A winch and cable for the Autonomous Vertically Profiling Plankton Observatory

High frequency (of order hours) sampling of plankton over extended periods (of order months) is essential in studying the response of plankton to their environment. The Autonomous Vertically Profiling Plankton Observatory (AVPPO) has been designed and built to meet this need in coastal areas. For this configuration of the video plankton recorder, an autonomous winch, resting on the sea floor, and custom cable have been developed. The system requirements were: low power, tolerance of slack in the table permitting the buoyant instrument platform to profile to and from the surface in 100 m of water, ability to telemeter video signals down to the system base which houses video recorders, and autonomous operation over extended periods of time. A custom, high-helix angle, electromechanical cable, with a central Kevlar strength member, was made to be light, flexible in bending, stiff in stretch, and tolerant of bending while containing two coaxial cables. The winch has two independent, oil-filled, pressure-compensated, brushless DC motors. The drum motor controls speed and position of the cable, while the powered sheave keeps cable tension on the drum even when the cable from the fish is slack, as when the fish surfaces. The system has been built and twice deployed autonomously in 80 m of water on George's Bank off the coast of Massachusetts.