Practical Ship Hydrodynamics

Distance
Lateral deviation
Length of track
= track reach
Propeller rotation
(or CPP pitch) reversed
Astern order Distance
Approach course
Figure 5.9 Results of stopping trial
Head reach
Ship manoeuvring 175
regulations (SOLAS 1960). This regulation is rightfully criticized as the
time limit is independent of ship size. The IMO regulation is intended to
avoid underdimensioning of the rudder gear.
7. Man-overboard manoeuvre (Williamson turn)
This manoeuvre brings the ship in minimum time on opposite heading and
same track as at the beginning of the manoeuvre, e.g. to search for a man
overboard. The rudder is laid initially hard starboard, at, e.g., 60° (relative
to the initial heading) hard port, and at, e.g., 130° to midship position
again (Fig. 5.10). The appropriate angles (60°, 130°) vary with each ship
and loading condition and have to be determined individually such that at
the end of the manoeuvre the deviation in heading is approximately 180°
and in track approximately zero. This is determined in trial-and-error tests
during ship trials. However, an approximate starting point is determined in
computational simulations beforehand.
5.3.2 Model tests
Model tests to evaluate manoeuvrability are usually performed with models
ranging between 2.5 m and 9 m in length. The models are usually equipped
with propeller(s) and rudder(s), electrical motor and rudder gear. Small models
are subject to considerable scaling errors and usually do not yield satisfactory
agreement with the full-scale ship, because the too small model Reynolds