Page 36 - Practical Ship Design

Introduction, Methods and Data I

The treatment of powering in Chapters 6 and 7 kept expanding under the
influence of the author’s advisers. Interestingly one of these favoured the newer
treatment of this subject as more scientific whereas the other felt that there was
much more useful data available in the earlier Froude format and believed that with
appropriate “fiddle factors” use of this data can still give satisfactory answers. The
chapters have tried to keep a balance between these two approaches.
Readers may feel with some justification that the treatment of powering falls
short of the full treatment they would like to have as the subject of propeller
efficiency has been omitted for the very good reason that the author can claim no
expertise in this science (or is it a black art?). He has instead always used the
shortcut to the quasi-propulsive efficiency which is given in Chapter 7, having
found this to be remarkably accurate.
Chapter 8 deals not only with the design of lines to minimise powering, but
looks at the qualities that the lines must have to ensure good sea-keeping, good
manoeuvrability and good stability for given dimensions.
Chapter 9, in its treatment of machinery selection, starts with a statement of the
criteria against which main engines are chosen and goes on to consider which of
these are important for different ship types and which types of machinery best meet
them.
Chapter 10 deals with the factors influencing structural design. Although no
detailed structural calculation methods are given, the chapter gives a lot of advice
on how to design both the general arrangement and the structure itself for economy
in steel-weight and in fabrication costs, whilst avoiding many of the pitfalls of
fatigue, brittle fracture, vibration, corrosion that can be the consequence of less
then satisfactory structural design.
Chapters 11, 12 and 13 deal with the main statutory rules for merchant ships, the
need to ensure compliance with which forms a prominent part of the work
undertaken in the later design spirals.
Chapter 11 has freeboard and subdivision as its subject and gives a full
treatment of the new probabilistic rules for the subdivision and damaged stability
of cargo ships. The corresponding rules for passenger ships are not dealt with in the
same detail as it is expected that they will be brought into line with the cargo ship
rules within a relatively short time.
Chapter 12 deals with stability and trim and after dealing with the statutory rules
for these subjects for merchant ships outlines the treatment that these are given in
warship design and operation.
Chapter 13 deals with some of the remaining subjects for which there are
statutory rules for merchant ships, such as fire protection, life-saving, marine
pollution and tonnage.
Chapter 14 deals with some of the special requirements which are involved in
the design of a warship.