A Wire-Guided, Free-Fall System to Facilitate Shipborne Hydrographic Profiling

Abstract

The design and performance of a new style underwater frame for supporting instrumentation and water collection bottles used in hydrographic sampling is presented. Unlike a conventional frame that is fixed to the end of an electromechanical cable, the new frame is free to slide vertically along its tether. Allowing the frame to move relative to the sea cable decouples the underwater instrumentation from ship roll on downcast. Improved data quality from CTD instrumentation and the ability to work in more severe sea states result. Furthermore, the chance of cable damage that occurs when wire speed (lowering rate plus ship roll velocity) exceeds the terminal velocity of conventional underwater packages is greatly reduced. Absence of direct electrical connection to the underwater instrumentation necessitates an alternative scheme for real-time data display and command of water sample collection. These are accomplished with an acoustic telemetry system, implemented using commercially available components.