When designing or optimising a ship, the software tool NAPA is often used for defining the initial hull form in order to use the model for further calculation.
We utilize NAPA for 3D modelling of hydrostatic models to be used in Computational Fluid Dynamics (CFD) calculations, fairing of hull lines, stability calculations, seakeeping calculations and loading computers. With the NAPA software, we have calculated stability for various vessels, e.g. passenger ships, cargo ships, special purpose ships, offshore supply ships, tankers, barges, tugs, mobile offshore drilling units, hopper dredgers, small crew and service boats and many more.
Some of the calculations carried out in NAPA are:
- Compliance with international intact and damage stability regulations.
- Compliance with Classification Societies’ rules and regulations on intact and damage stability.
- Water on deck: This refers to the ship’s stability with a specified load of water on the car deck. It is also known as “the Stockholm Agreement” and was adopted after the Estonia foundering in 1994.
- Compliance with national legislation: This refers to legislation ratified by individual countries, and could for instance be the inland waterways legislation for transport on Lake Victoria in Africa.
- National anchor-handling regulations: These are requirements for supply vessels moving anchors or rigs. They were adopted after the incident with Bourbon Dolphin in 2007, when a supply ship capsized because of the towing cable. Now, calculations for supply vessels must be made to show the forces in the anchor, cable and the draw in the cable during operation. The calculations have to be made for different conditions and result in a maximum pull of each drawing angle.
- Cross flooding: This is closely connected to damage stability on passenger ships. When a ship is damaged, the damage list angle makes evacuation and lowering of life-saving appliances difficult. In order to minimise the angle of heeling, a cross flooding system is installed in passenger ships and a calculation can be carried out to determine how long cross flooding between the void spaces will take in the damage condition in question.