Your kidding right captjohnr. The only cave diver I've ever seen take splits into a cave is a sump diver who has some kind of leg problem that makes it hard for him to frog. In the sumps he spends more time crawling than swimming. I think split fins would be great for crawling but a good old fashioned paddle is for cavin and frogin.
Split fins or Conventional?
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captjohnr
Registered
Hey Mike,
I did not say that splits are for caving... that is a reprint from an article that teaches folks to use the frog kick with the splits.
A lot of folks that have replied to this thread say they can not do a frog kick.... well here's how.
I use the old frog fins for caving. I use splits for teaching and slinging steel.
I did not say that splits are for caving... that is a reprint from an article that teaches folks to use the frog kick with the splits.
A lot of folks that have replied to this thread say they can not do a frog kick.... well here's how.
I use the old frog fins for caving. I use splits for teaching and slinging steel.
You can...but not with split fins the way they are currently designed.
In the 1960's through about 1975, I worked out an alternative design that I still use. The Plana Avanti is based upon this design. Basically, I did a lot of water flow research while in the Air Force (my own, not sponsored). If you want to analyze the water flow and see what's happening to the water from your fins, put a number of pins with threads on them in various places on the fin. I put them on straight blades, and vented fins, and found that the water flow for most fins has a "dead area" just beyond the toe. Even vented fins have this effect.
I took that research, and developed a home-made pair of fins with a flexible membrane (canvas at the time) between the two outside ribs. I cut the original material away to get that open area, then put the membrane onto the fin. I did it in such a manner that it tapered from the toe, where it was stretched tightly across the space, to the area at the end of the blade, where the membrane created a semi-circle. This I dubbed the "scoop" fin. It effectively channeled the water from the toe to the tip of the fin blade, and it did (and still does) do this more effectively that do any commercial blades now on the market (or that have been on the market).
I tried to patent this design in 1971, but a patent search showed that it was already patented by Frank N. Murdock, of Bellevue, Washington, patent #3,411,165 in 1968. This design has never hit the market, but split fins could easily be modified to incorporate it, as could some channeled fins (by cutting out the channel, and letting the channel become a single semicircle at the blade's tip).
What do you get if you make this modification? Well, how about this:
--Virtually no splash when the fins break the surface.
--Increased power due to efficient channeling of the water behind the diver (proven by my tests using strings to show water flow, by my incorporation of this design and by diving it ever since about 1968).
--The same decrease in leg fatigue that split fin users have, without the loss of power.
I have used them in spring diving (Warm Mineral Springs UW Archaeological Project--1973), in parascuba jumps, and every manner of diving (rivers, lakes, open ocean, etc.). They really have no down side, and you would do well to experiement with this to try to prove me wrong. I'm not.
SeaRat
dotyj
Contributor
Sounds cool. Do you have any photos?
I'm amazed on how some technologies never make it into the mainstream.
I'm amazed on how some technologies never make it into the mainstream.
richhagelin
Contributor
Strong vote for a picture of the design. Sounds interesting
Rich
Rich
I tried to get into the forum over the weekend, but for some reason wasn't able to. I will try to post a photo tonight, but will need to learn how first. In the meantime, here's my disclosure of invention:
Disclosure of Invention
1 July 1971
On the market today are many swim fins, most of which have the same basic design. They have a thirk, flat rubber blade which is further stiffened by rubber ribs. Two ribs are placed on the outside edges of the blade, and the blade area is usually further reinforced by one or two ribs in the center of the blade. The fins are made in varying degrees of flexibility to match the strength of the swimmer. However, each of these basic designs present an essentially flat blade to the water. In the stiff "competition" fins, it's almost like moving a piece of plywood through the water. The ribs of these models are used to channel the water "down" the fins. However, much of the wather seems to flow or "fall" off to the side instead of traveling rearward to propel the diver. There are two or three fins on the market which offer improved variateons of this basic design. One opens the blode for a couple of inches below the toe and puts a hinged flade behind. The water flows through the blade's opening, opens the hinged blade and flows rearward. Another excellent variation is a fin which uses two overlapping blades. Water was forced between the two fins and "jetted" to the rear through the opening. The disadvantage of these variations is that they work only on one portion of the kick, the downstoke. On the upstroke, the vent is closed and the opening is wrongly oriented. The only difference between today's fin and those of fifteen years ago, excepting the two variations above, is that they are somewhat larger, and the footpockets are larger and more comfortable.
A little over three years ago, I began looking into the possibilites ofg different swim fin designs. I also spent some hours watching aquariums fish swim, paying close attention to the movements of their tailfins. What most impressed me about the swimming movements of the fish was that the tail fin never presented a flat surface to the water. Rather, the outside spines of the tail are fairlf rigid while the inner "blade" area is flexible. This allows the fin to "cup" or "scoop" more water at a given rib interval.
I immediately set about modifying a pair of fins which had a flat plastic blade. I cut the inside of the blade out, leaving an inch or so for the outside ribs. I then had a sheet metal, horseshoe-shaped cover made to fit over the ribs as a backnig for a soft, flexible rubber blade. For rubber, I used an old car innertub. These fins were tested, first in a swimming pool, then at a beacdh and finally on at least two open sea dives, one to 70 feet and one to a depth of over a hundred feet. In the pool, over a distance of twenty yards, they appeared to give a somewhat greater speed with less effort. They worked very well and were comfortable in all open sea dives, the only drawback being that when the metal horseshoe was bent while walking on coral after a dive, the fin had to be taken off and straightened.
Since 1968, when these fins were made, I have also modified two other pair of fins, each of different brands. Each has flexible ribs, thus differing from the first pair. Both have shown excellent handling qualities, improved comfort and performance. In addition to this, I have found that the fins, even when forcefully slapped down on the water's surface, give very little splash. In the swimming position, when th fin is brought to the surface of the water on the upstroke, the blade is fglexed down. At the surface, when the downstroke begins, the blade is stationary until the ribs pass its lowest point. ath which time it flips and scoops downward. If the outside ribs come a couple of inches out of the water on the upstroke, the flexible blade is still underwater. Only the ribs break the surface and splash on the downstroke. If the whole fin is brought completely out of the water, the flexible blade softens the splash by gining away when it hits the water's surface.
SUMMARY
Instead of a fin blade which is flat, this fin is designed to have fairly stiff outre ribs, lighter inner ribs (or none at all) and a very flexible, rubber impregnated canvas blade which is pulled tight at the end of the footpocket, but gradually gets looser until at the fint's tip, the canvas is almost semi-circular in shape. On the stroke, the canvas flexes away from the direction of the stroke, thus giving more surface area in contact with the water, more volume of water under the control of the fin's outer ribs and a better angle of attack to the fin. THe canvas flips at the end of the stroke and therefore is useful on both the upstroke and the downstroke of the diver's kick. In addition, because of the fin's design there is much less splash when the water's surface is broken.
Signed,
John C. Ratliff
1 July 1971
______________
Because it was already covered by a patent, I did not pursue it further. I did write Mares twice, I think, telling them that they had not gotten the design correct. They still haven't.
It looks like I've figured out how to attach a photo, and later I'll put a drawing on too. You can see the strings I placed on the fin's flexible blade are mostly inside the blade's ribs, which is much better than flat bladed fins, or even ones with the ridiculously-small channels going down the fin's blade but starting beyond the "dead" area of the blade.
Enjoy,
SeaRat
Disclosure of Invention
1 July 1971
On the market today are many swim fins, most of which have the same basic design. They have a thirk, flat rubber blade which is further stiffened by rubber ribs. Two ribs are placed on the outside edges of the blade, and the blade area is usually further reinforced by one or two ribs in the center of the blade. The fins are made in varying degrees of flexibility to match the strength of the swimmer. However, each of these basic designs present an essentially flat blade to the water. In the stiff "competition" fins, it's almost like moving a piece of plywood through the water. The ribs of these models are used to channel the water "down" the fins. However, much of the wather seems to flow or "fall" off to the side instead of traveling rearward to propel the diver. There are two or three fins on the market which offer improved variateons of this basic design. One opens the blode for a couple of inches below the toe and puts a hinged flade behind. The water flows through the blade's opening, opens the hinged blade and flows rearward. Another excellent variation is a fin which uses two overlapping blades. Water was forced between the two fins and "jetted" to the rear through the opening. The disadvantage of these variations is that they work only on one portion of the kick, the downstoke. On the upstroke, the vent is closed and the opening is wrongly oriented. The only difference between today's fin and those of fifteen years ago, excepting the two variations above, is that they are somewhat larger, and the footpockets are larger and more comfortable.
A little over three years ago, I began looking into the possibilites ofg different swim fin designs. I also spent some hours watching aquariums fish swim, paying close attention to the movements of their tailfins. What most impressed me about the swimming movements of the fish was that the tail fin never presented a flat surface to the water. Rather, the outside spines of the tail are fairlf rigid while the inner "blade" area is flexible. This allows the fin to "cup" or "scoop" more water at a given rib interval.
I immediately set about modifying a pair of fins which had a flat plastic blade. I cut the inside of the blade out, leaving an inch or so for the outside ribs. I then had a sheet metal, horseshoe-shaped cover made to fit over the ribs as a backnig for a soft, flexible rubber blade. For rubber, I used an old car innertub. These fins were tested, first in a swimming pool, then at a beacdh and finally on at least two open sea dives, one to 70 feet and one to a depth of over a hundred feet. In the pool, over a distance of twenty yards, they appeared to give a somewhat greater speed with less effort. They worked very well and were comfortable in all open sea dives, the only drawback being that when the metal horseshoe was bent while walking on coral after a dive, the fin had to be taken off and straightened.
Since 1968, when these fins were made, I have also modified two other pair of fins, each of different brands. Each has flexible ribs, thus differing from the first pair. Both have shown excellent handling qualities, improved comfort and performance. In addition to this, I have found that the fins, even when forcefully slapped down on the water's surface, give very little splash. In the swimming position, when th fin is brought to the surface of the water on the upstroke, the blade is fglexed down. At the surface, when the downstroke begins, the blade is stationary until the ribs pass its lowest point. ath which time it flips and scoops downward. If the outside ribs come a couple of inches out of the water on the upstroke, the flexible blade is still underwater. Only the ribs break the surface and splash on the downstroke. If the whole fin is brought completely out of the water, the flexible blade softens the splash by gining away when it hits the water's surface.
SUMMARY
Instead of a fin blade which is flat, this fin is designed to have fairly stiff outre ribs, lighter inner ribs (or none at all) and a very flexible, rubber impregnated canvas blade which is pulled tight at the end of the footpocket, but gradually gets looser until at the fint's tip, the canvas is almost semi-circular in shape. On the stroke, the canvas flexes away from the direction of the stroke, thus giving more surface area in contact with the water, more volume of water under the control of the fin's outer ribs and a better angle of attack to the fin. THe canvas flips at the end of the stroke and therefore is useful on both the upstroke and the downstroke of the diver's kick. In addition, because of the fin's design there is much less splash when the water's surface is broken.
Signed,
John C. Ratliff
1 July 1971
______________
Because it was already covered by a patent, I did not pursue it further. I did write Mares twice, I think, telling them that they had not gotten the design correct. They still haven't.
It looks like I've figured out how to attach a photo, and later I'll put a drawing on too. You can see the strings I placed on the fin's flexible blade are mostly inside the blade's ribs, which is much better than flat bladed fins, or even ones with the ridiculously-small channels going down the fin's blade but starting beyond the "dead" area of the blade.
Enjoy,
SeaRat
erichK
Contributor
I am going to try closing the split in my ScubaPro Twinjet fins, using duct tape. While the outside ribs on these fins may not be quite as rigid as they should be, this should provide some of the scooping effect that is being touted here.
erichl
erichl
MARINABROKER
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Newbie here! My Twin Jets haven't gotten wet yet. I bought them based on research and my own personal strengths and weaknesses. Hope I made a good choice. Do you like yours?
As an old-time tape user, I have a few suggestions for you temporary modification. In the Air Force, we used tape to close off our scuba tanks when we put a parachute harness over it. It worked great to keep the harness from fouling on our scuba gear. We also used it to tape our fins onto our feet for parascuba jumps. There's nothing like jumping from 1250 feet into the ocean, and loosing one or both swim fins (or forgetting them, and going finless as one PJ who won't be named did--completed the installation of a floatation collar onto an Apollo capsule during an Apollo Sim-Ex too without fins, quite a feat).
Anyway, start at the top of the fin, and wrap around the fin, giving you the material you need when you get to the bottom. Don't try it lengthwise, as the tape isn't good enough to hold only by its adhesive action. Going around, and down the fin, should work. Give it a try and please do report your results.
SeaRat
Anyway, start at the top of the fin, and wrap around the fin, giving you the material you need when you get to the bottom. Don't try it lengthwise, as the tape isn't good enough to hold only by its adhesive action. Going around, and down the fin, should work. Give it a try and please do report your results.
SeaRat
erichK
Contributor
I've been using mine for most of the year. I'm reasonably happy with them, especially after trying them against a pair of Mares Vollos, which I found put more pressure on my knees and legs, but were really not faster.
But I do wish they were just a little stiffer, and am always happy to try a new idea.
erichk
saskatoon, canada
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