A comparison of LADCP and CTD performance on a slide-down-wire frame versus a standard CTD frame

An instrument frame to support ship-based, wire-lowered instruments has recently been developed at the Woods Hole Oceanographic Institution that is free to slide along the sea cable during deployment, thus decoupling the sensors from ship-roll-induced variations in lowering rate. A test cruise was performed aboard the R/V Cape Hatteras in July, 1998 to evaluate the performance of the General Oceanics, Inc. production prototype Slide-Down-Wire (SDW) frame. In operation, the SDW frame is effectively isolated from ship heave by paying out the cable from the winch at a speed exceeding the free-fall terminal velocity of the frame. At the end of the cast, the frame is arrested by an internal shock absorber mechanism when it reaches the cable termination. The cable is then hauled in with the frame held to the termination by drag, akin to a conventional frame hardwired to the cable. The authors report the performance of a Lowered Acoustic Doppler Current Profiler (LADCP) and a CTD mounted on the SDW frame in contrast with conventional lowerings of the same instrumentation. Performance of the prototype SDW frame is also discussed