A vessel has crossed into the water around a subsea cable. That does not automatically mean a strike is about to happen, but it does mean the movement needs to be understood while there is still time to act.
That is what a cable protection zone is for. It creates distance between the first warning and the cable itself, giving the monitoring team time to assess the vessel, make contact and keep the threat away from the seabed.
UltramapGlobal monitors subsea assets through AssetMonitor® and trained analysts working across three global teams. This is what happens from the moment a vessel reaches the outer zone.
How is a subsea cable protection zone configured?
A protection zone is a defined area around a cable or offshore asset. Inside it, the monitoring system applies rules to vessel movement, so activity that needs attention reaches an analyst quickly.
The zone is built around the asset. Its size and shape depend on the route, the traffic and the time available to respond. Where it helps, UltramapGlobal may advise a 1,000 metre early-warning perimeter with a 500 metre action-required perimeter inside it.
The outer ring buys time. The inner ring marks the point where the response has become urgent.
The zone is not a physical barrier, and it does not make every vessel inside it a threat. It is an operational boundary that creates a consistent point for assessment. The benefit comes from defining the response before an event occurs, so the team is not inventing the rules while a vessel is moving towards the cable.
What triggers an alarm inside a cable protection zone?
AssetMonitor receives live AIS information from shore-based receivers, satellites, guard vessels, patrol vessels and cable landing stations. When a vessel crosses a configured boundary or meets a threat rule, the platform raises an alarm.
At that point, the vessel may simply be passing. The alarm does not decide that a strike is coming. It puts the movement in front of a trained analyst early enough for that judgement to be made.
Alarm rules can account for more than a boundary crossing. Course, speed, vessel type and changes in movement can all affect whether activity needs attention. The aim is to bring the right events to the analyst early without treating every vessel in busy water as an emergency.
How does an analyst decide whether a vessel poses a threat?
Location is only the start. The analyst looks at the vessel’s course, speed, recent track and type. Is it passing normally? Has it slowed down? Is it loitering, fishing or moving towards an anchorage?
The route history helps answer those questions. UltramapGlobal has gathered vessel behaviour data continuously since 2009. A team that knows what normal looks like around a cable spots the abnormal sooner.
Where DAS is part of the watch, the team may also see activity at the seabed, including movement associated with a vessel that is not transmitting AIS.
The analyst also considers where the vessel is in relation to the cable and how quickly the situation could change. A slow vessel close to an anchorage may require a different response from a fast vessel crossing the outer edge of the zone. Context turns a plotted position into an operational judgement.
When will the monitoring team contact the vessel?
Not every alarm needs a call. A vessel may be following an established safe route or already moving away from the cable. The analyst decides whether the event is routine, whether it needs to be watched or whether the vessel has become a risk.
If it has, the monitoring team makes contact. The purpose is simple: tell the vessel about the cable and ask it to change course or behaviour before it reaches the inner zone.
A warning made early gives the bridge or crew time to respond safely. The best result is a vessel that alters course in the outer ring and never comes close to the asset.
The communication needs to be clear and practical. The vessel is told about the protected asset, why its current movement is causing concern and what change is required. The team then watches the track to confirm that the response has happened, rather than assuming the first call has resolved the risk.
What happens if the vessel does not move away?
If the vessel does not respond or keeps moving towards the cable, the event follows the escalation procedure agreed with the client. The team continues trying to establish contact and brings in the named client or operational contacts where required.
The process is set before the watch begins. A power interconnector, cable installation operation and telecoms cable may have different risk tolerances, contacts and response priorities.
The monitoring team stays with the event until the vessel has moved away, stopped the threatening activity or the situation has passed into the agreed escalation process. The watch does not end when the first message is sent.
A clear escalation plan prevents delay. It should identify who is contacted, in what order and what information they receive, including the vessel track and actions already taken. That allows the owner or project team to make the next decision with the same live picture as the monitoring analyst.
What is recorded after a vessel leaves the protection zone?
The vessel track, the alarm, the contact and the outcome can all become part of the client’s Activity Report. That record shows what happened and what the team did about it.
Over time, repeat behaviour and hazard hot-spots become clearer. Each event adds to the picture of how vessels move around the route and helps the protection remain relevant.
That evidence can support operational reviews and conversations with vessels, contractors or other stakeholders. It also gives the client a way to check that the agreed response was followed. A monitoring service should be able to show not only that an alarm occurred, but how the risk was brought to a close.
What happens after a subsea cable strike or near-miss?
Once a strike or near-miss has become an immediate incident, the need changes from ordinary monitoring to urgent support. UltramapGlobal RED is the emergency service for that moment and is available to organisations that are not already clients.
Existing clients are already protected. Non-clients can contact red@ultramapglobal.com, with a response inside 24 to 48 hours.
Urgent support may include establishing immediate monitoring around the location, reviewing vessel activity and helping the organisation understand what is still happening near the asset. The priority is to create a reliable picture quickly while the owner decides what remedial action follows.
How does early intervention help prevent a cable strike?
Most successful interventions are deliberately uneventful. An analyst sees the risk, contacts the vessel and watches it move away. The cable keeps working and the event becomes a line in the record rather than an outage and a repair.
That is the value of the outer zone. It turns distance into decision time, and decision time into prevention.
The intervention may look small from the shore: a warning, an altered heading and a vessel leaving the area. Operationally, that is the whole purpose of the system. The protection zone has done its job when the cable owner never has to experience the incident that might otherwise have followed.
Discuss a protection-zone response for your cable route
Protection zones should be built around the cable, the traffic and the escalation the owner needs. To discuss how UltramapGlobal would configure and monitor a particular route, contact us.
Frequently asked questions about subsea cable protection zones
Does every vessel entering a cable protection zone receive a warning?
No. An analyst first assesses the vessel’s course, speed, behaviour and route context. Contact is made when the movement presents a risk or meets the agreed response rules.
How large is a subsea cable protection zone?
It depends on the asset and route. A layered design may use a 1,000 metre early-warning perimeter and a 500 metre action-required perimeter, but the correct distances should be tailored.
Who responds to a protection-zone alarm?
A trained monitoring analyst assesses the alarm and follows the agreed contact and escalation procedure. Software raises the alert; the analyst decides what action it requires.
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