Today's photos and blog entry focus on Plow 101. The plow is 14.5 tons and capable of operating in water depths up to 1500m and 1.5m burial. The cable enters the plow thru the bellmouth, travels thru the plow and exits between the share and the depressor. The depressor ensures that the cable stays in the trench opened by the share. Plow speed is typically less than 0.5kts. There are three cables going from the ship to the plow.
1) The plow is rated for 40tons of bollard pull. The tow winch (center of photo at lower right) will render towing cable when tensions exceed 40 tons. Reducing ship's forward motion will also reduce tow tension.
2) The umbilical cable provides electro-optical connections to the plow to provide power and monitor/control plow equipment and provide live
video. The umbilical winch is on the starboard side in photo at lower right.
3) And, of course, the third is the telecom cable that is buried in the ocean floor, the OOI cable!
With three cables attached, launching and recovery of the plow is challenging. The plow will be lifted from the position in photo 1, moved to starboard over the cable trough and after the telecom cable is passed through the plow, the plow will be launched over the stern. There is a beacon on the plow that shows its exact position in relation to the cable ship. Combining this with the ship's GPS gives us a very precise geographical location of the cable. In the main photo at the top you also see the floats that will be used to float the telecom cable to the bore pipe during the shore landing.
--From Paul Hagstrom, Associate Project Manager/Senior Project Engineer (Regional Scale Nodes), Consortium for Ocean Leadership, onboard the TE SubCom Dependable.