List and features of jet fin clones

[Sbiriguda]

@Sbiriguda Very interesting historical information so far, but is that what you were interested in? Or was it currently available Jet type fin clones?

My question was originally about the currently available Jet type fin clones. The question was kind of practical, I have always used Mares Avanti 4 type and I was collecting some info about jet fin, especially in case I will buy a drysuit. I can put the question this way: should I consider only Scubapro jet fins or are there alternatives among the several clones that might be worth it in terms of different and better features?
Anyway I like the historical information very much, I really didn't know there was so much to learn about this specific type of fins. I thought there was one Scubapro jet fins model from the 1960s until the patent expired, and others were allowed to manufacture clones. It seems there were plenty of illegitimate clones in several countries since the very beginning, and even the Scubapro were actually a clone themselves, of the Beuchat fins...

 

[Popgun Pete]

The main change has been Jetfins made of lighter compounds and spring heel straps, plus sizes of foot pockets. The Lightning Jetfin from Scubapro was an economy move to use the same rubber used in their floating fins, it was stated in a “Skin Diver” article at the time. If you need more weight in your fins then you want rubber fins, not plastic hybrid versions. The Scubapro Jetfin was made in the USA under licence from Beuchat, so it is an authorized copy. Ultimately the fins have to suit you, what one person likes may not meet your requirements. To some extent availability and price determines what people buy. Jetfins only came in black until others made copies in a range of colors.

 

[JackD342]

My question was originally about the currently available Jet type fin clones. The question was kind of practical, I have always used Mares Avanti 4 type and I was collecting some info about jet fin, especially in case I will buy a drysuit. I can put the question this way: should I consider only Scubapro jet fins or are there alternatives among the several clones that might be worth it in terms of different and better features?
Anyway I like the historical information very much, I really didn't know there was so much to learn about this specific type of fins. I thought there was one Scubapro jet fins model from the 1960s until the patent expired, and others were allowed to manufacture clones. It seems there were plenty of illegitimate clones in several countries since the very beginning, and even the Scubapro were actually a clone themselves, of the Beuchat fins...

Well then, your quick answer is no, you don't need to limit yourself to Scubapro. Lots of variations in the marketplace, and you will probably find that for each of them there are some folks that love them and others that hate them.
My advice is to start by not limiting your choices to something that is as old as possible with an uncomfortable foot pocket and a difficult strap mechanism. There is nothing inherently wrong with newer, more comfortable, and easier to use.
As a general rule, the stiffer fins are denser and will be more negative in the water, and perhaps initially provide a few more leg cramps along with more power. More flexible version will still be heavy in your gear bag, but less so in the water.

Personally, I am diving Apeks RK3 fins and do like them. Since you are using Mares already, I'll point out their fin in this customer segment is the Power Plana. It is intended for the same needs and the same divers, but stands out by NOT being an obvious Jet/Rocket design variation.
Power Plana

 

[tursiops]

If you jump in a time machine and go back to the beginning then you will find that the aim of the Jetfin was to provide thrust without resorting to a very long blade fin which were also around at that time in rubber (mid-sixties). No plastic fins back then except for the Technisub “Caravelle” demountable blade fin and that was for transport when out of the water. The philosophy was for a wider fin that was short and had an efficient cruise when operated at a moderate kick rate as turbulence was reduced on the downstroke which is the power stroke and that reduced their hydrodynamic drag and any suction effect behind the descending blade. The venturi tunnels of a certain length that exited on the rear of the upper blade were the key to creating water flow on either side of that blade and their width was selected so that the fins did not hit each other as they passed each other on their respective strokes.

All fins work by driving water rearwards which pushes the diver forwards. Fin blades also push water up and down and slightly forwards, but that does nothing for forward propulsion, although it aids in turning and pivoting around in the water. If you watch a diver from directly behind then the area of fin blade that you can see as they pump up and down, which of course varies during the kick cycle, is what drives you forwards. The more area in terms of a component facing rearwards, then the more water is thrusted rearwards, or a component thereof if we think of a vector analysis. Jetfins aim to increase efficiency at a certain kick rate where the venturi action works best and swap blade width for length. Their rounded profile closed toe foot pocket allowed for best hydrodynamic flow pattern entering the blade area as you travel forwards. The ultimate aim was a fin that you could walk around in for short distances out of the water or in the shallows, while providing good thrust. Jet is for jet action, not jet performance as in swimming fast.

Split fins or propeller technology increase blade area by the central splits causing the blades to bend inwards much further up the fin in a sort of triangle on each side so looking from the rear you see a greater area driving water rearwards. What makes them work is the fat rounded side ribs are not only longitudinal springs, they are torsional springs that restore the blades to flat as they twist up and down laterally forming those triangular blade shapes. The propeller description is not that of rotating propellers, but oscillating propeller blades as obviously they don’t rotate through 360 degrees. As this flicking of the blade in a twisting motion in the lateral direction works with the fin blade going either up or down they produce thrust on both strokes and can perform with a jiggling motion of the feet that involves no great amplitude. If the fin blade side to side on the same fin gets out of sync then their performance evaporates, the blade halves have to work together. Cross currents can kill their performance if the fins are not moving, so you need to turn into the current, get them driving again and then with power switched on you can regain your original course.

Long blade fins show a greater area facing rearwards as they beat up and down, but only the end or tip sections drive you forwards and the front section below the foot pockets act as brakes. However the area projecting forwards is nothing compared to the rear sections which are driving rearwards and that is why those fins are very powerful. They are also nigh impossible to walk in out of the water, unlike Jetfins!

This explanation does not include the effect of the starting vortex, which is an unavoidable hydrodynamic effect of moving an object through the water. The starting motion -- each stroke of the fin -- leaves behind a vortex spinning in the water, caused by the boundary layer shed off the tip of the blade. This unavoidable spinning motion is energy lost so you want as little of it as possible....which implies long, slow strokes. The genius of the split fin is that a boundary layer is shed off each of the bent blade halves, and they spin in opposite directions as they go off the split blade. This forces some water away and gives some propulsion, so it not all lost energy. For this to be effective, you want a lot of small-amplitude fin strokes, so lots of pairs of counter-rotating vortices are produced. Big slow fin kicks with split fins provide little propulsion...little from the floppy blade and little from the few vortices.

 

[Popgun Pete]

I bought the first all rubber black Apollo Biofins in 1998 and they certainly work best at a quick, small amplitude kick, in fact at full pelt the water flow streaming past my face peeled my lips back on my snorkel mouthpiece, yet not a huge effort was required. However a lot of my diving is scanning for prey and at a slow long kick they were nothing exceptional as then the blades are not laterally twisting inwards with the slow strokes. Because I often wear a 7 mm full hood attached/long John wetsuit and hard sole 5 mm boots I need heavy fins to stop my feet floating. The fins that gave the best weight are my Farallon Fara Fin II models, but the Biofins are nearly as heavy. One thing I found if the Biofins are slightly loose on your feet then the performance is greatly reduced, but yank on the trailing fin straps to tighten them up and the power comes back on like throwing a switch. Any lost motion between dive boot and foot pocket ruins the efficiency of most fins. The deeper your boot goes into the foot pocket the better they are, but while Jetfins tended to have shorter pockets really hard sole boots eliminate this factor, such as Moray "Black Diamond" dive boots.

In fact here I am encased in rubber preparing to whittle down the local fish population. The catch bag contains my Farallon fins as they give best lateral support for loading a pneumatic gun off your foot.

 

[Sbiriguda]

I have found this thread
Jet fins vs Apeks RK3 fins....thoughts?

 

[Sbiriguda]

I am trying to list the several alternatives I found on the market

1) Scubapro Jet Fin
2) Apeks TEK RK3
3) Apeks Tek RK3 HD
4) Hollis F1 Bat Fins
5) Deep 6 Eddy Flippers
6) Beuchat Jetfin
7) Dive rite XT Spring Strap
8) De profundis Techfin 2
9) xDeep EX1 Medium
10) xDeep EX1 Soft
11) Mares Xr Power Plana Tec
12) Poseidon Trident Fin with Spring Straps
13) Pinne Tecniche OMS Slipstream

And so on and on... I suspect there are many more

 

[Popgun Pete]

Don't confuse jet action vents with fins that have holes or windows in them as they don't do the same thing. US Divers had a "Compro" fin where the three windows and entry lip curved the other way so that water flowed through the fin windows on the upstroke. Dacor had something similar in their "Turboflex" fin. This lessens effort on the upstroke and does not attempt to improve fin efficiency. Of course water flows through the windows on the downstroke as well, but the effect is aimed at bypassing water on the upstroke and having less of an effect on the downstroke. Many fins today have apertures in the fin blade, but they don't do a lot for performance. This has come about with plastic fins that can be made in more complicated and stylish shapes as their struts are stiffer than rubber fins while being less bulky overall, plus they have the advantage of color and can be produced in multiple colors in the one fin.

Many years ago Mares had the "OK" fin with flaps that opened either way on each side of the blade, so they had a bet each way on passing water through the fin blade during both the up and down strokes.

 

[David Wilson]

I chanced upon this image of Jet Fin clones recently, Pete:

Hanimex Pro Continentals for the Australian market. For those not in the know, Hanimex Corporation Limited was the photographic equipment maker and trader that took over Australia's best-known fin, mask and snorkel manufacturer Turnbull Rubber Pty of Sydney in 1969.

 

[Popgun Pete]

Well as you can see no venturi effect with these Rocket clones, just bypass vents. The venturi uses large area inlets and smaller area outlets that cause the water to speed up as it goes through the tunnels as the mass flow rate stays the same. However the effect does not work right through the kick speed range of the fins and over kicking Jetfins makes their performance fall off. The long blade Jetfins (not the "Super Jetfins") have much bigger vents and tunnels with both larger area inlets and exits and they can send you along much faster, but they too have their limits and what you are really interested in is power rather than speed, such as pedalling along the bottom moving against a current.