Protecting the Cable with the Latest Equipment
- Burying Technology of NTT-WE Marine－
At NTT-WE Marine, we use the latest burying equipment (Plough-type burying machine, ROV, etc.) to bury the cables.
In locations near the shore and at fishing grounds, cables are buried under the seabed in order to prevent damage to them.
We present here the burying operations using the latest technology that prevent damage to the cables.
The Necessity of Burying the Cables
In locations close to shore and in fishing grounds, the cables are buried under the seabed to protect them from getting damaged. There are many causes of damage, such as with anchors of large vessels near the shore, or with trawling nets in the fishing grounds. Considering these factors, and the soil conditions and the topography of the seabed, the cables are buried at a depth of 0.6 to 2.0 meters. (See diagram below.)
|Depth of Buried Cable
|Major Cause of Damage
Anchors of large vessels *1
*1 It is necessary to also consider deeper areas where anchors are dropped to function as a brake during a storm (to a depth of approximately 110 m), in addition to the areas where the anchors are normally dropped (to a depth of approximately 50 m)
*2 Fishing operations are believed to disturb the seabed to a depth of up to 0.5 -0.6 m.
There are two methods for burying cables.
Simultaneous Laying & burying
This is an efficient method where the cable laying and burying is carried out simultaneously. A plough-type burying machine (a machine that has the same principles as a farm plough) is towed by the cable-laying vessel (a wire connects it to a tow winch on the ship) and the cable is buried as it is being laid. Sometimes, a traction force of over 490 kN (50 tons) may be required to tow the plough.
Burying the Cable after Laying
In cases where plough-type burying machines cannot be used, the cable is buried after the cable has been laid. Various types of burying machines are used, depending on the depth, the distance to be buried, and the seabed soil conditions. ROV (Remotely Operated Vehicle, is like a submarine robot) widely used may bury the cables to match the meandering of the cable.
The CARBIS II ROV can dive to a depth of 2500 m and is actively used for burying and recovery of cables.