Split fin hate?

[Bob Evans]

So, each student came up to the cave with 2 pairs of fins, just in case?

Seriously, I am trying to get some answers here, not just the usual mantra "paddle fins are go-o-o-o-od, split fins are ba-a-a-a-ad!"

I already compared fins with kayak paddles. Why are paddles rigid but fins flexible? And not only splits are flexible, 95% of all fins you see are flexible here or there, like Mares X-Stream or Scubapro Seawing Nova that flex in the middle. If fins must be rigid too, why not make fins of aluminum alloy? In fact, I've seen such fins but I have no idea how good they are.

Now look at the fish. Tuna and marlin are the fastest fish of them all, and their tail fins look pretty much like split fins to me, only the blades are spread wider. I am sure that after 400 million years of evolution fish could have come up with a rigid bone tail fin instead, if this had any mechanical advantage. Yet I do not know any fish that uses a bone plate as a tail fin and the fastest fish prefer splits. Why is that?

I can see just one difference with a kayak paddle. The paddle moves in the water one way, while fish tails and diver's fins move back and forth. What difference does it make

Looking at fastest fish.

 

[tarponchik]

Looking at fastest fish.

These fins copy the shape, but how flexible they are?

 

[-JD-]

These fins copy the shape, but how flexible they are?

Quite - but not floppy.

 

[Bob Evans]

Quite - but not floppy.

Thank you Durometer measures flexibility, and the original force fin is optimized at 86A, the Pro Model optimized at 91A plus or minus standard deviation incidental to manufacture. The flexibility is scaled with more volume of material at heel where you need structure, and tapering flexibility as the blade arcs through to between wing tips. Adding to the balance is internal ribbing, which also exists within fish fins and marine mammal tails. That is how I engineer through sculpture.

 

[BoltSnap]

Thank you Durometer measures flexibility, and the original force fin is optimized at 86A, the Pro Model optimized at 91A plus or minus standard deviation incidental to manufacture. The flexibility is scaled with more volume of material at heel where you need structure, and tapering flexibility as the blade arcs through to between wing tips. Adding to the balance is internal ribbing, which also exists within fish fins and marine mammal tails. That is how I engineer through sculpture.
View attachment 793714

Bob,

Do you have engineering or science background/education?

 

[DeepSeaExplorer]

So, each student came up to the cave with 2 pairs of fins, just in case?

Seriously, I am trying to get some answers here, not just the usual mantra "paddle fins are go-o-o-o-od, split fins are ba-a-a-a-ad!"

I already compared fins with kayak paddles. Why are paddles rigid but fins flexible? And not only splits are flexible, 95% of all fins you see are flexible here or there, like Mares X-Stream or Scubapro Seawing Nova that flex in the middle. If fins must be rigid too, why not make fins of aluminum alloy? In fact, I've seen such fins but I have no idea how good they are.

Now look at the fish. Tuna and marlin are the fastest fish of them all, and their tail fins look pretty much like split fins to me, only the blades are spread wider. I am sure that after 400 million years of evolution fish could have come up with a rigid bone tail fin instead, if this had any mechanical advantage. Yet I do not know any fish that uses a bone plate as a tail fin and the fastest fish prefer splits. Why is that?

I can see just one difference with a kayak paddle. The paddle moves in the water one way, while fish tails and diver's fins move back and forth. What difference does it make?

The instructor tried to warn the student, but the student persisted, so I assume the instructor used it as a teaching moment. The student probably had to go buy new fins or borrow from the instructor. Usually, when showing up for a first cave class, the instructor reviews the student’s gear and suggests or demands changes when necessary. It’s not like an open water class.

When I took my first tech class in 2004, I spent thousands for new gear before the week long class was over. Tech classes can be a real money maker.

The fins on fish absolutely do not look like split fins. And, a tuna’s fins are very stiff.

Even the stiffest paddle fins will flex, if you put enough power to them. That’s the key. That stiff fin can then transfer that power to the water, where floppy fins can’t.

I have a video of Jet fins flexing when pressed hard. It’s too big to post here, but if you’re seriously interested, message me and I’ll email it to you.

 

[DeepSeaExplorer]

Interesting to note I made the Foil Force for a US Marine. He swam Turtleback and liked to scissor kick. The Force fin pro wing tips were interfering, so I lengthened the split and narrowed the blade. Thus your first " Split Fin" with Patents filed on design. These Patents allowed us to produce our product, Foil Force.https://forcefin.com/product/foil-force-fin/ Not my favorite, but it sure outperformsView attachment 793650 the other flat barn door fins. Here our friend is testing the Extra Force fin.

The US government tests lots of things. The question is did they setup a purchase contract?

 

[Bob Evans]

Bob,

Do you have engineering or science background/education?

I was very fortunate to have an Artist Father who attended the best Art Schools at the time. A US Marine back from the Pacific War and taught us, kids, how to observe and translate those observations, and how to sculpt, among other things. My father Gordon Evans in his studio:

is My My college education was trade - Film and Art School - Brooks Institute whose Trustees granted me an honorary Masters in Science for my contributions to art, science, and photography.

A sample of the projects I administered to warrant award is posted at Bob Evans Photography – Beauty in Pertinent Paradox

 

[Bob Evans]

The US government tests lots of things. The question is did they setup a purchase contract?

Force Fin regularly fulfills purchase orders from DOD, and its affiliated agencies, Navy, Air Force, Coast Guard, and NATO, and other countries. In the last month, shipped for delivery to Italian Admiralty, New Zealand and Australia armed forces. How do you think we have stayed in business without the support of dive stores over the past three decades? Photo by Dan Orr.

 

[drrich2]

I already compared fins with kayak paddles. Why are paddles rigid but fins flexible? And not only splits are flexible, 95% of all fins you see are flexible here or there, like Mares X-Stream or Scubapro Seawing Nova that flex in the middle. If fins must be rigid too, why not make fins of aluminum alloy? In fact, I've seen such fins but I have no idea how good they are.

When I've listened to people talk about dive fin experiences, rightly or wrongly, I've gotten the impression that if your legs are very strong, you can transmit more force to move water and propel yourself (e.g.: into current) with a very stiff paddle fin, but it demands more strength. This isn't just about split fins; someone complaining of a stiff paddle fin being like 'boards' on his feet might be an example.

I'm no kayaker. If you row one like rowing an aluminum boat, you hold the paddle/oar with both arms, your back factors into it a bit, you alternate side-to-side so there's a momentary break between strokes, and despite all that, it can be a workout.

A scuba fin's apparent surface area isn't that far off from the flattened area of some oars. A leg is stronger than an arm, but is it stronger than 2 arms and a back with the kayaker leaning into it?

Maybe the reason we need some flexibility in paddle fins is the need to sacrifice potential power for ease, since most divers don't have marathon runner legs? Maybe the sweet spot for recreational diving isn't a 'board,' but some argue it's not so far the other way as to warrant splits for everyone.

I may be totally off on this.