The practical meaning of lateral balance for a sail-assisted research vessel

Abstract

When equipping a research vessel with sails, the feasibility cannot be estimated only on the basis of the fuel economy. Therefore, other influences of the auxilliary sails shall also be thoroughly considered. After a rather short introduction to the philosophy of a scientific research vessel, this paper discusses one problem area faced when equipping a research vessel with sails: the lateral balance of the vessel. The equations of Inoue & Al (1981), developed to give the hydrodynamic derivatives for manoeuvering calculations, are used as a basis. They are changed to correspond to a vessel on a straight course, and simplified. As a result, we obtain equations for the determination of the drift and rudder angles, needed to balance the sail forces and moments. The angles mentioned are obtained as functions of the main hull parameters and sail forces. The drift and rudder angles, and the added resistance caused by them, are calculated for an existing research vessel equipped with 300 m 2 sails. It is verified that the lateral balance of sail-assisted vessels depends not only on the environmental conditions, i.e. the wind speed and angle, but greatly also on the longitudinal location of the sails. The optimal main hull parameters of a sail-assisted vessel, considering total resistance including the added resistance, are then searched for. The optimal hull form is found to have similar values of the main parameters as the tall ships did at the beginning of this century.