US Navy Study Efficiency of Best Fins

Navy SEAL fins, military fins, force fins

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.

The Innovative Designs of Bob Evans, Erik Buell and Burt Rutan


The Art of Design by Harry J. Wirth

Bob Evans was and still is an accomplished scuba diver. He initially became interested in the beauty of sea-life and thus became an underwater photographer. He is quite an accomplished man with the camera as his photographs have been published widely in books and magazines.

Having worked underwater extensively and after logging thousands of dives and expeditions, he became intimately involved with the many difficulties of swimming and maneuvering while attempting to photograph his submariner subjects. Evans literally grew tired of the constant pushing and pulling of water with the conventional fins as he watched the effortless gliding of the fish around him. He had observed and continues to this day his observation of water as a three-dimensional living substance. He realized the fin cannot be designed with the typical two-dimensional mentality.

fish tail fins, efficient finsAnother observation was the faster, more efficient fish had a split tail as a main thrusting feature. All of the fins on the market at the time were flat single fins. As Evans puts it, the flat type is very clumsy and inefficient for swimming and diving. The reinforcement ribs restrict water flow around the fin and increase unwanted drag. An astute and observant individual, Evans made intuitive connections between man and nature. He found that the highly evolved fish shapes could be adapted to the human form. Humans are “by nature” one of the most inefficient and awkward objects moving in the water. In essence, he wanted to make the human body more fish like, but in a simple manner with the application of an appropriately designed fin.

The original “Force Fin“, the first model, was physically conceived in 1980, however, the initial concept was realized in the early 1970’s. Evans painfully and diligently evolved the design through many developments of configuration, size and materials. His design methodology was the handling of the design as a dynamic object rather than that of a static one. There was an extensive undertaking of the study of the movements of the foot, ankle, and leg in order to get a good understanding of the dynamic movements of the parts together and separately. An interesting drawing Evans compiled from these leg-movement studies hangs in a prominent place in his studio as a work of art. The innovation was a result of observations of nature in the sea and the application of those observations.

Bob Evans, Fin Designer, Funk Zone, Santa Barbara, Force Fin, PrototypesQuickly made of crude materials, many designs were tested, rejected, and refined for quick evaluation. His many configurations were quickly prototyped with chicken-wire and newspaper. His feet would get cuts and bruises as he tirelessly tried concept after concept. Until he arrived at a shape that worked. Evans would make the molds himself in his shop, pull the product and run to the beach to try a new shape. To this day he still follows the same basic “hands-on” method of design development. Many new materials were tried, tested, and evaluated to seek out the best formula suited for his needs with the fin. He needed a stable compound with the necessary snap and flex that would augment and amplify the movements of the leg and foot.

The latest material being applied to the fins is a two-part liquid polyurethane with a good memory of shape. Evans found this material to be quite forgiving in his unique composite molds. Once the fin was formed and pulled from the mold, he discovered the polyurethane had a chain molecular bond arrangement that allowed t to be more durable, yet flexible on the flipper ends or as he calls them the deflecting foils. He found this product while perusing technical journals and saw that it wa good for mallet hammers and heavy duty wheels. It was resilient, yet very durable and flexible.

It is the split ends on the fin that are so special. Observing fish with split fins, Evans saw the tremendous maneuverability of these fish. Trying to do a roll underwater with conventional long stiff fins is quite difficult to accomplish. With the shorter Force Fin, and the flexible tips, which work independently of one-another, maneuverability underwater is smooth and easy. Divers who take their first swim with the Evans’ fins first remark that the fin isn’t working because they feel no resistance. Evans is quick to point out that this is the quality he was striving for, an efficiency that makes underwater kicking effortless.

Another unique feature of the Force Fin is its ability to flex and snap. This action-reaction of the polyurethane structure increases the divers thrust. As Evans states, “when in operation, it has power in one direction and then collapses while throwing water behind in the other direction so that it can get back to where you kick against it without strain.”

He saw that this action was the same action as what he had seen occur on the fins of a harbor seal on a slow motion video. The Force Fin is an elegant, organic, fluid-formed device that becomes a natural extension of the human leg. Looking rather strange in our dry conditions walking about on the pier, once in the water the beauty of the design is immediately apparent and functionally is better and more efficient than any other fin on the market. Other models followed as the design became more widely accepted. He now has the “Beaver”, the “Rip Force“, the “Tan Delta” and the most advanced the “Extra Force” with adjustable “winglets“.

The “Extra Force Fin” is an adjustable fin to suit the diving and the kicking preferences of the diver. Two, independent, small winglets are attached to either side of the fin. These are mounted with hex-head bolts to allow for adjustment in the field. A diver can increase thrust of the stroke by moving these winglets in or out dependent on the performance desired.

Navy SEAL fins, military fins, force finsRecently, the US Department of the Navy conducted exhaustive test of many diving fins. Bob Evans’ Force Fins came out on top in the tests. The tests concluded that divers using the Force Fin used less oxygen while active in diving than with any other design. Interestingly enough, the elite Navy Seals teams use the Force Fin as further proof of their superiority as a dive fin. “Eventually”, as Evans states, “all fins will be made this way.”

The Force Fin is continuing to catch on. The sales have increased to such a high level, Evans has to consider now the future of his small company and where he wants to go with it. His desire is to design newer fins and try new technologies, but at present the pressure of meeting the tremendous consumer demand for his superior product is taking most of his time.

— Harry J. Wirth for “The Art of Design: The Innovative Designs of Bob Evans, Erik Buell and Burt Rutan, Design ist okay Innovationstransfer, Herausgegeben von Heiko Bartels, Bauhaus-Universitat Weimarn, Universtatsverlag, 2000

Reprinted with the permission of
Harry J. Wirth © 2000

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 Truth About Dive Fins

manatee, force fin

Are you confused by all the theories, claims and opinions about dive fins? If not, maybe you should be. Since kicking is your primary physical activity when diving, and because the efficiency of your fins and your comfort in the water affects your bottom time more than almost anything else, dive fins are one of your most important pieces of equipment. But over the years, a lot of myths and misinformation have built up about them.

We’ve been designing and making improvements to fins for over 35 years, with millions of satisfied customers, and many major product design awards under our belts, we can honestly say that we are the experts in fin design.

That’s all we do, and we think our innovative fins are without equal in terms of comfort, efficiency, durability, performance, versatility and sheer value for your money. We pioneered fin colors, extended heel sections, leading edges, water channeling and accelerating through a split-V shape, fin, adjustability, flexibility, and the use of snappy and high performance materials, such as polyurethane. Just about every change and development in the way divers think about moving through water today came from Bob Evans and his Force Fins.








best fins for underwater photographyIf you’re used to traveling, packing, and lugging around two huge fins, get ready for a surprise when you take along Force Fins. They weigh less than 2 pounds each, are easier to handle, take up less room, fit in carry on luggage, are easy to get on and off, and you can even walk forward in them!

How well you move through the water is based on many factors including your kicking style and individual characteristics like leg strength and ankle flexibility in addition to your choice of fins. In the underwater world, you need all the help you can get, and we know that you want fins that are comfortable, efficient, durable and reasonably priced. That’s why we invented Force Fins.

jump with fins, force fins, military fins, what fins do Navy SEALS wearAmong those divers in the know, Force Fins are a closely held secret. Dedicated Force Fin users are a special group of divers who were willing to try a revolutionary diving product that delivers on its promises. They will never go back to other dive fins again. Would you like to join this elite group? We could go on forever describing the unique benefits of using Force Fins, but there’s only one way to really find out why our fins are the best diving fins in the world: try a pair. You’ll be happy you did.


Flutter, The Most Efficient Kick For The Most Efficient Fins


Since the kick is all that divers have to propel themselves, it’s important to do it correctly. Many people believe that divers should use a flutter kick that is deep or wide and slow and pushes water backward. But scientists studying animal locomotion along with swimming theoreticians discovered more than three decades ago that this simplistic “drag-dominated” propulsion theory (the movement of a canoe paddle is an example) does not tell the whole story of how boats, people and most animals move through the water.

Based on a more sophisticated understanding of fluid dynamics and bio-mechanics, we now know that other hydrodynamic forces such as “lift” propulsion are just as important and in many instances, more important in propelling you efficiently when kicking.

Force Fins are designed to use this more efficient kick style with its lower energy cost. how to kick force fin, divers kick, scuba kick, flutter kickNotice how streamlined this diver is. Her kick is no wider than the profile of her tank on her back and her bc in front.

Take a look at how animals do it. Contrasted with the inefficient pushing-backward paddling of ducks, energy efficient fish beat their tails side to side (or up and down in the case of marine mammals like dolphin) in a flapping motion, using a complex mix of lift and drag forces to overcome the resistance of the water and move forward.

The best way for humans to perform a flapping-style kick is not with a deep and slow kick, but with a shallow and quick motion that’s more streamlined, more energy efficient, and that consumes less air. Of course, some types of fins are better suited for this kind of kicking than others. Force Fins are designed to use this more efficient kick style with its lower energy cost. Our fin generates maximum thrust from minimal vertical movement because of its superb channeling ability, and the rate or frequency of the kick is easily increased because of the recoil and snap of the blade that speeds up the fin’s recovery. The snap of the blade feeds energy back to your muscles, increasing your efficiency and bottom time while propelling you forward.




Fin Propulsion and Force Fin’s Efficient Kick

Populsive Divers Kick, Efficient Kick

Divers propel themselves by moving their legs (and the increased surface area of their fins) back and forth against the water with a flutter kick motion. This kicking results in a complex combination of propulsive forces that move the diver forward as well as resistance or drag forces that hinder that movement.

With other fins, virtually all of the propulsion comes from the downward phase of the kick (imagine you’re horizontal in the water with your stomach toward the bottom) and almost none on the up-kick. You can test this yourself in the water by trying to kick up, with or without fins. You’ll go nowhere. But simply extend the lower leg down and watch yourself move ahead.

Force Fin KickOne reason for this uneven propulsion is that humans naturally have more strength when kicking down. The power or downward phase of the kick emphasizes the powerful quadriceps muscle group at the front and side of the upper leg. The kick’s upward phase uses the weaker hamstrings at the back of the thigh and is mainly a recovery movement setting up the leg for the next power phase. The result is a natural two-stroke kicking cycle of power and recovery for each leg. It’s the same with other continuous activities like running, bicycling or swimming where a power/recovery cycle is built-in to conserve your energy.

While most other fins make you work just as hard on the recovery as on the power phase, Force Fins take advantage of this two-stroke cycle and work in harmony with the body’s natural strength. The flexible blade of our Force Fin opens out to its maximum surface area to move a high volume of water during the powerful downward portion of the kick.

During the recovery, the blade folds down, channeling water behind while limiting resistance to conserve your energy. (If you have to put the same amount of energy into both parts of the kick, you fatigue much sooner.)

As you kick down, the blade opens out to its maximum surface area, engaging the muscles of the whole leg to push water and provide initial forward thrust.


At the end of the downstroke, the fin recoils, setting up to rebound to its original position during the recovery or return kick stroke.


The fin then rebounds to help begin the upward recovery phase of the two-cycle kick stroke.


The fin’s tips fold inward to aid the upward recovery and to prepare your leg for the next downward power stroke.


Force Fins are the only fins that provide propulsion consistent with your natural two-stroke kick cycle to this degree. By providing for more of a separate power and recovery phase, oxygen depletion is reduced, and the onset of fatigue is delayed. The result is that divers can kick continuously for longer periods of time.


Powerful Fins, Are They the Best Fins?


powerful fins, navy diverOne of the biggest areas of confusion regarding fins is the notion of “power.” Many divers believe that the more they can feel their fins, the more they’re getting out of them. And to capitalize on this belief, many fin manufacturers have responded by making longer and stiffer (more “powerful”) fins that fool divers into thinking that they are generating more propulsion with less effort.

However, the laws of physics don’t agree.

You are the power for your forward movement, the more you can feel your fins, the more energy you’re expending and the more you’re working for them, instead of having your fins work for you

“Power” is a measure of energy expenditure. More power requires more energy, and more energy requires more effort, not less. A 100-watt light bulb is more powerful than a 60-watt bulb. It puts out more light, but it also uses more electricity and costs more to operate.

The same with fins. What divers believe to be power in fins is really resistance. That’s what you feel. “Powerful” fins rapidly waste your energy supplies and actually transfer a much smaller percentage of the effort into forward propulsion than you think.

Since the name of the game in diving is to decrease energy use (which decreases oxygen consumption and increases bottom time), it makes sense to use more efficient fins, not more “powerful” ones, as long as they do the job of moving you through the water.

The fact is, no fins have power. You are the power for your forward movement, the more you can feel your fins, the more energy you’re expending and the more you’re working for them, instead of having your fins work for you. Force Fins are specifically designed not to be felt; Force Fins are designed to work efficiently for you.Extra Force Fin, Powerful Fin

And, for those of you who still want “power” our EXTRA FORCE FIN is the best fin.

The Extra Force Fin has the largest surface area for extra leverage under load. The way Master Fin Designer Bob Evans puts it, “You don’t fly a learjet to carry a herd of elephants. You fly a 747 or C130. The EXTRA FORCE FIN is our C130.



No Pain, No Suffering, Fins Without Cramps

tan delta force fin

Pain & Suffering a Thing of the Past

One of the most common complaints that people have about diving is that their feet and legs hurt when they try to kick with today’s long or stiff fins. Their arches or calves cramp, their toes are smashed into the end of the foot pocket, their legs tire… Sound familiar?

The primary cause of all this pain is that most fins are designed to concentrate much of the force from kicking on the smaller muscles of the lower leg and feet. And those muscles simply can’t take the stress of powering a large fin blade through the water. The result? Fatigue and cramping.

But with the trail-blazing Force Fin, our unique foot-pocket design transfers much of the effort of moving the blade to the largest muscle group in your body, the quadriceps, removing pressure from the toes and feet. Because your entire leg is now doing the work, muscle fatigue and cramping is significantly reduced.

Force Fins are designed to let your toes really breathe, move and wiggle about like they’re meant to do. Because of our true, open foot pocket, your toes are finally free!

Try this simple test to see the difference between how our fins work with your body as compared to other brands.

While seated, cross your ankle over your knee, grab your toes and pull them in the direction of the sole of your foot. Do you feel the stretch and tension running from the top of your foot up and along the shin? Those are the primary muscles that other fins work because the fin blade extends from your toes.

Now, hold the top of the foot – pull again toward the sole of the foot and resist with the leg. The tension has moved up to the upper leg, hasn’t it?

Because of their unique design based on human bio-mechanics, Force Fins work the larger muscles of the upper leg in addition to the lower leg. These muscle groups are large and powerful. They are best equipped to efficiently power your fin blade.


The Truth About Swim Fins

Force Fin Swim Sponsor


Increase fitness and cardiovascular conditioning
Increase ankle flexibility
Develop leg and swim kick strength
Improve body position and technique so you can swim fast


Foot-Pocket Design that leverages power from your strongest kicking muscles in the upper thigh
Snappy Blade Design promotes high turnover, with power and recovery for aerobic workout
How Force Fins are made, hand crafted in the USA using highest quality polyurethane


We’ve been designing and making improvements to fins for over 30 years, with millions of satisfied customers, and many major product design awards under our belts, we can honestly say that we are the experts in fin design. That’s all we do, and we think our innovative fins are without equal in terms of comfort, efficiency, durability, performance, versatility and sheer value for your money.

We offer a variety of fins and each as been developed in response to your needs, comments and suggestions. Studying marine animal locomotion and human biomechanics, we have researched and designed our fins to take advantage of the laws of nature and physics. Not to mention common sense.

Open Toe Pocket Design

Slim Fin fins for swimming


Unlike all other fins, even those with open toe boxes, only FORCE FIN swimming fins are designed to concentrate the force of the blade further back on the foot, using the muscles of the whole leg, not just the lower leg.

Your toes are free to wiggle about to feel the water.

Patented Blade Design

Force Fins fins do not have flat blades like most other brands. Instead the blade curves up or away from the bottom of your foot to provide more resistance on the power or downward (during freestyle) phase of the kick. The blade then snaps back to assist on the recovery. This two-stroke cycle does several things for a swimmer:

By kicking against a load that provides for a separate power and recovery cycle as opposed to the traditional power-power cycle of other fins, oxygen depletion is reduced, the legs and body work more aerobically and less anaerobically, and swimmers can maintain their workout efforts for longer periods of time.

Independent research has shown less lactic acid buildup (lactic acid is the proof of anaerobic activity) and more oxygen absorption with Force Fins. Flat fins, other fins bring on symptoms of fatigue and cramping more quickly.

Other fins, flat fins want to go through the water along the path of least resistance, which is sideways! Don’t believe it? Hold a flat, heavy object at the surface of the water, let go and watch what happens. It turns on its edge and heads for the bottom. Or, if it’s light like a sheet of paper, it will zig-zag or “dish” its way down. Neither action is going to help your kicking. With flat fins – even small or cutoff flat fins – a swimmer is constantly fighting all this twisting and torquing, and any effort spent this way is wasted.


Force Fins are our original design, and being somewhat larger than Slim Fins, they provide a more concentrated leg workout (more resistance). They are a more versatile fin, in that they can be used for other sports, such as snorkeling, SCUBA and float tube fishing. From a swimming perspective, they are a very specific training tool and are excellent for butterfly, “new-wave” breaststroke, and the backstroke dolphin kick.

Slim Fins are narrower than the Force Fin and are specifically designed for pool swimming – especially freestyle – applications. With Slim Fins, the blades don’t touch, flip turns are no problem, and high stroke turnover or cadence is easily maintained. Slim Fins can be used either while swimming or in kicking-only drills. They receive the highest recommendations from swimming coaches and professionals, and will do the best job for and are probably the best choice for most swimmers.


Manufactured in the USA and backed by more than 30 years of research and development, Force Fin swimming fins are made of ultraviolet-, abrasion- and chemical-resistant polyurethane and heat-treated for 16 hours at temperatures where other fins melt. This process allows the molecules to cross-link giving the blade its snappy, high-performance characteristics and extreme durability. Unlike other brands, Force Fin swimming fins will not melt on hot pool decks or mark the sides of pools, and should last season after season, even when used daily.

We could go on forever describing the unique benefits of using Force Fin swimming fins to improve your swimming. But there’s only one way to really find out why our fins are the best swimming fins in the world: try a pair you will be happy!