This paper presents a new thrust-allocation scheme which significantly
reduces the fuel consumption for dynamic positioning of ships when ro
tatable azimuth thrusters are used. Thrust allocation is the problem o
f determining the thrust and the direction of each of the n thruster d
evices of a ship, given the desired forces and moment from the control
law. The problem of singular configurations is pointed out and solved
by using a modification of the singular-value decomposition. A filter
ing scheme is proposed to control the azimuth directions to reduce the
wear and tear, and to minimize the required thrust and power in a gen
eral manner, allowing the enabling and disabling of thrusters. Both ne
w theory and full-scale sea trials are presented. Copyright (C) 1997 E
lsevier Science Ltd.