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Post by SeaRat on Oct 24, 2017 16:47:48 GMT -8
I conducted some fin trials in 2010, and here are the results. I used two different types of kicks, firs (on top) the kick was a crawl kick, without arms, swimming four times 25 yards in the pool. The second was with the dolphin kick, hands streamlined in front. It will give an idea of the fin's efficiency in propulsion. John
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Post by SeaRat on Feb 8, 2020 16:05:40 GMT -8
I swam my USD Aqualung Professional fins yesterday (#D in the photo below). They actually were very good fins, performing well. They were U.S. Divers Company's reply to the Duck Feet fins, and were used by the U.S. Navy for a while, and issued to the U.S.A.F. Pararescue too. They have no heel support, at all. But this allows those who can handle them to get a better angle on the water, for more power in the blade. NED catalog001 by John Ratliff, on Flickr The only problem I had was that I was using cutoff booties, and I cut them too low. That caused some abrasion of my inside ankle skin where the strap met the skin. These fins need a full bootie to be worn comfortably. I still have Band-aids on the inside of my ankles because of the abrasions (blisters???) cause by the open heel strap on my skin. I swam these fins using both the regular flutter kick and the dolphin kick. Both were powerful using these fins. I also tried using a frog kick, such as cave divers use, and to my astonishment they actually worked with the frog kick. It was not as powerful as the flutter kick, but it did work using these fins. I also looked at these fins by using one in my hand, and pushing it down like a kick from the surface so I could see the bubble track left by the fins. These fins left two powerful stroke vortices of bubbles spiraling from the inside (away from the propulsive side) of the fin. IMG_1403 by John Ratliff, on Flickr Note how closely these fins appear to be like the Duck Feet fins. IMG_1404 by John Ratliff, on Flickr Unlike Duck Feet fins (see previous posts) these Aqualung Professional fins have a curve to them. This enhances the angle of attack for the down stroke, but somewhat limits the upstroke. John
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Post by DavidRitchieWilson on Feb 9, 2020 4:48:46 GMT -8
Impressive research, John. Remarkable too how similar the US Divers fins are to the Duck Feet, except for the inclination and curvature. Fred M. Roberts' Basic Scuba has an appendix devoted to "straight-blade fin analysis" and "offset-blade fin analysis" with the following figures: DRW
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Post by nikeajax on Feb 9, 2020 17:16:49 GMT -8
GRRRRRR! I'm not sure how to interpret this data: can one of you please break it down for me in simpler terms? JB Dyslexia is a very cruel mistress
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Post by SeaRat on Feb 9, 2020 22:59:37 GMT -8
GRRRRRR! I'm not sure how to interpret this data: can one of you please break it down for me in simpler terms? JB Dyslexia is a very cruel mistress Fred Roberts has quite a bit of analysis in this chapter on Swim Fin Analysis. Aside from the math involved, he gave the following commentary: Now, saying that, I did a similar vetor analysis of my own design for the scoop fin. Fin Vector Analysis by John Ratliff, on Flickr You can see that analyzed using force vectors, the scoop fin design has a better horizontal component than does a flat blade. (I did this analysis over two decades ago, and have since lost the original sheets I wrote this on; it was only with this computer search that I found I had scanned them.) The other thing is that Fred Roberts referred to the tip action. Some fins are so inflexible that they don't bend at the tip. These are like trying to move boards through the water, and are very, very uncomfortable. One example of these kinds of fins is the USD Spoiler fins shown below. This in why I decided to convert them into scoop design. Not only did the blade-long vents not work at all, they made the fin so inflexible that they were completely inefficient, and hurt the foot when used. _MG_5878 by John Ratliff, on Flickr With the scoop modification, at least the fin blade bent so as to give a horizontal component to the vector analysis. John
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Post by DavidRitchieWilson on Feb 9, 2020 23:56:32 GMT -8
Fin tip flexibility is a particular requirement of the Soviet, and now Russian, Standard GOST 22469—77, whose official English subtitle is "Swimming rubber flippers. General specifications". This Standard describes the fin-tip bending test apparatus, method and results thus (My rough translation from the Russian): 4.6.1. Equipment • A device enabling a fin blade to be bent for a given time in a 180º position. A diagram of the device is given in the appendix. • An incubator or oven supplying heat up to 70 (± 5) ºC. • A 180º protractor in accordance with GOST 13494 with divisions of 0.5º. 4.6.2. Test procedure• A fin with a metal insole previously inserted in it shall be placed in the device so that the axis is perpendicular to the axis of the bend of the fin. The rear of the fin shall be secured with a clamping screw. • The tip of the fin blade shall be blocked under an immobile spindle with a diameter of 18 (± 0.1) mm. The distance from the tip of the fin blade to the centre of the axis of the spindle should be 100 (± 5) mm. • As the bending plate acts upon the fin, the tip of the blade shall be bent to an angle of 180º relative to the immobile spindle, which is the axis of the bend. • A pin connecting the plate to the base of the device shall lock the bending plate in position. • The device with the fin shall be placed in an incubator or oven and maintained at 70 (± 5) °C for 30 minutes, then removed from the oven and cooled for 1 hour at 23 (± 2) °C. The fin shall be released from the effects of the bending plate and allowed to recover for 15 minutes. • The protractor shall measure the residual deformation from the bending of the fin to an accuracy of 1º • The result shall be the value of the bending angle of the tip of the fin blade. AppendixThe blade tips of Russian Alfaplastik Del'fin (Dolphin) model fins with their marbled foot pockets can really bend right back 180º on themselves without damage or permanent deformity: I know this because I have a pair in my collection and I've tried bending their tips back manually. I wonder how many other fins can do that! To find out how these fins are manufactured and to view them in action in the pool, here's a Russian-language video: The relevant sequence is between 4.45 minutes and 8.12 minutes into the video. DRW
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Post by SeaRat on Feb 10, 2020 8:58:22 GMT -8
DRW, Loved that video, and the humor of the supposed rescue scene at the end. The working conditions for making fins seems to allow some exposure to airborne vapors coming from the curing rubber though. How the fins were made is interesting, as was the finswimming shown. Thanks! I have a 2 pair of Fara-Fins, which have a brace allowing a large force to be applied to the blade. Fara-Fin Mod-2 by John Ratliff, on Flickr I have a video which shows these fins bending to a 90 degree angle. I'll try to find the still photo I took off it and post it below. Sea Turtle-Dolphin Swimming by John Ratliff, on Flickr John
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Post by nikeajax on Feb 10, 2020 14:03:57 GMT -8
So what you fellers is saying is thars a sweet spot between floppy and stiff for good fins, eh? ...The working conditions for making fins seems to allow some exposure to airborne vapors coming from the curing rubber though... John At least for the time being we still have laws that protect American workers from such things-- HEE-YIKES! DRW, that mask and cap combo for better aqua-dynamics was crazy: I've never seen than before. JB
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Post by SeaRat on Feb 10, 2020 17:59:19 GMT -8
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Post by DavidRitchieWilson on Feb 10, 2020 23:23:38 GMT -8
...The working conditions for making fins seems to allow some exposure to airborne vapors coming from the curing rubber though... John At least for the time being we still have laws that protect American workers from such things-- HEE-YIKES! JB It's somewhat ironical that Al'faplastik, the Moscow Del'fin fin manufacturer shown exposing its employees to unhealthy working conditions in the video, may be best known in Russia for its medical products (e.g. catheters): Медицинские изделия. The firm's range of fins can be viewed at Ласты. DRW
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Post by nikeajax on Feb 11, 2020 11:29:22 GMT -8
So, Komrad Weelson, what was moral of story? Was it that the gear will make you super fast in the water, but, takes too long to put on so is no good for savink lives, da?
JB
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Post by SeaRat on Feb 11, 2020 23:06:06 GMT -8
I was going to tell you that last week, when I put the U.S. Divers Company Aqualung Professional fins in the water, I remarked to a lifeguard as I was getting out that the fins were way older than she was. Then the other lifeguard on duty asked if they were older than her too, and she said her birthday was in the 1960s. I said, "Then you and these fins are about the same age." I don't know what these workers in Russia were exposed to. if the components are natural rubber, the exposures probably are minimal. Here's the Safety Data Sheet on one rubber material: www.astlettrubber.com/pdf/nr/msds.pdfBut if it is a synthetic rubber, then there is the potential for exposure to butadiene. www.prevor.com/en/chemical-risk-in-plastic-and-rubber-industryI just looked up in my ACGIH TLV Booklet, and 1,3-Butadiene (CAS #106-94-5) has a time-weighted average for an 8-hour exposure of 0.2 ppm. There is no short-term exposure limit, and the Notation is "A2," which is a "A2--Suspected Human Carcinogen: John
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Post by nikeajax on Feb 13, 2020 8:42:58 GMT -8
So, DRW, what's in your bag: what do you actually use. You're a snorkeler, but do you ever do any free-diving: tell us more. I b'lieve you a drysuit guy too...
JB
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Post by snark3 on Feb 13, 2020 11:37:42 GMT -8
I will certainly agree with John on the USD Spoiler fins being very inflexible, I've often said they are as flexible as plywood. Currently I dive with USD/Aqualung Blades, not vintage but I love them.
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Post by DavidRitchieWilson on Feb 13, 2020 12:28:55 GMT -8
So, DRW, what's in your bag: what do you actually use. You're a snorkeler, but do you ever do any free-diving: tell us more. I b'lieve you a drysuit guy too... JB I admit it, JB, my priorities have drifted from vintage equipment snorkelling to collecting and researching historical fins, masks, snorkels, suits and other basic diving gear from the past. Some of my proud possessions can now be viewed on Luigi Fabbri's Blue Time Scuba History site. There are images of my Britmarine Clipper and Dunlop Aquafort fins on display at Virtual Museum: Fins. It's been quite a while since I've driven to the coast for a dip in the North Sea. When I did so, I would be wearing what I call classic gear made by modern manufacturers, e.g. a pair of Mexican Escualo Clasica fins, because I have broad feet: a Russian Spine Nimfa mask because the model fits narrower faces: a French Sommap Annelé snorkel, because the corrugated hose drops out of the way when not in use and a full length Hydroglove vintage-style dry suit to keep hypothermia at bay. I now have an Aquala Coronado historical suit too. Why modern classics? Because they're easier to replace if I lose any in the waves. Unless they are new-old stock, historical diving articles are likely to be the worse for wear through ageing and therefore far from ideal for their intended purpose. The seawater off the beach wasn't deep, so freediving was never an option. For me, snorkelling is a spontaneous activity, which is its attraction for me, while open-water freediving would require the presence of a buddy for safety and more planning. When I did my vintage snorkelling on early summer mornings, I would enjoy the glow of the rising son, the scent of the saltwater, the clarity of the waves. Marine fauna and flora were conspicuous by their absence - just a little seaweed here and there, but what I was after was a little calm and relaxation as I swam on and under the water, nothing more, nothing less. Sometimes, when the sea was rough, I had to forgo my dip in the interests of self-preservation. Perhaps I'll be tempted one sunny day later in the year to resume what was once my passion. We'll see. DRW
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