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Post by SeaRat on Dec 5, 2005 20:37:11 GMT -8
Luis, I have now looked at these sites, and it will take some time to digest what Dr. Grier has written here. Suffice it to say that this is the most comprehensive study of diving fins that I have seen. Thanks, and it will result in a better understanding of fin design for us all to look at these studies. John
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Buzz
Senior Diver
Posts: 64
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Post by Buzz on Dec 6, 2005 6:49:18 GMT -8
SeaRat Well......since this is not going to be a real test of the fins capabilities (rather a swimmer against swimmer). why not use hands too? Buzz
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Post by luis on Dec 6, 2005 7:10:56 GMT -8
SeaRat Well......since this is not going to be a real test of the fins capabilities (rather a swimmer against swimmer). why not use hands too? Buzz You mean like the real guy… as in Mike Nelson?
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Post by Gomez' echo on Dec 6, 2005 7:42:41 GMT -8
One of the techniques a local dive store uses to "sell" various types of fins, namely splits verses paddle, is to attach the end of a long bungee chord or elastic cord to the side of the pool. The experimenter holds the other end of the chord at his waist and swims as hard as he can against the tension of the chord. When he feels he had progressed as far as possible, he places a weight at that point on the pool bottom. He then rests a bit and tries the other fins. In theory the fin that allows him to go the farthest apparently shows the "power" of the fin. Might be worth the try.
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Post by luis on Dec 6, 2005 9:01:50 GMT -8
Hi John I thought you may find Jim Grier web site interesting. From what I recall he is doing all this testing as a hobby (just like you). I think you out to get in touch with him; he may be willing to collaborate in some fin testing. Independent testing of your fins may bring it some good exposure. I do like your scoop fins idea and I think it is great that you are making and testing them. I would have a hard time cutting a good pair of fins. I have used Scubapro Jet fins for over 34 years. I always thought they were great and Grier’s test shows they are pretty good. This past summer I tried the Atomic Aquatics split fins and I haven’t been able to go back to the Jet fins much. The only draw back may be that the longer flexible blades tend to kick up silt a bit easier, but all other performance factors seem to be equal or superior. Speed, static thrust, maneuverability, leg stress, air consumption, and ease of use with different kick styles, all seem to be better with the Atomics. Then again I don’t think that all splits are created equal just like not all flat fins are equal. Since reading about your scoop fins I have been thinking about doing some (non-destructive) testing with my Atomics. I was thinking about using some elastic tape on the split of the fins. I figure if Nemrod can swim past dolphin, I should be able to try that wile pulling some water skiers with a pair of modified Atomic…lol Simonbeans The test you are describing with the bungee is basically a static thrust test. It is a useful and a simple comparative test, but it won’t give you the whole picture. I like it, it does sound like fun do. When you stop kicking does it pull you back like bungee jumping?
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Post by SeaRat on Dec 6, 2005 9:46:58 GMT -8
Hi Luis,
Thanks, I have already sent Dr. Grier an e-mail with an attached link to this thread. I can also provide him a set of fins to test sometime, if that option is made available.
Buzz, I hope to have you some times in the next few days. We can play with this a bit; it should be fun.
John
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Post by SeaRat on Dec 6, 2005 20:27:45 GMT -8
Buzz,
I went to the pool this evening to renew my pass for the next three months, and stayed long enough to get some times. These were self-timed, and I did three different swims with only about 200 yards warm-up (not really enough). I swam with my PlanaPlus/Scoop fin design (the PlanaPlus is a full-foot fin), a racing swim suit, very streamlined Dacor mask, and racing snorkel (except the last swim). This is a 25 yard pool, so each swim involved either three (for 100 yards) or one (for 50 yards) turn(s). I did racing flip turns. So here they are (in minutes:seconds.hundredths of seconds):
100 yard surface, no arms (streamlined in front): ~1:13 100 yard surface, crawl stroke with fins: 1:10.51 (took me two tries to push the darned button though) 50 yard apnea (underwater, no snorkel): 0:34
I feel pretty good about these times, as it is the first time since last winter that I've really swam hard in the pool, and in a few days I'll turn 60 years old. These are not quite as fast as my earlier monofin times (several years ago), but very respectable for the size of these fins. What I should do is compare my fastest times with each style fin. These are approximate times, as I did not have anyone timing me (that could come later). But it gives us some benchmarks to look at. By the way, bicycling does help keep in shape.
I received a nice reply to my e-mail from Dr. Grier, and it looks like we'll be doing some collaboration this coming year.
John
PS--I forgot to mention that I started from a standing start in the water, pushing off the wall to get going (which is normal for swim team swimmers doing a workout).
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Post by SeaRat on Dec 12, 2005 8:41:15 GMT -8
Buzz, Have you been able to get wet yet? For the others, I will be doing more swims over the holidays to test out my scoop design against the original design, and the split fin design. By making all these from the same blade set (Mares PlanaPlus), I think I have a reasonable way of evaluating these. For those of you interested, please do look closely at Dr. Grier's web pages concerning his evaluations of swim fins. This is the most comprehensive measurement methodology I have yet seen published (and I've been following this for the last thirty years). I am still reading these pages, and understanding Jim's methodologies. He's put a great deal of time, effort, and most importantly thought into the evaluation of current designs of swim fins for divers. John
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Post by nemrod on Dec 12, 2005 10:53:42 GMT -8
SaRat, I had read that report quite some time ago. Notice that while he gives the traditional Jetfin good marks he gives top marks to the Apollo split fin and also he seems to pretty much discount the Tech diver idea that only Jetfins can do alternative kicks and have good manuverability. I think the reason the Jetfin and Apollo fins perform well is that they are made from RUBBER. To bad he did not test the UDT. I wold be curious how it would perform. I have suspicionsthat it might give the Jetfin a bad time. I think I am going to buy a set of Apoolos. I just cannot decide if I want full foot. I have alwys been a warm water diver and most of my diving has been off boats, kayaks, zodiacs etc so full foot fins rule the day. Nothing can be more comfortable or fit bare feet better. Of course, when you need to hike to a shore diving site or scramble over slippery rocks or deal with cold water one can understand why open heel fins have become so popular despite their lower performance and reduced comfort. Over the Christmas period I am going to cut up an old pair of UDT and I also plan to split an old pair of SkinDivers.
Going back to stiff paddle fins like my UDTs or Jdets. I can see how from a stationary position I can use a wide, strong kick to produce instant acceleration compared to softer fins like my Force Fins. However, the thing is that I suspect that once that initial accelration is gone the split fin, Force Fin types would quickly out speed the Jets and UDTs.
The Frog kick. Imostly learned that kick in the early daves cave diving. It makes sense there. I really find it inefficient in open water diving other than to use it to vary your kick so to let other muscles rest. This seems to be the big thing all of a sudden with everyone Frog kicking all over the place. I don't get it. You know, the dog paddle is a useful swimming stroke to learn for when your just paddling around the swimming pier but in a long distance swimming race who would dog paddle or frog kick, they would be miles behind anyone swimming any sort of crawl stroke. I just think the Frog kick stuff is very useful in certain situations and about totally useless in everything else. I could be wrong. When I save up my allowance I am getting some bright yellow Apollo splits!!!! for my non-vintage diving--ya know. I think I will be buried in my UDTs however. James
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Post by nemrod on Dec 12, 2005 10:59:56 GMT -8
I don't suppose that along with yellow hoses Santa could bring me yellow--pure yellow----UDT fins!!!! Now, wouldn't that be a sporty comboalong with good ol' yellow USD oval mask? Hey, Santa, bring me one o those too.
I am tiring fast of this all black stuff, give me the traditional diving colrs, blue, yellow, orange, and of course---natural gum rubber. Talk about cool, an oval mask, and UDT fins in natural gum rubber---holy cow. James
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Post by SeaRat on Dec 12, 2005 11:51:19 GMT -8
SaRat, I had read that report quite some time ago. Notice that while he gives the traditional Jetfin good marks he gives top marks to the Apollo split fin and also he seems to pretty much discount the Tech diver idea that only Jetfins can do alternative kicks and have good manuverability. I think the reason the Jetfin and Apollo fins perform well is that they are made from RUBBER. To bad he did not test the UDT. I wold be curious how it would perform. I have suspicionsthat it might give the Jetfin a bad time. I... The Frog kick. I mostly learned that kick in the early daves cave diving. It makes sense there. I really find it inefficient in open water diving other than to use it to vary your kick so to let other muscles rest. This seems to be the big thing all of a sudden with everyone Frog kicking all over the place. I don't get it. You know, the dog paddle is a useful swimming stroke to learn for when your just paddling around the swimming pier but in a long distance swimming race who would dog paddle or frog kick, they would be miles behind anyone swimming any sort of crawl stroke. I just think the Frog kick stuff is very useful in certain situations and about totally useless in everything else. I could be wrong. When I save up my allowance I am getting some bright yellow Apollo splits!!!! for my non-vintage diving--ya know. I think I will be buried in my UDTs however. James James, Good observations. Actually, the original Swimaster UDT (as opposed to the AMF Voit, which came later after Swimaster was bought and destroyed their dyes for these fins) were not strictly "paddle" fins. As they wore, with the original gum rubber, they did do some of the "cupping" that I use in the Scoop fin. I'll load an old US Navy photo which clearly shows this later (I'm at work now). I used the original Swimaster UDT Giant fins for many years, and they got me through the U.S. Navy School for Underwater Swimmers and Pararescue training. We later went to the ScubaPro Lightning Jet fins, which I still have. But I also still have a pair of the original Swimaster UDT fins. So I'll do some work with them too. The Jetfin, and later the Lightning Jetfin, had the same basic problem that all these fins have (Rockets, and the others that have similar designs). They have a big "dead" area in the center of the blade on the up stroke. Concerning the "frog kick," there are actually two different types of kicks involved. A traditional frog kick, used on the breast stroke, uses the bottoms of the feet. What is called the "frog kick" by DIR divers is much different from what swimmers call the a frog kick, or a whip kick. It is actually an illegal kick in competitive swimming (I used to be a US Swimming Stroke & Turn Judge), as the foot would break the surface during the kick the way the DIR divers do it. The DIR frog kick is done with the top of the foot doing the thrust. They do this to keep the feet high, and not stir up the bottom (such as is seen in my photos of the scoop fins). It is not meant to be efficient, but to give some forward propulsion with a lot of control of where the thrust goes, so as to not stir up things. It is very good in closed environments (inside ships and caves), but pretty inefficient otherwise. The scoop fin can easily be used with the frog kick, and I do it in current when I am trying not to disturb the bottom. It is interesting that a side-to-side motion of the scoop fin can give interesting variations to the thrust. When I'm under a strong current, it can be used to keep my feet from straying into the high current areas above me too. So it has its place in open water, but not as the most efficient kick. John
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Post by SeaRat on Dec 12, 2005 19:54:46 GMT -8
Here's the photo I promised of the US Navy diver using duckfeet fins. Note that the fins do "cup" more than the current paddle fins. These are the original Swimaster Duckfeet, which had a square top to them (the later AMF Voit Duckfeet fins had a molded, rounded top). The squared top allowed them to be worn upside down. I wore mine with a thin bootie too. The foot pocket was a bit too narrow for a heavier wet suit bootie (then made of 1/4 inch neoprene). The slight cupping action of the blade is not as good as my Scoop Fin concept, but does help the Duckfeet fins provide more power. These were gum rubber fins, as Nemrod suggests above. Official US Navy Photo published in Skin Divers In Action by Erik Bergaust and William Foss, G.P. Putnam's Sons, New York, 1965. Because they are official photos, there is no copyright on the photo itself. In the original Beuchat patent, #3,183,529, what is known now as the Jetfin was a full-foot fin, and was manufactured that way in Europe before ScubaPro started manufacturing it. John
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Post by duckbill on Dec 12, 2005 22:10:33 GMT -8
Hi John, I've been reading some of Dr. Grier's work. I have found it interesting how he mentions that shallow, rapid kicks are more effective and efficient than wider strokes. I can't wait to experience this principle at work during my Monterey dives this next weekend. In regard to the scoop fin design, wouldn't much of a shallow kick be used to just reverse the scoop before any power would be achieved? Depending on the amount of scoop, would longer strokes be more efficient because of the reversal lag time inherent in the design? I think you really have everyone here thinking! It's very interesting how something so seemingly simple as a fin can have so much thought and research invested in it's design. Thanks for sharing all of this with us.
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Post by SeaRat on Dec 12, 2005 23:06:02 GMT -8
Duckbill,
In an air environment (air as the fluid), you'd be correct, and there would be a lag. But in a water environment, what I've seen happen is that the water's inertia (and movement after the foot stops) quickly reverses the flexible scoop blade. You don't experience much lag. What you do get is a reduction in foot fatigue due to the stresses placed on the foot by the normally flat blade being reduced by the flexible action (which is why the split fin is also popular).
The shallower kick is something I really did not think much about, as I've been swimming and fin swimming so long that my kicks are not something I think about when I do them. But after my timed swims last week, I noted that I don't use a deep kick when I use the flutter kick. I kick deeper when I dolphin kick (which is my primary kick in many instances). But my experience shows that a quick, very shallow kick is very effective too.
John
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Post by nemrod on Dec 13, 2005 1:40:21 GMT -8
I have another older pair of UDTs that are beginning ot come apart from wear. I was thinking to cut a split into the center removing the lower 1/2 of the center rib and leaving the remainder of the center rib in place thus producing a semi split fin.. I am then going to cut the two sections slightly on a camber or Vee to provide clearence between the two split sections. I am curious how this might do.
When you make your "scoop" fins how do you attach the new material and what mateial are you using?
I find it strange that a fin like the UDT that has a strong center rib would have any "scoop" action at all. I see the photos--thanks----I wonder how the new UDTs behave. While they are fairly stiff I do not think them to be a stiff as some of the Voit versions. I have a natural colored Voit version of the UDT, it may be gum rubber also but it to is beginning to fail--it is actually very flexible. Perhaps I shall modify them as well. I actually have been thinking to put a spring strap on them and get some more use since it is the heel strap that fails on a UDT first.
It makes sense to me as an ex swimmer that small quick strokes (feet and legs) are more efficient that a wide, open kick, I have never felt otherwise. With a wide kick the legs move into the slip stream creating great amounts of drag. A faster but smaller flutter kick does not put your legs far apart impeding the oncomng water and creating drag. With any type of scissor of flutter kick there will be an angle created by the legs/knees. At some point this angle becomes great enough that the drag produced counters or exceeds the propulsive benefit provide by the greater leverage and longer stroke of the wider kick. Of course, comparing to a competive crawl stroke is not completely legit because such a swimmer is getting upwards of 60 or even 80 percent (or even more)of their power form their arms. A diver gets 100 percent of his power from his legs (except on SeaHunt were they arm swim---lol) When I was doing long distance open water swimming events I mostly let my legs trail behind me acting more like steering/stabilizing vanes. Most near all of my power came from my arms and this would be pushing a 20 minute mile in open water which is not exactly slow.
Yeah, I know the DIR type frog kick is not the swimmers kick but it is still a specialized kick and there are people using this kick as their main propulsive kick and swearing it is faster and more powerfuller and more torquier and with stronger whiteners and brighteners---yeah--right.
Looking at those pics of the UDT in action it ocurrs to me that it may be the perfect scoop fin if it had been molded with no center rib--leaving everything else the same. I also still think a molded in bend line or flex line down the center where the current center rib sits would enhance the "scooping" effect. I think I suggested that earlier many posts back but don't know if you caught it. James
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