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.