I want to build a small remote-controlled submarine, and have been thinking about how to handle the ballast tanks. The simplest option seems to be a piston shaft, which fundamentally needs some kind of (sealed) linear actuator with sufficient force to overcome water/air pressure at reasonable depths (say 0m to 50m).
The problem is I don't have an infinite supply of power available on-board and all the linear actuators I found use ludicrous amounts of it, such as over 1 amp at 12 volts... but I only need to move the piston every now and then, most of the time it just needs to sit wherever I tell it to and not move.
My question is, once a linear actuator has been "actuated" into place, can I de-power it and expect it to hold up to its maximum rated load? Does it depend on the design of the actuator? If not, what are some engineering approaches I can use to mechanically lock the piston into place until I need to unlock it, so that I can trade off precious electrical power for mechanical strength?