Numerous grounding incidents in the Indonesian Archipelago in recent years have involved depth anomalies, causing owners and charterers to incur significant losses. Grounding incidents on charted obstructions are avoidable, but what about uncharted obstructions such as shoals or reefs?

The Indonesian Archipelago is challenging to navigate due to the high traffic density, lack of sea-room, and outdated hydrographic data. Our article in July 2020 discussed these incidents in some detail using case studies and focusing on the risks associated with uncharted obstructions and how to avoid them. Below is a summary of the key points.

Movement data

In all cases, the groundings occurred in locations with infrequent vessel transits and were well away from the central axis of the archipelagic sea lanes. This is where analysis of vessels’ AIS-generated historical movement data can add value by providing helpful insights on how frequently routes are followed, do the routes follow the advice provided by various publications, details such as draft and other dimensions of other vessels, seasonal traffic patterns, and speed of transit.

Sailing Directions

In a few cases, guidance provided in Sailing Directions was not considered when planning the voyage. There was a disconnect between the safety management procedures and onboard practice. The Sailing Directions contain valuable information that may not appear on charts. Mariners are advised to refer to these publications and record when any advice is not followed.

Hydrographic data

Most groundings occurred in regions with old hydrographic data or the seabed had yet to be surveyed in detail, indicated by sparse or unevenly distributed soundings. The discrepancy was also noted between the information in local Indonesian paper charts, British Admiralty (BA) paper charts and the Electronic Navigational Charts (ENCs). We recommend considering survey data quality and positional accuracy when choosing a route. Mariners need to be cautious when relying solely on information from charts or electronic navigation systems.

Role of ECDIS and electronic passage planning programmes

Automated features such as the route check functionality on ECDIS or the routes suggested by a computer programme may not always consider all the factors for safe voyage planning, for example, the Categories of Zone of Confidence (CatZoc) and guidance in Sailing Directions. Mariners will have to perform these manually.

Clearly marking all dangers

For the safe execution of the passage plan, all relevant information on navigational hazards should be presented on the charts and/or the passage planning document in a clear and understandable manner for the bridge watchkeeper.