Underwater Diver Propulsion

By Robin Battley

For many, the underwater sensation of weightlessness and the freedom of movement are exciting when simply wearing fins and a tank. Gliding, "free falling" over boulders, twirling around because it feels good...we can all relate to the magic experienced when we slip into the water and are released from gravity. Now let's take that feeling to the next level. Let's experience ultimate diving.

It is possible. Imagine yourself cruising underwater at a speed of over three knots. At such a speed your mask would be vibrating. The reef beside you would take on the characteristics of the median of a highway as you soar past. Instead of using leg power and fins, molded aluminum with solid state, digital control circuitry would provide infinite variable speed control at your fingertips. Actually at your dual fingertip trigger controls.

No, this isn't a description from the latest James Bond movie or the next James Cameron Oscar nominee. This describes some of the features now available to recreational divers in diver propulsion vehicles (DPVs). The technological jump in these machines has been significant within the past few years. Standard equipment includes the digital controls mentioned above, viewports to keep tabs on battery charge status, riding saddle, battery chargers and believe it or not, owners manuals. DPVs now come in a range of sizes, optional silver zinc batteries with various range capacities and differing weights. Twin systems can be set up to create a platform or sled for transporting equipment underwater or more than one person.

Who uses these things? Good question. Contrary to popular belief, these units are not designed to create the ultimate scuba diving couch potato. Rather, they are designed for a wide range of professional and quasi-professional uses. These include underwater inspection of buildings, piers and docks, search and recovery operations, underwater mapping, research, underwater filming and photography. Often these activities involve extended bottom times and anything that enables a diver to use less energy, experience less fatigue and extend their range could become an indispensable tool. Long-range batteries and overnight charging capability would also be attractive to an ongoing project.

Before you run to the nearest dive store, or your computer to order a DPV, consider the type of diving you do and that you enjoy. Are you embarking on long range "big picture" quests on a regular basis? Most of us are not. These tools, or toys, depending upon your frame of reference are not cheap. Have you tried renting one? Was the range it displayed in your home waters satisfying? Was the visibility at your favorite dive site sufficient to allow you to go careening at two to three knots? Was the unit easy to get into and out of the water by yourself or with the assistance of your buddy? Were you trying to deploy it from shore or from a boat? Are you able to let your buddy "hitch a ride" or will you need two of these machines?

A DPV will provide manufacturer specifications on optimal speeds, ranges and battery charging times but remember that many factors in the field will also influence these statistics. Not only current, it's rate of flow and diver volume affect these values, but also a diver's equipment configuration (drag coefficient) and their posture while underway. In Canada, the cold water in which we dive will always decrease battery output compared to a manufacturer's stats. How warm was the water in which the units were tested?

If you have considered these options along with many of your own and decided that a dpv is for you, research the various models available to find the one best suited to your needs. There are many. As you steer yourself through the water like a dolphin or seal angling it's body at mach 1 to multiple sites within one dive, just keep one thing in mind...you have to swim the thing back to shore/boat if the batteries give out. Have fun.