Experimental study of the effect of forward speed and heel angle on lift roll damping of small fishing vessels

Leung, Kirk Sing-Keung (1993) Experimental study of the effect of forward speed and heel angle on lift roll damping of small fishing vessels. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

An experimental study was carried out to investigate the effect of forward speed and heel angle on the bare hull lift component of roll damping. The effect of the presence of a rudder was also studied. Experiments were performed on two ship models with different hull characteristics. One of the models was also tested fitted with a rudder to investigate the effect of the rudder. The experiments were conducted in calm water with the ship model restrained from moving freely in any of the six directions. Models were oriented in different combinations of fixed heel angles and yaw angles, and towed at various forward speeds. The lift force and moment acting on the ship hull were measured and the lift coefficient and moment arm were calculated. -- Experimental results show that the lift coefficient is a nonlinear function of the angle of attack. It is also dependent on heel angle and forward speed. The moment arm was found to be a nonlinear function of both heel angle and forward speed. Its value decreases as heel angle increases. An empirical formula was derived from the experimental results to determine the equivalent linear damping coefficient for lift roll damping. The empirical formula shows that the equivalent linear damping coefficient is a nonlinear function of forward speed. The lift roll damping will increase with increasing forward speed. On the other hand, increasing heel angle leads to a decrease in the value of the equivalent linear damping. Comparison between the empirical formula and Ikeda's formula indicates that Ikeda's formula underestimates the equivalent linear damping. The discrepancy increases with increasing forward speed. Effect of the presence of a rudder is significant only at low speeds. -- Neither Ikeda's formula nor the experimental results consider the sinkage of the ship while moving. This may be covered in future work.

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