History of the Atlantic Cable & Undersea Communications
from the first submarine cable of 1850 to the worldwide fiber optic network

Submarine Cable Ploughing
by Stewart Ash

Submarine Cable Ploughing

Since the advent of fibre optic technology, the burial of submarine systems on continental shelves to protect against external aggression has become ubiquitous. However, in an industry that celebrated its 160th birthday in August 2010, simultaneous lay and plough (plow) burial is a relatively young technology. For the majority of the telegraph and telephone eras, cables were surface-laid, and external aggression was managed by heavy armour cable protection and network diversity.

Although a number of attempts to bury submarine telegraph cables on the UK continental shelf were made in the early part of the 20th Century, it is generally accepted that the Western Union Telegraph Company was the first company to develop a viable, ship-towed cable plough. By the end of the 1930s Western Union had completed development of its design and concluded that a trench depth of no more than 10 inches (25cm) would be practicable, given the tow forces that would be necessary. In 1938 this plough was deployed from CS Lord Kelvin off the coast of Ireland to bury sections of three of Western Union’s transatlantic telegraph cables.

Another twenty years was to pass before the number of faults caused to TAT-1 (1956) and TAT-2 (1959) by fishing activities on the eastern continental shelf of the USA made it apparent to the system owners that some improved form of protection was necessary. From the early 1960s, Bell Labs, on behalf of AT&T, developed a series of plough systems (Sea Plow I to V), which were used in the 60s and 70s to bury AT&T’s transoceanic telephone cables on the continental shelf of the USA. These plough designs owed much to the Western Union plough; they produced an open trench 24 inches (60cm) deep, and could operate to water depths of 500m.

In the Far East, the first ploughing of a long haul submarine cable took place in 1976 on the East China Sea Cable (ECSC). The equipment used was a multi-blade plough developed by the KDDI group and towed by the KDD Maru. It was capable of a burial depth of 60-70 cm in water depths down to 200 metres. The PLOW system was also used during the laying operations for the Okinawa - Taiwan cable in 1979, Japan - Korea and Kuantan - Kuchin in 1980, and the MST cables in 1982.

By the early 1980s fibre optic technology was promising system owners an unheard-of increase in cable system capacity. At the same time, commercial fishing was becoming more intensive and trawlers were getting larger and were operating in greater water depths. This combination made system security an increasingly significant consideration. In the UK, British Telecom International (now BT) conducted a thorough investigation into the risks to submarine cables from external aggression in the English Channel, North Sea and on the Atlantic Continental Shelf. They concluded that:

  1. It was uneconomic to bury cable to protect against anchor faults. 
  2. Subject to soil strength, a burial depth of 600mm was sufficient to give good protection against all known fishing techniques.
  3. Burial should be carried out down to the 1,000m contour.

From this study, BT, in collaboration with Soil Machine Dynamics (SMD), developed a new design of ship-towed plough. This plough was successfully sea-trialed in early 1986 and was first used to install the historic UK-Belgium No. 5 system the same year. The plough design was a major step forward from the Sea Plow designs, solving a number of technical drawbacks such as cable residual tension, catenary management, ability to steer, and self-loading/unloading of the cable without cutting it. In the same year, KDDI modified its existing PLOW system, in order to increase its burial capability to 1.5 metres. This improved system was first used to enhance the burial protection for the ECSC system.

From 1987 BT Marine and C&W Marine were equipped with SMD ploughs and in 1992 KDDI introduced the SMD-designed and -manufactured PLOW-I. All these companies were then capable of 1 metre burial to water depths of 1,000 metres. By 2000 this plough design had became the de-facto industry standard.

Over the last ten years, through SMD in the UK and companies like Perry Tritech Inc. in the USA, development of plough technology has advanced even further. Today we have, 1, 1.5, 2 and 3 metre burial ploughs, plus jet-assisted and rock-ripping ploughs. Ploughing on the edge of continental shelves regularly takes place into water depths of 1,500m and, where conditions allow, ploughing in even greater water depths has been achieved.

Modern Submarine Cable Plough

Article text copyright © 2016 Stewart Ash

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Last revised: 30 September, 2016

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