Estimation of Steel Weight Increase due to Polar Class Applied on a Cruise Vessel
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- Institutt for marin teknikk 
Reduced level of sea ice, exploration of resources and many other factors have increased the international interest in exploring polar waters. The climate change opens new areas accessible for exploration, and the interest of expedition cruise holidays has increased. In the design process the level of ice strengthening needs to be decided. Polar Class is one way to strengthen a ship which is intended to sail in polar waters. Increased ice strengthening of the hull gives possibility to sail in heavier ice conditions, but is on the other hand heavier and increase the building cost. The ship owner needs to evaluate the costs and benefits before deciding which classification to use at the new vessel. The main objective of this thesis is to estimate increased steel weight due to Polar Class. To make it accurate and specific, the estimations are ship specific, and are in this case valid for an expedition cruise vessel. Ice classes which shall be considered are PC6 and PC7. They are compared to a non-ice-strengthened reference vessel. The dissertation is written in collaboration with Vard Design AS, and is confidential and in property of the writer and the company. Newbuild 870 is used as basis for the hull structure design under consideration. This is a polar cruise vessel ordered by Hapaq-Lloyd Cruise Design and has Polar Class 6. DNV GL Polar Class rules are carefully studied in order to understand which parameters are important for further calculations. NB 870 has a complex structure and a simplification of the hull structure where therefore needed in order to simplify the calculations. The work simplifying the structure was challenging because the simplification needed to be done in a way that did not give to inaccurate results. The simplified hull structure was then dimensioned according to PC6, PC7 and non-ice-strengthened rules. A spreadsheet was made in order to do the rule calculations and weight estimation. Plating and stiffener scantlings for PC6 and PC7 were calculated directly using DNV GL Polar Class rules for plates and transverse frames. Plates needs to fulfil a minimum required gross thickness criteria. Stiffeners needs to fulfil requirements due to section modulus, section area and several profile stability requirements. In the calculation the stiffeners are manually optimised to get lowest possible section area, and therefore also lowest possible weight. The DNV GL software Nauticus 3D-beam is used when deciding web-frames and stringer dimensions. Different profile-dimensions are tried and failed until the resulting von Mises stresses for all primary support members are below required maximum value. To get a reference weight for the design without ice strengthening, DNV GL Pt3 Ch6 Hull Local Scantlings are used. Minimum requirements for plating and stiffeners are calculated directly from rules, while web-frames and stringers are decided using Nauticus 3D-beam.