my legs stuck together.
I continued practice with just the monofin, to get used to it's affect. It was surprising how much easier it was to swim with it than it was just pretending as the amount of force possible with the monofin is quite surprising. While floating in the deep end of a pool, it only took a single kick to lift myself up a foot out of the water, something I could not have done with my legs alone. I almost wish I had switched to using the monofin earlier.
Take care with this, and have someone around just in case.
For more confidence, there are an increasing number of mermaid schools popping up around the US, so you could learn with an instructor if you'd like.
There are a number of commercial mermaid tail products out there, mostly for children. Most of them are a flat cut sheet of acrylic placed inside a neoprene sleeve. The sleep simply has sock openings. This means your feet are not firmly attached to the fin itself, and can flop around. While I've not tried this style, it seems to me like you would not be able to get nearly as much power with it, and I wouldn't bother buying this kind. I would only go with a kind that is strapped on, and has foot compartments molded into the plastic/rubber so that the fin moves firmly with you. For instance any of the FINIS monofin products are like this, and are sometimes used by divers showing the actual effectiveness of them.
There are a number of monofins with foot compartments which are already shaped like mermaid flukes, but only for children. If you are looking for something for a child, or someone who has a child sized foot, you might just go with that approach. That said, the surface area of those are much much smaller, so would not have nearly the same power.
After some research into adhesive types, I came to the conclusion that I really wanted silicone adhesive, for it's flexibility and low adhesion.(so I could remove it later) I could get 100% silicone caulk, but it uses the same curing method with moisture from the air, so wouldn't work. Purchasing a two part silicone would work, but it's expensive, and I didn't really have time for an order. I remembered that cosplayers have been using silicone caulking without this problem.
There are a couple methods for getting silicone caulk to cure without air(usually this is because it is a thick layer such as making a mold. The cornstarch method is probably most popular, but it seemed like the stickiness was lost with this. Likewise, the water and dish soap method seemed to be effectively creating a barrier between the silicone and the surface preventing adhesion. While this is perfect for making a mold, it is not helpful for using it as an adhesive. Some deeper digging resulted in the answer though, glycerin.
Mixed with 3-4 drops glycerin to 1oz 100% silicone caulk, and the result would cure quickly without exposure to air/humidity. Glycerin is available in many drug stores, usually in the beauty section sold as a skin treatment. Ideally find the bottle of liquid, and not the suppository which is probably harder to use and more expensive. For example, http://www.cvs.com/shop/beauty/skin-care/body/cvs-usp-pure-glycerin-6-oz-prodid-1015638 For the caulk, I used white because it was on clearance at the hardware store, but most people use clear.
Testing this, it did work great. I used a solo cup with it's convenient graduated markings to measure out 4oz, and put in 15 drops of glycerin. I used a plastic knife to mix it. The smell is overpoweringly terrible, so be sure to do this outside. I mixed for a couple minutes, not sure how to know if it was enough before applying it. I would recommend adding a small amount of acrylic paint(the cheap $2 paint bottles at craft stores) along with the glycerin. This way you can use the color to see when it is evenly mixed.
Using the knife to spread it on the monofin, I re-attached the plastic
I used some more to spread across the edge transition, and a scrap "credit card" the smooth that section out. I left it to cure for a bit, and repeated the process for the other side, but this time I applied it to the plastic as well, to glue both sides together.
This time, it cured perfectly. I didn't pull too hard to test because I knew the adhesion level was low, and I didn't want to pull it off. To ensure it had cured, I left the extra from each batch I mixed pushed up in a ball, which ended up about 2" diameter. Despite the thickness, it completely cured after a day, which ensured that what I put on the fin was also cured.
That inspiration video simply used standoff bolts to screw the plastic to the monofin. As can be seen in the end, it results in a bit floppy fin, with extra lumps, along with the future rusting of the washers. Instead I wanted to glue it on.
I am not 100% sold on this pattern for the fluke, so I wanted it to also be removable. The pattern I went with, pulls in, and then past the edge of the original monofin, fans out again. This was done because the monofin has an edge made for rigidity, which I did not want to remove. I did some swimming with the monofin unmodified, and the extra power is amazing, which I did not want to lose by making it more flexible. My fear was that by cutting part of the edge off, I would reduce this. So I'll try with this pattern, and if I don't like it, I can modify again later.
To do this, I hit upon the idea of using caulking as an adhesive. I started with some silicone/latex blend that I had around:
It was easy to lay down a bead, and press the parts together, as well as to smooth the transition edges:
Once I got this all on, and dry, I remembered a problem with caulk that would make this approach fail. Caulk cures using humidity in the air. This means that while the transition caulking would cure fine, the bead I layed down between the plastic and the fin would never cure. And sure enough, a day later, I pulled the plastic off, and it was still uncured.
Time for a different approach.
The plastic sheet can be difficult to find, but is available at home depot. It is in the wall paneling section as it is intended to be glued to commercial bathroom walls.
It comes in 4'x8' sheets for about $20 USD. This is the 0.060" thickness, and it does not have the fiber reinforcing, making it much more flexible. That is, you do not want the FRP version. Home Depot does carry this, but it does not appear to be on their website. Lowes carries it as well, and lists it on their website, link in the components list.
I made a copy of my tail pattern, with just the fluke part, and you can see how it will fit on the monofin:
I used pattern weights to trace it onto the plastic. I use ceramic toroids from large inductors for my pattern weights as they have a nice coating which prevents marking, good weight, and easy to pick up.
To cut the plastic, I started by using metal shears as I had both left and right curved ones. They did work, but were more awkward than I needed, and I later switched to just using utility scissors, which worked fine.
That plastic doesn't lay flat because of the re-enforcing bars on the monofin. I will adjust this by cutting slots out of the plastic to match.
Because 4 of the re-enforcing bars go pretty close to the trailing edge, I decided to trim some of the bars flush, simply using a strong wire cutters.
This results in a flush fit
As can be seen above, a small portion of the monofin protrudes out into the split in the fluke. I simply used a utility knife to cut it back a bit. The monofin is 1/8" thick, and probably HDPE, so wasn't too difficult to cut.
I repeated this process for the backside as well. Next up is to attach the plastic.
I had previously made the fabric cover for the tail, but had not modified the monofin. When initially worn, the monofin was not required as the tail was only worn for show, not actual swimming. For an upcoming event, I need to be able to swim in it, so need to complete the project.
When I originally made the cover, I planned it out for the monofin, so my pattern already took it into account. I started by pulling out the original paper pattern, the monofin, and the plastic sheeting.
This method of modifying the monofin was based on this video:
I liked some of the ideas from the video, but wanted to make some adjustments in how I did it. I am using the same monofin and plastic sheeting as shown in the videos.