Page 138 - Practical Ship Design

Weight-Based Designs 1 os

Group 5. Deck nzachinety
- steering gear
- bow and stem thrusters
- stabilisers
- anchoring and mooring machinery
- anchors, cables and mooring ropes
- cargo winches, derricks and rigging
- cranes
For both weight and cost this group shoL e estimated by a summation of the
individual items, but as a cross check there should be reasonable correlation with
the same group for a similar type of ship.
Whether the suggested groupings are used (or some other variant), practising
naval architects should make a point of equipping themselves with a notebook or a
computer file in which to record weights. Such records should include both
weights of individual items and rates per square metre for such items as deck
coverings, joiner bulkheading, etc.
Individual weights should be accompanied by sufficient information to enable
them to be used intelligently in estimation. Great care should be taken to keep this
record up-to-date, as new materials and products are constantly coming into use.
Chapter 18 recommends that costs should be kept in the same record.
In the 1976 paper, the author noted changes in outfit weight of approximately
similar ships built from those built in 1962 and similar changes have continued in
more recent years. The reasons for these changes seem worth noting as a guide to
future trends:

Factors leading to increases in outfit weight noted in 1976:
- higher standards of crew accommodation - all ships
- fitting of air-conditioning and sewage systems - most ships
- fitting of more sophisticated cargo gear - cargo ships
- fitting of stabilisers, bow thrusters - passenger ships
- patent steel hatch covers now in outfit - cargo ships, container ships, bulk
carriers

Noted since 1976:
- fitting of self-tensioning mooring winches - most ships
- new IMO rules, MARPOL, etc.

Factors leading to reductions of weight noted in 1976:
- reductions in weights of most deck machinery for the same duty -all ships
- reductions in weight of deck coverings - cargo ships
- elimination of wood decking, ceiling and sparring