The Effect of Waves on Marine Propellers and Propulsion

Abstract

Ship design is evolving around ever-increasing market demands in quest of competitive and cost-effective solutions. The global increase of shipping activities has raised concerns regarding the environmental impact of sea operations- transportation, fishing and exploitation of offshore resources. These conditions have driven naval architects to look for novel and energy efficient ship designs. Currently, there is increasing demand to optimize ships for actual environmental conditions i.e. in the presence of wind, waves, etc. The work in this thesis explores the effect of waves on ship propulsion; it consists of two major parts. First, the analysis of propulsion system in the presence of waves where the effects of added resistance, wake variation, propulsion losses and propeller-engine interactions have been studied on engine efficiency, propulsion efficiency, power and RPM fluctuations in waves. It was found that the effect of waves on engine performance is relatively small, for the studied cases, however; wake variation and propulsion losses can cause considerable changes in vessel performance. The second part deals with propeller performance in terms of cavitation, pressure pulses and efficiency in the presence of waves. The effects of wake change, speed loss, RPM variation and ship motions have been investigated. It was found that wake variations in waves has by far the largest impact on pressure pulses. Therefore, it is recommended to consider wake variation in waves while designing propellers. Due to the practical difficulties in doing this, which mainly are related to determining the wake variations, the recommended compromise is to consider the wake variation in one regular wave of length close to the ship length. A framework of systematic analysis laid out in this thesis would be useful for analyzing different propulsion systems and propeller designs in the presence of waves. Methods and tools used in the work can be further incorporated into the optimization process to consider the effect of waves. The investigation in this thesis will help the optimization as various factors affecting the propulsion have been recognized and their effect has been quantified