Over the past several decades, divers mostly used what’s now referred to as paddle fins. They have a flat flexible blade that provides thrust and mobility for a scuba diver. Recently, another type of fin shape has made an appearance, and it’s shaped like a fish’s tail with a split down the center. While fish and whales were the original inspiration for the design, they encompass a wide range of fin styles. However, most have a simple split down the center.
Advantages of Split Fins
The whole purpose is to decrease the amount of energy required to kick while keeping propulsion equal or greater than the paddle fin counterpart. The split does several things. It lets water flow through the blade instead of around it. This removes the “dead” spot found on the upper part of flat bladed fins right below the foot pocket. This is an area of inefficiency because it traps water without providing any thrust. Water now flows down this area and through the split eliminating the dead zone. As water flows through the split it provides lift much the same way a plane’s wing does. The rushing water provides an area of low pressure on the back of each side of the split which sucks the diver forward. Therefore, pressure differences actually help move the diver forward instead of just his or her kicking force.
Disadvantages of Split Fins
The increased efficiency obtained by this new design is not without drawbacks. The main one being its maximum speed. Diver’s utilizing the split design cannot increase their swimming speed past a certain point. By design, the flow through design limits forward speed because it becomes less efficient as the diver makes longer and harder kicks. This is why divers normally use a high frequency low amplitude flutter kick with this fin type. It makes kicking easy, but swimming speed is relatively low. For most people using scuba gear, this is not an issue because they swim pretty slow anyway with all that gear strapped on. Free divers are a different story. They always use paddle fins because they need to get where they are going as fast as possible because they have a limited air supply. They are also very streamlined and can make use of powerful kicks to swim really fast.
Paddle Fin Advantages
The paddle shape is a proven design, and it consists of a flat flexible blade attached to a foot pocket. Many types have a full foot pocket, and other have a heel strap. The main advantages is that they can make use of wide powerful kicks very efficiently. Divers who need to swim fast to chase fish will choose the paddle shape. Free diving fins, as discussed above, are always paddle shaped, and some are very long to provide more speed. Length and stiffness of the blade contribute to speed and required kicking force. As the blade stiffness increases, it become harder to kick, but it provides more forward speed. Likewise, more flexible blades are easier to kick, but they provide less propulsion.
Paddle Fin Disadvantages
This design doesn’t have any significant drawbacks except higher required kicking force. In theory, this makes the diver work harder leading to more air consumption which shortens a dive. However, the differences are small, and divers who are exerting themselves will use more air regardless of fin blade design. It’s far more important to get a fin that’s comfortable than to go for any particular style. It’s also a matter of personal preference. Many people who get used to one blade shape are happy with that and don’t want to change.