DIR fin technique questions

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Due to the variations as you mentioned there is always a variable. We arn't running time trials at Indy so a little fudge is acceptable

Absolutely - it'd be difficult to set up a test that wouldn't include some fudge factor.

My point was that while individual testing is a great way for the a diver to get a more accurate perspective on which kick styles work well - for them - and in which situations, I think it'd be a stretch to apply those individual tests to generalized statements about the efficiency of a particular kick style as it relates to air consumption.

Henrik
 
Absolutely - it'd be difficult to set up a test that wouldn't include some fudge factor.

My point was that while individual testing is a great way for the a diver to get a more accurate perspective on which kick styles work well - for them - and in which situations, I think it'd be a stretch to apply those individual tests to generalized statements about the efficiency of a particular kick style as it relates to air consumption.

Henrik
I wouldn't disagree as the concept of air consumption has never been a concern in my style of diving so that portion of dive planing wouldn't be a strong point. I have done overhead environment diving but not as a favorite. As for general efficiency I feel the flutter kick is likely the best. As I have stated previously I have done a few assists across open ocean in current and kelp and the bigger the prop the more the push. Doing breathold diving is where I might consider the efficiency concept to show it's head, the better you are at all aspects of being in the water the longer time and more area you can cover between surfacing. I may be really oversimplifying it but it would seem comparisons made in that style of diving may get honorable consideration
 
Given the resistance to movement in water, I think for any "efficiency" swim tests, you'd have to very accurately time the swims over a set distance.

I.e. in order to accurately determine the most efficient kick wrt. air consumption, each kick style test would have to be perfectly timed to match: swimming 4 x 100' (two laps in each direction) at constant speed and each kick style test should take, for instance 10 minutes (arbitrary number).

Any variance in time would probably invalidate a judgement on air consumption. It may also be that certain kick styles are more efficient at a particular speed than at an other.

Henrik
You're right, and you're also starting to describe a really neat experiment.

I'm picturing a pool swim with three marks on the floor, maybe 25m apart each. There is a swimmer and an observer. The swimmer ideally has a very basic scuba rig with a preset amount of air - it really doesn't matter how much, as long as it's constant. There are refilled cylinders all at the same weight and PSI load available for each trial, or a compressor to top off the bottle at the end, to ensure that pressure and cylinder weight are not a factor. Equipment doesn't have to be weighed as long as any given swimmer doesn't change gear during the trial.

Swimmer starts at the 0m line and swims for 25m using the stroke in question at a constant speed, or as close to as possible. The swimmer has a timer s/he can see during the trial. Swimmer checks air remaining at the end of this: this is the "speed up" air use. Swimmer then swims the next 25m and checks air again. The "slow down" air use. The separation between the two is to account for any fatigue from the swim. The 25m times should be identical, ie. if the first swim took 75s so should the second.

For each stroke, the swimmer should make at least 5 swims, with time to relax in between. The trial should also incorporate several swimmers: male/female, trained/untrained, overweight/physically fit, split fin/paddle fin.

The observer's purpose is to note any abnormalities in a given trial, eg. does the swimmer breach the pool surface with a fin or bottle to create drag. Does the swimmer change speed drastically during the swim.

Assuming I haven't missed any big variables, This would not be that hard to set up. Anyone in Calgary interested in trying is welcome to PM me, I wonder if the Dive Shop would be willing to help.
 
I tried to maintain a constant speed during my time trials by checking my split time at each turn-around point. In other words, if my first 100 feet took 125 seconds, then I should look for 125 seconds for each 100 feet thereafter. I was never far off on my split times, only minor adjustments were necessary. You could put markers at 50 feet and check your split times every 50 feet if you wanted more accuracy.

When you're doing your maximal exertion trial speed trial, it's very difficult to keep up your speed, you get tired pretty quickly.

When I plotted out my SAC versus gas consmption for all the different trials, I got some pretty good curves that seemed to indicate that the data was good. I am going to repeat the trials again soon.

BTW, you've got to have plenty of recovery time between trials for the data to be any good.

HenrikBP has a good point, the data that you get is likely to be good only for you. I'd be interested in comparing my data with other's data.
 
Guy, I agree with you about flutter kicking and leg fatigue in Jets. They just aren't made for that, and if that's the kind of swimming someone is doing, I think a fin with more give to it is much better.

I'm not sure that it's the Jets' per se that are the problem, more the SIZE of the blades on the XL Jets. Unless you've got really powerful leg muscles, just pushing the XL jets is noticeably hard work. I don't find that to be the case with the smaller blades of my L Jets although it's still more effort than my Bio-Fins, and I'm sure either Jet would be more likely to cause cramps. I believe part of my cramping problem with the XL Jets is due to the loose fit on one foot; I think I unconsciously curl my toes on that foot to try to keep the fin from slopping around, and may well do the same on the other foot (which fits the fin pocket much better) in unintentional sympathy. I don't know what % the blade stiffness and the toe curling each play in cramping, but I'm willing to bet that they both contribute.

The cave divers I know who use flutter more than frog, use a softer paddle fin -- and they kick very slowly.

I don't think there are very many divers doing the kind of dives you're describing, though. If I had to do a long surface swim followed by 3/4 mile of swimming over featureless sand, I think I'd look for another site. We DO have a dive or two like that up here, but they are not done by swimming divers, to my knowledge; only by scooter users.

Don't get me wrong, I'm saying the total swimming distance (i.e. out and back or round the course) is 1/2-3/4 mile, not that I'm going that far over nothing but sand. With a few exceptions, at most sites there are intermediate reefs or human artifacts to look at every 1-300 feet or so before I get to the final site, and I use those features as waypoints. But every so often when I want a challenge, I'll choose a site that requires a 600-1,000 foot leg over featureless sand to a waypoint, just to keep my navigation sharp or because I feel like getting some exercise. I'm sure that I'm part of a very small minority of divers who like this sort of thing -- fortunately, I have a buddy who's also a member of the lunatic fringe!:D And another way to challenge myself is to try to do a dive swimming that has only (to my knowledge) been done with scooters. We've got one planned and are just waiting on the availabilty of a loaner Navimate to try (to give it a realistic test), although we've already swum ~2/3rd of the route to select waypoints. As it happens we'd been thinking about trying this dive even before someone local (my Fundies instructor's team, as it happens) did it with scooters; their success just encouraged us.

The DIR principle is to use the right tool for the job. It wouldn't make sense to burn gas and acquire deco obligation swimming through things you don't want to look at, when you can use a scooter to do the job faster. Of course, a lot of scooter use is just because they're fun!

Well, different strokes, but I find that swimming over relatively featureless sand (especially in limited vis) forces me to concentrate on my nav and how my body's functioning and can be quite enjoyable, as long as there's something to see at the end of the leg. I'd go nuts if I could only dive someplace like Lake Tahoe, because there usually isn't anything at the end of the leg except more of the same!:D

As to burning gas and acquiring deco, note that I specified single tank recreational shore dives at moderate depths (typically averaging<60', with max. no more than 130'), where running out of MDL is rarely an issue (even using air on the very conservative SSI tables I use). For technical dives where you're paying through the nose for tri-mix and extended ocean deco is a bad idea, the situation's different, and the task may require scooter use for reasonable safety.

As to scooters being 'fun', not for me. To me, a scooter is a tool, not a toy. I find being pulled or pushed along by a motor gets boring very quickly, because I'm almost totally disengaged (it's too easy). When my progress depends on my own efforts/skills I'm much more aware of what I'm doing, and I appreciate getting to a site more because I had to earn it. After all, aren't the challenge and the reward usually commensurate? People value a Fundies pass more than a "Pay your money and get your card" certificate from one of the major agencies for the same reason.

Which isn't to say that I'm not perfectly happy to buy my sports gear pre-made and haul it to the activity site in my car before setting off on a test of my conditioning/discipline/training/skills, instead of walking there naked and making every item on site from natural materials; I'm at least as big a societal parasite and hypocrite as Thoreau was.:D

Guy
 
I simply like the frog kick because it has more fine tuned control at all times. I don't always want to go forward. Sometimes I want to go backwards, and sometimes I want to go up, down, or turn left or right. If my feet are in position for a frog kick, I can do any of these kicks with re-positioning them first. It's just automatic.

But I'm a lazy diver. I'm never giving more than on kick every seven seconds, and most of the time it's not even a whole-hearted kick. Just a little one with just my ankles. If I really want to get somewhere in a hurry, I'll pull and glide if I can. Otherwise, I switch off between a feet-up flutter, and a frog kick. I never go to a fully-extended flutter kick for a couple reasons. First off, I'm almost always diving dry, and I like to keep some air in my feet to keep them warm :) And second, I like my feet up high because it's easier to change gears, and turn, back up, etc. If I have my feet down, I need to bring them up in order to back kick.

I was a pretty strong supporter of split fins for a long time, but I was finally converted to some stiff paddle fins when I finally got a pair and used them for a couple weeks. They offer a lot more fine control, and they are a lot less likely to kick up silt. I don't think they are as comfortable though for a strong flutter kick, and honestly, my feet cramp up if I try to flutter kick too hard or too fast, so I don't do it as much.

There is no one perfect way to get around under water. Efficiency is good, but it isn't the only thing you have to worry about either. You also need to be maneuverable.

Tom
 
Well, different strokes, but I find that swimming over relatively featureless sand (especially in limited vis) forces me to concentrate on my nav and how my body's functioning and can be quite enjoyable, as long as there's something to see at the end of the leg.

So for you, the goal is having fun, and indeed, swimming is the right tool for you to accomplish your goal.

Tom
 
2) Again, as a competitive swimmer, frog kick is really hard on the knees. Those of us who used to race the stroke can attest that long workouts of breaststroke did not leave us with happy knees. While I don't have bad knees yet, I'm expecting some in a couple of years due to rowing injuries. Does DIR actually address this or is it just a HTFU issue for them?

If you do have bad knees, how do deal with frog kick? Or do you just not do it?
:confused:


I busted my right knee quite spectacularly in 2004. My car was not in much better shape either...

The only kick I can keep up for as many hours as necessary is, um, the frog kick. I can only guess we're doing it differently...
 
Jet fins were originally a military fin, I think but anyway they wern't designed to be easy to use. They were designed to do a tough job by young strong divers. They make your legs tired for a reason, they were designed before comfort level was a consideration. I used them for years and liked them. I started using the Plana Avanti's as I got older and you know the rest. Scooters and split fins is like putting electric starters on Harleys, it civilized the sport so everyone could participate. What's next? LOL
 
Scooters and split fins is like putting electric starters on Harleys, it civilized the sport so everyone could participate. What's next? LOL

Electric starter, kick start, what's the difference? A Harley is going to be slow and sluggish regardless of mode of ignition. But I digress.

I agree with you. What's next? Dive computers so that people don't have to memorize and calculate dive tables? Drysuit so that people won't have to shiver? The horror!!!
 

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