Sea trials vs prediction by numerical models—Uncertainties in the measurements and prediction of WASP performance

Abstract

Accurately predicting the power saving from wind-assisted ship propulsion is one of the most discussed topics in alternative and complementary propulsion methods. Aero- and hydrodynamic interactions between the sails and the ship increase the difficulty of modelling the propulsion contribution theoretically, but the sensibility of sail performance on the wind conditions increases the demands on measurement accuracy if the performance is to be measured in sea trials. This paper analyses and compares the uncertainties of sea trial tests and model predictions by means of parameter variation and Monte Carlo simulations. The results show that sea trials have an uncertainty of 23 %, well above 100 % of the measured savings, if performed using normal onboard equipment. Model uncertainties were found to be between 6 % and 17 % of the predicted savings.