Ensuring design meets operating reality


Monitoring - Does your ship perform as expected? Is the


operating environment as anticipated? Should the next vessel be the same? MARIN helps provide some of the answers.


D


iiscrepancies between design assumptions and op


ational


screpancies between design assumptions and operational reality can be costly. Overdesign


reality can be costly Overdesign


or overestimates of the operating conditions raise newbuilding costs, while design flaws or underestimates reduce efficiency, safety and raise the probability of early damage and the consequent downtime. Confidence in design standards is therefore essential.


One of the core services of MARIN is to understand and improve ship design and operating principles by carrying out meas- urement campaigns on board ships at sea. When it comes to the structure of the ship, it is often the fatigue lifetime that is of interest. In the design stage the hull’s structural capacity is compared and matched to the loading profile. A multitude of disciplines are involved in the process, each with its own uncertainties. The ratio between capacity and loading is typically increased


with a safety margin. It is clear that the safety margin is a compromise between cost and reliability that depends on the accuracy of the design parameters.


Ingo Drummen & Jos Koning j.koning@marin.nl


18 report


With respect to fatigue, unexpected cracks can develop if loading during the operation is larger than anticipated or when capacity


is overestimated in the design. On the other hand, a design may be overly conservative and unnecessarily expensive when the


. On the other


hand, a design may be overly conservative and unnecessarily expensive when the capacity ends up being much larger than the loading, or when service loads are less than expected. Operational handling of the vessel adds a large variation on the loads that act on a ship in a given sea state. It is the role of the crew to keep the vessel safe.


The effect of crew actions on actual loads in comparison to design values however is an area that certainly needs more exploration. A sharp design with well-considered safety margins therefore relies on a thorough understanding of both the loading environ- ment, structural capacity and the way the vessel is handled.


MARIN performs long-term measurement campaigns on board ships to gain insight into understanding and improving ship design and operating principles. Typically, the ship is instrumented with sensors measuring waves, motions and accelerations, as well as global and local strains. Crew feedback from logs is used to assess the “human factor”. Projects can be conducted for one customer or executed as Joint Industry Projects, such as the Valid JIP and TULCS


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