[PSUBS-MAILIST] Another option...

Instead of using hydraulics (messy, very expensive, heavy, not pressure-proof), why not use a series a series of spring-loaded solenoids to do the work for you. It might not be very strong - and you'll have to carry a couple batteries, but I doubt you're going to be lifting car-wrecks out of the lake anyway. You could have the spring-loading of the solenoids such that they maintain the arm steady and the claw in the closed position and only deviate from that when you command them otherwise. The positions of the arm and the claw could be maintained by a series of potentiometers built into a non-spring-loaded joystick configuration (probably 2 joysticks, and a button to open the claw). With non-spring-loaded joysticks like that, the position you leave them in will translate directly into the position the arm remains in - making life a little easier for you.

Considering the fact that a manpowered sub is going to be very limited in terms of it's duration and what it can carry, an arm that utilizes solenoids as opposed to hydraulics should be more than adequate. The other advantage of this system is that you can get the unique satisfaction of building it entirely yourself. I would say that it could probably be done more cheaply than a comparable hydraulic system - and with no resistance due to water pressure. The fact that it is inherently pressure-proof and requires no mechanical or fluid linkages through the hull also makes the whole thing a bit safer. You might chew up your battery power pretty quickly depending on big you want your arm to be, but like I say, we're not talking about raising the Titanic here. I hope this will be of some use to you. Enjoy!