NBP09-01 Cruise Report - British Oceanographic Data Centre

Figure 19: Planned mission profiles beneath PIG, with short missions shown in red and long missions inblue. The ice thickness profile is taken from the southernmost radar flightline of the four shown in Figure 6,starting near X=50 km, Y=1630 km. The bold, dashed line joins the two points of known seabed depth atthe ice front and the grounding line.ship’s sonars switched off, ranges on the Autosub LinkQuest rarely exceeded 3 km, or less than half thatachieved on the RRS Discovery, RRS James Cook, and the MV Terschelling. The emergency beacon wasclearly audible to a range of 10km, and could be detected intermittently in quiet weather (particularly withthe ships propulsion system disengaged) up to 20km away.3.4 Recovery operationsOn the first recovery we kept with the method we had developed over the preceding years. This requires asmall float, jettisoned from Autosub, to be grappled. The float is connected by a light line to heavy lift lines,held within the Autosub vehicle, which are pulled aboard and coupled to the Autosub gantry. Autosub isthen winched aboard.R/V Nathaniel B Palmer is a twin screw, direct drive, fixed RPM, variable pitch ice breaker. During the firstrecovery it was found that the cut away counter and the huge suction generated from the main propellerswould draw the Autosub under the stern. This was only averted by the fact that the ship has a very lowfreeboard enabling the use of boat hooks (Figure 16).NBP09-01 Cruise Report (p. 23 of 83) Revised February 27, 2009