Subsea trenching is the process of cutting a trench into the seabed to bury and protect offshore cables and pipelines. It is usually done by remotely operated trenching machines using one of three main methods, mechanical cutting, water jetting, or mass-flow excavation, chosen according to seabed conditions. Burial protects cables from anchors, fishing gear and currents, and is essential to offshore wind, interconnector and telecoms projects. Delivering it safely depends on specialist offshore engineers and crews.
Once an offshore cable is laid, it has to be protected, and the most reliable way to protect it is to bury it beneath the seabed. Subsea trenching is the engineering discipline that makes that possible, cutting a trench into the seabed so a cable or pipeline can sit safely below it. As offshore wind, interconnectors and global data links expand, demand for trenching expertise has grown with them. This guide explains how subsea trenching works, the methods and equipment involved, and the people who deliver it. It is part of our wider guide to subsea cable installation, alongside our pieces on cable ploughing and cable lay.
What is subsea trenching?
Subsea trenching is the excavation of a trench in the seabed to bury offshore cables or pipelines, protecting them from external threats. Burial depth is typically in the range of one to three metres below the seabed, depending on the risks present and the ground conditions. The work is usually carried out by purpose-built trenching machines, often remotely operated and deployed from a trenching support vessel, which travel along the cable route cutting or fluidising the seabed so the cable settles to the required depth. It can be done as the cable is laid, or as a separate operation after the cable is on the seabed, known as post-lay burial.
Why are subsea cables buried?
Burial is about protection and reliability. On the seabed, a cable is exposed to a range of hazards, and a single failure can be enormously expensive to locate and repair, as well as interrupting power or data. Burial guards against:
- Anchors and fishing gear, the most common causes of cable damage in shallower waters.
- Currents and seabed movement, which can cause an exposed cable to move, chafe and fatigue.
- Impact and abrasion from debris, boulders and other seabed activity.
By placing the cable safely beneath the seabed, trenching dramatically reduces the risk of damage and extends the asset’s working life.
What are the main subsea trenching methods?
Trenching is not one technique but several, selected according to the seabed. The main methods are:
- Mechanical trenching. Cutting wheels or chain cutters physically excavate a trench, suited to harder, more cohesive soils and weak rock where jetting alone is ineffective.
- High-pressure water jets fluidise softer, non-cohesive sediments so the cable sinks into the trench, well suited to sands and softer seabeds.
- Mass-flow excavation. A controlled flow of water is used to displace soft sediment, often to de-bury, deepen or clear material around a cable or structure.
Many modern trenching machines are designed to switch between modes, for example cutting and jetting, so they can handle the varied ground a single cable route can cross. The closely related method of ploughing, which cuts a trench and lays the cable in a single pass, is covered in our dedicated guide.
What equipment is used in subsea trenching?
Trenching relies on specialist subsea machinery. The central tool is the trencher itself, which may be a tracked, self-propelled vehicle, a towed sled, or a remotely operated vehicle fitted with trenching tools. These machines carry cutting wheels, chain cutters or jetting swords depending on method, and are paired with real-time sonar and cameras so operators can monitor and adjust burial depth and speed as ground conditions change. The trencher is launched and recovered from a trenching support vessel, which provides power, control and positioning. Survey equipment and boulder-clearance tools often prepare the route in advance.
What roles deliver subsea trenching projects?
Trenching campaigns are delivered by specialist offshore teams. Typical roles include trenching or burial engineers, ROV pilots and technicians, offshore and project engineers, survey engineers and surveyors, cable engineers, marine and vessel crew, and offshore managers and client representatives, all working under strict offshore safety and quality standards. These are demanding, often rotational offshore positions that call for specific technical expertise and offshore certifications, which is exactly the kind of talent that can be hard to source without sector knowledge.
How WRS supports subsea trenching recruitment
Subsea and offshore work is core territory for WRS. We recruit the specialist talent that trenching and cable-burial campaigns depend on, across offshore and maritime, subsea and offshore wind. Our recruitment solutions and contractor services cover permanent and contract hiring, mobilisation and compliant payroll, so you can crew trenching projects worldwide with confidence.
If you are staffing a subsea trenching or cable-burial campaign, get in touch to discuss your requirements, or submit your CV if you work in subsea and offshore.
FAQs
What is subsea trenching?
The process of cutting a trench into the seabed to bury and protect offshore cables and pipelines, typically one to three metres below the seabed. It is carried out by specialist, often remotely operated trenching machines deployed from a support vessel.
What are the main methods of subsea trenching?
Mechanical trenching (cutting wheels or chains for harder soils and weak rock), jetting (high-pressure water for softer sediments), and mass-flow excavation (displacing soft sediment with controlled water flow). Many machines can switch modes to handle varied ground.
Why are offshore cables buried?
To protect them from anchors, fishing gear, currents and impact, the main causes of subsea cable damage. Burial greatly reduces the risk of costly failures and extends the cable’s working life.
What is the difference between trenching and ploughing?
Ploughing cuts a trench and lays the cable in a single pass, with the seabed falling back to bury it immediately. Trenching more broadly includes post-lay burial, where the cable is laid first and a trenching machine buries it afterwards. See our cable ploughing guide for more.
How can WRS help with subsea trenching projects?
WRS recruits the specialist offshore and subsea talent trenching campaigns need, from trenching and ROV engineers to survey and marine crew, across more than 90 countries. Visit worldwide-rs.com or contact us to discuss your project.
