This is an apparatus for taking water samples at different depths. The science party uses the crane to lower it over the port (left) side while the ship maintains a slow slide to starboard. They can lower the CAST equipment thousands of feet. Each of the little vertical canisters can be programmed to open at a different depth, fill with water, then close. They check the vertical strata of water for temperature, salinity, density, particulates, biota, stuff like that. Scientific stuff is cool.