Fins for diving currents?

[Kaiviti]

Even though I've never used split fins I'll hazard a guess.
I've used various types of hinging fins and these are very efficient at low speeds - exactly because the hinge translates your up & down movement into rearward thrust.
The problem comes when you have to fight a current and you start to force the fins to the point where they hinge 90 degrees and then you're using a lot of muscle for almost no thrust, ie efficiency falls off drastically.
I suspect the same thing happens with splits. At lower power levels the fin should be very efficient because the controlled amount of water coming through the split cuts down the turbulence & hence the induced drag. However as you get into higher power levels, the lack of rigidity around the split will allow excessive curving of the fin and loss of thrust area.
So coming back to the original comment above, few divers really push themselves to the limit in still water whereas a current may force you to give all you've got. Then the loss of efficiency comes into play and the fact may well be that splits are not good in currents.

Personally I gave up on flexible fins and nowadays I swear by my Avanti Quattros. Some flexibility to maintain reasonable efficiency at low power levels, but when the chips are down and I fin hard, then I feel the thrust.

You have some very valid points here. The excessive curving of the splits does in fact happen. This is very technique is extremely important. Its a lot easier to explain using pictures but i will try anyway. The flutter kick should have a very small range of motion. This will limit the excessive curving of the fin because by the time the fins starts to curve dramatically, you are already into the opposite stroke. This results in a balance. I try to limit my range of motion as much as possible. I try to keep the distance between my legs, when they are the farthest apart, to around 30 cms. I know this might sound really small but it improves the efficiency of the split dramatically.

As others have stated, many people who are used to traditional fins, panic in currents and increase their range of motion. This will dramatically reduce power in the way that you have mentioned. If anything, in a current, your range of motion should actually decrease and the speed of your kick should increase.

A good way of practising is to go out to a beach and try paddling out against the waves coming in. This will help you to optimize your kicking strokes.

 

[bradshsi]

So coming back to the original comment above, few divers really push themselves to the limit in still water whereas a current may force you to give all you've got.

I'd agree with that statement. However I don't agree with the loss of efficiency theory.

A diver in a current has to fin at a certain speed top maintain position. However from the fins hydrodynamic (or efficiency) point of view this is no different than finning at the same speed through still water.

So from the divers point of view finning @ 1 knot through still water requires the same effort as finning to hold station in a 1 knot current.

Now given the above, clearly the make of fin that gives that particular diver the best top speed will be the best for finning against any level of current. The testing I've seen suggests that on average split fins yield higher top speeds and therefore are better in a current. However all of us are different and the fin that gives you top speed isn't going to be the same as my choice.

Some good independent testing on the topic can be found here:

http://www.ndsu.nodak.edu/instruct/grier/fins.html

Personally I think the divers experience, mindset and technique contribute to the perception (not reality) that a particular type of fin is worse in current.

 

[Stu S.]

Dealers tell me that half the people who buy split fins are not satisfied. Instructors and divemasters also comment that they are not the best for currents. The split fin and those long Cressi fins are like riding a 15 speed bike in top gear. These are fun, but not practical in all situations. A good all-around fin is Tusa Tri-X. That and Mares work well in most conditions. I recently saw the show where divers were below the ice in Antarctica. They were using Mares Quattro. That says something.

 

[bradshsi]

Dealers tell me that half the people who buy split fins are not satisfied.

So conversely a lot of the people who bought paddle fins were not satisfied either. I'm not sure what the point is here other than the obvious one that fins are a very personal choice.

Instructors and divemasters also comment that they are not the best for currents.

All this tells us is that those instructors and divemasters don't have a good grasp of basic engineering principles.

The split fin and those long Cressi fins are like riding a 15 speed bike in top gear. These are fun, but not practical in all situations.

I think your analogy is off here. What you meant to say was the Cressi fins are like top gear, the split fins would be more like a low gear.

A good all-around fin is Tusa Tri-X. That and Mares work well in most conditions. I recently saw the show where divers were below the ice in Antarctica. They were using Mares Quattro. That says something.

What it says is that those divers found that those were the best fins for them. I don't see how you can extrapolate a fin used ice diving to general usage. Why would the fin be better just because it was used on an ice dive ?

 

[rescue teen]

scuba pro twin jets im 14 and purty small and there are great... i also like the ff twinspeeds

 

[hopeitsapar]

I have both split and regular, my Mares Volo are great for currents etc, if I am just out on "easy" dives, I use my splits as they are so much easier on my legs. If I am needing power then I use the Mares, a big difference in what they do.


Can anyone suggest a good fin for diving currents? I know, I know.... You are supposed to just sit back & relax in a current (aka drift dive).... But I was in the Maldives recently & was using my Atomic split fins.... Current was so strong & I felt like I had no control... Used the same fins for my Rescue class--BAD maneuver. Turned into the laughing stock during the "tired diver tow" in some swells--seemed to be kicking but going no where. (I am also very petite-- 5.2 at 93 lbs-- towing a 200 lb man, which could have been part of the problem-- when all else fails, blame the fins, ha ha.) And don't even think about frog kicking or backing up with the split fins!

Looking for a fin that gives me some power with out wearing me out after 25 yds (remember, Hotshot 200 lb dive boys-- I am petite.) Ability to frog kick & back up a plus too. What about the Apollo bios? I know they are split but maybe more power that Atomics in heavy currents?[/QUOTE]

 

[TheFoggyMask]

Can't go wrong with ScubaPro Jets...

Quoted for high truth content. Get some jet fins, steel heel strap, never think about fins again.

 

[Daylonious]

I just picked up a pair of scubapro jets on ebay, and I'm not sure what the technical term is, but the Texas term is "them boys skee-daddly like nuthin' else" in the water.

D.

 

[prittykitty]

I understand the Stu S. posting. In Florida, Blue Springs flows 100 million gallons a day. When the water's high, you have to swim against that flow to make it to the head spring. Divers with split fins often can't keep up with the others, and have to stop for a breather. You rarely see split fins "down in the hole". Some divers have both paddle fins for "the Spring", and split fins for drift dives off the coast. Mares is popular for both types of diving.

 

[Red Sea Shadow]

I dive the Red Sea all the time. Some diving spots are famous for severe currents. I have a pair of Aqua Lung Blades 2 and I'm very happy with it.