FINS: Myths
by Jim Grier, Dept. of Biological Sciences, North Dakota State Univ., Fargo, ND, USA
There are several myths or "Old Dive's Tales" regarding fins! Here are some of them:
"Some types (paddle, split, or [insert type of your choice]) are better in current than others."
From both theory and actual tests and experience, that simply is not true. I myself have dived with and compared many different fins in strong current, both ocean and river. The fins that do better or more poorly 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 of reduced drag from less leg surface area against the water movement. For actual tests proving this, for both split and paddle fins,
click here.
"Split fins are not as good in alternative kicks or maneuverability as paddle fins."
Some split fins might not do as well in alternative kicks and/or maneuverability as some paddle fins, but the reverse is also true. The same principal applies to all performance characteristics that have been tested: it depends on which specific fins one is discussing. Furthermore, any given combination of performance characteristics probably depends on which fins are involved. 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 either good or bad for other characteristics. They can only be tested to see ... and more of that needs to be done, that is, testing for combinations of performance characteristics. The ScubaLab fin testing has done some of this, as briefly reported in the tables at the ends of the reports in the July and August 2003 issues of Rodale's Scuba Diving. Those results show that performances tend to be similar among different characteristics for a given fin, but not always. The ratings published so far, however, do not provide much resolution on the issue and further testing would be useful.
Speaking subjectively at this point, not with my own hard data but partly from my personal experience as one of the ScubaLab team members in the maneuverability group plus years of routine use of both paddle and split fins, I can categorically say that neither paddles nor splits are necessarily better at alternative kicks or maneuverability. Again, it all depends on which paddle or split fins one is talking about. For me, the fins that are best in basic characteristics seem to also be excellent in alternative kicks and maneuverability. For a related issue, finning backwards, I do have some actual data (click here).
"(given type) fins stir up silt more than (another type)."
This is only partially true and the answer is somewhat complicated. Assuming that one is not stirring up silt through direct contact between the fins and the substrate, silt is stirred up by water movement from the fins. The majority of water movement is coming off the ends of the fins, thus, it depends mostly on which way they are pointing, regardless of what kind of fin is involved. If the fins and the water coming off them are angled toward the bottom, then silt will be stirred up. If instead the fins are angled more parallel to or slightly upward from the substrate, then the water will be directed away from the substrate and silt will not be stirred up, at least from water coming off the fin tips. However, there is also water turbulence that rolls off the sides of fins and this turbulence can stir up silt. Split fins, by directing more of the water backwards through the split, with less spilling off the sides, create much less silting from side turbulence (and also less drag, one of the reasons they are more efficient, all other things being equal). 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) then is accentuated and, as a result, greater silting can occur. Thus, the answer is that it depends on which type of fin (split or paddle) is involved and the angle of the kick relative to the substrate (and also, obviously, how close one is to the substrate).
