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Friday, March 11, 2016

Fins and Fin Selection

 
There are three factors to keep in mind when you are selecting a fin; the specific
design characteristics of the fin, the physical attributes particular to your body, and
operational constraints. Fins, by increasing the surface area of the foot, serve to magnify
the thrust delivered by the legs. Kicking with fins involves a forward stroke and a backward
stroke. Several examples will illustrate how the three factors interact to influence the
SEAL’s fin selection.
  • SDV operations require an operator to sit with fins on for a long period of
    time. The operator may require thermal protection and he may have a flexible
    ankle. Space is limited, so a shorter fin is necessary. For this situation, the
    operator should select a short, wide fin with a strap that can be adjusted for
    varying amounts of thermal wear.
  • Surface swimming with gear will involve a sidestroke flutterkick. In the sidestroke,
    forward is toward the front of the swimmer's body and backward is
    toward the swimmer's back. Applied force is typically much greater during
    the forward stroke, and fins are often designed with this fact in mind. When
    power is needed for both forward and backward kick, like in sidestroke, a
    straight symmetrical fin may be more efficient for you.
  • Underwater swimming involves a face down position, where the forward
    stroke is down and the backward stroke is up towards the surface of the water.
    In this position, gravity assists with the downstroke and produces a less symmetrical
    type of thrust than seen with sidestroke kick. You should select a
    high-tech diving fin with moderate flexibility and an integral type footbox.
    The fin should have an offset design to allow a more efficient transfer of propulsion
    force.