The Dutch Safety Board has found that asymmetric loading conditions on beam trawlers with a length of less than 24 metres can rapidly compromise vessel stability. It comes to this conclusion after investigating the capsizing of two trawlers in 2019 and 2020 respectively. According to the Board, this risk needs to be addressed in the design and certification of trawlers.
The accidents concerned are the capsizing and sinking of the trawler UK-165 Lummetje on 28 November 2019 and the capsizing of the UK-171 Spes Salutis on 9 December 2020. Two crew members of the Lummetje died in the accident.
According to the Safety Board, the accidents had to do with the vessels losing stability as a result of asymmetric loading. An asymmetric loading condition can for example occur if fishing gear is suspended from the outrigger boom on one side of the vessel, but not on the other side. In that situation, the ship no longer floats upright in the water, but adopts a permanent list. Even a small further increase in the angle of list – for example as a result of wind, waves and weight displacements on board – can result in the rapid capsizing and sinking of the vessel.
Stability compromised rapidly
These circumstances occur regularly and as such represent a real risk, states the Board. It became clear that the same level of risk applied to the TX-21 Pieter van Aris, another vessel investigated by the Safety Board. The TX-21 is a modern trawler of a commonly built type. The fact that under asymmetric loading conditions stability decreases is in itself not new. However, the fact that stability can be compromised so rapidly that it leads to a real risk of capsizing surprised both the Safety Board and external experts.
The rapid and dangerous compromising of stability was until now barely known or recognised, if at all. Until now, no attention was focused on this aspect either in ship design, certification, training or practice. Traditionally, vessel stability has been considered from the point of view of symmetric loading conditions.
The Safety Board considered the newly identified safety risk to be so serious that in advance of the publication of the full investigation report, it decided to address an interim warning to the fishery sector on 8 April 2021. The most important aim of this interim warning was to inform the crews of similar trawlers to the UK-165 and UK-171 as quickly as possible of this risk, to allow them to take appropriate action.
Looking for structural solutions
The sector responded to the interim warning. Not only the trawler crews, but also other parties involved in sea fishing in the Netherlands were duly informed. In addition, the sector aims to start coming up with structural solutions for the risk. The response from the sector to this warning is a first step towards reducing the acute safety risk of capsizing and sinking as a consequence of asymmetric loading conditions.
Both in the long and short term, this warning must be heeded, stresses the Board. For the long term, preventive measures are essential. These could include the systematic analysis and calculation of asymmetric loading conditions for trawlers to assess stability risks. To date, despite being a statutory assessment criterion, such analyses and calculations have not been carried out.
The occurrence of a risk of this kind is not taken into account in the design or certification of trawlers. This means that further knowledge will have to be developed regarding the stability of trawlers, including those with a length of more than 24 metres. This new knowledge will have to be taken into account in ship design for future generations of beam trawlers and when making changes to the existing fleet.
In the short term, the Safety Board warns that people must remain alert to the safety risk. Risk management must also be given a permanent place both in practice and in fishery training programmes, as quickly as possible. By investing in this way in improving awareness of the risk in daily practice, it is possible right now to make a start on reducing the risk of a repetition of serious and fatal occurrences.