echidna's monofin speed test

[Echidna]

This is interesting. I'm thinking that dolphin kicking with bi-fins, vs a monofin, results in two differences.
First, there are some bio-mechanical differences. Your feet may be farther apart, and they are not forced to move together. How much of a difference this makes will vary from swimmer to swimmer.
Next, if the bi-fins are used to make a monofin, the hydrodynamics are different. No flow can pass between the two bi-fins.

It would be interesting to see the speed difference between bi-fins separate, and bi-fins used to make a monofin. It would also be interesting to see what happens when a monofin made from bi-fins is put into a tail. A tail can have material to left and right of the fins, material that is not well supported and will tend to move with the flow. This could add drag while not giving any improvement to propulsion. In that case, would a wider regular monofin be better than bi-fins?

alright, so we tested this today.

I only have one comparison pair so far, which was done with the same tail, a long, flowy big-fluked fabric one.
Using a pair of bifins in it, a lap took me roughly 38 seconds on average (fins without tail: 17-18 seconds).
Using a monofin in the tail (Finis Rapid), it took about 28-29 seconds.

Without a tail, the pair of bifins is about the same speed as the Rapid, but as soon as a tail is on, the Rapid was much more effective, namely almost 10 seconds faster in one lap.

Monofin + tail was also a slice faster than if I swim without fins and tail (despite the drag).
If we hadn't timed it, it probably wouldn't have been noticeable.
Again, this was with a flowy, big-fluked tail with a lot of fabric.

Edit:
and today, we did another tail with bifins in.
This tail was tighter and with a smaller, differently shaped fluke and, lo and behold, it was faster than the tail with monofin.

So there doesn't seem to be a rule of thumb, it always comes down to circumstances which combo is faster.
I still want to test a tail with the competitor in, a neoprene tail, and the snake tails.

Note also that all speed results are practically sprints.
If one would slowly but steadily swim 500m instead, a big monofin might just come out even or maybe even faster than bifins.
I just don't know until I can try it out in summer.

[suzanne86]

Any time comparisons (dolphin kicking only in all cases) with monofin only, bifins only, and bifins converted to monofin--without tail and fluke?

[Echidna]

I have all the time comparisons for fins only on my page (see OP).