Introduction

General

The methods of presenting propeller data are described in Section 12.1.3. A summary of the principal propulsor types is given in Chapter 11. It is important to note that different propulsors are employed for different overall design and operational requirements. For example, a comparison of different propulsors based solely on efficiency is shown in Figure 16.1, [16.1]. This does not, however, take account of other properties such as the excellent manoeuvring capabilities of the vertical axis propeller, the mechanical complexities of the highly efficient contra-rotating propeller or the restriction of the higher efficiency of the ducted propeller to higher thrust loadings.

As described in Chapter 2, the propeller quasi-propulsive coefficient ηD can be written as follows:where ??O is the propeller open water efficiency, and ??H is the hull efficiency, defined as follows:where t is the thrust deduction factor, and wT is the wake fraction. ??R is the relative rotative efficiency. Data for the components of ??H and ??R are included in Section 16.3.