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HomeFreedivingGear Review: The DOL-Fin Orca

Gear Review: The DOL-Fin Orca

In the beginning, there were bifins.  Then came the monofin.  And now, there is the DOL-Fin Orca freediving hydrofoil.  It could be the next generation propulsion device freedivers have been waiting for.

The DOL-Fin Orca was designed and built by aerospace engineer Ron Smith.  Ron visited my home town of Vancouver recently, and I had a chance to test out the Orca both in the pool and the ocean.  The device I tested is one of only two proof-of-concept prototypes presently in existence.  They were constructed to validate performance predictions and to anchor a waypoint along the design path to a production model, which will hopefully be available around the end of 2010. 

This review is based on my own personal testing — I have no affiliation with Ron Smith or his company, Smith Aerospace.


Design Concept

The beloved monofin used by freedivers has many areas for improvement.  It is only efficient at one particular stroke amplitude.  It is often uncomfortable, and it is often difficult to get proper fitting footpockets.  Being glued together, monofin parts cannot be replaced.  If the blade breaks or if the footpockets tear, it must be thrown out — an expensive proposition for a $600+ monofin.  And most importantly, the monofin could still be even more efficient than it already is.

Many elite freedivers have had intuitive insight on how the monofin’s performance could be improved.  Most agree that some sort of wider, rigid blade, or wing, placed some distance away from the feet, seems the best idea to try.  I myself shared that opinion, and in 2002 I began trying to build such a device.  Like most others, I failed or gave up. 

Ron Smith, founder of Smith Aerospace, did not give up.  He started experimenting with monofins in the early 1980’s and had built his first working prototype of what would later become known as Dynamic Oscillating Lateral-Fin, or DOL-Fin, technology in 1992.  DOL-Fin technology was different from other monofins, in that it used a rigid hydrofoil for propulsion.  Working in private, Ron developed the DOL-Fin concept into a new form of monofin that provides super efficient propulsion for scuba divers.  Then he turned his sights on trying to build the ultimate freediving monofin.  Eventually, he produced the DOL-Fin Orca, the propulsion device so many freedivers have imagined, but could never actually build.

Smith used advanced fluid mechanics combined with extensive lab testing and inspiration from marine mammals to design the DOL-Fin Orca.  In my opinion, the Orca’s design solves every single problem of the monofin for freediving applications:

  • The Orca is efficient over wide ranges of stroke amplitudes and power inputs, allowing many more possible swimming techniques than traditional monofins
  • The Orca is both durable and modular, so if one part breaks, it can be easily repaired or replaced
  • The Orca has adjustable bindings that will fit almost any size foot, eliminating sizing problems or the need for a custom footpocket
  • The Orca drastically improves the power transfer from the foot to the fin
  • The Orca’s shape and buoyancy do not change with depth — it can be built with negative buoyancy, neutral buoyancy or even positive buoyancy
  • The Orca combines extremely low surface area with aggressive streamlining and a 30 degree blade angle, which lowers drag to allow for an immense ‘glide’ phase


The first thing you will notice about the Orca is that it is built exactly the opposite of the traditional monofins.  While other monofins are built of flexible materials (fiberglass, foam and rubber), the DOL-Fin Orca is primarily made from rigid parts.  The blade of the Orca is made from extruded aluminum, hard anodized and laser engraved.  Its cross section and shape took years to perfect.  The blade rotates in pitch relative to the rest of the Orca’s structure.  Its rotation angles are governed by a simple looking, but sophisticated, non-linear suspension and control system which keep the blade flying efficiently in the water to prevent wasteful energy loss.

The diver’s feet are set on a sturdy aluminum plate, and each foot is secured independently to the plate by textile binding straps locked down by Velcro.  A fiberglass fairing streamlines the diver’s feet and the device’s underlying aluminum sub-frame.  Inside this fairing are thousands of incompressible micro-spheres which offer consistent buoyancy independent of depth. 

The Orca is incredibly lightweight, weighing less than half of a hyperfins ‘Andronov’ style monofin, and it can be disassembled for easy traveling.  You can fit multiple DOL-Fin Orcas inside a single suitcase!

Pool Testing 

I first tried out the Orca at our local 25m swimming pool.  Ron explained how the foot straps work and how best to fit my feet inside the device.  This is a critical step, and it works backwards from how a traditional monofin works.  Whereas with the monofin you slide your feet as far inside as you can, with the Orca you slide your feet as far back as you can, and then tighten one strap around your ankle, and another over the top of your foot.

Once in the water, I did sets of 50m FRC dynamics as Ron checked my technique.  For most of the pool session I was still just using the DOL-Fin Orca like a traditional monofin.  I later found that it performs best if you learn techniques specific to the Orca, but regardless, if you use it like a traditional monofin, it still works incredibly well.  After a dozen or so swims I tried upping the distance to 100m FRC to see how that felt, and it felt very good.  I did some stroke counts with the Orca over 25m, and then switched to using my Chen-Bin monofin, with which I recently dove 100m CWT at the Vertical Blue 2010 competition.  I swam with the Chen-Bin and did stroke counts to get an immediate comparison against the DOL-Fin Orca.  There was no comparison.  Putting my Chen-Bin back on felt awful and I couldn’t believe how my favorite monofin could be so bad.   Everything is relative, I suppose.

Covering 25m with the chen-bin required:

                kick-kick-glide, kick-kick-glide, kick-kick-glide, kick (7 kicks). 

With the Orca it required:

                kick-kick-glide, kick-kick-glide, kick (5 kicks). 

These results were from using the Orca like a monofin, with monofin style technique — which is not necessarily an ideal technique to use with this device.  I did not learn any of the Orca specific techniques until the following day in the ocean.

Fattah in the DOLfinOrca

In the pool, my only complaint was turning around.  There are only two prototypes in existence and I was unsure of technique and afraid I might damage the device, so I was careful at the turn around to avoid the fin contacting the pool walls.  Afterword, in discussions with Ron, he said that the design allows you to push off the wall with your feet using spurs on the back of the device which are a part of the blade’s suspension and control system as load-transfer points.  Pushing off the wall isn’t really possible with most monofins due to the suction load the blade forms against the wall.  I did not get to try wall push-offs with the Orca.

I also tried doing some sprints with the Orca.  It was not designed for sprinting, and it was not clear that it would be particularly good for that.  Ron said that a sprint optimized fin would have a different shape and size blade than what this fin has.  My initial impression is that the Andronov style monofin would win a race, although again I had not mastered Orca specific techniques, so there is still some testing to do.

Ocean Testing

The next day Ron and I went to the ocean for more testing.  I was still learning tricks to get my feet secured properly, and Ron showed me that I could descend to 7m and tighten the straps further, while my neoprene socks were compressed.  That helped a lot to keep the fin feeling snug when I was at depth.

The water was 13C and I was using a very thick 7.5mm Yamamoto suit with 10kg of weight.  I spent almost two hours in the water, and I did repetitive dives from 20m to 37m, as well as leisurely horizontal dives in the 10-15m range.  I also tried doing some large horizontal distances.

As the testing continued, I began to learn how to use the Orca more effectively.  Once you start to understand it, you realize that you must throw away all your previous habits to get the best results.  While most divers will eventually get good results through trial and error, I think in the future some sort of Orca specific training course would be great.  Some of the techniques are not that intuitive.  As an example, with a monofin you need to maintain certain minimum amplitudes of fin stroke.  With the Orca you can use almost any amplitude, even ultra-small amplitude techniques which would simply have no effect with a traditional monofin.

Ocean Testing Results

After a couple of hours in the water, and after learning some of the Orca specific techniques, I was blown away by the device and fell in love with it.  Here are some of the highlights:

  • It was completely comfortable; I had no sign of any type of discomfort
  • Power transfer to the fin was way better than with a monofin
  • The hydrodynamic design and parallel blade angle to the body meant I felt virtually no drag when gliding horizontally, or sinking down through the water column
  • Using low amplitude strokes I was able to cover inhuman horizontal distances even when diving with my lungs half full
  • The maneuverability of the device was similar to other monofins
  • It worked much better with my arms extended
  • Enjoyment of my recreational dives was dramatically increased

Since I was diving with a very thick wetsuit and 10kg of weight, I was extremely heavy after 35m.  When ascending under such extreme negative buoyancy conditions, it took some time to learn how to use the device effectively.  Once I improved, ascending under such heavy negative buoyancy was similar to other monofins — in other words, the huge advantage of the Orca seemed less clear under heavy negative buoyancy. 

Ron said that, in theory, it should have better static thrust than a traditional monofin and that he was surprised this was not showing through more prevalently.  From our discussion, it appears I may not have found the optimum swimming technique for such conditions and it may yet prove to have advantages here as well.  Also keep in mind that no one ever reaches this level of negative buoyancy during competition style dives or during warm water dives.  When feeling negative buoyancy similar in magnitude to a competition dive, the device worked splendidly.

In fact, I think I could reduce the amount of ballast I use when diving with the DOL-Fin Orca due to the possibility of using low amplitude kicks to provide efficient propulsion in the near-neutral zone, where the traditional monofin often ceases to flex at all.  This may allow for lowering my neutral depth point without requiring huge amounts of energy to get down quickly.

Competitions, Records and Recreational Diving

Ron already used the DOL-Fin Orca at an AIDA freediving competition in Kona, Hawaii.  Without any previous formal training he did remarkably well, beating his PB in dynamic by 56m and posting 136m with the Orca.  In my mind it is only a matter of time until all dynamic apnea and constant weight world records are set with this device.

However, what blows my mind is that the same record setting device can be worn in full comfort while diving for fun, even in cold water!  In my case, I cannot use a hyperfin style monofin in cold water because I can’t fit thick socks inside the foot pockets with any degree of comfort and power transfer.  During cold water diving I’m forced to dive with bifins or a 1st generation monofin.  Switching then to the Orca makes an even bigger difference to the enjoyment of recreational dives.

I was extremely sad that I had to give back the Orca when testing was done. 

The price is tentatively set for $1200 USD.  Although this may seem expensive, actually it is a steal considering that:

  • You only need one fin for both recreational diving and for competitions
  • It is designed to last decades
  • It can be easily repaired
  • It travels easily and can save you money from checking extra airline baggage
  • It is a sophisticated high-tech device with many years of research and development behind it.

I put my name down for a pre-order, and production in 2010 will be extremely limited.


The DOL-Fin Orca freediving hydrofoil is, in my opinion, a revolution in human underwater propulsion.  This single product solves almost every problem inherent to monofins for freediving, and has the capacity to increase comfort, enjoyment, and performance, all at the same time.

More information on the DOL-Fin Orca as well as the other scuba versions of the DOL-Fin can be found at http://www.smithaerospace.us.