Propulsion Factors Estimation

The propulsion factors (wake fraction, , thrust deduction fraction, and relative rotative efficiency, ) can be estimated either by employing one of five different empirical methods (see list below), or by entering a constant value for each of the factors.

The five empirical methods use a selection of the hull parameters from those entered for the resistance prediction, together with selected propeller parameters - diameter, effective blade area ratio and pitch/diameter ratio. Since these propeller parameters are initially unknown and in fact depend upon the propulsion factors, an iterative approach is adopted to determine both sets of parameters.

The wake fraction is corrected using the ITTC 78 formula, References 11:

where:

and

The following methods can be used to estimate the propulsion factors and the same hullform restrictions apply as described in Powering Calculations - Resistance Estimation.

Note:
The BSRA Methodical Series and Series 60 methods cannot be used to estimate the propulsion factors for twin screw ships.