Meesier: The Navy did test our fins @ the swimmers school and we do sell quite a few to the military on both coasts. We do know that many fins are in use, not just bio-fins.
Split Fin Physics
- Thread starter Blackwood
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awap: I do not know exactly how the bid process works. We sell through Prime Vendors and we normally see three or more vendors competing for the bid. I do know that there are often other items on the bid not just our fins. The last large bid we had was last month-210 pairs, this month
we have shipped another smaller one for 48 pairs. They are, usually all large or XL size with standard straps.
As mentioned before we do know that Jets and Blades and others are being used as well.
we have shipped another smaller one for 48 pairs. They are, usually all large or XL size with standard straps.
As mentioned before we do know that Jets and Blades and others are being used as well.
you should go out to Ford Island sometime, you'll see lots of Jets, Blade, Mares, Bio-Fins laying about, but in 2 years I haven't yet seen a single pair of them in the water. They just lay on the pool deck and in the dive locker, the guys in the water all use Force Fins
testing doesn't mean they endorse the product. Plain and simple, the Navy does not endorse any product period. Its entirely up to the diver using them. Jets and many many others are in common use with Navy MDSU (Mobole Diving and Salvage Unit) divers, but even there I have only seen a few Bio-fins.
Selling to prime vendors really doesn't mean that much, they sell to many many places, the military is only one, for example AMRON- I can log on right now and buy from them,
testing doesn't mean they endorse the product. Plain and simple, the Navy does not endorse any product period. Its entirely up to the diver using them. Jets and many many others are in common use with Navy MDSU (Mobole Diving and Salvage Unit) divers, but even there I have only seen a few Bio-fins.
Selling to prime vendors really doesn't mean that much, they sell to many many places, the military is only one, for example AMRON- I can log on right now and buy from them,
Well, I'll say it again....you have WAY too much time on your hands to post this much about the physics of $65-85 split fins. But to each his own.
I think this type of post is what scares most new people away from diving when subjects become overkill and over done. Did anyone give a **** this much about fins in the 70's and 80's?
I think this type of post is what scares most new people away from diving when subjects become overkill and over done. Did anyone give a **** this much about fins in the 70's and 80's?
Yes, some of us did. That's why we have better fins now then we did then. Fins have undergone an evolution just as other pieces of dive equipment have. We now have fins which cover the bottom of the foot, for instance, and don't lead to the foot cramps we had in the 1960s with some of the fins then. The evolution of the long-bladed fin from finswimming and spearfishing competition is an example. People who really cared were competitors in finswimming, who designed their own blades from fiberglass in the 1970s and 1980s. More recently, people like those who developed the split fins, and Bob Evans and his Force Fins, showed that innovation is still very important in today's diving. Cousteau himself changed his divers from using regular fins to the Jet Fin style in the 1960s. And there is still a lot of room for improvement.
I was in the pool last Friday with my home-made split fins (see my earlier posts), and noted that the boil just under the surface from split fins is different from my scoop fins, and probably from the regular blade fins. It is a double-boil, rather than one larger single boil. So there are different dynamics for the split fins than for other fins at work.
My own thoughts about the split fin physics is not based upon a propeller, but rather on the split allowing more of a channeling of the water to the rear than it would without the split. What happens in my mind (from hours of swimming with these and other fins, feeling the water, watching surface boil patterns, etc.) is that the viscosity of water tends to pull the water along the parting surfaces, and creates a greater volume of water affected than would happen without the split. That would explain the Force Fins too. If the water had less density, then it would go easier through the split. But because of the density, it flows along the lateral length of the fin as it rotates through the water at the end of the diver's foot.
One of the problems fin manufacturers have is that everyone's ankle and foot are different. My feet and ankles are very flexible from a lifetime of diving and finswimming. This allows me to point my toes beyond the horizontal plane of my leg. This means that a fin designed for someone with only a 30 degree bend at the ankle will, on my feet, provide almost no thrust. I can point straight fins (my Duckfeet) behind my shin bone's plane. So different people will have different responses to the same fin regardless of the design benefits of that fin. Something to think about...
SeaRat
SeaRAt:
Thank you for your latest post. I hope it will help keep the OP question on topic. This is not about
one model fin against another, who sells more to whom, some rabid fans personal preference, etc.
This thread is about the physics of split fins.
Several folks have had good contributions; your comments are honest and always interesting.
Jim Grier has no ax to grind, but he is a careful academic with valid test methods and comments.
Others have commented in an informative manner with their observations.
I hope this thread will continue in a non confrontational manner.
Thank you for your latest post. I hope it will help keep the OP question on topic. This is not about
one model fin against another, who sells more to whom, some rabid fans personal preference, etc.
This thread is about the physics of split fins.
Several folks have had good contributions; your comments are honest and always interesting.
Jim Grier has no ax to grind, but he is a careful academic with valid test methods and comments.
Others have commented in an informative manner with their observations.
I hope this thread will continue in a non confrontational manner.
Hatul
Contributor
I have to agree with you. The lift vectors don't seem to point the right way to explain anything and I doubt there is enough lift to have much effect one way or the other.
The Apollo video I quit half way as I did not see any info aside from an ad promo.
The one thing I do notice is the split fin flexes more and during the flex the fin is pushing the water backwards. It has nothing to do with lift but a better angle to push water back. The center split may also help stabilize the side forces on the fin.
On the other hand a study quoted in Undercurrent some time ago found that some split fins did better if the split was fused closed, again undercutting the lift theory.
Personally, I tried the Apollo yellow splits once and found them heavy and uncomfortable. I sent them back and went back to my Force Fin Pro.
Adam
Bob Evans
Contributor
Sometimes we forget that water is 3 dimensional. Water is running up to, around and off the blade from all around. That is why it gets confusing. How fins really work is a question of fluid dynamics - it is a complex science.
Through years of fin research, we have concluded that curved shapes take advantage of the water better than straight lines and flat surfaces. Split Fins are a good concept, but approach the problem 1-dimensionally. Its profile is still flat. That is why similar results are found when you tape it shut.
I found a dramatic change in the flow of water when I curved the Force Fin blade. The same is true with the extended split of the Foil Force Fin. As I curved the trailing end of the blade the water spiraled into and off the cupped trailing end.
A flat paddle fin spills water to the side. A flat split fin spills water up and down.
I'm always experimenting and thanks to Blackwood asking the question that started this thread, I now have a solution, a foolproof way to show how water is flowing off fins.
Blair and I are gathering the tools together and we'll keep you posted.
Through years of fin research, we have concluded that curved shapes take advantage of the water better than straight lines and flat surfaces. Split Fins are a good concept, but approach the problem 1-dimensionally. Its profile is still flat. That is why similar results are found when you tape it shut.
I found a dramatic change in the flow of water when I curved the Force Fin blade. The same is true with the extended split of the Foil Force Fin. As I curved the trailing end of the blade the water spiraled into and off the cupped trailing end.
A flat paddle fin spills water to the side. A flat split fin spills water up and down.
I'm always experimenting and thanks to Blackwood asking the question that started this thread, I now have a solution, a foolproof way to show how water is flowing off fins.
Blair and I are gathering the tools together and we'll keep you posted.
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I have two different versions of Bob Evan's Foils and I love them!
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