Wind and appendage resistance may also be accounted for in the resistance calculation.

Entering the frontal area of the vessel, the drag coefficient and the air density will cause air resistance to be included in the analysis. Setting any of these values to zero will ignore air resistance.

The frontal area is the above-waterline area of the vessel when viewed from the bow, A_frontal. The drag coefficient, C_d, will depend on how ‘streamlined’ the vessel is. A very streamlined vessel would have a drag coefficient of less than one, say 0.8, while a less streamlined vessel would have a drag coefficient of greater that 1, say 1.2.

The wind resistance is calculated as follows:

Where r_air is the air density and V_rel. is the relative wind speed.

Entering the wetted area of the appendages, and nominal appendage length (for calculation of appendage Reynolds Number), as well as an ‘appendage factor’, will cause the resistance of these appendages to be estimated by Hullspeed.

The wetted area of the appendages, A_appendage, is the total wetted surface of appendages, while the appendage factor, f_appendage, is an indication of the resistance of the appendages. Value for the appendage factor typically vary from 1.0 to 3.0.

The appendage resistance is calculated as follows:

Where r_water is the water density and V_boat is the vessel speed. The skin friction coefficient, C_f, is calculated from the ITTC’57 formula, using the nominal appendage length to calculate the Reynolds Number.