• Stephen J. Aynsley

Split Fins or Solid Fins? - the age old question

Updated: Jan 5

Split or solid, what’s your preference? No, we're not talking about personalities here (although that would be equally as fascinating a topic!), today we’re talking about fins and the differences and benefits between the two as well as how and where to actually use them.


How does a split fin work?

I once heard an old instructor of mine say “there are two types of divers, those who love split fins and those who just don’t know how to use them” so we’ll look at some tips for proper use as well as the mechanics of how they function (when used correctly).

Split fins are difficult to mistake, for there is a large separation of the blade running down the centre creating two narrower blades. In well designed split fins we will notice that the outside framework of the fin blade is a thicker, sturdy material designed to give the fin structure and strength whereas the actual blades on the inside of this frame will be shallower/thinner to allow for them to flex and counter rotate towards the split down the centre. On the blades themselves we often find grooves or channels, which, if we look closely, are directed inwards towards the central split of the fin and down to the tip - this is beautifully evident in the Scubapro twinjet fin. These channels help direct the flow of water to emphasise the characteristics of the design which, on the downstroke, is in essence is to create a vortex (or a rotational swirling) much like the propellor of a boat as well as the natural propulsion generated form the kick cycle because a moving vortex carries with it some momentum, energy and mass thus creating extra propulsion. The upward stroke provides the least amount of drive so the split allows water to pass through the fin and the blade to more easily return to the start of the kick cycle which conserves diver energy and saves on gas consumption.


How to use a split fin.

So now we know how they are designed to work, how do we get the most out of them?

The best kick for a split fin is not about the force you apply inside the strokes, however it is about keeping the kick cycles inside the area of your body’s slipstream so it is a narrower kick than with a solid single blade fin. It should also be a faster flutter style kick, this generates lift as well as emphasises the propulsion effect created by the vortex, remember that a boat travels faster when the propellor spins faster, so for increased diver speed we need only also make those narrow flutter kicks faster, not stronger.


How does a solid, single blade fin work?

Some people use solid, single blade fins which, as the name suggests consist of one solid fin which is absent of the aforementioned ‘split’ but may still contain similar design features like ridges, grooves and vents depending on the model and/or brand. Not unlike split fins, a good solid blade fin is designed to transfer energy from your foot down through to the blade. It achieves this by channelling water to the tips of the fin increasing drive effectiveness, this is achieved by the various hinges, ridges and grooves you will notice around the blade. As well as increasing the drive effectiveness of the fin these features are also designed to release stress on joints and ligaments. Hinges are design features intended to take the pivot point of the fin away from your foot causing less strain and injury or soreness potential. These features are perfectly evident in the Scubapro Seawing Nova or the Mares Volo. Vents are often present to reduce drag and increase efficiency, the Apeks RK3 is a classic example of this. When selecting a solid fin be sure to check the flexibility of the material. Cheaper, lower end fins are often made of stiffer compound and have less elasticity so are more likely to warp out of shape and become fixed in a permanent 'arc'. The features previously mentioned in this section not only aide with propulsion and stress relief but they also help maintain the integrity of the fin structure.


How to use a solid, single blade fin.

Because this style of fin provides more power within the kick cycle, it lends itself to a fuller range within the kick. In essence, the propulsion potential is directly dependent on the strength of the kick. Simply put, the harder the diver kicks, the more propulsion is generated.


So…Split vs Solid?

In conclusion, split fins are generally considered beneficial in terms of kick efficiency, reduced gas consumption and require less physical output. For anyone prone to muscle soreness and leg cramps a switch to a split fin could prove to be the difference.

However, solid fins are more powerful and many divers argue that split fins don’t provide enough power to navigate through stronger currents, also, in more technical dives where there is an increased equipment requirement (ie, sidemount, tec diving, self-reliant diving, research diving to name a few) then solid fins would also be beneficial because they provide more powerful kicks to aide the diver in transporting any additional gear. Solid fins also allow for a diver to more effectively backfin in those instances where it is necessary and a split fin is all but useless at this particular skill.


As with everything, there is ‘the good, the bad and the ugly’, and fins are no exception. Whether you opt for open heel or full foot versions of a split or solid fin just remember performance results will vary between model and brand but at least now you might be able to more readily identify features that would benefit you. Ultimately, both types of fin will get divers where they want to be, and many divers are comfortable using both. Find the Apeks RK3 Full Fins in the SAGA Shop here: https://www.divesaga.com/product-page/apeks-rk3-fins Use coupon code insta10 for a 10% discount.

Our contributor Stephen J. Aynsley is a 4-year PADI Platinum Awarded Course Director in Utila, Honduras. Follow him on Instagram @padicoursedirectorsja or on Facebook

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