Hi. I use bilge pumps for my thrusters (akin to http://www.homebuiltrovs.com/howtobilgeconversion.html). This has generally worked very well, but today I started having a weird problem: one of the thrusters works fine when it's on dry land or when it's in a couple feet down, but it's failing consistently at depth (anything greater than 10 feet). The other thrusters work great (down to 60+ feet). When I pull the ROV out of the water, the problemsome thruster works again, but it will fail again when it's at any depth.
This is in salt water, in the Pacific Northwest.
Any ideas at what could be causing the failure?