Leg 3 Short but Sweet and Rewarding

The goals to be accomplished during the annual Cabled Array (CA) maintenance cruises are based primarily on the required refurbishment schedules for the various components of the CA infrastructure. These “turns” of components occur on a 1 to 5 year or more cycle, depending on the type of instrument, platform (e.g. Shallow Profiler), power-communication node (J-Box), or cable.  Additional goals or tasks, such as adding a new instrument or a required survey, are incorporated into the annual schedule as needed. Then, sometimes, a totally unexpected event, such as the inadvertent trawling of one of the CA Shallow Profiler Moorings by a fisherman, as occurred at the Oregon Offshore Site in September 2017, adds another more complicated goal to the agenda, ie. a full replacement of a mooring well before its scheduled turn. The number and length of the various legs, defined as a round-trip to port to exchange personnel and/or equipment, are determined by the number and types of tasks that must be performed overall, but are further constrained by external factors such as availability of appropriate expertise; hardware (platforms and instruments); and, more often than not, shipboard deck space for the necessary infrastructure.

All of the above factors are carefully considered during cruise planning. The primary goal of Leg 3 was the replacement of the trawled two-legged Shallow Profiler Mooring at the Oregon Offshore Site in ~ 600 m water depth. After loading the Medium-Lift (MLW) and Heavy-Lift (HLW) Winches required for such a mooring deployment as well as the mooring itself, the limited deck space precluded expanding the goals of the leg beyond a single mooring deployment. Consequently, Leg 3, which began on July 14th was destined to be shortest in both duration (4 days) and transit distance (48 miles).

While the scope of work for this leg was limited to just the single Shallow Profiler Mooring replacement, its scientific value was significant because, for the first time since the mooring’s loss last fall, real-time data once again began flowing to shore from the attached winched Science Pod as it rises from its dock on the fixed platform at 200 m up to as high as 5 m below the sea surface. The physical, chemical, and biological parameters that are measured during its 9 vertical profiles per day will now continue providing scientists with the data critical to better understand the processes that occur at this intrinsically dynamic offshore region of the Oregon coast.

The completion of this mooring deployment on July 17th, also attained a milestone.  Until now, all maintenance of these two-legged moorings was limited to replacement of the two instrumented “saddle-bags” on the 200 m platform, the winched Science Pod Assembly and the Platform Interface Assembly.  The additional full replacement of the platform and mooring legs that was completed on Leg 3 was the first such activity since the three (3) CA Shallow Profiler Moorings were initially deployed back in 2014.

Although the short duration of Leg 3 might have potentially limited the breadth or variety of sea-going experiences for the six (6) VISIONS’18 students that sailed on it, the singular goal of a full Shallow Profiler Mooring deployment also provided a beneficial focus.  The students were offered a rare opportunity to observe in detail and often participate in, via deckwork, the difficult and complex deployment of a two-legged mooring.  In addition, they all took part, in one way or another, in fully documenting via hours of HD video, still photographs, and interviews the various steps that are necessary to successfully deploy such a mooring.  It was a rewarding experience for the students as well as the CA Team. A couple of the students will continue working through the fall on producing a full video compilation that can be used by the CA for training new staff on such deployments as well as a shorter version for public outreach.