On the 16th of January 2021, the Maersk Essen made a splash (literally) when it lost 689 containers overboard on a routine voyage from Xiamen, China to Los Angeles, USA..
The Danish Maritime Accident Investigation Board (DMAIB) decided to initiate an investigation to clarify the events and circumstances leading to the loss of cargo because of the impact on the marine environment and the hazards such an event poses to the ship and crew..
Maersk Essen, a 13,600 TEU capacity container ship with a length overall of 366.45 m lost the containers approximately 450 nautical miles off Hawaii due to heavy rolling..
While the DMAIB made several findings in terms of what happened on the Maersk Essen, the investigation determined that the heavy rolling was most likely a result of parametric rolling..
The main conclusion that was reached was that the Maersk Essen encountered heavy rolling of the seas with roll angles reaching between 25° and 30° which was much more than the cargo securing equipment was designed for or able to withstand.
The ship’s loading condition required the ship to avoid roll angles exceeding 19.18° in order to stay within the stress load limits defined in the ship’s loading and stability computer..
Parametric rolling is the result of a dynamic stability failure mode where the main cause of extreme rolling lies within the ship’s oscillating system.. Thus, heavy rolling can occur in wave and swell heights that are not perceived as adverse to the ship..
To understand parametric rolling further, I sought the view of an experienced and active Master Mariner for a technical explanation of how parametric rolling works..
Before we get into what parametric rolling is, a ship has 6 different motions when traveling in the ocean as shown below..
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