FINS: Synopsis -- details

by Jim Grier, Dept. of Biological Sciences, North Dakota State Univ., Fargo, ND, USA

The information used for calculating the ratings of the fins is shown in the table below and explained in the following paragraphs.

Because different measures of fin performance, including maximum speed, air consumption efficiency, and static thrust, are all highly correlated (for details, see the 2002 report), the average maximum speed was used as the criterion for rating. Different divers vary in their performance measures, so, to reduce variability among divers, I only used data that I personally generated myself (diver "g" in the tables). The data come from the various tests as reported on other pages in this series of reports.

Even my own measures varied over time, with a large difference between the 2002 and 2003 open water tests. As seen in the table below, the difference for fins that happened to be tested both years averaged about 0.7 mph increase for 2003. I believe that the differences were caused by a combination of using different BCs during the two years (but the same BC was used throughout each year's testing, respectively) and my improved performance from better physical condition plus experience with testing.

Ratings were standardized by comparing each fin with the Apollo bio-fin blue data from the same year, since I frequently used the Apollo blue fins on an ongoing basis, somewhat as a testing standard. During 2003, my speeds with the Apollo blue fins averaged mostly around 3.25 mph. One exception, however, was with the tests of the different Apollo bio-fins themselves, including the blue, black, and XT (see separate report page for them). All of the bio-fins, including the blue ones, seemed to do better during that set of tests, averaging about 0.1 mph higher than what I was getting from them in other tests. I'm not sure why that increase showed up, perhaps because all of the fins were so good that they somehow facilitated each other in the series and did not wear me out as usually happens when I'm testing some fins that don't perform as well. Anyway, to avoid a bias resulting from that one set of tests, I reduced the values by 0.1 for all of the bio-fin averages from that test. Thus, their relative ratings compared to each other would remain essentially the same, but they would not bias all of the other fins downward. Thus, to obtain the standardized ratings, each fin's speed was divided by 2.52 for 2002 and 3.25 for 2003. Then the 2002 and 2003 ratings were averaged to further improve the estimates (for those fins that were tested both years).

Summary data for determining the final rating for each kind of fins

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James W Grier
North Dakota State University