Sea Technology

NOV 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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www.sea-technology.com November 2018 | ST 31 and 8 cm in diameter) and light weight (6 kg in air) are well suited to CTD deployments, and with its pressure rating of 120 megapascals and ultimate tensile load of 8 metric tons, it can be used in the deepest locations. Its body is made of stainless steel, and the slip ring inside it is immersed in oil. An electrical connector attached to the end of a 2-m-long resin tube filled with about 200 mL of oil is connected to the slip ring. At depth, the tube is compressed so that the oil pressure inside the slip ring matches the seawater pressure out- side it. In a test cruise of RV Kaimei in 2017, a slip ring swivel performed well in CTD measurements at pres- sures up to 100.53 megapascals in ocean trenches. Since 2017, a total of 443 CTD casts were conduct- ed from RV Mirai without the slip ring swivel needing any maintenance. During an Arctic Ocean cruise, a small amount of seawater invaded the oil-filled tube but was trapped at the bottom of the U-shaped tube. This allowed the slip ring swivel to remain in use with- out causing a short in the electrical circuit. During cruise MR17-07C of RV Mirai in October and No- vember 2017, we investigated the effectiveness of the slip ring swivel by attaching a simple azimuth meter to the termination of an armored cable that was deployed and retrieved by a traction winch and motion-compensated crane. We attached an azimuth/inclination meter to the CTD package to monitor its rotation. The CTD package had a large stabilizing fin (90 cm long and 50 cm wide) at- tached to its frame to resist its rotation. In a typical deep CTD cast, up to 61.9 mega- pascals (in which the cable was unreeled out to 6,040 m), the CTD package rotated six times clockwise during the down cast and four times clockwise during the up cast for a cumulative ro- tation of 10 times clockwise. On the same deploy- ment, the armored cable rotated 54 times counter- clockwise and then 94 times clockwise during the down cast, and rotated 147 more times clockwise and then 69 times counterclockwise during the up cast. During the 18 CTD casts in this cruise, the cable underwent as many as 281 clockwise rotations. Each time the CTD package was on the deck of the ship and the armored cable was free of tension, the cable was completely free of hock- les and loops. Despite the rotations of the cable during casts, there was minimal rotation of the CTD package thanks to the slip ring swivel, which (Top) Cumulative rotation numbers (counterclockwise) of the armored cable and the CTD package during cruise MR17-07C of RV Mirai. (Right) Typical temperature differ- ences between two CTD thermometers and their relation to the rotation and motions of the CTD package.

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