Vents on Jet Fins?
- Thread starter Eric Sedletzky
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OP
Eric Sedletzky
Contributor
Jets have been out since 1965, I don’t think they were big into DIR style modified frog kicks, heli turns, and backing up in tight quarters back then so that’s not what the design was about.
According to people I know who dived back then, the standard kick was a flutter kick from the hip, and Jets were not that great for that. I have a friend who is older than me (I’ll be turning 60) who was a competitive freedive spearfisherman in the early 1970’s. He’s been all over the world competing.
Back then freedive long fins had not been invented yet so a lot of divers used Duck Feet and other fins that were popular in the day, but all the guys that I’ve talked to who were in that scene said nobody liked Jet fins and they were absolutely terrible for freediving (standard long alternate fin kicks) and nobody used them.
I rate fins on how they perform freediving to gauge their worth. If a fin works well for freediving in a purist form then they will work for my style of scuba diving. For the style of diving I do I want fins that work well doing a standard alternate flutter kicks. But unfortunately long freediving fins are too difficult and impractical to use for beach diving in full scuba gear.
I don’t do caves, wrecks, or tight spots. I don’t need to back up, I go forward. I do open ocean dives and like to cover a lot of ground. I also do long surface swims. I am a typical California beach diver.
@David Wilson is a fin expert, maybe I need to summons him about what they were thinking when they incorporated the vents. According him the American copy of the original French Beuchat Jetfin is a pretty poor copy and doesn’t come close to what the originals were. But as I recall seeing in old photos and magazine ads, the originals were vented too.
Apparently it’s a “Dead Zone” in that area for most fins. For a non-vented fin, the resistance that the water faces just below the ankle area (that is tapering into the foot) contributes the least to forward thrust (imagine 10% or less). Venting that area allows the water to flow through and reduces the effort needed and muscle fatigue over repeated downward kick movements. Free diving fins are relatively quiet narrow in that area so the drag from that location is relatively minimal compared to the rest of the long fin.
David Wilson
Contributor
I'm not a physicist, so forgive me if I won't go into the science of fin blade venting. I recommend reading one of Beuchat's Jetfin patents, e.g. GB1223664.
Forgive me too if I just copy over here some text and images from another thread to save time.
I'm old enough to have been around in the early 1960s when the original Beuchat Jetfin first came out. The model was described in French as a "palme à tuyères" ("fin with jets" or "jetted fin" in English) and given the product name "Jetfin" as a single word. Here is an early flyer in French about the fin's mechanics:
Note how the fin was first conceived in the early 1960s as a full-foot fin because "palmes chaussantes" were considered to be the design of choice at the time for serious divers in Europe. Closed-heel fins back then were much more expensive than open-heel ones. As you have discovered, however, Beuchat did produce an open-heel version of the Jetfin to fit bigger foot sizes and Scubapro stuck to open-heels when the American company sold Jet Fins (two-word spelling) States-side.
Beuchat produced an open-toe version of the Jetfin in the late 1960s and early to mid 1970s. This version appeared in Beuchat's French (Dispositif d'accélération de poussée pour palme de natation) and British (Improvements in or relating to swim-fins) patents of 1971. The British patent drawings below:
And here is a picture of a pair of closed-heel and open-toed Jetfins:
However, the story doesn't finish there. Here's a 1969 Jetfin ad from the wonderful bibliotecadiunapneista.it site:
Note how this version has two jets instead of the usual three through the blade.
And there's more still. Here's a version with a closed heel, an open toe and the buckle points for a heel strap:
And here's another closed-heel with heelstrap version with a closed toe. Note the different blades:
It would appear that Beuchat developed many full-foot Jetfin designs, realising perhaps that Scubapro had no intention of releasing a closed-heel version of Scubapro Jet Fins and that Beuchat could therefore continue making and selling their own Jetfins in a variety of versions for the European market.
And to avoid disappointing the fans of open-heel Jetfins, here's a couple of pictures:
I read somewhere that the largest size Jetfins were open-heel because a closed-heel version would have cost too much. During the 1960s and 1970s, the full-foot fin was king in continental Europe.
Forgive me too if I just copy over here some text and images from another thread to save time.
I'm old enough to have been around in the early 1960s when the original Beuchat Jetfin first came out. The model was described in French as a "palme à tuyères" ("fin with jets" or "jetted fin" in English) and given the product name "Jetfin" as a single word. Here is an early flyer in French about the fin's mechanics:
Note how the fin was first conceived in the early 1960s as a full-foot fin because "palmes chaussantes" were considered to be the design of choice at the time for serious divers in Europe. Closed-heel fins back then were much more expensive than open-heel ones. As you have discovered, however, Beuchat did produce an open-heel version of the Jetfin to fit bigger foot sizes and Scubapro stuck to open-heels when the American company sold Jet Fins (two-word spelling) States-side.
Beuchat produced an open-toe version of the Jetfin in the late 1960s and early to mid 1970s. This version appeared in Beuchat's French (Dispositif d'accélération de poussée pour palme de natation) and British (Improvements in or relating to swim-fins) patents of 1971. The British patent drawings below:
And here is a picture of a pair of closed-heel and open-toed Jetfins:
However, the story doesn't finish there. Here's a 1969 Jetfin ad from the wonderful bibliotecadiunapneista.it site:
Note how this version has two jets instead of the usual three through the blade.
And there's more still. Here's a version with a closed heel, an open toe and the buckle points for a heel strap:
And here's another closed-heel with heelstrap version with a closed toe. Note the different blades:
It would appear that Beuchat developed many full-foot Jetfin designs, realising perhaps that Scubapro had no intention of releasing a closed-heel version of Scubapro Jet Fins and that Beuchat could therefore continue making and selling their own Jetfins in a variety of versions for the European market.
And to avoid disappointing the fans of open-heel Jetfins, here's a couple of pictures:
I read somewhere that the largest size Jetfins were open-heel because a closed-heel version would have cost too much. During the 1960s and 1970s, the full-foot fin was king in continental Europe.
Compact and powerful the vents help along with the flex of the fin tip to make them very good for flutter type kicks, they aren’t free dive powerful but do very well for being a few feet shorter, they still kick a** to this day and the only thing I’ve found to perform as well (if not better) is the Zeagle Recon which isn’t vented but does have a downward angle on the blade to help with the dead zone.
Bob Evans
Contributor
goldfishtornado
Registered
The dynamics would be hard to work out, but in general overlapping lifting surfaces generate more lift/thrust before stalling.
I think the claim is that you can over-kick a fin, and you effectively stall the foot pocket. One option to over come this is dynamically changing the angle of attack, which is roughly the idea behind the Seawing line of fins. The second option is to add an additional device to change the local dynamics. On an aircraft wing, such a fixed additional overlapping surface would be a leading-edge slot. This This isn't free though, it normally comes with a higher angle of attack and more induced drag.
This seems consistent with the observation OP made that you can wear yourself out faster with Jets vs long freediving fins. Those prioritize efficiency and are more akin to extreme high aspect ratio wings seen on gliders.
The idea for overlapping surfaces was promoted by Handley Page in the early 1900's. Here is a figure from his 1921 paper showing an extreme example:
I think the claim is that you can over-kick a fin, and you effectively stall the foot pocket. One option to over come this is dynamically changing the angle of attack, which is roughly the idea behind the Seawing line of fins. The second option is to add an additional device to change the local dynamics. On an aircraft wing, such a fixed additional overlapping surface would be a leading-edge slot. This This isn't free though, it normally comes with a higher angle of attack and more induced drag.
This seems consistent with the observation OP made that you can wear yourself out faster with Jets vs long freediving fins. Those prioritize efficiency and are more akin to extreme high aspect ratio wings seen on gliders.
The idea for overlapping surfaces was promoted by Handley Page in the early 1900's. Here is a figure from his 1921 paper showing an extreme example:
Bob Evans
Contributor
After swimming I realize this venting issue might be a can of worms, if not handled right. . I was given one of the first pairs of Jet Fins when I worked at Dive N Surf. 1966. "Big Jim" Christian of Scuba pro became a long life friend and his daughter Vicki helped built Force Fins years later. I dived those Jet fins for thousands of dives, over 2o years. I will work on this blog and show how vents do not function in the matter most thing they do. I did mess around with venting with some surprising results.
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