US Navy Study Efficiency of Best Fins

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SEAL Team members are pictured wearing Pro Model Force Fins. Their wing tips are secured in an upward position for entry.

Summary of US Navy Sponsored Research on Fins

Following are actual results of US Navy sponsored studies on efficiency of divers wearing Force Fins as compared to two popular name brand fins which had been shown in speed tests to be the most efficient of 15 fins. The tests were conducted in a doughnut shaped flume (current) tank to control for speed and simulate open water conditions. Efficiency was determined by the actual oxygen consumption of fin kickers. To date, we know of no other fin test conducted by any facility that has the resources and objective control exhibited in this 4-year US Navy sponsored study..

Note that 75% of the divers tested did not reach the VO2 max, or fatigue level, only when wearing Original Force Fins. Only those subjects that were S.E.A.L Team members and, therefore, in outstanding physical condition, were able to sustain a kick speed of 50 meters per minute for 6 to 8 minutes with any fin tested.

Throughout the test, divers could achieve a maximum sustainable speed of 40 meters per minute with any fin. However, they burned less air when wearing Force Fins. Interestingly, all 200 participants, when surveyed for their subjective opinion, believed that the longest, stiffest fin, that which they felt was most powerful, was also the most efficient, but their actual oxygen consumption levels showed the opposite to be true.

fin efficiency, navy research on fins

The upper plate shows the energy cost to swim with the four fins at speeds from 30.8 m/ min-1 to 40.6 m/min -1.

Reprinted with the permission of the US Department of Naval Research, The US Navy endorses no products.

Text of letter from:
WASHINGTON DC 20372-5300

To:   Ms. Susanne E. Chess, Vice President, Force Fin

Dear Ms. Chess:

This responds to your Freedom of Information Act request of March 25, 1993 addressed to the Chief of Naval Research in which you request copies of reports of fin studies conducted by the University of Buffalo. Your request was received in this office May 6, 1993 for a determination on whether the documents you seek are releasable.

Your request (censored) if disclosed, is likely to cause substantial harm to Force Fins competitors and were determined exempt from disclosure under title 5, United States Code, Section 552(b)(4).

The documents:

Part l

The purpose of this series of experiments was to determine the metabolic cost of underwater swimming with “force” fins as compared to fins that previously had been shown to be the most economical out of 15 fins tested. Two versions of Force fins, amateur and professional, were compared to (censored) and (censored) fins. The latter two fins have previously been shown to require the least energy to swim at several speeds. Our previous work has shown that the swimming speed influences the selection of the “optimum” fin.

The data from these experiments are presented in Figure 1. The upper plate shows the energy cost to swim with the four fins at speeds from 30.8 m/ min-1 to 40.6 m/min -1. Although eight subjects swam at 30.8 m/min-1 to 40.6 m/min-1, only two subjects could sustain 50.4 m/min-1 for the six to eight minutes required for the test. The two subjects who could sustain the effort at 50.4 m/min-1 had VO2 maxs of about 2.5 l/min-1 , while the other subjects were about 2.0l./min. -1 .

There were no statistically significant differences between the energy cost of the four fins at any of the investigated speeds. The energy cost was about 74 l./km- 1 , 74 l/ km-1 and 79 l/ km -1 for speeds up to 40.6 m/min-1 . The values for the better swimmers were about 65.5 l/km -1. Over the entire range of speeds, kick frequencies increased from about 35 k/min -1 to 45 k/min -1 However, the subjects kicked had a 10 k/min -1 higher kick frequency with the Force fins (amateur and professional) than with the standard fins.

A further conclusion is that the amateur [Original] Force Fin, which is more flexible, required less energy for all speeds than the professional fin, which is more rigid. The observation that a more flexible fin may require less energy than a more rigid fin confirms what we observed with other fin manufacturers.

Progress Report for contract number (censored): Diver’s swimming efficiency as a function of buoyancy, swimming attitude, protective garments, breathing apparatus, swimming technique and fin type September 1991 to January 1992

During this period, we have continued our study of the effectiveness of selected fin types on the swimming performance of divers. During the previous period, we reported on the energy cost of swimming with these various fins.

In review of the fin combinations tested, the small, flexible non-vented fins had the lowest energy cost (200 kcal/km-1 ).

The larger, stiffer fins required about 25% more energy, while vents did not effect the energy requirement (Fig 1). Although this difference is small, when extended to 10 km the difference is 250 kcal or 50 l 02, requiring an extra ventilation of about 1250 l.

It should be emphasized that the factor that effects the swimming cost the most was the swimmers skill. The highest values (300 kcal/km-1 ) were observed in novice and the lowest values (150 kcal/km -1) in elite swimmers (Fig 2).

Our recent data analysis has suggested that the cost of swimming cannot be determined from the kick frequency. This is somewhat paradoxical. If the frequency is low, the force per kick can be high; while, if the frequency, is high, the force per kick can be low. Therefore, one can observe energy requirements for any combination of kick frequency and kick force.

As far as fin selection is concerned, the differences between the fins were not remarkable underwater. It would appear that for short swims there are no differences; however, for longer swims the small differences become significant.

The most economical fins were the smaller, very to moderately flexible styles. The larger, less flexible fins were the least economical.

The presence of vents did not seem to be an advantage under any condition. It would appear that the smaller, more flexible fins did not compromise neither speed nor force underwater. At the surface, it would appear that the greatest force and least fatigue could be generated by the larger, less flexible fin.

*The United States Navy does not endorse any product.

Force Fin Challenge

Force Fin, How to Kick Fins, How to Kick Force Fins, Fin rebound

Force Fins Work for You

The Force Fin Challenge is a test you can do for yourself and on your own. It will tell you how well your fins are working for you, or if you are working for them.

Force Fins work for you and harness the force of the water to maximize thrust with each kick. That means more speed with less energy expended by you. To prove our point, we offer this test and challenge:

Take the heel strForce Fin, kick finsaps off any other fins and kick; Do this test in a pool only as your terrestris, flat fins will fall off. That’s the drag of the fins working against you. Drag is the resistance you feel when kicking against these other fins.

No matter how secure it may feel. No matter how it may make you think you are moving. That feeling of resistance is working against you when in the water.

Try the same test with Force Fins; they will not kick off. With each kick, Force Fins drive you forward with the in-water freedom of an aquatic being.

If you want to drag your fins through the water, then your choice of terrestris fins, all other fins, is vast.

If you want the freedom of an aquatic being, with fins efficiently propelling you with each kick, then there is but one choice – Force Fin.

The First New Fin Since Fins Were Invented

The first swim fins were a lot like the one on the right – a shoe with a stiff board bolted on. Most still are. Other, more flexible fins still retain the old paddle shape, and most  split fins are simply double paddles.

Then there is Force Fin – in a league of its own.

If you’ve ever tried to raise a board flat out of the water, you know how hard it is to lift. The other fins require the same effort to up-kick when you are swimming. After a while your foot gets tired and cramps set in.

The Force Fin folds in on the up-kick to reduce water resistance and snaps open for full power on the down-stroke. Swimming with the Force Fin at first gives the impression that nothing has been attached to your foot at all. That’s because the water flows backward, rather than up and down. You don’t have to work hard to make the flexible Force Fin work.

And since there are no thick ribs on the fin, the blade moves in any direction you want and doesn’t veer to the right or left at an awkward angle, as other fins do.

The other fins have a stiff foot pocket that causes your toes and arches to cramp. The Force Fin doesn’t cause cramping because the fin is flexible and the toes are free of the pocket, so they can bend naturally, without restriction.

The Force Fin is made of high quality polyurethane instead of rubber and weighs a mere 32 ounces. Strong, adjustable nylon straps hold your foot comfortably in the pocket.

So, by wearing the Force Fin you’ll be able to swim longer and enjoy it more.

Which is a bit like re-inventing swimming.

Why Force Fins are Made In the USA

 Force Fins are made in the U.S.A.

I wish I could say this was a political decision. I am well traveled, and I sincerely believe that the U.S.A. in which I grew up is the very best place on Earth. The decision was financial.

Notwithstanding soundbites to the contrary, there are thousands of quality factories in the United States. They are competitive with offshore production, particularly when it comes to custom molding for small business or start up companies. Absent the subsidies given to the long-established, big boys, China, or any other country is hard pressed to compete with America, when the real costs of production are taken into consideration. The real cost of production includes quality, shipping, lead time, inventory control, and the control over cash flow that follows from a well-managed supply chain. Something that is best done locally.

Working in the U.S.A. is not an abstraction for me, nor is being an entrepreneur. I was born in Detroit, and transplanted to California at an early age. My parents owned a few industrial uniform companies. The smell of shop towels brings memories of my childhood, as we serviced gas stations, auto body shops, tire stores, auto industry manufacturers, and sports venues. Dodger Stadium, Angel Stadium and the Forum were on our truck delivery routes.

My first job was for my parents’ company. Under the scrutinizing eye of my father I was tasked with altering uniforms to fit their wearer, and sewing patches uniquely identifying each uniform to the client’s Company brand and its wearer. My first lesson in quality control was when my father made me tear out the stitches and redo hems I had sloppily sewn in a rush to get the job done, so I could join my friends. I remember him scolding me, “Men have to wear these pants to work. You have to take as much pride in your job as they will in wearing them to theirs.

My father’s first Company was his newspaper route, or should I say newspaper delivery enterprise. He expanded outside the immigrant neighborhood in which he lived to deliver papers to the the offices of the then bustling business buildings of downtown Detroit. I co-founded Force Fin with my husband, Bob Evans in 1985, when we were just 26 and 32 years old. It was our first international manufacturing and distribution company.

The first entrepreneur was not born with the U.S.A. What is unique to America is their historic percentage level of contribution to its economy. I believe that this is born in the idea that opportunity exists to anyone who can take the experience of sewing patches as a foundation for understanding corporate brand identity, and a reprimand as a lesson in the importance of quality control.

I also believe that this is the case because the words from the Declaration of Independence are etched into the American psyche throughout our early educational years:

“We hold these truths to be self-evident, that all men [and women by virtue of the 19th Amendment to the Constitution] are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”

In other countries where we might manufacture, dreaming big, if dreams of starting one’s own business exist at all, most frequently end with one’s first job sitting before a sewing, injection or any other machine.

I can visit on demand the factories where our Force Fins are made. I can see the quality of the environment in which the individuals who make Force Fins work. It appears to me that they are not slaves to their employers, and that they are doing so with the expectation that it is toward benefiting their life and that of their families.

In the future, Force Fins may very well be made offshore. I am proud to say at this time, it makes the most sense, economically, politically and ethically to make them here.