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Note: OFF-DESIGN STATMETHODE

Abstract: This paper discusses a newly developed approach to ship design. It employs Monte Carlo simulations in order to reproduce and prognosticate lifetime operation conditions of a projected (or existing) vessel. On basis of statistical environmental data in combination with direct calculations of the vessel´s propulsion it is possible to benchmark different designs regarding e.g. fuel efficiency and rudder cavitation. After the vessel´s operating condition (drafts and speed) and the environmental conditions (wind and sea state) are determined, by applying the Monte-Carlo-Method, the corresponding equilibrium condition for each propulsion point is computed by utilising an already implemented manoeuvring algorithm. Following this procedure, it is possible to identify the specific requirement profile and to align the vessel´s design with this profile. Since this methodology computes fairly fast, it offers the possibility to perform an optimisation analysis and to qualitatively assess the impact of design variations economically and ecologically. This assessment can be adjusted to different vessel types, shipping routes and connected to this the commodity flow, tailored to the customer´s specific needs. In order to validate the calculation method´s feasibility, the algorithm´s results have been checked against measured long-term data from various vessels in operation. In addition to the power demand as one optimisation parameter, each manoeuvring situation lead to a specific flow condition around the rudder which results directly from the required rudder angle for the task of course keeping. On basis of the determined vessel speeds and rudder angles, the cavitation distribution on the rudder can be estimated. Therefor the flow around the rudder geometry is calculated for all combinations of the prognosticated rudder angles and ship speeds, considering the propeller load resulting from the ship´s resistance, its floating condition and the wake field. The occurrence of cavitation for each situation is weighted by the relative frequency of the operation condition. Thus the implemented method provides a prognosis of the cavitation risk distribution on the rudder considering the complete operational profile. Now it is possible to evaluate different rudder designs for the vessel on the basis of differences in the cavitation risk.