Split Fins in Reverse

[MikeFerrara]

Cave Diver once bubbled...



So you pretty much just paid someone to take em off your hands.

Got any other stuff you wanna get rid of?

Doubles?

Compressors?

Fill station?

Awww hell, I'll even be generous and split the cost of shipping with you!

I think I have another pair of split fins. PM me your address.

 

[MikeFerrara]

Uncle Pug once bubbled...

... but evidently Sandy wanted to see them fly away in a hurry.

Don't worry though, I couldn't let you eat that... I reimbursed her (she did tell you didn't she?)

I think so?

 

[pufferfish]

Grajan once bubbled...
I'm not sure that split v non-split is what is being measured here.

The Apollo is a VERY soft fin. I tried it and hated it but I now use the Atomic Aquatic splitfin and really like it. It's stiffness is much more comparable to my old Avantis.

My gut feeling is that if these 'tests' were conducted on fins of relatively equal stiffness the picture would be quite different.

I am not an engineer but this paper would be a mech engineer's dream paper if a diver. What is interesting is when looking at the 'energy cost of swimming' measured using oxidative metabolism (not ventilation) as a function of velocity the eight fins tested could be grouped into three groups from most economical to least. Stiffness did not seem to correlate with oxygen consumption.

From "Evaluation of fins used in underwater swimming"
Pendergast, D. et al
UHM 2003 Vol. 30, No. 1, p57-73

Stiffness (Nm2)

Apollo 1.32
Apollo taped 1.32
SP Jets 1.92
Quattro 1.95 (notice similar to Jets)
Oceanic Ocean Pro 1.95
US Diver Blades 2.45
US Divers Compro 2.72
Mares Attack 5.45

Lowest O2 consumption : Attack (stiffest), Apollo, Jets
Intermediate : Quattro, Ocean, Blades
Highest : Compro

"Interestingly, both rigid and flexible were in the most economical group"

As far as maximal aerobic speed (m/sec) the Attack and taped Apollos were 6% higher than the average and the Compro were 10% slower. The rest were around the average.

It seemed the only two factors to optimize in fin construction are kick depth (drag, high for stiffer fin) and kick frequency (less efficient for softer fin).

"In our studies, the divers invariably ranked the stiff fins as the best and the flexible as the worse, which did not correlate with the objective evaluation of these fins.,...

It is clear that the venturis, vents, trauths, splits in the tested fins did not improve the performance of the fin. Further work is needed to develop the optimization of fin characteristics, by lowering drag (kick-depth rigidity) and maximizing efficiency (kick frequency-flexibility), to minimize energy requirement and maximize performance of fins."

I am not sure what an Mares Attack looks like, but from this study if one is looking for a fin that is optimized for flutter kick and the alternative kicks one might try the taped Apollos or the Jets.

As far as what fins might be best for the alternative kicks it would seem that a shorter blade would be best with moderate stiffness. The Apollo is .33 m and the Jets .30 m. The Mares Attack have a length of .62 m!The Atomic splits from what I can remember are quite long.

I think UP needs to take out his Jets and compare them against the taped Apollos. I imagine the Atomics would be no better than the Apollos with regards to flutter efficiency but would be less than ideal with the alternative kicks due to their blade length.

 

[pufferfish]

Uncle Pug once bubbled...

As for foot *box* issues with the Jets... have you ever tried the Turtle fins? They have a much large foot pocket.

UP I use my XL Jets with size 9 wetsuit boots. The size L was too small and with the XL there is a lot of slop in the foot pocket. It seems to me that the better the foot fin-pocket fit the more efficient and precise the finning. I am looking for a negatively buoyant efficient fin with a soft pliable foot pocket and good with alternative kicks. The foot pocket in the Jets is very rigid compared to other brands and doesn't seem to mold as well. That is why I am eagerly awaiting your test results with the taped Apollos

 

[Grajan]

pufferfish once bubbled...


I am not an engineer but this paper would be a mech engineer's dream paper if a diver. What is interesting is when looking at the 'energy cost of swimming' measured using oxidative metabolism (not ventilation) as a function of velocity the eight fins tested could be grouped into three groups from most economical to least. Stiffness did not seem to correlate with oxygen consumption.

From "Evaluation of fins used in underwater swimming"
Pendergast, D. et al
UHM 2003 Vol. 30, No. 1, p57-73

BUT...... For some completely inexplicable reason, I am much more interested in UP's subjective assesment.

 

[Genesis]

UP I use my XL Jets with size 9 wetsuit boots. The size L was too small and with the XL there is a lot of slop in the foot pocket. It seems to me that the better the foot fin-pocket fit the more efficient and precise the finning. I am looking for a negatively buoyant efficient fin with a soft pliable foot pocket and good with alternative kicks. The foot pocket in the Jets is very rigid compared to other brands and doesn't seem to mold as well. That is why I am eagerly awaiting your test results with the taped Apollos

Yep.

What I've found is that if the foot pocket does not fit well, you can forget about getting good results from ANY fin.

I HATED the Jets that I had, but it was not the fin - it was the fit.

 

[pufferfish]

Yep.

What I've found is that if the foot pocket does not fit well, you can forget about getting good results from ANY fin.

I HATED the Jets that I had, but it was not the fin - it was the fit.

So what fin are you using now? I am open to any good suggestions but still waiting for UP's report on those taped Apollos

 

[Uncle Pug]

taped Apollos... I conveniently forgot... OK... next week sometime.

 

[Genesis]

So what fin are you using now? I am open to any good suggestions but still waiting for UP's report on those taped Apollos

IDI Power Fins.

Very close to the Jets, but ironically, the foot pockets work for me.

I'm going through this now with my new drysuit again though - trying to find a combination of footwear and fins that fit correctly. My first attempt was servicable but not great - still working on it.....

 

[Uncle Pug]

still waiting for UP's report on those taped Apollos

I applied strips of my best Duct Tape (basic silver) to both sides of each Apollo Split Fin and made sure the tape stuck together in the slot and was burnished around the edges.

First dive today turned out to be in a ripping current first up slope then side slope and then down slope... in that order and of course we were swimming against it most of the time except for the few minutes we gave up and drifted with it.

Aaaarrrggggghhhh!!!! Why did I leave me Turtles at home?!!?

I could only move against the current using a flutter kick... trying to frog kick it felt like I had two dish towels Duct Taped to my feet and gave no headway against the current... forget a reverse kick.

We survived.... but I burned through 40 cf in 24 minutes with a SAC of .68!

Second dive in only slight current and I had the opportunity to actually try reverse kicks with the taped Apollos. They work much better for reverse when taped but no where near as good as Jets or Turtles. However the surpise was with the frog kick... no improvement at all. I had thought that taped they would frog better than they did. I used another 40 cf but this time over 40 minutes with a SAC of .48 (still high for me but passable.)