Fin Vents

[b1gcountry]

A lot of people around here really like the Jet style fins. I've always thought that the fin vents would be an entanglement hazard; especially on wrecks where you have dangling wires, or metal objects to get impaled on. Anywhere with low vis and swift currents would seem to make this worse.

I know some one will reply that your fins should not be near the bottom anyway, but your fins should also not be near the line, and it is common practice to reverse and tape your fin straps, or replace them with spring straps. Entanglement seems to be a big point raised whenever split fins are discussed as well. So why aren't fin vents ever brought up as a problem?

The other question is: what's the point? I can't understand what sort of physics advantage the holes in your fins would give you. They sort of seem like the "fin gimmick" of the '80s that just never went away.

Tom

 

[nadwidny]

A lot of people around here really like the Jet style fins. I've always thought that the fin vents would be an entanglement hazard; especially on wrecks where you have dangling wires, or metal objects to get impaled on. Anywhere with low vis and swift currents would seem to make this worse.

I know some one will reply that your fins should not be near the bottom anyway, but your fins should also not be near the line, and it is common practice to reverse and tape your fin straps, or replace them with spring straps. Entanglement seems to be a big point raised whenever split fins are discussed as well. So why aren't fin vents ever brought up as a problem?

Because real world experience has shown that they aren't.

The other question is: what's the point? I can't understand what sort of physics advantage the holes in your fins would give you. They sort of seem like the "fin gimmick" of the '80s that just never went away.

More like a "fin gimmick" of the '60s. I remember reading the official S'Pro line on them a long time ago. It seemed gimmicky. Something to do with the flow through the vents created a low pressure area on the downkick cycle resulting in more lift so therefore more propulsion, blah, blah blah. The same crap that all fin manufacturers still use in promoting their latest wacky design. Some things never change.

 

[muddiver]

I reversed the straps on my Jetfins for two reasons - 1. it helps keep the kelp from getting tangled in the loose end of the strap, 2. It helps keep the strap from slipping out of the buckle.

Basic hydrodynamics supports the theory behind fin vents. They are really an attempt at channeling the water displaced by the fin to the rear, thus acting like a small water jet. You will only find them on fairly ridged fins like Jet fins or Rocket fins.

The flexable plastic and/or composit fins use the flexing action of the center channel of the fin to scoop the water that is being displaced and force it to the rear in the same manner. I find that I have to work harder with flexable fins to get the same amount of foreward movement than with a stiff fin. I also have relatively strong legs too which is an important factor in choosing your fin type.