List and features of jet fin clones

[Popgun Pete]

A note on full foot pocket Jetfins with heel straps which seem an odd combination at first as adjustable straps are usually associated with open heel versions of fins. Under certain circumstances when exiting on a steeply sloping beach or one with a gutter running along where waves dump it is possible for a strong run back moving out to sea under the water on the surface that is coming inwards to neatly peel full foot fins off your feet. The rushing water bells out the fin's pocket on your feet, even if they are a good fit, and the foot you are just lifting up has the fin swept off before you know it. I lost one of my Voit “Skin Diver” full foot fins just like that, however the replacement fins were my first pair of Jetfins and being full foot and with a heel strap they never came off under similar water conditions.

 

[David Wilson]

A note on full foot pocket Jetfins with heel straps which seem an odd combination at first as adjustable straps are usually associated with open heel versions of fins.

That's quite a collection, Pete, and thank you for that explanation of the effectiveness of full-foot fins with heel straps. I believe Beuchat was the only French company to make such fins and the Marseilles firm's invention of the "fixe-palme" fin grip (patent drawing below) in 1959 proved to be a more enduring and versatile product on the market for closed-heel fin security:

I believe the first full-foots to be fitted with heel or instep straps may have been made in the late 1950s by the Italian diving equipment manufacturer Cressi for Healthways, which was Cressi's American distributor:

From my current online research, I tentatively conclude that just one full-foot Jetfin clone fitted with straps and buckles remains in production worldwide nowadays:

The model above is the "Süper Jet" made in Istanbul by Turkish rubber products manufacturer Adalılar Kauçuk. The same company also continues making the all-rubber long-bladed fins below, presumably using old Mares Concorde moulds:

 

[Popgun Pete]

The Turnbull "Giant Continental" was a full foot fin that had an additional strap much like the fins shown above, its claim to fame was the angled blade that made it lie more horizontally in the water with the feet held at a natural angle. Cressi-Sub's "Rondine" full foot pocket rubber fins had a similar blade angle and Turnbull probably copied it.

 

[David Wilson]

The Turnbull "Giant Continental" was a full foot fin that had an additional strap much like the fins shown above, its claim to fame was the angled blade that made it lie more horizontally in the water with the feet held at a natural angle. Cressi-Sub's "Rondine" full foot pocket rubber fins had a similar blade angle and Turnbull probably copied it.

I'd forgotten about the Australian Turnbull Giant Continental with its instep strap, which Lillywhites of London also imported for the British market in the early days:

I wonder whether the Soviets also copied the Healthways/Cressi instep strap when their Mosrezina factory in Moscow manufactured "Model 3" closed-heel fins:

The last image is from a 1959 issue of the Soviet magazine ЖУРНАЛ ТЕХНИКА МОЛОДЕЖИ.

 

[Doctor Rig]

I would like to try to list the most important jet fin type fins and to understand if they really differ one from the another. Which ones are best? What are the differences? Are Scubapro jet fins still the best or someone improved the original design?

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

 

[Sam Miller III]

I agree with @Doctor Rig (who is a vacation diver and doesn't log dives

SDM

 

[Popgun Pete]

There are copies that are exact duplicates made in Asia and come in a wide range of rubber colors and then there are close replicas such as these OMS Slipstream fins. The relief holes are much larger and outside the venturi tunnels rather than inside the tunnels as they are on a Jetfin. OMS Slipstream Fins | Dive Gear Express®

Scubapro tried to update the "Jetfin" with the first "Sea Wing" open heel fin that was a plastic fin with the side rails cut off and the fin blade and pocket somewhat angular with straight lines replacing the previous curves, but it was still a vented blade system. These vents had some blade overlap, but to get them out of the mold the lower blades were angled back at each corner which stymied their effect as venturis as water was not constricted by the channels. They were disappointing fins as they were not as good as their predecessors and Scubapro tried many blade materials and even a version molded in rubber. One key difference was that the tab like lower blades were intended to close the vents on the upstroke as can be seen illustrated in the patent drawing. I owned a pair with the translucent crystal clear blades in teal colour and foot pockets in black with the revised buckle system, but could get no real thrust out of them.

One thing for sure is they looked entirely different and almost sculptural, especially in the clear blade version.

 

[Popgun Pete]

Last year I purchased another new pair of open heel French "Jetfins" made by Beuchat with spring heel straps as supplied by the company. On special they were only 130 bucks, including shipping, so why bother with clones?

 

[Popgun Pete]

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!

 

[Popgun Pete]

Pivoting hinge blades such as the “Volo” aim to have more blade area facing rearwards by creating a fin that bends up and down just below the foot pocket so that most of the blade does what only the tip section did before, however rather than distribute stress along the side ribs in a more even fashion they impose stress at a more localized point. Unless the fin is constructed from material that has a long fatigue life then they will break in two, something that has happened to hinging fins in the past, including the “Sea Wing” fins.

Long blade carbon fiber and other reinforced resin blade fins don't have hinge points, but need their long length to enable a sizeable area in the rear section to push rearwards. Water is being pushed up and down with the forward section which does nothing for performance, but that is the price you pay for a large rearward area pushing water backwards. The long blades also act as long springs, flicking back and pushing water even after the leg action stops pushing.