The picture below shows the ESP in the housing with a side cut away for illustrative purposes. The E/M (electromechanical) cable connects the ESP to the radio modem on the surface float, allowing reception of commands and transmission of data. (Although it does not appear so in the illustration, the instrument housing is firmly attached to the battery housing.) At deployment, locking pins at the top of the housing are removed. The bail pivots at the bottom and flexes independently of the housing, reducing pull on the instrument that might be generated by waves and currents. The whole assembly weighs over 370 kilograms (>800 pounds), but air trapped in the housing makes it sufficiently buoyant, that an anchor—shown in the mooring diagram below—is needed to keep it at the required depth and location.
The ESP mooring
After the instrument is deployed, all that can be seen at the surface is the float—a yellow buoy with the antenna and radio modem.
The current mooring configuration for surface-ocean deployments (less than 50 meters) is shown below. The RR (railroad) wheel is the anchor. The lengths of the polyester lines determine the depth. The elastic tether assembly absorbs shock and vibration from currents.