Fins-Advanced Propulsion Experiments

[william]

A while back,there were experiments being done by a VSS Forum member, ( John Ratliff ) to see if an Advanced Fin Design were possible. What he was doing looked very interesting and was the 1st time I have ever seen any information on what really worked. It looked like valuable information was being discovered and collected that could help find out when a fin design was good and improved or only Looked good but did nothing at all. There have been several attempts in the past and in other countries but with limited to no success. Like the Sea Pro Fins here. Designed to "Flip" in the angle of the fin, when direction of kick of the fin changed, so it would greatly improve the direction of propulsion, so, MUCH more propulsion could be produced with much less effort by the diver. The angle changed something like 30 Degrees at the Metal Joint at the top of the Flipper. But they are very heavy and I have never seen any test results of this design. There are other Very unusual designs. I can not find the Thread where the member did his tests here. William

[william]

Here is a special Aircraft Wing design that attempts to use an Airfoil in the Fin to greatly Improve the ( Propulsion->to->Effort ) Ratio, for the better. I would love to see any test data to see what the amount of improvement actually was, or if they even worked at all would be great to know, ha, ha. Is there any test data on the Jet fin, a.k.a.=(Rocket-Fin)? It seems that every single Company had their Own name on a set, so there MUST have been something to the design that made them work Much Much better, ha. William

[SeaRat]

William,

I have done a lot of work on fins, and have put some results of my experiments with the "scoop" fin on this site:

vintagescuba.proboards2.com/index.cgi?board=general&action=display&n=1&thread=588

I have done a lot of study of fin designs, and the one you show above, the Sea Fin, is very interesting to me. I still have my set, which I have modified quite a lot. Tonight, I'll try to get a photo of it for this thread. I also, somewhere in my archieves, have a paper upon which these fins were based. Unfortunately, they changed the shape of the fin blade (or should I say its "wing") in a manner that decreased its efficiency. Also, I had to bend the metal braces to about a 5 degree bend, from its original 20 or so degree bend, to make them work on my feet. Divers who have been diving awhile can point their toes pretty well, and the original bend really screwed up the angle of attack of the wing. I also put two springs on my blade, which dampened the hard "hit" of the wing when it hit the stops. The connector buckle for the strap on mine finally tore free, so I only have one which still works.

The second set that you show, above, are fins I've never seen or heard of. That's quite a find.

John

[SeaRat]

William, and others,

I have worked with fins for a long time, perhaps longer than with regulators. At one point, I was the Fnswimming Director for the Underwater Society of America (1980s). We were trying, ultimately unsuccessfully, to get finswimming into the Olympics (too specialized, and hard for spectators to watch). But the US Olypmic Committee members were amazed that we had athletes who were still making their own gear.

Anyway, I have done a lot of experimentation with fins, and while I love my double hose regs, and I write about them, I think that the fins are my favorite area for experimentation. First, it's a lot less expensive, and second, it's better for fitness to finswim or actively exercise. I'm still hoping to apply some new principals for underwater swimming at one point in the future.

Which gets me to my experiments with the SeaFin. These were pretty unique fins, and held a lot of promise. I cannot find the research paper that they were based upon (it'll turn up sometime--I've still got it, 'just don't know quite where). But I also still have my modified fins. Here is what they look like:

You will notice a wooden blade in the middle. This is one I made when I became frustrated with the commercially made one, as it has the principals that the researchers used. It is a wing design, and it is designed so that the front part of the wing goes away from the slip stream of the foot, and captures "virgin" water (not influenced by the foot or leg). Here is a closeup of the blade I made for the SeaFin:

I thought that the SeaFin itself could be improved with springs, and so not only straightened out the metal rods so that they only bent about 5 degrees (instead of the 20 degree bend in the original), but also I carved away the "stops" built into the blade. That way, the blade could go over as far is it would go with the spring tension. I found that it went too far, and so added strings inside the springs to bring the blade to a stop at a reasonable angle. But because they are made of nylon, and stretch a bit, it is not a sudden stop like the originals had. Here is a closeup of the modifications to the blade:


I haven't had them in the water for over five years now, as I did break the strap buckle on one (it tore out of the side of the fin). But at one point I can put them back into the water while wearing another fin for comparison purposes, and may do that this summer.

John

[william]

That is really good. A great amount of information and experimentation to be sure. One thing that surprised me about the (Sea Fin) )(aka the Sea Pro)was how very Heavy they were. That weight and Bulk and Strong Inercia created, would seem to Cancel-Out any benefit of the Sea Fin's original design. I am sure that for actual use in diving the design would have to be made Much lighter. If too heavy the strong inertia of that weight would have a bad effect when changing dirrection of the Fin Kick by the diver. That would cancel out any improvements given by the new design . If the Sea Fin could have been made with much less weight and bulk and then, the design on the Scoop Fin incorporated into it also, then it most likely would be a Great Improvement over any Fin Design in existence today. The following is a Fin ( Technisub Idea 3) that seems to have taken technology, something like the Scoop Fin showed us and made it and Marketed it. They claim that it is rated #1 in many of the Dive Magazines of today in the (Ratio of-Effort Demand/Thrust Received.

[william]

I think that this Fin, the (Technisub Idea 3) made in Italy, has been known of by most people, except me, ha. This is the 1st time I have ever seen it. I was surprised when I came across it and read what it claims to be and do because I had just read very similar things in the Scoop Fin threads, which the tests and design of it has been around for quite a long time. It seems to be a Scoop Fin Like Design. It uses 3 different types of rubber (1) Foot Pocket type (2) Stronger Wishbone Shaped Rigid Rubber for holding the (3) Pre-Deformed Central Section Rubber which gives Variable Geometry to apparently catch a greater volume of water and direct it in the correct direction for very improved performance with less effort. If this Fin is Different than the Scoop Fin, I would like to know.

[SeaRat]

All of the commercial fins with a partial "scoop" idea lack one basic thing--they don't scoop enough. Here, with the Technisub Idea 3, the scooping is dependent upon the deformation of a flat surface. That cannot make a semicircle at the end, which it needs to do to incorporate fully the scoop design. Other fins don't start the scoop action high enough on the blade, and present a flat surface for an extended length of the fin's blade. The new Mares Avanti fins only partially incorporate the scooping action. The split fins use a scooping action, but allow a lot of the water to escape between the blades. That is my main criticism of today's fin designs. The scoop portion of the blade should inflate using the water pressure, and provide a dramatic channel to the rear (away from the feet) for the water to follow.

John

PS--in case someone is coming into this thread without having read the Scoop Fin thread (see the link above), the photo of the Voit Viking fins with the scoop modification is a photo of my scoop fin design taken in 1970 in Alexander Springs State Park, Florida.

[william]

I see what you are saying now and it makes sense. It really brings the two designs ( Scoop-Fin & Sea-Fin ) together in a way that would work with the least amount of the Divers Energy being lost. The Fin Blade would make a fairly strong "Angle of Attack" change when reversing your kick in swimming and the Scoop Fin (Pocket) contain and project the larger volume of water, rather than it falling off to the sides and being wasted energy. This does remind me of discussions of when an aircraft wing "Stalls" an the lift is lost. There must be a Special Fin Design that would put these ideas together in a way that will actually work just right and not be heavy and bulky. Then leasurely swimming with Fins will be less tireing to cover even more territory. William

[JohnA]

Lots of great work, but remember what we were all taught in economics 101, the Law of Diminishing Returns. The biggest variable is the swimmer, you can design the perfect fin for one person (V1) and it will be totally wrong for V2. Notice fish, every fish has a different fin "design", specific to their body/need.

Get yourselves some H Dessalts (or the like), and swim like the fishes!

John

[william]

Hi I would like to see what they look like. Is there a website or other, to see them? William

[JohnA]

Free diving fins, made by Sporasub, also related are Omers, Cressi-Sub GF 2000, ect. That is all I use for single tank diving. For tech I was using SP Jets but recently picked up on ebay a pair of Fara-fins with the spring straps. Need some leg muscels for those paddle fins, but they really move me with doubles and my deco bottle. ( my buddy bought a pair of Faras and hated them!, weak legs)

John

[william]

Special Experimental Fin Designs is something I have been fascinated with for some time now. I have some very unusual ones, like the Force Fins with the black "Bat-Wings", designed to channel large amounts of water,to help you "Fly Underwater"as they flex back & forth looking like the flying wings of a bat as you swim, ha, ha. I also have a slightly less extravagant set that uses what is called blue "Whiskers" to channel water in the optimum direction, rather than having it just fall off to the sides of the fin on the down stroke. It is a treat, seeing the eyes of the children get big when walking down and into the water, ha. William
and the blue "Whiskers"

[SeaRat]

William,

So, how do the Force Fins with Bat Wings work? They must be interesting to swim in.

John

[william]

Hey John I used the Blue Whiskers version so far. I could not really tell any difference from my Vikings when just slow swimming around. I did not do any tests either though, like swimming distance timing, kick counting or anything like that. I guess I really should try and do some type of comparisons the next time Cyndy and I get out Vintage Diving. The really Big Difference was the attention I was receiveing from the Youngsters. They looked Totally Fascinated by them. It was really cute to see their expressions when I put them on, ha, ha. That alone made them worth every bit that they cost me and they are very expensive. Example: the Bat Wing add-on alone for the 4 little wings is $100 extra. The fins were something like $200. So you are talking $300 for the set of Bat Wing Force Fins, ha. But (Bob Evans), the inventer and owner of Force Fins is a Wonderfull person. So I would be willing to bet that they could be purchased at a Much lower price if they were simply asked. William

[denniscarman]

Well I guess I just have to put my 2 cents in here. I accidently came to own a pair of IDF fins. Very simple but very flexible. They did propel me through the water with a lot of ease and I didn't really realize how much until students and dive buddies alike would ask what my hurry was. There wasn't any hurry, it's then I realized that besides using less effort I got more for what I was putting in. I do know that I could either catch up quick or when playing around get away from someone. I ended up thinking out of the box and realized that modern fins are with all their fancy do dads and the like have one thing in common. A relatively stiff fin which for most people becomes inefficient because they lack the muscle to use them to their potential.

I recall when I took my instructor training course one of the candidates who was a girl couldn't do the half mile snorkel in the 18 minutes as I recall. At the time I did I was the fastest of the bunch. She was upset and I told her she could do it but would have to get different fins. I asked if she could get some size 12 pocket fins and she could and did. The reason for the size 12 is so they will fit over the booties. Much more comfortable. She did her test again and while her feet paddles perhaps 2 3 times as fast as before she was comfortable and ended having the quickest time. Not something she intended but just the way it worked out.

I think many of the fins that have all of these fancy designs probably have more eye appeal than anything. Take for instance the one with the wing extension. I'm guessing that might work better in air then water because air is compressable and water isn't. So basically a design for air propulsion can't be used for water.

I've looked at fins on fish. Most fish have very thin and flexible fins. I think we have a chance to learn by observation. I also suspect that we shouldn't be able to wear a good efficient pair of fins on land. Which basically means that fins today are made so we can walk on land with them to some degree. I have always thought there should be an optimum angle so that the fin in a nuetral position would extend straight back from our feet. Perhaps not completely though because we can extert more power in a downward kick then return but there has to be an optimal angle.

Well I said I'd get my 2 cents in. I would like to see any feedback or comments on this.

Dennis