APPROXIMATE FORMULAE FOR THE SPEED LOSS DUE TO ADDED RESISTANCE IN WIND AND WAVES

Approximate formulae are presented for containerships and for tankers, laden and in ballast, to calculate the percentage speed loss in head weather defined by Beaufort number. Speed loss in bow, beam and following weather may be estimated as fractions of head weather speed loss by simple formulae in terms of Beaufort number, derived from Aertssen's data. The head weather formulae are interpretations of detailed calculations of speed loss due to wind , motions and wave reflection resistance . Comparison is made with some published model and full scale data for speed loss.