Thanks for the reply,
I wasn't inferring that we can use the current RC Sub technology directly, it would quite obviously need modification to fit in with the greater depths that ROV's attain.
The link I sent was merely for those that wish to explore, adapt and consider alternative solutions to the ROV project. E.g. I have seen enquiries on this project regarding ballast, trim, recovery and alternative methods of testing.
For someone wishing to 'test' an ROV, RC will work! to a limited depth (<=10m) i.e. bath, pool, pond etc.
Regarding 'shaft seals' it is literally a case of 'tolerance' & the number & composition of 'O' rings used. I personally work in the 25m - 100m range, and not a single piece of LSE (Life Support Equipment) I use in my work has more than 3 inline 'O' rings, in fact, I regularly use a CCR (Closed Circuit Rebreather) and most if it's components only have one 'O' ring, it's all down to the composition and tolerances of those 'O' rings.
Adaption of a standard RC Controllers to use an umbilical (my apologies I'm an engineer diver, and use the term 'umbilical' seeing as it supplies (think - unborn baby), as apposed to a tether, which restrains (think - animal)), is a very reasonable option while you learn, understand, build & test the umbilical & comms system, I believe Eric did this & we do it in our company.
Thanks for the Pressure calculation tool link, however, there is a difference in water salinity and composition i.e. Fresh Water, Brackish water, Sea Water & the industrial chemical properties contained within it and the effect of high and low pressure weather systems & altitude above sea level, all of which is quite difficult to calculate at a given time and location.
In our company we use the following algorithms for calculating depth:
Fresh Water Applications
Because most fresh water applications are shallow, and high precision in depth not too critical,
we use a very simple approximation to calculate depth:
depth (meters) = pressure (decibars) * 1.019716
For Seawater Applications
We use the formula in UNESCO Technical Papers in Marine Science No. 44. This is an empirical formula that takes compressibility (that is, density) into account. An ocean water column at 0 °C (t = 0) and 35 PSU (s = 35) is assumed.
The gravity variation with latitude and pressure is computed as:
g (m/sec2) = 9.780318 * [ 1.0 + ( 5.2788x10 -3 + 2.36x10 -5 * x) * x ] + 1.092x10 -6 * p
x = [sin (latitude / 57.29578) ] 2
p = pressure (decibars)
Then, depth is calculated from pressure:
depth (meters) = [(((-1.82x10 -15 * p + 2.279x10 -10 ) * p - 2.2512x10 -5 ) * p + 9.72659) * p] / g
p = pressure (decibars)
g = gravity (m/sec2)
This has proven to be as accurate as needed for Human Exploration of the Subsea environment and is therefore greater than that needed for ROV exploration.
I do hope this clears up any misunderstanding, I'm only trying to offer and give others idea's.