TECH-SPEC
As appeared in Immersed Magazine,
Winter 2001, p18-19.
Copyright, Rodney Nairne.
It's easy for divers to forget we are exposed to an alien
environment comparable to the hostility of space. While we don't
have to deal with the vast complexities of escaping the earth's
gravity we are still, especially as technical divers, reliant on our
life support equipment for survival.
Like astronauts, we are weightless and have the sensation of
flight. As divers we have the added hurdles of both elevated
ambient pressure and fluid drag. In what could best be described
as a downward spiral, as depths increase, we compensate with
arger gas supplies and often multiple deco gasses. This in turn
magnifies the problems of fluid drag: we now have to deal with
added exertion caused by swimming with all this equipment, and
exertion at depth significantly increases both gas consumption
and decompression obligations.
Decompression is a serious consideration for the technical diver.
Every avenue is explored in order to reduce decompression time,
from using multiple gases, mixed gas computers, new
decompression theories and even minimizing inert gas exposure
with the use of constant PO2 closed circuit rebreathers.
Ironically, DPV's (Diver Propulsion Vehicles) are one piece of
equipment that can significantly reduce inert gas uptake, but
are seldom considered from this perspective.
Inert gas loading is a function of not only partial pressures and
time but level of exertion. As an example, in the case of a
strenuous dive, Buhlmann advises to use the next longest bottom
time. Buhlmann-Hahn tables recommend adding 50% to the bottom
time for strenuous dives. Depending on the profile this can often
double or triple the required decompression.
Unfortunately, almost all our diving requires a degree of mobility
and exertion, whether it's to survey a reef or wreck site, or
penetrate cave passageways. As free swimming divers, even if our
dive site position is static we may have to deal with strong currents.
Good divers can adapt to these demands by utilizing proper finning
techniques, streamlined gear configurations and maintaining a
decent level of physical fitness.
DPV's provide the solution, although many divers consider DPV's as
a toy rather than a tool. Many are designed for a single tank diver
and are under-powered for use in technical diving. Additionally, few
makes have the structural integrity to be used for deep diving.
I started technical diving in Australia in its infancy, 1993. It was
several years before I discovered the advantages of DPV's for deep
diving when I imported a custom deep ride-on scooter from the USA.
In 1998, I moved to US and started diving in the Florida caves.
Floridian divers must hold the record for per capita use of
diver propulsion vehicles DPV's, and it was in the Florida caves that
I was exposed to tow behind scooters for the 1st time.
Tow behind scooters have many advantages over ride on scooters,
most noticeably ease of use, maneuverability and the ability to fit
through tight places in both caves and wrecks. For extreme cave
dives, they offer the only practical solution to redundancy, as 1 or
more backup scooters can easily be towed directly behind the divers
cylinders. It is no surprise that tow behind designs hold the cave
penetration record in both the US and in Europe.
Having a background in manufacturing and a desire to produce a
professional scooter that I personally could depend upon, it was
not long before I founded Submerge Inc and invested in the
production of a new scooter, the UV series. In 2 short years we
have catered to the demands of technical divers the world over.
The successful introduction of the UV scooters was dependant on
recognizing and implementing certain design features into the
underwater scooter.Simplicity was an overriding objective.
This leads to reliability and usability.
The UV scooters use a minimum number of components
resulting in a scooter that is easily field serviceable with only a
handful of tools. Through-hull penetrations were avoided in favor
of using a magnetic switch. Electronic motor speed control was
rejected in favor of less complicated and more reliable adjustable
pitch propellers.
In order to minimize diver fatigue, the sealed lead acid batteries
center of gravity is offset to partially counteract the torque of the motor.
Under full power, the handle naturally gravitates to the 12'oclock
position, which allows the scooter to be controlled by either the
left or right hand.
UV's are the first and only scooter to incorporate a true tow behind
handle, allowing ergonomic single-handed operation from the
12 o'clock position. This riding style utilizes a towrope, which is
attached to a ring on a crotch strap, so that you only steer with
your hand or fingers, not dragged around by both your arms. The
scooter is held at arms length to take advantage of the nautical
engineering law that longer waterline lengths reduce drag.
The hull and fore and aft sections of the scooter are made of highly
impact resistant polyethylene plastic. No surface finish is required for
corrosion protection so there is no coating to chip, peel or crack. The
standard color is black so that dive lights will not annoyingly reflect
back into the divers eyes from high power dive lights. Furthermore
the black color contributes to the excellent UV light resistance of
all the plastic parts of the underwater scooter / diver propulsion vehicle.
UV scooters are also modular in design, and the hull size can be
easily and quickly changed to extend the range potential of the
scooter. As side benefit of this feature is it is inexpensive to own
essentially 2 scooters: 1 short hull for ocean and wreck diving,
plus a medium or long hull which can double the range of the
scooter for extended range cave dives of up to 2 miles penetration.
Technical details aside, I doubt there is a single piece of
equipment that can increase your diving enjoyment more than a
scooter.
The ability to transform a previously arduous dive into a carefree
"flight" around familiar dive sites adds a new dimension to a dive.
Plus there is the benefits that only a scooter can provide, such as
surveying an entire wreck in deep water in 1 dive, or cruising for 2
or miles looking for underwater sights you would otherwise take
dozens of dives to see.
_______________________
Submerge