Vents on Jet Fins?

[gbf]

Doesn't matter what or how it works, or doesn't.

In 1967 I bought a pair. 15 years old and they were the baddest-azz, coolest thing going, and chicks dug them.

That's them in my profile pic, 30 years later. They were still the baddest-azz, coolest thing going. Chicks were fickle.

 

[tursiops]

In the Spring of 1967 I was "hired" by Sam Davison -- a.k.a. DACOR -- to consult on a new fin he'd developed...his answer to the Jet Fin. It also had vents, but were sufficiently different (I don't remember how) from those on the Jet Fins to avoid patent issues. The fin was a two-part fin...the blade was a rather stiff polymer, the foot pocket was rubber, all nicely molded together. I was a brand-new PhD in hydrodynamics who had taken a scuba (DH) class in college. My contribution was to go to a swimming pool with him and observe some swimming trials of several divers with the new fins, Jet Fins, and some others, and to try and explain any differences they felt in using them. Terrible experiment, no controls, totally inconclusive results. My opinion was that there was more difference caused by the several kicking styles than by the fins themselves. He didn't like that, but thanked me and bought me a hotdog for payment. He also used his "use of a PhD hydrodynamicist" as a selling point in some of his advertising material later, and there was even a story about it in Skin Diver magazine at some point. Years later, I bought a pair of the fins; they were pretty good and I used them for a long time. I liked them much better than Jet Fins, mostly because the foot pocket was more comfortable and the fins were lighter in the water....just like Eddys.

I found the Skin Diver article (Sept 1958) on the Internet Archive. It is attached.
There is mention in the article of flow visualization studies; I suggested that in my one visit with the team....and am pleased it made a difference to them.

 

[dm9876]

How @goldfishtornado described it is the same as how I think about it. Exactly like an airplane wing. On the down stroke it has a very high angle of attack to the water and the vent delays "stalling" by keeping the water flowing across the back of the fin in laminar flow attached to the blade instead of turbulent. Look at the jumbo jet wings when they extend the flaps for landing. Exact same thing.

Dean

 

[Bigbella]

Is anyone actually using JetFins for single-tank diving?

I do and have done so, for decades . . .

 

[undrwater]

I do and have done so, for decades . . .

JetFins, Jet Fins, or both?

 

[Bigbella]

JetFins, Jet Fins, or both?

Yeah . . .

 

[ark7750]

What exactly are the vents supposed to do on Scubapro Jet fins?
I was looking at them and wonder if they are actually counter productive?
It looks to me like on the downward stroke of a standard from the hip flutter kick that water will gush through those vents but what would be the benefit?
It seems like that’s wasted thrust.
I know those Scubapro version fins are from a 1965 design but what sort of science were those fins based on? Or was there any?
Was it a marketing gimmick?
People use them now doing all sorts of frog kicks, helicopter turns, backing up, etc. and love them, but back then nobody was doing that stuff (that I’ve heard about anyway), it was all standard flutter kicking.
I can confirm that they do suck for regular flutter fin kicking, but they do work well for everything else.

The vents just make a stiff fin easier to kick when you are kicking slowly, that's all. Stiff Jet fins are still hard to kick slowly and you don't get much speed when kicking slowly.

I think it was Pendercast (spelling?) or some university that did testing.

 

[Eric Sedletzky]

It looks like I’ll be headed back to a pool somewhere to test out more fins.
I’ve been using Jet’s for 20 years now but was never fully thrilled with them. They’re kind of the fin that I love to hate.
I’m finding that trying out fins these days is not as easy as it once was. Stores are not stocking as many different models as they once did since so much stuff is online now. I used to be able to try a lot of different stuff out in a pool before buying but that is limited now.
So I’ll have to round up friends who have different fins and test them out.
My LDS has Nova’s for rent but I’m not super excited about those.
I just want to see if there’s something around the corner that better than Jet’s that maybe has been hiding in plain sight the whole time.

 

[lexvil]

It looks like I’ll be headed back to a pool somewhere to test out more fins.
I’ve been using Jet’s for 20 years now but was never fully thrilled with them. They’re kind of the fin that I love to hate.
I’m finding that trying out fins these days is not as easy as it once was. Stores are not stocking as many different models as they once did since so much stuff is online now. I used to be able to try a lot of different stuff out in a pool before buying but that is limited now.
So I’ll have to round up friends who have different fins and test them out.
My LDS has Nova’s for rent but I’m not super excited about those.
I just want to see if there’s something around the corner that better than Jet’s that maybe has been hiding in plain sight the whole time.

I think you’ll find nova’s to respond to your free dive friendly kicks better than most scuba fins, standard Sherwood Tritons are really good cross over fins too.

 

[Jim Lapenta]

I was under the impression that this was solely to mount the mini rockets to take out the guy trying to sneak up and cut your airhose? Learn something new every day.