FINS: Full Foot (2003)

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

I wanted to do more testing of full foot fins during 2003 than in 2002, including some that performed good during the ScubaLab tests and some other new ones of interest. The full foot fins that I tested during 2003 were: Apollo bio-fin uni, Agua Lung Caravelle, Oceanic Caribe, Oceanic V6, ScubaPro Twin Jet Monprene black, ScubaPro Twin Speed, Tusa full foot split fin (FF-9), and the Mares Volo Race, plus I threw in the old Contempro fins (which did good in 2002) for comparison. The Aqua Lung Caravelles were modified (shortened) half way through the tests, as explained further below (after the main results and discussion). Having a new mix of fins produced some new, interesting results, including the fact that some of the new ones outperformed the few that I had tested in 2002.

There were 9 fins tested during 9 days over a period of three weeks, with at least one day for my legs to recuperate between test days, with the tests being mostly every other day plus a few other days thrown in for logistical and scheduling problems. I ran 6 fins per day, 4 runs per fin that were averaged for each trial, which required 2 tanks of air per day. Everything was randomized and balanced so that each fin was run once at each of the 6 sequence positions. The randomized and balanced design permitted an analysis of several of the factors that can affect the results.

Summaries of the results are shown below. If you’re interested in the actual, raw data, they are provided in a table at the bottom of this page or, for the spreadsheet computer file (MS Excel), click here.

It is important to note that how the results appear depend partly on the scale that you use to look at them. All of these fins are good fins and they perform perhaps more similarly to each other than if a wider mix of good and poor ones were included. Thus, at the large scale ("zoomed out") they don’t look all that different from each other. But at a closer scale ("zoomed in"), the differences become more apparent. A statistical test of the results show significant differences (P < 0.01) among the fins. However, it mostly takes good measurements and a carefully designed test to give enough resolution to bring out the differences. For all practical purposes, most divers would not be able to tell much difference between the fins in routine diving. (And that is also probably a contributing cause of some of the debate among divers as to which fin is "best." That is, it is difficult to distinguish among them on subjective grounds.)

Here is the summary, at both scales of presentation (scale, in miles per hour, on the left axis).

Large scale ("zoomed out") view. (Speed in miles per hour.)

Close scale ("zoomed in") view. (Speed in miles per hour.)

As explained above, because of the randomized and balanced design, it is possible to consider some of the confounding factors. Some of them, such as time of day and lake were not randomized and balanced, but I looked at them anyway. Briefly, using familiar hypothesis testing via analysis of variance and/or regression analysis one factor at a time, most factors were not significant, including day (P = 0.12), lake (P = 0.99 ... the results from the two different lakes where testing occurred were nearly identical, practically zero difference), and time of day (P = 0.09). Interestingly for this set of fins, the category of fin (whether paddle, split, or other) was not significant (P = 0.28)!

The difference among the particular fins was the most significant factor of all (P < 0.01). But there were also some other differences that cropped up. Considered singly, the tank (first vs second, P = 0.01), run per tank (1, 2, or 3, P = 0.04), and sequence (1 through 6, P = 0.01) were all significant, however, they are also highly correlated because they all pertain to the order of running the tests each day and, hence, are all just saying the same thing: subsequent trials get slower. In plain English, it demonstrates that the legs muscles get fatigued, which might be expected.

The different days, while not significant statistically, showed lots of variation in speeds from day to day. I think there are genuine differences and I could feel it when running the tests. Some days I felt in better condition, the water and weather were "right," and I was more into running tests, whereas other days simply weren’t as good (including toward the end, into September, and the water was getting colder). The time of day that I ran tests, while also not significant and having lots of variation, nonetheless showed a slight trend. I think I feel and do better earlier in the day and tend to slow down in general later in the day.

Examples of three of these factors are graphed below. (Sorry for the quality of the graph. The figures lost quality when I reduced them; but they aren’t worth taking the space to keep them larger. They should still be more or less legible.)

The presence of all of these various factors highlight the importance of proper design in testing. Otherwise some of these confounding factors could easily interfere with the main factor of interest, the fins, or even create false impressions. Without randomized and balanced tests, one could misinterpret results to be differences (or lack thereof) among fins when, in fact, they were caused by some other factor!

One aspect of fins that I have not yet been able to get a good grasp of yet involves the role that leg strain plays in fin performance. I tried to measure stiffness from a whole-fin standpoint in separate physical measurements of fins tested during 2002 (see the 2002 report). But those measurements didn’t reveal much. However, after experiences with fins that I consider "too stiff" and causing too much leg strain, enough that it might interfere with speed and efficiency, I tried doing subjective estimates of the strain for kicking with this set of full foot fins. I recorded my impression of strain with each set of runs, on a scale from 1 to 10 with 1 being the least, and deliberately didn’t pay attention to what I called it each time after recording it (so I could repeatedly re-estimate during subsequent runs). I found my subjective impressions to be sloppy and relative. How much strain was felt each time seemed to depend partially on the strain of the preceding fins. That is, the feeling of strain was relative, compared to the feeling of other fins just tested. Within the range of these full foots, none of which really felt like "too much" strain to me, there appears, visually, to be a trend between speed and strain (stiffness?) but, because of all the variability (and sloppiness), it is not significant (P = 0.56). The graph of speed versus strain is shown below.

One of the kinds of fins, the Aqua Lung Caravelle, a paddle fin, seemed too long. They look sort of like full foot versions of Blades but they wobbled slightly during flutter kicks and I stumbled on things while trying to wear them. However, they still seemed to have good potential, and they weren’t bad performers as they were. Out of curiosity, I wondered how they might do if shortened. So after I did three of their runs, I cut them shorter (by 3 inches). That reduced the wobble but made them feel stiffer. It didn’t affect the performance much, only slightly reducing the speed. I’m still puzzled by the role that length plays in fin performance. As seen in my 2002 tests, length seems to be only partially related to how well a fin does.

I also did several pool tests with full foot fins. Those results are being reported in a separate page.

Overall, although these fins differed significantly (statistically, plus I could tell differences based on my experience from running different fins), they were all pretty good. As can be seen in the synopsis of all fins tested both years, full foot fins on the average do much better than open heel, adjustable fins. The two groups really need to be considered separately. They tend to perform quite differently but they also have different places in scuba diving -- full foot fins can only be used with conditions that don’t require boots for thermal or physical foot protection. In those circumstances where full foot fins are appropriate, they’re great! And some are better than others.

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The actual data:

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James W Grier
North Dakota State University              

19 November 2003