Fins: what I wish I’d known

by Twain

I wince when I think of the money I’ve wasted on bad gear as I was learning to dive. Maybe it’s my propensity for shiny new toys, but I’d rather blame it on a communications gap between the “technical” and recreational dive worlds.

Every year dive gear manufacturers come out with new features for their regulators, wetsuits, and BCs. There’s a good business reason for this: manufacturers need to differentiate their product and get consumers to buy more each year. It’s hard to build a business around a commoditized simple item. I suspect golf is like this too.

The irony is that diving is one of the few gear-intensive sports where the best stuff is the simplest and often cheapest. By the time you get to technical diving you know this, but meanwhile you’ve wasted a fortune on recreational junk which you could have avoided had there been a nearby technical diver to ask.

So here is the first of my “I wish I’d known that” gear posts.

Fins

Fins are important. They are how you control your movement under water: forwards, backwards, and turning. (Yes, turning – your hands are for handling gear not swimming.)

I recommend two things to consider when choosing fins. One is obvious, the other maybe not.

Fins Shape – Split or Paddle?

Oh, I wish someone had pointed this out to me before I’d started buying gear.

A very popular design these days is the “split” fin. (I used a set of these for several years.)

What split fins do well: high-rpm flutter kicking. When you flutter kick, each “leaf” twists creating a propeller-like effect. This makes it quite good for fast flutter kicks and straight-line speed tests. Sounds great, right?

However, here’s the kicker (sorry, couldn’t resist!) — you are not high-rpm flutter kicking when scuba diving!

First of all, you shouldn’t be swimming hard to begin with — if you are working hard, something is wrong. Working hard will chew through your gas if you’re on open circuit or put you at risk of carbon dioxide buildup if you’re on a rebreather. If I could drift or get pulled (scooter!) the entire dive that would be just perfect.

Second, the kick of choice for advanced diving is not a flutter kick. Flutter kicks push water downwards to cause billows of visibility-killing silt or disturb reef life. If you flutter kicked through a wreck you would likely piss off or endanger nearby divers with clouds of silt.

What split fins lack: the stiffness and body you need for frog-kicking, turning and backing up.

Frog kicking – this is the kick used by technical divers because it pushes water behind you where it won’t stir up silt. The short, sideways motion of a frog kick does nothing if you have a fin designed to be moved vertically.

Turning – you pivot your body underwater by moving your fins in small vertical circles. Doing this with a split fin makes the “leaves” of the fin flutter and inhibit the sideways foot motion, accomplishing almost nothing.

Backing up is even worse…you are trying to pull water towards yourself but your “scoop” is functioning like a fork instead of a spoon. OK, maybe a spork. You might as well be barefoot.

In summary: a split-fin shape is great for fast flutter kicking but you shouldn’t be doing that anyway. Meanwhile split fins are poor at the types of fin movements do you need.

The other main shape is a “paddle” fin. This is the fin shape used by most technical divers I know. If I had read a post like this ten years ago I would have bought a paddle fin instead of a split fin.

Paddle Fins
What this fin does well: slow, deliberate movements in any direction.

It’s very stiff, so with a frog-type kick you get a lot of power from a very small motion (contrast this from the fast motion necessary with a split fin).

Pivots are easy with the large cross-section of the edge of the fin.

Backing up is easy due to the stiffness and surface area of the body of the fin for scooping water.

What this fin does not do well: I’ve heard that some divers find it too stiff and that it causes calf cramps. I personally haven’t found this to be true, and I’ve got skinny legs, but I also try to not swim that much while diving.

In summary: in my opinion, a traditional old-school paddle fin is the best shape for scuba-diving purposes.

Fin Buoyancy – Positive, Negative, Neutral?

Fin weight occurs at one extreme of your body and therefore has a relatively large effect on your trim. Unlike shape, the best buoyancy choice for fins will vary based on the rest of your kit.

Some considerations:

Open circuit or rebreather? Open circuit rigs are usually oriented with the tank valves near the diver’s head for a slightly “head-heavy” weighting. Rebreathers usually invert their tanks so the valves are near the diver’s butt, for a “butt-heavy” weighting. So if you are diving a rebreather you may want to think twice about adding very negatively buoyant fins and making your trim even more butt-heavy.

Wetsuit or drysuit? Drysuits undergarments can cause a lot of buoyancy in the legs. In addition, if you are carrying a lot of gas in your suit, things can get ugly if your legs get above your body and the mass of air shifts to your legs and suddenly inverting you in the water. You may not need the ankle weights some drysuit divers use, but heavy negative fins are probably a good idea for drysuit diving. OK, but what if you’re both a drysuit diver and a rebreather diver, like me? Go with a neutral fin.

As an example, here are some fin buoyancy characteristics based on Scubapro’s line:

	Split Fins	Paddle Fins
Positively Buoyant	Blue/Yellow Scubapro Twin Jets	Most “recreational” fins
Neutrally Buoyant	(not sure)	OMS Slipstreams
Negatively Buoyant	Black Scubapro Twin Jets	Scubapro Jetfins

In summary: choose the fin buoyancy that will help keep your overall trim balanced and flat.

Posted in Gear, Techniques, What I wish I had known
Tags: fins, Gear, paddle fins, scuba fins, split fins
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5 Comments

Jan 13th, 2009

Tim
"paddle" fins are more commonly (at least down here) referred to as 'blade'……
The Grey ScubaPro splits are close to neutral….
Jan 15th, 2009

Sergey
Omega Aquatics Flipfins are paddle fins and also Neutrally Buoyant. http://www.Flipfins.com
Jan 17th, 2009

pocky
I was incredibly lucky to have people in person (including Twain himself) set me straight on paddle fins before I wasted money. I was also very lucky to get my dad's 30-year-old Aqua Lung Rocket Fins for free.
I'm sure there are many lurkers out there looking forward to your obviously forthcoming "I wish I'd known" article on BCs. Write it quickly before they buy what their LDS tells them to buy!
Jan 24th, 2009

John
I do a lot of shore diving where we do 500 meter or so swims to and from our descent points, and then dive in relatively light current with some surge and no overhead obstructions. I use a bent-knee flutter kick if I'm close to the silt and wouldn't trade my splits (apollos) for jet fins for anything, for these specific diving conditions. I think that using a one size fits all criterion developed by (a) crotchety old dudes that also don't believe in nitrox and computers or (b) DIR enthusiasts whose methodology is careful and soundly motivated if you're diving caves or deep wrecks, does not find the optimal solution for all divers. To be fair the splits cost a pretty penny and I tell students routinely to buy a $40 pair of paddles first and borrow someone's fancy schmancy fins later to see if they feel they're worth the premium for how they use them.
Apr 17th, 2009

Luke
I think you bring up some good points, but it is important to remember that not all things best for tech diving are best for recreational diving. As a rec inst. and avid tech diver, I use both sets of fins, and can say that is has saved my life. I use full foot split fins for reef dives. I am diving walls in a drift, and the splits are easier to kick (I do a slow gliding kick). I use paddle fins for tech dives.
A few months ago I was doing exploratory diving and the local on the boat fell asleep, I got caught in a rip and swam for 5 hours to another island. I would not have been able to swim for five hours straight in my jet fins. I got on the island broke into a house and borrowed the radio (the owner was compensated ). So just remember when you change your dive location or objective, changing some gear might help.

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