Browsing by Author "Steyn, Barend Johannes"

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    A study of the longitudinal open-water performance of an ice-class ship.
    (Stellenbosch : Stellenbosch University, 2024-02) Steyn, Barend Johannes; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: The hull and propeller of vessels engaged in operations in open water and ice are exposed to the encumbering effects of marine biofouling and the abrasive scouring of ice, both affecting ship resistance and performance. This thesis investigates the long term performance implications of such an operational profile, characterised by extensive open-water operations interspersed with ice navigation through a longitudinal study of the open-water performance of the Polar Supply and Research Vessel, the SA Agulhas II, with a specific focus on the hull and propeller condition. This study is enabled by a repository of measurement data and complementary information on the SA Agulhas II, spanning an equivalent period of ten years, the outcome of an extensive full-scale measurement campaign initiated in 2012. Key voyages within this period are selected for which the open-water performance is determined before, after, and intermittently during ice navigation. A tailored ship performance analysis method is formulated for the SA Agulhas II, utilising the available data to quantify the performance impact arising from the condition of the hull and propeller. Within the analysis method, three constituent elements are developed. First, a performance correction method, to differentiate between the effects of the degraded hull and propeller from those of environmental and operational disturbances, achieved through a constructed deterministic ship performance model. Second, a performance quantification method, to evaluate the performance losses, and third, a data conditioning method, to compile and filter the dataset to reduce uncertainty in the results. The efficacy of the formulated analysis method to exhibit the performance losses due to hull and propeller degradation is assessed through the review of four qualitative and quantitative measures, including an uncertainty analysis. The performance analysis reveals a cyclic pattern in the ship’s hull and propeller conditions, marked by progressive deterioration and subsequent near-baseline performance for the pre- and post-ice periods with each voyage. This cyclicality is attributed to the resurgence of biofouling growth between voyages, subsequently removed by ice scouring during ice navigation. Protracted docking periods in a temperate port contribute to biofouling growth, further exacerbated by anti-fouling coating degradation due to ice-scouring. Consequently, pre-ice operational penalties manifest, resulting in speed losses of up to 19% or power increases of 121%, driven by complete anti-fouling coating loss. Ecologically, the open-water performance results, recorded during operation in intermittent open-water passages after initial ice contact, indicate a gradual and near complete removal of the nonnative biofouling within a 200 km stretch into the marginal ice zone.