Split fins?

[Blackwood]

it is impossible to claim one style of fins is better than other.

Agreed.

Chances are that one could develop successful non-silting kick style with split fins that would outperform blade fins.

How are you defining "outperform?" Seems that different people have different requirements. For example, I don't need the underwater hockey sort of movements, and I rarely need to go fast (when I do, I double-click up to my scooter's highest speed). What I do need are fins that

1. Give me feedback (I can feel them),
2. Can easily move me fully loaded (which I'll define as doubles, drysuit, multiple bottles, and maybe a stowed scooter), and
3. Are gas efficient (distance gained per gas consumed) when used with an appropriate kicking style.

When I dove split fins in Mexico I didn't like the feedback, and when I dove small blades in CA they didn't move me nearly as effectively as I'm used to. In both cases, when I switched to a flutter kick, my gas consumption spiked.

Your mileage likely varies.



But all that is really beside my initial reason for responding, which was to question the alleged fundamental difference in how these two varieties of fins work. I've read multiple claims (read: marketing lingo) about "lift" and "vortex channeling" associated with split fins, but have never been able to wrap my mind around them (hence the thread almost as long as this one I started in the equipment forum: http://www.scubaboard.com/forums/fins-masks-snorkels/325435-split-fin-physics.html). My goal there was the same as my goal here is: to clarify if they are functionally different, and if so, how. You're encouraged to contribute.

 

[elmer fudd]

I've been pondering the same thing myself, and here's my theory. I think split fins are more efficient when flutter kicking due to their flexibility and lack of resistance.

When you flutter kick a stiff paddle fin, the blades never bend more than a few degrees, so some of the energy is wasted pushing water sideways instead of propelling you forward.

With the split fins I think there are three phenomenons that aid forward movement.
1) I think the fins bend more and therefore apply more force in a forward direction. To visualize this, imagine drawing a line perpendicular to the tips of the fins. With split fins this line will be closer to being parallel to the diver and the water is being pushed more to the rear than it is to the sides. You see this same thing with freediving fins.
2) I think the split allows for less resistance at the top and bottom of the stroke making it easier and faster to proceed with the next stroke.

So far however, I think that paddle fins could be designed that would do both these things and probably do them better than splits, but...

3) I think that as the split fins are kicked, the splits separate and that the elastic nature of the forks drawing them back together also creates forward propulsion. Basically each fin makes it's own little frog kick with each stroke.

Two things that I think are utter BS though are that split fins propel you forward due to hydrofoils or vortexes.

 

[Carlos Danger]

I own several pairs in each catagory. On the full-foot side, my splits sometimes give me a blister on my right big toe, while my paddles sometimes blister the back of my left heel. In an effort to resolve this, I've been wearing a paddle on my right foot and a split on my left foot. Aside from the fact that one is blue and the other is red, there isn't really all that big of a difference. Now I'm more comfortable, and easy to spot too.

:banana:

 

[livetwodive]

My first post but I had to chime in instead of mearly lurking...

I just recently purchased a set of splits to use in addition to my old paddle fins and want to feel that I didn't waste my money on the new fins. That being said I was impressed how they held up in current in a recent dive. We had a fairly strong current and my newly certified son was with me. I said we'd just do a free decent quickly to the bottom but my son ended up having trouble equalizing. I grabbed his bc strap and started towing him and held my own against the current even with the extra drag. Eventually he equalized but I was a spent puppy by then (along with a bunch of my air). I'm curious how I would have done with my paddle fins but I'll never know, I was happy with the performance of the splits in a strong current with a lot of drag.

On the down side, as others have said alternative kicks don't work so well so I'm hanging on to the paddles for my cavern dives.