Benthic:
Nice rhetoric. In the passage I quoted Pendergast simply said that the physical principles that apply to airfoil and propeller design may not necessarily translate directly to the design of fins. I don't know how the heck you leapt from that to 'aerodyamically impossible.' :shakehead
Look at his results. It's right there in black and white. Paddles are more efficient than split fins. However I see that you, and many others have your minds made up. So I'll go away and quit bothering you with documented and published empirical data. Feel free to resume the objective speculation at your leisure.
Brian
I hadn't read it at first, because you hadn't mentioned any specifics, and it requires a registration to view. After your previous post I registered tonight and read it through fairly thoroughly. Have you read it Brian or did you just skim it? I can understand just skimming such a long report, but I can't understand holding something up as truth without reading it and agreeing with it.
Reference: Evaluation of fins used in underwater swimming.
Pendergast et. al. Undersea Hyperb Med. 2003 Spring;30(1):57-73.
RRR ID:
3936
Before I get started, note that the only 'paddle' that comes close to the Apollo is the Mares Attack, a full-foot free-diving fin. I thought we were talking about scuba fins. Not to mention that full foot fins compared to open heel fins will have significant performance differences. So right off the bat we're not talking apples to apples here...
I noticed a great number of internal inconsistencies, that as a member of Rubicon, perhaps you could clarify for me. I doubt you'll read through my whole post, but just skimming it gives an impression of the quality and applicability of the science.
Here are just some of the issues I've found with the report, it's conclusions, and your conclusions from the report (pretty much in order from least to most relevant):
1. There are several typos, which while aren't necessarily salient to the findings, they do speak to the 'professionalism' of the report itself. Table 3 lists Maximal Tethered Force as being measured in
Neutrons, for crying out loud! Apollo fins are referenced as Appolo fins. Table 2 is referenced as Table 3, etc.
2. While mere typos aren't that important, much more serious errors can be found. The report confuses the fins it is speaking about, referencing one when it means the other. While describing Table 5, the report writes "The Apollo fins possess the lowest Froude efficiency", however the table clearly shows the Apollo fins as possessing the highest Froude efficiency, with 72%! Later in that paragraph it states that "the Apollo (Taped) and Quattro fins each have Froude efficiencies well above 60%" The chart lists the Apollo (Taped) fins as having the lowest efficiency at 44%. This error is obvious as the inconsistency directly contradicts itself. You must ask what other results did they confuse, were these most and least efficient fins (Apollos and Apollos with duct tape) confused elsewhere?
It's not just the analysis that is inaccurate, if you look at point 4, you'll see the data itself has typographic errors as well!
So, I caught a few substantive errors in the analysis and data, because they were glaringly obvious, but one has to wonder where else is the data just incorrect?
3. The tests were done in an Annular pool. An annular pool is like a water treadmill. I'll be the first to repeat that current is relative, so it shouldn't matter, but an annular pool is circular.
As such every result was for a diver swimming in a 30m radius circle. I have no idea how it affects the results, but it does cast serious doubts about the validity or aplicability of the results to a diver swimming in a straight direction.
Further for measurements of Efficiency, Work, and Thrust both legs were assumed to be doing the same thing. Again, it's definite that when swimming a circle, the legs will be performing differently. How this affect is different for each fin is unknown to me or anybody else. This casts serious doubts on the validity of the efficiency, work, and thrust data.
4. The standard deviation of the results is often quite high. Several examples: In Table 2, for VO2 max, the average standard deviation of the results was over 28% of the mean. This value is quite high, and indicates poor reproduceability of the results (poor reproduceability = poor science). In Table 3 for aerobic velocity of Apollos the report lists the standard deviation as 114% of the velocity! Doubtless they meant "0.09m/s" instead of "0.90m/s",
but this is another glaring transcription or recording error in the data being used to draw conclusions. Let's assume the data was transcribed incorrectly, and they meant 0.09m/s, that's still 11.4% relative standard deviation. And when the difference between the top fin and the second from bottom fin is only 0.08m/s, you have to wonder how they can find it possible to draw any conclusions at all (one of their conclusions on aerobic velocity is that the top fins were 6% faster, that's half the relative standard deviation, well within the margain for error!).
5.
Average velocity measurements for all fins have different start speeds, different durations, and different accelleration of effort! Average velocity was not measured from a stop, but measured from "the slowest kick speed the diver could maintain". Further, the divers then took 20 to 40 seconds (Holy smoke 100% difference!) to accellerate their kicking to their fastest possible. They didn't take those 20 to 40 seconds to reach top speed, rather they gradually increased their effort to maximum. What does this tell you? Well it tells you that the velocity measurements are complete bunk. I can't comprehend how you can extrapolate any data out of a test like this. The diver is gradually changing his amount of effort during the run. That means that from run to run the accelleration curve of effort will be significantly different. If that accelleration curve is different, then the average velocity will be different for the same fins from run to run. Perhaps this is one of the reasons the standard deviation was so high. Had they run a test which was from a stand-still to a set distance as fast as the diver could, you could draw some conclusions, but as it is, it's useless.
I could continue pointing out curiosities and problems (take a look at how they calculated efficiency. They used 4 of the 8 fins to determine a diver's base drag and then used that for calculation for all fins), but I think my point is more than proved:
This report is questionable at best.
But wait! What if we assume that this report is perfectly scientifically valid?
Assuming the report is valid (not a great assumption), then the report's own conclusions state:
1) Apollo split fins are the most efficient of the fins tested (more efficient even than the full foot free-diving fins!)
2) Apollo split fins have a higher aerobic velocity than all other scuba fins tested.
3) Apollo split fins and the full-foot free-diving fins have better performance than the other fins tested.
Personally, I don't think any of those conclusions are actually supported by this report.
Craig
