Fins and manoeuvrability

[REVAN]

This is a prescription for suffering shallow water blackout (SWB), and if done alone could be life-threatening. Quite simply, DON'T DO THIS!

Shallow Water Blackout Prevention

SeaRat

By design, it is a prescription for a BO. It should be self explanatory to have a reliable safety in place when deliberately pushing a BO condition. But, good to say it anyway. This is an advanced freediving training technique and not something to be attempted by someone without a clue that having a BO underwater will kill you if you don't have a good safety diver shadowing your swim.

 

[John C. Ratliff]

This is a prescription for suffering shallow water blackout (SWB), and if done alone could be life-threatening. Quite simply, DON'T DO THIS!

Shallow Water Blackout Prevention

SeaRat

By design, it is a prescription for a BO. It should be self explanatory to have a reliable safety in place when deliberately pushing a BO condition. But, good to say it anyway. This is an advanced freediving training technique and not something to be attempted by someone without a clue that having a BO underwater will kill you if you don't have a good safety diver shadowing your swim.

REVAN,

I know that your profile states you own some sort of record, but realize that you are really flirting with disaster in this recommendation. "By design, it is a prescription for a BO." BO is "blackout." When you do blackout, your blood oxygen level is somewhere below about 35 mm of mercury (mm Hg) partial pressure in your blood (normal is a pO2 of somewhere around 95 mm Hg). Your brain has already been depleted of oxygen for a sustained period for this to occur. Having a "good safety diver shadowing your swim" may, or may not, get you out of your fix, as you have essentially less than a minute left for this rescue to occur. You are hanging it way out there, and completely depending upon the buddy to essentially save your life. To do this as a fin test, multiple times, is unconscionable. To recommend it to others is irresponsible, especially on ScubaBoard, which is an on-line medium where you have no idea who is reading what you write.

Take a look at the graphs I put together years ago to explain shallow water blackout (SWB). The human brain does not survive well on very low oxygen levels, and that is what you are recommending.

I have my own ideas, and have done fin tests myself in the past. But this is not a way to do these fin trails. So I repeat, DON'T DO THIS! By the way, it is the very experienced divers, such as yourself, who are most at risk to die of SWB.

SeaRat

 

[gkrane]

By design, it is a prescription for a BO. It should be self explanatory to have a reliable safety in place when deliberately pushing a BO condition. But, good to say it anyway. This is an advanced freediving training technique and not something to be attempted by someone without a clue that having a BO underwater will kill you if you don't have a good safety diver shadowing your swim.

There is no way in hell I would risk SWB to test the efficiency of a pair of fins. Someone could kill themselves in their swimming pool following this recipe. Just not even close to being worth it.

 

[danvolker]

I am thinking that this was worth discussion, more from the theoretical of how hard it is to actually test efficiency of fins...and how unlikely it would be for most scientific studies to come anywhere near a close to accurate efficiency such as revan's test would render....no one would do it, other than a few freedivers....the point being, testing of fins by a small group --scientists or print magazines, will never mean much....and this means, you need to demo fins yourself

 

[Eric Sedletzky]

The only way to test fins is for individuals to just put them on and try them. The ones that feel the best, work the best, and provide the power, win (for the individuals' current level).
Over time as the diver develops, his/her needs may change. When skill level, knowledge, and fitness (muscles for fin use) improve then a different more advanced fin may be needed. Fins aren't a mask or a BC, they are the prop that converts horsepower to thrust. A brand new diver will not be ready for the most advanced most powerful fin on the market.
Fin selection is just too complicated and subjective to generalize.
However, there are some established "knows" that can at least be a starting point for somebody wanting to explore more advanced fin technology. This thread has done a pretty good job of discussing those options.

 

[John C. Ratliff]

Eric and Dan,

There have been some very good studies, but most are rather old, on fins and work underwater. Dr. Glenn Egstrom put together an apparatus to do such measurements, and published it in the book, Human Performance and SCUBA Diving, Proceedings of the Symposium on Underwater Physiology, Scripps Institution of Oceanography, La Jolla, California, Apral 10-11, 1970. The following diagram from page 10 of this book illustrates the type of apparatus he built:



Here is some of what Dr. Egstrom published in that book:

Our early efforts measured instantaneous static thrust generated by the swimmers. Mea thrust values were compared for leg position and thrust force during sub maximal and maximal efforts using bare feet and two fin configurations. Additionally, an acceleration occurred when the legs changed direction and that the acceleration signal was reduce to near zero while the legs were crossing.

A second, more comprehensive study of fins4 has recently been conducted in which nine subjects randomly worked each of nine fins under three swimming work loads -- two measures were taken on each work load. Nearly 500 sets of measurements were taken on thrust level, kick rate, heart rate, minute volume, CO2 output, oxygen uptake, leg length, leg strength, body weight, age and water temperature. This data was then programmed for computer analysis and reviewed. A complete report is forthcoming but I should like to present a few preliminary observations ethos time.

The first observation is that there is a remarkable lack of consistency in answer to the question "which fin is best?". Individuals appear to exhibit some preferences but if the three fins which scored highest for each individual were plotted, every fin in the study would end up as "one of the top three" for at least one of the subjects. There did appear to be a tendency in favor of some of the more flexible fins for the subjects who were less experienced and in lower states of condition, but to identify any fin as "obviously superior" would be impossible. However, the reader should recognize that only top of the line fins in the extra large sizes were used in the study, and that four of the styles were of the adjustable heel strap type.

It appears that the divers with the longer legs are able to use the fins at a lower energy cost than the divers with the shorter legs. It is possible that fins should be fitted to individuals with the same care that shoes are fitted. It is hoped that criteria for this type of evaluation will be forthcoming.

A little further on in this discussion, Lt. CDR. Tommy Thompson (Ret.), Public Relations Director, U.S. Divers Association (probably U.S. Divers Company), had this to say in answer to an audience question, "Is equipment reliable?"

The gist of the question that I have there is, why do manufacturers make and promote a full line of equipment although it may not be the best. We really can't say. I can't say. Extreme can't say. You can't say. No one can say, this is the best snorkel or this is the best fin under all conditions. A snorkel that is good for Bev Morgan to swim two miles on the surface at a know and a half is no good for a kid in the swimming pool. You have to look at the over-all market. The same thing in fins. The fin that perhaps will give you the best thrust would not be suitable for a youngster in the pool. manufacturers, of course, have to look at it to try to cover all the bases, have anything that anyone wants to buy as long as its safe. Now, I won't say a snorkel that has a eighth-inch bore to it is safe for a professional diver or any type of diver, but he should know better than to buy it, frankly. Although we're good guys, we're not in it to educate the whole world, really.

Dr. Bradner: Am I not right in recalling that the ping pong ball snorkel's been removed from the market even though it was very popular?

Lt. Cdr. Thompson: It's still there. You can still buy them. As the gentleman says, the 29-cent snorkel -- except that inflation now makes it $1.50 -- and you do see those so-called unsafe snorkels on the market...

That gives you an idea of what is in this book.

SeaRat

PS--this type of experimentation will give data, but the type of experiment that REVAN advocated above would not be allowed under ethics rules for experimentation in a university setting.

 

[David Wilson]

In my humble opinion, one of the finest models for fin evaluation is still W. G. Fischer's Naval Experimental Diving Unit, Washington DC, report of 1 March 1957 Comparative Evaluation of Swim Fins, which has been scanned and uploaded at http://www.dtic.mil/dtic/tr/fulltext/u2/780665.pdf. I think it illustrates very well the difference between what is measurable in fin analysis (e.g. dimensions, weight, hardness) and what is likely to be a subjective factor reflecting the experience of one individual rather than a universal value (e.g. comfort rating, efficiency in propulsion). I would like to see manufacturers and suppliers providing first more information about the former, particularly foot pocket inner dimensions (the maximum space for foot length, width and arch height) so that purchasers can make a better informed decision whether a particular model of fin will accommodate their feet. The existing size ranges used by the producers aren't fit for purpose, particularly in the case of full foot fins, where a common size, say 10-12, can fullly contain a diver's foot in the case of one of model of fin, while a 10-12 in another model can leave the diver's toes entirely protruding beyond the toe opening. Giving the internal length and width of the pocket in inches or millimetres would immediately tell the online buyer how well the fin will fit. The 1957 report is also interesting because of the underlying frustration of the authors with manufacturers' descriptions of their products, e.g. what material the fin is made out of. Wouldn't it be nice if a comprehensive product data sheet accompanied all fins to answer some of these questions?

 

[REVAN]

Well, I'd like to just say that I'm not advocating that anyone do the testing I described previously. It was more of a point of how hard it is to get accurate data on swimming efficiency of a diver. It's near impossible!

Back when I was training hard (and only when I was working with a team of well trained individuals for support), I was doing hypoxic interval training leading up the the freediving world championships. When I did that, the differences between fins became apparent. That environment amplifies the small differences to the point where they become obvious. It would be on the extreme side of things to do this just to collect data for someone else's fin experiment.

SWB is a real concern in freediving. I've known more than one person who has died from it (or at least that is the assumption). I don't do that kind of training anymore simply because of the fact that it is so hard to put that kind of support structure together to be able to dive in that performance realm without ending up dead. Freediving competitions are a good example of the kind of support structure that is required. No one has died from a blackout or SWB in a freediving competition (yet). But, a lot of people die when the conditions are not so well controlled as can happen when training, or when they start to think "I've done this before and was OK, so I don't need a safety for this". That's when accidents tend to happen.

Enough talk on the dangers of freediving; next topic:

The load cell experiment described above only tests static thrust performance. Divers are moving when they swim. It is testing a non-operational performance characteristic of the device. It is possible to track total body caloric expenditure if you can measure the O2 and CO2 flux, but how do you get that data without the diver dragging hoses along for the ride to deliver the gases to a machine to make the measurements; again, the thing you are trying to measure has been altered by the attempt to make the measurement.

It is similar to the problem physicists have trying to measure the motions of atoms. It's like there's a Heisenberg Uncertainty Principle that applies to fin performance. So, I think we can expect there will always be a debate swirling around this topic. Like Eric said, the only way to know is to try it yourself and if you like product 'A' better than product 'B', great! You've got a datapoint. Just know that what works better now, may not work better later. Different fins work better with different techniques, and as you learn more, you may be able to tap into something that just didn't gel for you previously.

Monofins are a strong example of that. If you don't know how to use a monofin, you will think that it absolutely sucks for a dive fin. However, once you learn how to control the fin and balance yourself in the water with it, and also after you learn the body wave motion of the monfin core undulation, a good monofin is simply an amazing piece of equipment; you can seriously fly through the water with those things. However, the results are all based on the skills of the user behind the use of the equipment. Product 'X' + bad skills = bad performance. The same product 'X' + good skills = amazing performance.

The same will apply to scuba fins. A cheap $90 fin from the LDS may work great for you when you are a noob getting your OW cert. But, after you've done thousands of dives and maneuvered yourself into more challenging diving environments and developed better skills, both physical and knowledge/technique skills, those may no longer be great fins anymore. At that point, maybe you need something like Dan's DiveRs and FF combination to perform all your neat underwater tricks. For me, I need my monofins to do what I want to do. Other divers can listen to our stories and maybe they will be inspired to try some of the equipment and techniques we employ. Or, maybe not. More new divers simply quit after 20 to 50 dives than go on to do thousands of dives. But, it is through talking about these subjects that the knowledge spreads and the seeds of inspiration are planted in the next generation of super-divers.

 

[John C. Ratliff]

REVAN,

First, I appreciate your post above. Now, the other posts make more sense.

As the former Finswimming Director for the Underwater Society of America, I second your comments on the monofin. For those who may not have seen finswimming, I recommend a little excursion to YouTube and type in "finswimming" (all one word) to see the pool competitions with monofins. The difference between what you described previously, and finswimming apnea competition, is that this competition is limited to 50 meters (yards in the USA, sometimes) and is done for time. Finswimmers do not try to go until they black out, but instead need to cover a given distance breath-holding, and that distance is 50 meters. I was going to say that the CMAS world record for 50 meters apnea immersion was around 16 seconds, but it is actually less, 13.85 seconds by Pavel Kavanov of Russia (1985).

Your critique of the study I posted from Dr. Glenn Egstrom from 1970 is valid, although they were trying something different from what you described. The more recent study I posted had a somewhat different method (it's a few pages back). But I wanted to show that these studies have been done in the past, and that there are ways of showing actual fin performance. However, Dr. Egstrom's comments bear a re-read too.

SeaRat

 

[John C. Ratliff]

Well, I'd like to just say that I'm not advocating that anyone do the testing I described previously. It was more of a point of how hard it is to get accurate data on swimming efficiency of a diver. It's near impossible! ...

...The load cell experiment described above only tests static thrust performance. Divers are moving when they swim. It is testing a non-operational performance characteristic of the device. It is possible to track total body caloric expenditure if you can measure the O2 and CO2 flux, but how do you get that data without the diver dragging hoses along for the ride to deliver the gases to a machine to make the measurements; again, the thing you are trying to measure has been altered by the attempt to make the measurement.

I participated in a study by two fellows, Joe Russel and Alex McNeill, who were doing physiological experiments on divers for their Ph.D. in Exercise Physiology from the University of Oregon (Joe transferred to the U of C Institute of Environmental Stress shortly thereafter). This was in 1970 when I dove in Clear Lake, Oregon. I came home from the USAF and dove these experiments on June 14 and June 16, 1971. (At the time of these dives, I was only days out of DaNang, RVN after my discharge.) You can see my dive log for these dives. But what was interesting is that they took my EKG, pulse, and respiration rate, and sampled my exhaled breath using a vacuum tank as I swam a horizontal line at various depths. This is one method that data could be collected, and was on one occasion, concerning fin usage.

Dan,

I dove today with my Dacor Nautilus CVS and with my Force Fins (the originals). You are correct that the kick needs to be modified to use these fins. The "kick shape," as you describe it, is much different as the original Force Fins do not have any "heft" on the up-kick at all. I found them to be good when I was submerged if I practiced a "kick shape" that emphasized the down-kick, hard, and de-emphasized the up-kick. When hovering, I was able to maneuver pretty well around a wreck of an SUV in my small dive site on the Clackamas River. The frog kick, which I tried in two ways, had mixed results. If I kicked the traditional breaststroker's frog kick, with the bottom of my feet, the Force Fins collapsed and provided very little kick force. But if I turned my foot over, and did the frog kick with the top of my feet (which is weird for a former competitive breaststroker), they worked well. On the surface, because it is difficult to impossible to put the down kick in the correct position, they were harder than my fins ("scoop fins," which I have not yet identified here). One of the foot straps had come loose, and was under my heel, but that made no difference as these fins tend to stay on even without the fin strap (they push upwards on the foot pock, rather than sliding off).

I actually have three of these Force Fins (original), and am hoping to get my hands on a fourth. If I do that, then I'll take one of the pairs and remove the foot pocket, then bolt them onto the underside of the other set to see how they perform together. That way, I would have both the up-stroke and down-stroke to work with. Has anyone thought of that? It would mimic the way some seals swim, with their hind fins collapsing on one side and the other side taking the stroke, then the reverse process happening. That would make it rather difficult to walk with these fins, though.

John