Sep 13, 2023 | Ship design & naval architecture news

In support of the transition of the shipping sector to more sustainable fuels, Dutch naval architecture practice C-Job has taken a step back and is applying a risk-based design philosophy to accelerate the design process for sustainable ships.

Currently, most ship design is based on a prescriptive, rules-based system codified by the Classification societies. This sets a standard for how vessels should be built in order to ensure certain levels of safety, based on historical risks. According to C-Job, when safety is treated as prescriptive rule compliance, it can hinder design optimisation and omit life-cycle issues from design decision-making, it can even make the entire sustainability transition unfeasible.

The introduction of radically new fuel types requires the use of an approach that predicts the risk factors that these fuels bring. Risk-based design with functional rules, instead of following prescriptive rules, starts with analysis of the risks inherent in the fuels themselves and then proceeds to deliver vessel designs and engineering solutions that mitigate these risks.

Risk-based design is already used in other industrial sectors such as power generation and chemicals, and also for the design of offshore platforms. Methods developed by these industries are now increasingly being applied in the maritime sector. It is an approach that requires more thought and more detailed designs as all the potential scenarios need to be considered, using methods such as Hazid (hazard identification study) and Hazop (hazard and operability study). This calls for a level of creativity and a change in attitude. Energy saving on its own is not enough. Renewable fuels in all their forms are vital to delivering a sustainable maritime sector.

Systems integration for alternative fuels is complex, especially where various pressures and temperatures are involved. Sourcing the right components is vital and so identifying what can go wrong at each stage of a system using risk-based assessment is critical. Conducting the risk assessments and ensuring that the recommendations that come from them are applied accordingly and approved by Class is what risk-based assessment is all about.

C-Job’s work on sustainable designs has covered a wide range of alternative fuels including liquid hydrogen, ammonia and methanol. In all these we have found that the application of prescriptive rules can result in too conservative or highly impractical results, often due to a lack of experience or knowledge combined with rules that are just not flexible enough. This also applies to other systems, such as fuel cells. The latter are fundamentally different from combustion engines and so the vessels that use them require a new design approach.

An early risk-based design project undertaken by C-Job was the ro-ro ferry Texelstroom, which featured CNG/diesel hybrid propulsion and peak-shaving batteries at a time when the IGF code was still in development. Risk assessments proved designs for the CNG systems, using components that were both technically feasible and safe. Another project was with Amogy on the design of an ammonia-fuelled demonstrator vessel. The ammonia will be converted into hydrogen for the polymer electrolyte membrane fuel cell (PEMFC) to provide power on board. C-Job was responsible for the concept design and Hazid and is now working on the basic and detail design, with the first Hazop completed. DNV is observing the entire process so that the correct steps are followed, allowing it to form a basis for future class-approved designs.

Broader research into hazardous zone studies is laying the groundwork for future projects. This involves analysing zones on board vessels where there is a risk of encountering flammable substances. By having more accurate calculations to work with, hazardous zone plans can be made more practical and adapted for each zone based on its outputs. This is especially useful for smaller vessels where a one-size-fits-all approach is impracticable.

The traditional, prescriptive rules-based method of designing vessels will no doubt continue to have a role to play into the future. But with a new generation of vessels using radically different fuels and power sources now on its way , risk-based design will enable radical changes in the way that these vessels will be designed, delivering better solutions without compromising on safety. C-Job is helping to lay the foundation for future prescriptive rules, by using risk-based design we are helping the industry move forward towards sustainability.

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