August 2006

Vol. 21, No. 8     What's this?

Fin Myths

from the August, 2006 issue of Undercurrent  

Jim Grier, a researcher in the Departmernt of Biological Sciences at North Dakota State University and a tester for ScubaLab, a team of independent testers who produce objective evaluations of scuba equipment for Scuba Diving Magazine, debunks several myths or “old dive’s tales” regarding fins:

Some types (paddle, split or others) are better in current than others.

From theory, tests and experience, this is not true. I have dived with and compared many different fins in strong ocean and river currents. Fins that do better or worse in calm water will do the same in current. It is all relative to the diver moving through the water, whether the water itself is moving or not.

Split fins require a different, narrower kick style.

A narrower kick does better for all fins, because it reduces drag due to less leg surface area against the water movement.

Split fins are not as good in alternative kicks or maneuverability as paddle fins.

The same principle applies to all performance characteristics that have been tested: it depends on which specific fins. High performance by any given set of fins for one characteristic, such as flutter kick speed, probably does not necessarily mean that the same fins are good for other characteristics.

Some fin types stir up silt more than others.

This is partially true. Assuming that one is not stirring up silt through direct contact, silt is stirred up by water movement from the fins. Most water movement comes off the ends of the fins; thus, it depends mostly on which way any fins are pointing. If the fins and the water coming off are angled toward the bottom, then they will stir up silt. However, water turbulence also rolls off the sides of fins and can stir up silt. Split fins, by directing more water backward through the split, with less spilling off the sides, create less silting from side turbulence. On the other hand, because split fins direct more water off the end of the fins (as fins are supposed to do), if they happen to be directed downward toward the silt, well . . . the first problem (directing thrust water toward the substrate) is accentuated, and as a result, greater silting can occur. So, it depends on which type of fin (split or paddle) is involved and the angle of the kick relative to the substrate.(and obviously, how close one is to the substrate).