On 11 May 2010, deck preparations began for will will likely be our longest dive this cruise. Dive objectives are threefold:
- Install a new seismometer auxiliary platform
- Inspect the ODP 1027 instrument platform
and nearby CORK - Lay a 12.5km cable and install the ODP 1027 NE bottom pressure recorder
Seismometer Auxiliary Platform
The second of two auxiliary platforms was installed near to the ODP 1027 broadband seismometer. Like its twin at ODP 889, this platform hosts an acoustic current meter, a differential pressure gauge and a back-up battery for the seismometer. Installation of this platform was aborted last fall, when an electrical ground fault was detected on the unit. We're hoping no such faults will visit this time!
Platform Inspection
Several months ago, we stopped receiving data readings from the northwest bottom pressure recorder (BPR) at ODP 1027. We weren't sure what may have caused this outage, but after inspecting the instrument platform, we know why. There appears to have been damage to the media converter canister that joins the BPR cable to the platform connection hose. Although the causes are uncertain, the effect, for now, will be a continued live data outage for this instrument, as we lack necessary equipment to repair the media converter canister connector on-ship. On the bright side, the BPRs are equipped with batteries, and data collection is ongoing. We will retrieve the data on a future cruise, and add it to the data archive.
Cable Lay and BPR Installation
Once the first two tasks were complete, we commenced with a very time-consuming task, the laying of a power and fiber-optic communications cable from the instrument platform extending 12.5km to the northeast.
On-ship preparations for this cable lay began the afternoon of 11 May, when the CCGS Tully deck crew, along with ROPOS and NEPTUNE Canada crew members, began setting up an intricately choreographed deck ballet involving two cranes and a winch. ROCLS, the ROPOS Cable Laying System, was too heavy to deploy beneath ROPOS with such a long and heavy cable spooled onto it. As with the other two long BPR cables deployed last year, ROCLS had to be lowered to the seafloor by ship's winch. To do this, the Tully crew had to pick it up by crane, swing it out over the water and around the back and transfer the load to the winch cable. It was a delicate operation, requiring all able hands on deck holding the heavy piece of equipment fast with tag lines and trying to prevent the possibilities of damage or injury. Rough seas on the 11th prevented the operation, but it went off without a hitch on the 12th, when seas had calmed considerably.
After lowering ROCLS to the seafloor, it was released form the winch cable using acoustic releases. Then, ROPOS dove to find ROCLS, attach the cable end to the platform and begin the marathon cable lay, which lasted over 16.5 hours.
When finished, ROPOS detached the connector and media converter canister from ROCLS, plugged in to the bottom pressure recorder, and recovered to ship. We've got our fingers crossed that the BPR will be happy in its new environment and provide years of reliable data.
