Re: [PSUBS-MAILIST] New comer w/ROV Question

["Sean T. Stevenson" <ststev@uniserve.com>]

Jonothan, I have some experience with ROV's, having worked for both International Submarine Engineering and the Canadian Scientific Submersible Facility.  I also do swiftwater (up to river class 4) 
and other SAR diving with the Canadian Amphibious Search Team, so I think I understand what you are trying to do.  Difficult design direction for an ROV.  As a diver in swift water, when you are in the 
flow, it is more akin to rock climbing than diving, since you are manipulating yourself between hand and foot holds on the bottom, against the "gravity" of the flow.  Your comments lead me to believe 
that you have not actually been trained in SAR diving.  Carrying a 35 pound lead anchor?  How do you effect a recovery with that burden?

The power requirement for a vehicle operating against such a current would be tremendous, even if it was designed to take advantage of ferry angles.  The problem is that this necessitates having a 
high drag umbilical, which further increases the power the vehicle has to have.  Also, you have to consider the effectiveness of a camera, profiling sonar or other tools in an application where the 
vehicle may be subject to vibrations or frequent thruster corrections.

Perhaps a better idea for this environment, short of putting a diver in the water, is to use a towed video or sonar array, with a hydrodynamic tow fish suspended from a vessel or from shore upstream, 
where applicable.  This allows you to use a low drag towline, since the only cables you need to run are a few optical fibers and low power for your control surfaces (you could even power the controls 
from a battery).  Cross current movement is done by moving the tow point, up/down stream movement by taking up or letting out cable.

The other thing you want to consider is that, in the case of body recoveries, you need to recover, which implies either putting a diver in the water anyway, or a vehicle with manipulators - not practical 
for a necessarily lightweight and low drag vehicle.

For an ocean ROV, you put whatever you want on it , since drag and weight are not as much of an issue, and you can use more effective tools.  I've had a hand in building a few ROVs for ocean 
research purposes.  With an ROV, you are not building a pressure hull, so the depth doesn't matter apart from your camera housing.  You just need to oil fill and pressure compensate your electronics 
and optics.

Let me know if I can be of further assistance.

-Sean