Software designs stability into new ferries

According to the Napa group, after applying the optimising features implemented into NAPA, the designer was able to search for the maximum safety level that was obtainable according to the SOLAS 2009 probabilistic damage stability regulations regarding the vessel’s operational and technical limitations. The work resulted in the optimum general arrangement with the optimum number and location of watertight bulkheads and the optimum bulkhead deck height.

The company says that in addition to the safety benefits, the area for large storage below the car deck was optimised and the effect of the different variations in building cost and steel weight were studied.

Targets for the compartment arrangement solution were:

• The shipowner’s requirement to find the safest possible solution for the subdivision;
• The search for the best design in respect of the number and position of transverse WT-subdivisions;
• The search for the optimum height for the bulkhead deck.

After the initial design was agreed and the modelling accomplished, the actual calculations were made in a relatively short time. All of the necessary results were available within three weeks.

The selected design was further assessed against scenarios involving extensive water on deck. The shipyard’s designers had to find a way to comply with the owner’s strict requirements, which exceed the current regulations. A number of flooding scenarios needed to be generated and simulated in sea states typical for the operational area. The study was carried out using Napa’s flooding simulation feature. The case animations helped the designer to understand the flooding mechanisms in damaged conditions and to take these into account.

Napa says that the SOLAS 2009 damage stability regulation have opened the way for innovative concepts in designing passenger ship subdivisions. “We have found the optimisation tools implemented in NAPA to be very useful in developing new subdivision concepts and in optimising the watertight boundaries of our ships in accordance with the preferences of our customers,” says Jukka Vasama, chief of department at STX Europe Rauma shipyard.