What's perfect should not be improved....

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  • And now for the biggest, most interesting point:
    I've never seen any physics or hard experimental evidence proving that the jet fin vent (or indeed any other) design really IS better than all the other gimmicky fin efficiency features out there. Does the vent really make jet fins that much better than an unvented paddle of equal stiffness and weight? Is the vent optimally designed? I would love to see some good independent science done on this. That said, they do seem to work, and anecdotally work better than similar knockoff fins with less vent overlap (eg. RK3s).
"Work better" at what? Fin design (product design in general) is about deciding what you want to accomplish and what tradeoffs you'll have to make to accomplish it. For some products, you can improve everything if you are willing to increase the price. But fluid dynamics requires you to make performance tradeoffs. Making things better in one area is inevitably going to make them worse in another.

I'll give a couple of examples. If you watch cycle racing, you'll have seen time trial helmets become increasingly longer and weirder shaped Greg Lemond's 1989 Tour de France win until 2 seasons ago when they abruptly returned to near normal. It wasn't a rule change. What happened is that helmets were developed with the goal of the least drag when a rider was in an ideal position on the bike. Something like this:
aero_training_01042015.jpg


But then the technology got sophisticated enough to model what happens with crosswinds and a rider's actual position over the entire course of a race and they found that the average drag was worse with extreme helmets. It turns out that a whole lot of the small advantage accrued from the above can get cancelled out by just a little of this:
nZnqXf-b56D90w1IGI-qqfH4d7DuQbKGiXAE9xdt3OboqZnHozYQTo16gz2z8lazTtLtOCZBf1Xro1qGhx_8ZMq2T0vxV49k.jpg


Another example would be propellor pitch on airplanes or boats. You can pitch for a higher cruise speed at the expense of climb/initial acceleration or the reverse. But you can't have both with a fixed pitch prop.

Back to fins. Jet Fins are popular because their compromises match what their users are looking for. First would be precision, small foot movements immediately turning into predictable thrust. Basically a "climb prop". Second would be ability to work with several different kicks. Third would be a convenient size.

So what are the tradeoffs? Top speed for one, a monofin or long freediving fins are a lot faster. Low effort is another. Split fins became popular for a reason, if you stick to their preferred kicking style you can maintain a moderate speed with lower effort than jets.

I should mention Force Fins here. Bob knows this stuff more than anyone and has designed fins that can do pretty much whatever you want. Including fins with user adjustable aerodynamic surfaces, so you can adjust the tradeoff profile mid-dive. The downside here is cost. Not that many people are willing to spend $300 to $400 for what may turn out to be marginal gains for their purposes.
 
Years 1968 to 1985 yes, after that Mares fins, if I was in the market for new fins for dry suit diving I would buy Mares Power Plana.
Could never get Jet fins to fit just right .
Oh, and love the Trappist beer,yum.:cheers:
 
Years 1968 to 1985 yes, after that Mares fins, if I was in the market for new fins for dry suit diving I would buy Mares Power Plana.
Could never get Jet fins to fit just right .
Oh, and love the Trappist beer,yum.:cheers:
My post was already too long. But I was going to mention Mares Avanti Quattros as another fin with a set of characteristics that hits a sweet spot. In this case for warm water instructors and DMs. Compared to Jets, they give up a little in precision and initial thrust and are quite a bit longer which can be an inconvenience, but in return they provide an easy kick at moderate speeds, a higher top speed for chasing down straying charges and most people find them more comfortable.
 
"Work better" at what? Fin design (product design in general) is about deciding what you want to accomplish and what tradeoffs you'll have to make to accomplish it. For some products, you can improve everything if you are willing to increase the price. But fluid dynamics requires you to make performance tradeoffs. Making things better in one area is inevitably going to make them worse in another.

I'll give a couple of examples. If you watch cycle racing, you'll have seen time trial helmets become increasingly longer and weirder shaped Greg Lemond's 1989 Tour de France win until 2 seasons ago when they abruptly returned to near normal. It wasn't a rule change. What happened is that helmets were developed with the goal of the least drag when a rider was in an ideal position on the bike. Something like this:
View attachment 643907

But then the technology got sophisticated enough to model what happens with crosswinds and a rider's actual position over the entire course of a race and they found that the average drag was worse with extreme helmets. It turns out that a whole lot of the small advantage accrued from the above can get cancelled out by just a little of this:
View attachment 643908

Another example would be propellor pitch on airplanes or boats. You can pitch for a higher cruise speed at the expense of climb/initial acceleration or the reverse. But you can't have both with a fixed pitch prop.

Back to fins. Jet Fins are popular because their compromises match what their users are looking for. First would be precision, small foot movements immediately turning into predictable thrust. Basically a "climb prop". Second would be ability to work with several different kicks. Third would be a convenient size.

So what are the tradeoffs? Top speed for one, a monofin or long freediving fins are a lot faster. Low effort is another. Split fins became popular for a reason, if you stick to their preferred kicking style you can maintain a moderate speed with lower effort than jets.

I should mention Force Fins here. Bob knows this stuff more than anyone and has designed fins that can do pretty much whatever you want. Including fins with user adjustable aerodynamic surfaces, so you can adjust the tradeoff profile mid-dive. The downside here is cost. Not that many people are willing to spend $300 to $400 for what may turn out to be marginal gains for their purposes.

I think your helmet anecdote illustrates my point. Fluid dynamics is extremely complex and it's common to design things that LOOK like they're optimized for a purpose when they're actually not. There are significant design differences between fin models meant for the same purpose. I'd like to see some proper testing and comparison beyond that old navy study or crappy magazine reviews.
 
I'd like to see some proper testing and comparison beyond that old navy study or crappy magazine reviews.

The fact that so many cave divers doing extreme penetrations still use Jets is a testament to their design.
Seems like proper testing to me. Every tester having no reason not to switch to a "better" fin.
Since personal differences come into play, some may prefer to switch but there is no denying the dominance Jets have in technical diving.
Like vehicles, unless you're drag racing, the "best car" isn't a nitromethane funny car. It's the car that does everything YOU need it to do.

Cheers
 
upload_2021-3-3_16-43-55.png

It's been improved. Although the lighting is a gimmick, it's got genuine cherry mx hardware switches like the IBM. You can choose clicky or various levels of force required like the IBM. It also brings to the party modern keys (like windows) and most importantly: hardware macros (they require no software on the computer). It also has anti-ghosting and MKRO; it can register a press of every single key simultaneously without confusing the presses. One more thing it shares with the IBM; both are expensive.
 

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