Nautical charts and submarine cables

Photo by Denys Nevozhai on Unsplash

Nautical charts and submarine cables

Submarine telecommunications cables form the invisible backbone of the global digital economy, yet they rest in one of the most complex and heavily used environments on Earth: the seabed, often described as the “last frontier” of the planet. Their protection depends not only on engineering resilience and regulatory permits, but also on something far more traditional — accurate nautical charting. Nautical charts serve as the official reference for mariners, identifying submarine cables as features that require caution and, in certain cases, avoidance. Without proper charting, cables remain exposed to preventable risks from anchoring, fishing, dredging, and other maritime activities.

Unlike commercial cable maps or industry visualization platforms, official nautical charts are produced and maintained by national hydrographic offices in accordance with international standards developed by the International Hydrographic Organization (IHO). These charts carry legal authority and are used for navigational decision-making by vessels engaged in international voyages. What appears on a nautical chart has legal consequences: it shapes expectations of prudent seamanship, influences liability determinations, and establishes whether adequate notice of submarine infrastructure has been provided to third parties.

This article explores why nautical charts are central to the legal and operational protection of submarine cables. It examines how cable positions are communicated to hydrographic authorities, how updates following installations and repairs are incorporated into official charts, and what risks arise when data flows are incomplete or delayed. 

1. Nautical Charts vs. Global Cable Mapping Platforms

Over the past decade, global submarine cable mapping platforms have become increasingly sophisticated and widely used. Industry publications such as SubTel Forum, offer interactive maps that illustrate the routes, landing points, and ownership structures of cable systems around the world. These tools have significantly improved transparency in a sector that was once comparatively opaque, especially when dealing with telecom national regulators that may be unaware of the presence of these vital infrastructures in their waters.

Such platforms are undeniably valuable. They support:

• Market transparency and competitive analysis

• Public policy discussions and strategic planning

• Investment and financing decisions

• Infrastructure coordination

• Academic and geopolitical research

They allow stakeholders to visualize global connectivity patterns and identify regional or national infrastructure concentration points, redundancy gaps and regional dependencies. For analytical and strategic purposes, they are indispensable.

However, their function must not be confused with that of official nautical charts.

Global cable maps are not nautical charting systems. They are not designed for navigation, nor do they constitute authoritative hydrographic products, and of course they are not recognized as official sources for safe passage planning.

This distinction is not merely technical — it is legal and operational. A nautical chart issued by a national hydrographic office is an official state document. It is a legally recognized navigational instrument and, in many jurisdictions, its use on board is mandatory when navigating within territorial waters. Nautical charts — whether in paper format or as Electronic Navigational Charts (ENCs) displayed through 30-years-old Electronic Chart Display and Information Systems (ECDIS systems) — define the maritime safety baseline. They are relied upon by masters, insurers, port authorities, courts, and maritime administrations when assessing prudent seamanship and liability.

By contrast, a cable map published by an industry platform is informational in nature and designed for strategic or commercial visibility rather than operational navigation. For example, such maps typically do not display the precise cable route on the seabed, nor do they systematically identify detailed cable crossings, protection zones, burial status, or post-repair deviations. If they did, the visualization would become overwhelmed with technical detail that would obscure its primary purpose: providing a clear, general overview of global connectivity patterns for non-navigational users.

Even if highly accurate, a cable map does not carry hydrographic authority. It does not provide formal notice to mariners. It cannot be invoked as an official navigational reference in the event of a dispute or maritime casualty.

The difference has direct consequences for safety and liability. If a submarine cable is properly depicted on an official nautical chart, mariners are deemed to have constructive notice of its presence. Activities such as anchoring or bottom trawling near the cable may then expose operators to legal responsibility in case of damage. If the cable appears only on an industry map but not on an official chart, that protective effect is almost non-existent.

The global standardization framework underpinning official charting is coordinated by the IHO. Founded in 1921 and headquartered in Monaco, the IHO develops the technical standards for marine geospatial data used in both paper charts and ENCs. These standards ensure consistency, interoperability and reliability across national hydrographic products.

Crucially, the IHO operates within a unique institutional structure. Its Member States do not merely adopt technical standards; through their national hydrographic offices, they also produce, update, and distribute authoritative charts. These offices are operational authorities with statutory mandates. Their charts are official instruments of the State and carry legal and commercial consequences worldwide. In addition, the IHO has extensively described submarine cable safeguards to be included in nautical charts in its regulation. 1

Some coastal States do not have hydrographic services agencies and instead rely on neighbouring countries or regional arrangements for chart production. Even in such cases, however, the charts covering their waters are issued under formal state authority and within the IHO framework.

2. How the Telecommunications Industry Works in Practice

The interaction between submarine cable operators and hydrographic authorities follows a relatively consistent pattern worldwide.

2.1 Cable Installation and Permitting

Whenever a new subsea cable deployment is planned, cable owners must obtain national permits from the relevant coastal state(s). These permits may involve multiple authorities, including:

• Maritime administrations

• Environmental agencies

• Defence authorities

• Fisheries regulators

• Hydrographic offices

As part of the permitting process, the national hydrographic office typically provides an opinion, particularly concerning:

• Navigational channels

• Anchorage areas

• Military exercise zones

• Existing subsea infrastructure

• Marine protected areas

This review is essential to ensure that the proposed route does not create navigational hazards or conflict with existing maritime uses.

2.2 Post-Lay Notification and Charting

Once the permit is granted and the cable is laid, the definitive cable position is formally communicated to the national hydrographic office. This is not optional in practice if operators seek legal protection.

The hydrographic office then incorporates the cable into the official nautical charts in a subsequent edition or via a Notice to Mariners update. 

Each national hydrographic office publishes its own nautical charts. There is no centralized global nautical chart authority. Instead, IHO standards ensure interoperability and technical harmonization across national products.

2.3 Cable Repairs and Route Deviations

Cable repairs introduce additional complexity. When a fault occurs, the repaired section of the cable may deviate from its original position. In both deep waters and shallow waters, deviations may differ but they are still operationally significant.

These updated positions must also be communicated to the national hydrographic office so that nautical charts can be amended accordingly. Failure to do so creates legal exposure and navigational risk as we will see below.

4. The Gap in International Waters

In areas beyond national jurisdiction (ABNJ), the situation is more complex.

There is currently no national hydrographic office that is systematically responsible for charting submarine cables in international waters. Historically, the United Kingdom performed a de facto coordinating role for certain oceanic charting functions, but this practice has ceased.

Today, in practice:

• Cable owners share new project coordinates on an informational basis through the International Cable Protection Committee (ICPC).

• The ICPC circulates this information among its members.

• This exchange has no formal charting or authoritative status.

It is a coordination mechanism, not a hydrographic function. This structural gap raises policy questions about the long-term governance of cable charting in areas beyond national jurisdiction, particularly in an era of intensified seabed use and offshore energy development. 

While the recently adopted Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction (commonly referred to as the High Seas Treaty or BBNJ), in force since early 2026, does not directly regulate nautical charting, it may offer an alternative institutional avenue for improving spatial governance in the high seas. 

Its mechanisms for area-based management tools and enhanced international coordination could, over time, facilitate more structured approaches to seabed information-sharing. Whether this will translate into clearer responsibilities or cooperative frameworks for the authoritative depiction of submarine cables on the high seas remains to be seen, but the treaty introduces a potential platform through which such governance gaps might eventually be addressed.

5. Why Nautical Charting Is Essential for Submarine Cables

Submarine cables must be marked on nautical charts to obtain minimal legal protection against third-party damage. The rationale is simple: if a cable is properly charted, mariners are presumed to have constructive notice of its existence. Activities such as anchoring or bottom trawling in proximity to a charted cable may therefore expose operators to liability if damage occurs.

If a cable is not charted, legal protection becomes significantly weakened — and in many cases practically non-existent — unless the cable owner can prove that the vessel had actual knowledge of the cable’s location or that it should reasonably have known about it through other means. In such situations, the burden of proof shifts substantially toward the cable owner.

At this point, an important caveat must be introduced. Military submarine cables are rarely marked on public nautical charts for obvious security reasons. States generally avoid publicly disclosing the precise routes of defence-related communications infrastructure. However, several practical considerations should be noted:

• Cable-laying vessels operate for weeks and cannot realistically conceal their activities.

• Local fishing communities often know where such cables are located.

• When damage occurs, legal claims against fishermen are rare.

6. Liability Risks of Incorrect Charting

Charting is not merely a protective mechanism; it also creates responsibility. There is potentially unlimited legal liability for incorrectly marking a cable on a nautical chart.

Consider a hypothetical scenario: during a storm a fishing vessel becomes entangled in a submarine cable that was inaccurately charted. The vessel loses stability and sinks. If the error originated in incorrect data provided by the cable owner, the financial and legal consequences could be catastrophic.

Hydrographic offices rely on accurate, certified information. The chain of data integrity must therefore be robust. For this reason, cable owners should systematically and promptly communicate any updates in cable positions, particularly following repairs, rerouting, or post-lay adjustments, as further described in Recommendation 7 of the International Advisory Body on Submarine Cable Resilience, Working Group 2 (Risk Identification, Monitoring & Mitigation). 2

Beyond navigational safety, accurate charting protects cable owners themselves. There have been cases in which cable operators failed to send updated coordinates following repairs. Subsequently:

• A fishing vessel operated in an area that was, according to official charts, safe.

• Damage occurred.

• Courts found that the vessel had acted within charted safe zones.

In such cases, cable owners have lost legal claims because the updated cable position had not been properly communicated.

7. Additional operational awareness measures 

Some incidents in the past that involved fishing vessels have shown that submarine cable information is not always actively displayed during fishing operations, especially in bottom trawling activities where masters may reduce chart display layers to limit visual clutter. Furthermore, certain seabed-interaction operations — such as the recovery of lost fishing gear using grapnels — fall outside traditional anchoring scenarios but may pose a comparable or even greater risk to submarine cables.

In this context, a possible practical measure could be to regulate through IMO the development and use of alerting functionalities within electronic navigation equipment, including ECDIS and widely used chart plotters that are capable of generating warnings when vessel speed or operational patterns indicate non-transit activity in proximity to submarine cables. Such alerts could be triggered independently of whether specific cable layers are actively displayed by the operator.

The availability of standardized and reliable submarine cable datasets, potentially aligned with the emerging S-100 data frameworks 3 launched earlier this year that will gradually replace the ECDIS system and which will be mandatory by 2029, could facilitate such developments and provide added value for end users, particularly in the fishing sector. Logging of proximity alerts may also support post-incident analysis and enforcement processes in cases of cable damage. In fact, hull insurers should start controlling the application of these alerts.

Conclusion: Charting as a Pillar of Resilience

Nautical charts are not merely technical documents; they are instruments of legal certainty and maritime order. They translate complex seabed realities into authoritative navigational knowledge and provide the formal notice upon which liability, prudence, and maritime discipline depend. In the context of submarine telecommunications cables — critical infrastructure underpinning the global digital economy — charting is not ancillary to protection; it is one of its foundations.

Global cable mapping platforms play an important informational and strategic role, enhancing transparency and supporting policy, investment and research. Yet they cannot substitute for the authoritative function performed by national hydrographic offices operating under the standards of the IMO. Only officially issued nautical charts create enforceable navigational expectations, establish constructive notice, and integrate submarine cables into the legal architecture of maritime governance.

For policymakers, hydrographic authorities, and cable operators alike, the message is clear: resilience is not achieved solely through redundancy, physical protection, or rapid repair capabilities. It also depends on information governance. Resilience begins with accurate coordinates — and with the institutional discipline to communicate them promptly, maintain them rigorously, and reflect them authoritatively in the charts upon which the maritime world relies.

1. See Part B- 440, paragraph B-443 (Submarine Cables, page 273) of the IHO Publication S-4 Chart Specifications of the IHO. Available at: https://iho.int/en/standards-and-specifications

   
   

2. Recommendation 7 of the International Advisory Body on Submarine Cable Resilience, Working Group 2 (Risk Identification, Monitoring & Mitigation), 2 February 2026. Available at: https://www.itu.int/digital-resilience/submarine-cables/iab-working-groups/

   
   

3. See demonstration prepared by the Australian Hydrographic Office: https://www.hydro.gov.au/prodserv/S-100.htm

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Andrés Fígoli is the author of the two-volume book “Legal and Regulatory Aspects of Telecommunication Submarine Cables” and is the director of Fígoli Consulting, where he provides legal and regulatory advice on all aspects of subsea cable work. Mr. Fígoli graduated in 2002 from the Law School of the University of the Republic (Uruguay), holds a Master of Laws (LLM) from Northwestern University, and has worked on submarine cable cases for more than 20 years in a major wholesale telecommunication company. He also served as Director and Member of the Executive Committee of the International Cable Protection Committee (2015-2023).

This article was first published in Submarine Telecoms Forum Magazine  #150 – July 2026.