Software Support for enhanced Seakeeping Ability: Potential for a safer and more efficient Ship Operation
Jaap-Jan Stocker, ABB NL
Containers loss at sea remains a serious issue to both voyage and environmental safety. There is a cumu-lative effort from all parties involved to decrease the number of such events despite the fact that only roughly one thousandth of 1% of total containers shipped each year are lost. With more than 130 million containers shipped annually1, this accounts for more than a thousand containers, despite the low percent-age. This causes economic, environmental and reputational damages.
Under the aspect of preventability, how can we divide the occurrences per cause? A simple method will first separate potentially catastrophic events like grounding and collision, to which various circumstances may lead to. A main contributor to this is the human factor. Remaining cases, on the other hand, are mainly caused by the environment. Putting aside bad lashing we are left with two main reasons: extreme weather and a phenomena called parametric rolling. The effect on the vessel can be summarized as high motions, causing high cargo accelerations.
It was not always easy to avoid the weather effect. Waves are a natural occurrence and can carry a lot of energy, which may be transferred to the ship. This depends not only on the wave height, period and relative heading, but also on the vessel properties. Every ship is different in its dimensions and each voyage may have a different loading case. It therefore requires sufficient experience from the operators to make the right choices when it comes to speed and heading. It was even harder to predict parametric rolling as it requires special attention and understanding of the phenomena.
Today this is becoming less of a challenge. More and more container vessels are equipped with a combi-nation of sensors and software allowing you to predict certain risks. Such a software can not only warn you in advance based on your route and the expected weather but also will perform additional calculations like local accelerations and display their results. As a result you get an advice on combination of speed and heading in time.
Some will say that experience is enough and that those systems have no place on board. Others will say that the size of the biggest container vessels we have now makes them immune to bad weather. Recent events with the MSC Zoe prove otherwise2. Experience gets less relevant with more than one wave system acting on a vessel. If you add to it limited visibility and night conditions then the final decisions made by even experienced operator will be impaired. Large vessels may be less affected by adverse weather condi-tions but the same time new challenges arise. With the constant increase in cargo capacity, like the new 20.000 TEU ships, the amount of tiers the containers are stacked on also has risen. The taller the stack is the higher the accelerations acting on it will be. The combination of environment, cargo location and the efforts taken to secure the cargo via lashing is what remains crucial. Seakeeping software can predict expected forces on every single container and sensors can help document, analyze and validate. It is also possible to use the real time measurement of accelerations as a short term indication, even if the forecast seems not to be spot on.
What is the accuracy of such a seakeeping solutions available at the moment? It is safe to say that they are as accurate as the given input parameters. The weakest point in most cases is the weather forecast itself, as it may change in a short time span, while the loading condition remains relatively stable. Hindcast data and sensor measurements may help investigate and improve the model accuracy. Additional benefits of such a system can be on-the-sail voyage planning based on weather forecast, improvement of efficiency by predicting the influence of trim on the fuel consumption and documented decision making. Knowing that prediction of the weather is getting more and more accurate and that the whole process is fully automated – which removes the human factor from the equation - we are looking at a very effective solution which can pay itself within a year.