In our previous article in this series of twelve, we explored some of the financial challenges that exist in maritime navigation today. In this article we will explore some other challenges that exist including ambiguity in under keel clearance.
Areas deemed safe or unsafe for vessels to navigate are determined by safety contours on an ECDIS. One of the most critical parameters for determining if a vessel can safely enter a body of water is the Under Keel Clearance (UKC). The UKC refers to the minimum vertical distance between the vessel’s keel and the seabed.
The mariner will calculate the UKC by combining the charted depth of the water, the vessel draft, the tide height, squat, and the safety margin. The safety margin is added to account for uncertainties, such as changes in water density, waves, and ENC data quality. This safety margin is meant to account for the potential inaccuracies in the data or other unforeseen factors.
The challenge today with S-57 is that there is often a lack of bathymetric contours in the ENC data. This means that they are typically displayed in relatively large intervals (around 5-10m).
A lack of detailed bathymetric contours can lead to inaccurate UKC calculations.
In shallow or complex areas (like ports, channels, or coastal waters), a lack of detailed bathymetric contours means that mariners do not have enough granular information about the seafloor’s bathymetry. If the depth between two contours jumps from 5m to 10m, it might be difficult for the mariner to calculate an accurate UKC.
If the UKC is calculated to be higher than it actually is, the margin for safe vessel transit will be lower, increasing the risk of grounding or severe damage to the vessel’s hull. In one incident described by the Nautical Institute, it was found that the bridge team on a ferry had not considered the effects of squat adequately during their passage planning and as a result, had failed to allow sufficient UKC based on the current state of the tide. The ferry ended up being grounded. The Marine Accident Investigation Branch (MAIB) has also published a series of reports, that highlight how miscalculated UKCs, among other factors, have contributed to vessel groundings. Inaccurate calculation of UKC can also lead to a restricted flow of water beneath the vessel. As a result, hydrodynamic resistance heightens, which in turn increases the fuel consumption of that vessel.
If the UKC is calculated to be lower than it actually is, this can cause the master to believe that there is insufficient clearance for the vessel to continue its transit path and as a result more caution is taken. In turn, this can result in route alterations, which could increase fuel consumption and heighten the risk of the vessel missing its assigned berth slot. The vessel may have to wait for another slot, adding to the congestion outside of the port and delays in loading and unloading cargo. As a result, the entire supply chain is impacted.
This is especially true in today’s port environments where increasingly large volumes of traffic are affecting the space available for ships to pass. The more space a vessel has between itself and the coastline, the lesser the risk of grounding or a collision.
To learn more about the challenges discussed in this article, download our thought leadership report ‘New Waters’, created in partnership with the UK Hydrographic Office. Based on the findings of a comprehensive maritime research project, this report explores the five key steps to supporting the successful adoption of the International Hydrographic Organization’s (IHO) S-100 data framework.
