Pervasive Fallacy about Split Fins

[Soggy]

I disagree. 1ft per second equals .6Kt. How many seconds would it take to swim the length of a 25 yard pool at 1Kt?

What do you disagree with? It would take 45 seconds to go 75 ft at 1 knot. Go put on your full scuba kit, go to your local pool and see how long you can keep that pace up. You can probably swim 1 knot for a reasonably decent amount of time. Now bump it up to 1.5 or 2 knots and see how long you last.

Now stick on a set of doubles, a drysuit, and a couple deco bottles and see how it works out for you.

 

[Prostar]

The US Army tried the old Oceanic split fins crossing a river with a full ruck sack. No good. Those early fins just went blub blub and went nowhere. They were ok in a calm lake.

Fast foreward a few years and I'm in St. Thomas hanging onto two 275 lb, BOBs and pulling them against the current wearing my Atomics. The boat captain gave me enough grief that I finally broke down and put my old Quatros on. I switched back after about the third dive when I blew out a buckle. It was also much less work on my poor old body. My Atomics are fast and have power.

 

[Wiggsy]

I get my gear for free - so I'm not motivated by cost or trying to convince myself that the fins I've just bought are the best. But I've tried split fins in Palau and found them heavy and ineffective - it took a long time to reach "planing speed" as such and they didn't suit my kicking style. Straight afterward I tried Mares Volo fins (the hinged type..witht he holes in the middle section.... black/yellow fellas) and found them lightweight and incredibly full of thrust. I now recommend them highly - my wife loves them diving in currents and I genuinely feel she is a safer and more more competent diver with them. I notice with the Volos that the thrust continues through the entire range (up and down) of the kicking stroke. Any other fins I've used has a "push and glide...push and glide..." effect.

Anyhow, they work for me and being lightweight is a bonus when one travels quite a bit.

 

[Splitlip]

What do you disagree with? It would take 45 seconds to go 75 ft at 1 knot. Go put on your full scuba kit, go to your local pool and see how long you can keep that pace up. You can probably swim 1 knot for a reasonably decent amount of time. Now bump it up to 1.5 or 2 knots and see how long you last.

Now stick on a set of doubles, a drysuit, and a couple deco bottles and see how it works out for you.

No thanks. I dive a single steel tank on an aluminum or steel plate. I have done 2kts with an aluminum plate without much difficulty in a 45ft pool.
I actually use both split fins and paddles (including Jets).
My only point I ever make in these threads is that splits work more effciently in a full on straught ahead flutter kick than paddles, particularly my Jets. At least for me. This I find to be especially true in current. I did my own test one day where I held my position in a pretty stiff current with my Jets for 15 seconds and then my Apollos for 15 seconds. I was felling winded and burning with the Jets, like running up stairs. With the Apollos I felt like I was running on a tread mill.
Now granted, I don't doubles nor carry stages.
Having said all that, the splits are not my favorite fins.

 

[Soggy]

No thanks. I dive a single steel tank on an aluminum or steel plate. I have done 2kts with an aluminum plate without much difficulty in a 45ft pool.

If you say so...

 

[SparticleBrane]

Scuba is a race, Soggy. Didn't you know that?

 

[djanni]

There are a few here at SB who want people to believe they'll silt up a swimming pool. Mainly, I was addressing the myth those people propagate.

No. It doesn't.

• Split fins provide more cruising thrust.
• For every action, there is an equal and opposite reaction.
• Greater cruising thrust, then, directly correlates to greater net force propelling water rearward.

I will gladly concede that split fins may provide greater cruising thrust. It naturally follows, however, that there is increased potential for silting.

It's certainly possible in many circumstances to fin along without silting regardless of the fins you're wearing, but if split fins are more efficient at moving water, they are necessarily more efficient at silting. Q.E.D.


Okay, here's an interesting idea for everyone to ponder and discuss:

• For a given amount of effort, split fins can provide more cruising thrust than paddle fins, or split fins require less effort to produce a given amount of thrust.
• When diving in inclined trim (i.e. upright or "leaning forward", as opposed to horizontal), to maintain depth while kicking, a diver must be negatively buoyant equal to the vertical component of the thrust vector. (Thrust_v = Thrust * Cos(Theta), where Theta is the inclination from horizontal)
• If the diver in inclined trim is kicking at all while maintaining constant depth, the diver must maintain constant thrust in order maintain constant depth.
• In split fins, the effort required from the inclined diver to maintain constant depth (by kicking to provide constant thrust) is significantly less than that required if paddle fins are used.
• Therefore, divers in inclined trim who are diving split fins may well have significantly less motivation to correct their inclined trim.
• Therefore, any perceived difference in the rate of silting divers between those wearing splits and those wearing paddles may be a secondary effect of the efficiency of the split fins.

In other words, could split fins simply be reducing the penalty divers would be paying for inclined trim, which results in less incentive for the divers to learn horizontal (non-silting) trim? If that is the case, it could be said that the "problem" is that the fins are too good for the inclined divers' benefit.

(In some sports, athletes train with equipment which magnifies any errors in their form. By augmenting the penalty for poor form, they force themselves into proper form and become much more skilled. Would divers learn better form by diving cumbersome fins? )

 

[Splitlip]

I am sorry guys. Did I say something wrong? Oh yeah. I am not supposed to say anything negative about Jets right?
Truthfully, I love my Jets.
Scuba is not a race but there are times I need the splits. More times than not I use a paddle. 2 kts for 15 seconds or so is not all that hard in the splits. Not so with may paddle fins, especially the Jets.

 

[SparticleBrane]

There are a few here at SB who want people to believe they'll silt up a swimming pool. Mainly, I was addressing the myth those people propagate.

I have actually been in pools where you could kick up a good amount of silt...

 

[MildlyDamp]

Sheesh! This topic has been rehashed a zillion times and generates more controversy than global warming. In fact, maybe all the hot air we're expending on it is the cause of global warming. In the immortal words of Rodney King, "Can't we just all get along?"

P.S. I switched from paddles to split fins and absolutely love them. It would be harder to take my split fins away from me than to take a carbine from Charleton Heston.