Best cable protection and less enviromental damage

This comparative analysis is a desk top study based on our long experience with our own embedding systems and diving inspections made for costumers, and during the participation of repair work on cables embedded with different systems.

At the moment there are two trends in the market of jetting equipment.

The first trend is the light jetting unit working at a relatively high pressure, jetting a deep and narrow trench in the seabed, at a moderate speed.

The second trend is the heavy equipment which at a very high pressure scatters a lot of material up in the water and forces a wide channel in the seabed, wherein the cable lies open. The heavy equipment moves rather quickly along the seabed but leaves the cable free on the seabed if hindrances occur.

Characteristics of the two systems:

The Light Equipment, e.g. JD-Contractor A/S´ Jetting Equipments "LIGHT-JETS"

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Makes a narrow trench.

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Jetting with relative high pressure, but not high enough to damage the casing of the cable.

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Good backfilling in the trench, often up to a 100%.

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The cable is covered, and protected against corrosion, fishing tackles and small anchors.

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The system is friendly to the environment due to a small build up of sediment.

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The light jetting equipment has no problems when jetting down the cable where the cable is meandering.

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Removing hindrances in front of the jetting unit is very easy.

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High certainty that obstacles on the seabed are removed.

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Only a small chance of damaging other objects on the seabed, e.g. unmarked cables, historical artefacts, wrecks or ordnance.

Heavy Equipment

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Makes a big and often very wide channel in the seabed.

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Jets with a pressure so high that the casing of the cable faces the risk of being damaged if the water jet is directed against the cable.

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Due to the high pressure the cable trench is made very wide and the material is scattered away and up in the water.

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There is hardly any material left for backfilling.

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The cable is exposed in the bottom of the wide trench for many years, open for corrosion, fishing tackles and anchors.

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Causes a sediment build up of up to 2.5 to 3 cm per metre, thus it is not environmental friendly.

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The heavy equipment has difficulties jetting down the cable where the cable is meandering.

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The removing of hindrances in front of the jetting unit is not possible.

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Hindrances on the seabed are skipped or crossed over, and the cable is left without protection at those positions.

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The systems are faster than the light systems.

It is our definite opinion that the light jetting units are superior to the heavy ones when it comes to quality, safety and observation of public regulations. The light equipment does not touch the cable during the embedding. The equipment is under constant video monitoring and is remote controlled from the surface. Every part of the equipment is rounded and assembled in a lightweight construction, which in no way damages the cable.

Only on rare occasions when obstacles are to be removed, a diver is needed at the unit. Normally it is possible for the diver to remove the hindrance without touching the cable.If the diver decides the cable has to be handled, the position is marked and the work is carried out when the cable is swithed off. In the meantime, the jetting is continued from another position.

The water pressure while jetting is only 10 to 14 bars, which avoids the incurrence of any damages to the cable by the jetting equipment and makes it safe to carry out the jetting on the cable while it is powered.

We see the following problems with heavy equipment: The systems work at very high water pressures and are capable of jetting a cable down at a high speed in a very wide trench. The missing backfilling material makes the trench stay open, and the cable is left unprotected against fishing tackles, corrosion and anchors in the wide and open cable trench for perhaps many years.

The environmental conditions and restoration of the seabed after the completion of the work, which is very much in focus while new projects are planned, makes the heavy jetting equipment less attractive.

JD-Contractor A/S has chosen to use the system which we have found to be the friendliest to the cable and the environment, and afterwards offers the highest level of protection for the cable.

Our equipment meets the official requirements and demands in the “Guide for the laying of communication cables and pipelines”, published by The Danish Marine authorities, regarding the excavating deposits of material along the cable trace and the ban against the reduction of the water depths caused by the ditches along the cable trace as left by some jetting equipment.

When jetting with our equipment the ultra light material, which is does not settle into the cable trench as backfilling, will be suspended in the water and over time settle over a wide area thus it will not make any reductions in water depths.

Best cable protection and less enviromental damage

Characteristics of the two systems:

The Light Equipment, e.g. JD-Contractor A/S´ Jetting Equipments "LIGHT-JETS"

Heavy Equipment

Conclusion:

Quality sometimes takes more time, but does not necessarily cost more money