Page 189 - Practical Ship Design

Chapter 6

Powering I

6.1 AN INTRODUCTION TO POWERING

The subject of powering in all its aspects usually takes up a number of chapters in
textbooks on naval architecture and there are also several specialist books which
are confined to this one subject. The treatment in this book has therefore been
written on the understanding that all naval architects undertaking ship design can
be expected to be familiar with the theory of the subject, but that many will
nevertheless appreciate some help with its practical application as few books seem
to be specifically directed to the primary needs of the designer, which are:
(i) How to estimate with an acceptable accuracy the machinery power which
must be fitted to a new ship design to enable it to attain the specified speed.
(ii) How to minimise this power so as to reduce the capital cost andor improve
the fuel economy and therefore the operating efficiency of the ship.
The aim of this chapter and Chapter 7 is to meet these needs as concisely as
possible.
The first section of this chapter starts by dealing with resistance in some detail
because the treatment of this subject has changed considerably in recent years and
few books so far seem to have caught up with this. Because familiarity with the
theory is assumed, the next section jumps to providing an aide memoire on most of
the components of powering, which are then dealt with in more detail in the rest of
this chapter and in the subsequent one.
In the course of writing the chapter, however, it became apparent that recent
changes in the methods used by test tanks to estimate ship powers had not yet been
written up in naval architecture textbooks and this has led to some extension of the
original intent of the chapter.