A Free Fall Tethered Instrument Platform

This paper describes the design goals, theoretical limits and preliminary achievements in the development of an innovative tethered profiling instrument platform. This profiler free falls with an approximately neutrally buoyant synthetic fiber line paying out its stern. The shipboard equipment will include a winch with a removable mandrel. After recovery of the profiler the mandrel (with tether) will be transferred to the profiler for redeployment. The feasibility study has been directed towards a system with rapid deployment-recovery rates. At the same time size and manageability have been prime considerations. The profiler´s speed of descent will be independent of shipboard dynamics, the drop rate being a function of hydrodynamic shape and mass (both of which are constant). The speed of recovery will depend on several parameters, the principal factor being tether drag. The strength of the tether is a key variable and influences many critical aspects of the overall system design. Limiting the ultimate strength of the tether has a positive effect on many system traits, including manageability and power requirements. The design goal is an instrument platform capable of carrying any 8 inch O.D. scientific instrument to a depth of 6000 meters and back at velocities which can be defined by the user in the range of 3 to 8 meters per second.