Split Fin Physics

[Blackwood]

Cool, thanks! The original site linked required an expensive paid membership. Hopefully I will be able to follow it. Patents are somewhat obtrusively written.

 

[Crush]

I am interested in learning if the improved performance of split fins is fact or fiction, but I will not be reading the entire patent application as such documents are long on definitions and short on data.

My work spans the range between fundamental research and the evaluation of engineering development models. Whoever the researcher is, they would have had to have convinced their managers and investors using tables and figures which contain experimental data. That would be useful to have in evaluating split fin performance.

 

[SCUBASailor]

This sounds like a job for Mythbusters!

 

[ptyx]

This sounds like a job for Mythbusters!

Righhht.... "Between a split fin and a paddle fin, which one [-]is most efficient[/-] can go through 12 inches of concrete if propelled by enough dynamite".

More seriously, although studies about fin mechanics seem quite rare, there are plenty about swimming mechanics, including some about freestyle kicks. It's all greek to me, but you might find your explanations in there.

 

[Bob Evans]

Actually, there is a patent for a split fin dating back to the 1960's. The name of the patent holder is Mann. Bob Evans came up with the design independently and with improvements in the 1980's. The original Force Fin patent includes a disclosure of an elongated Force Fin, eg., a split extending as long as in its Foil Force Fin, which, incidentally, does work on lift because of its compound curvatures, not because of its split.

This is not Bob responding, although I am on his computer.

And, Michael Brennan at Apollo, you lost the right to ascribe yourself credibility by mentioning Bob's name the night we looked at the stars together. Don't do it again.

 

[meesier42]

When Apollo was first approached with the Nature's Wing fin it had already been declined by most major SCUBA manufacturers. They were afraid. They thought it was too radical.

The Founder and President of Apollo Japan, Seiji Hattori, a very experienced and talented engineer, when he first tested the prototype fins directed that we sell our paddle fin molds-which we did-Dive-Rite purchased the molds. Dive-Rite now has an excellent paddle style fin.

Mr. Hattori then went on a quest to find the right material and the right design parameter to produce the optimum split fin. It took more than a year and a half and many millions of dollars. We use all natural rubber and the very time consuming and expensive compression molding process to produce the Apollo bio-fins.

hahahaha, that must explain why he "borrowed" a pair of split fins from the Force Fin table at DEMA a year prior to Apollo releasing them, and months prior to "mccarthy" filing a patent for them.

The others soon copied us, naturally, many using injection molding, inexpensive materials, and pricing up against us, just because they could. That's business. We do not dwell on that. What we want to do is produce the finest fin we can.

well that's true, of all the Splits out there, the Apollos are the only ones I can honestly recommend to people.

The split fins, as you have noted, work on the basis of different pressure flow. Since water is much denser than air the fluid dynamics work to create the forward thrust.

well this is just stupid, I know you believe in your product, but there is nothing about that statement that is even remotely true. stick to your marketing and let science (such as that done by the University of Buffalo) explain how the fins work, or don't work as they have shown.

SPLIT-FINS - SPLIT-FIN TECHNOLOGY has several illustrations that illustrate the method that produce thrust and force with split fins. These illustrations have been posted a number of times.

There will always be the types who say-this can't be true-I love my "whatever" fins. So be it.

Paddles work for ducks and frogs. A properly designed split fin, using the correct materials, provides power, thrust, without excessive strain. Just a look at a Dolphins fin or a whales tail should be enough to know that Mother Nature did not design paddle style fins for these mammals, their fins deflect and twist like a properly designed split fin.

Another good design is the Force Fin, based on Bob Evan's study of the Marine world.

This argument will go on and on. Decide for yourself. All the best for lots of good diving, no matter what fins fits your fancy.

again that is just plain stupid, split fins look about as much like a dolphin tail as a bird wing looks like the wing of a 747. If there is a fin that models after a dolphin tail it would be Force Fins. a whale tail has a wide span and short chord (short and wide), splits are narrow in span and long in chord. also, check your history books, the marketing information released by Apollo and Nature's Wing is nothing but a recreation of the marketing used by Force Fin, specifically the "vortex" diagram from the split section.

With regard to the split fin patent, I read somewhere that Bob Evans (Force Fin) was the first person to come up with the split-V design...but the "full" split fin was patented by Nature's Wing which employed Peter T. McCarthy (patentholder on record). Does anyone know if there is any truth to this? I see this as relevant to the design "genealogy" of the split fin.

the Split Fin was first patented in Italy many years ago by Mann. Force Fin, introduced the Foil Force Fin at DEMA a year prior to Apollo or McCarthy trying it.

I am interested in learning if the improved performance of split fins is fact or fiction, but I will not be reading the entire patent application as such documents are long on definitions and short on data.

My work spans the range between fundamental research and the evaluation of engineering development models. Whoever the researcher is, they would have had to have convinced their managers and investors using tables and figures which contain experimental data. That would be useful to have in evaluating split fin performance.

there was a very long study performed at the University of Buffalo that discussed the split fins, however its highly technical and thus poorly understood. it showed that in short sprints split fins are very effective, however they also showed that they are more efficient when the split is duck taped shut. My anecdotal test allowed me to conclude that splits can be fast, but due to the furious kick frequency that speed is not sustainable, few of the divers I was with could maintain that speed for more than 30 seconds. When we taped the split, the speed didn't change but endurance improved to upwards of a minute, and there was a significant drop in kick frequency.

If the question is to explain the dynamics of how/why a split fin works, well to paraphrase UofBuffalo study, the dynamics of a swim fin is a vaguely understood art, further study will be required to quantify how and why fins work and explain their interaction with the human. its a really tough problem, as the shape of the fin changes relative to force imparted, which is of course already a non linear problem as both shape and angle of attack are independent variables, and the interface with the human leg is even more poorly understood and changes with each diver (based on technique and fitness, among others) and the fin itself as short or flexible fins allow high cadence, while longer or stiffer fins use slower higher power kicks and both concepts have been shown to be very efficient.

although I am not out to bash Apollo, just to say there information is purely marketing. IMHO- Apollo's and the Force Fin designs are the only split fins on the market that are worth a damn. but I will caution those looking at them the issues and limitations. Of course most divers will abort dives that are challenging enough that the limitations of splits become a real safety issue.

 

[Blackwood]

If the question is to explain the dynamics of how/why a split fin works, well to paraphrase UofBuffalo study, the dynamics of a swim fin is a vaguely understood art, further study will be required to quantify how and why fins work and explain their interaction with the human. its a really tough problem, as the shape of the fin changes relative to force imparted, which is of course already a non linear problem as both shape and angle of attack are independent variables, and the interface with the human leg is even more poorly understood and changes with each diver (based on technique and fitness, among others) and the fin itself as short or flexible fins allow high cadence, while longer or stiffer fins use slower higher power kicks and both concepts have been shown to be very efficient.

Here's to wishing I'd paid more attention in my computational fluid dynamics course. I'd model a run myself, but you know... garbage in garbage out.

Happen to have any documentation from the UoB study?

 

[Bubbletrubble]

Actually, there is a patent for a split fin dating back to the 1960's. The name of the patent holder is Mann. Bob Evans came up with the design independently and with improvements in the 1980's. The original Force Fin patent includes a disclosure of an elongated Force Fin, eg., a split extending as long as in its Foil Force Fin, which, incidentally, does work on lift because of its compound curvatures, not because of its split.

This is not Bob responding, although I am on his computer.

And, Michael Brennan at Apollo, you lost the right to ascribe yourself credibility by mentioning Bob's name the night we looked at the stars together. Don't do it again.

Who's on Bob's computer?
Who was staring at the stars with Michael Brennan?
Actually, I really don't want to know...

@meesier42: Could you please disclose your relationship with Force Fin and Bob Evans? Are you an employee of the company? Have you done any consulting work for Force Fin? Are you or were you ever financially connected to the Force Fin company? Or are you just a happy costumer? Sorry for all of the questions. I'd just like to gain some perspective on your comments. I do want to make it clear that I appreciate your participation on this thread. Thanks for filling in some of the gaps in our knowledge.

there was a very long study performed at the University of Buffalo that discussed the split fins, however its highly technical and thus poorly understood.

Here's a link to the 2003 UHM paper by Pendergast et al. (Univ. of Buffalo).
I'm providing this link so that others will view the data and can decide for themselves whether the authors' conclusions have merit.

 

[Crush]

From this point onwards I will assume that this thread will have become polluted with feelings and devoid of scientific fact. I am a scientist by training and profession. If there is some concise scientific research that can be looked at (preferably peer-reviewed), I will take a look at it- please PM me. Until such time, bicker on in this post all you want.

Have a pleasant week.

 

[Bubbletrubble]

From this point onwards I will assume that this thread will have become polluted with feelings and devoid of scientific fact. I am a scientist by training and profession. If there is some concise scientific research that can be looked at (preferably peer-reviewed), I will take a look at it- please PM me. Until such time, bicker on in this post all you want.

@mpetryk: Read the paper I linked to in my previous post. It contains a lot of interesting info.

FWIW, UHM is a peer-reviewed journal.