Hullspeed is essentially a resistance prediction program. A number of regression-based methods and one analytical method can be used to predict the resistance of the hull form.

It is normal naval architecture practice to break down the resistance into components which scale according to different laws. Hullspeed can calculate the resistance components in coefficient form. However, since different methods use different formulations, not all the resistance components may be available.

Total resistance is normally broken down into a Froude number dependent component – wave resistance (residuary resistance) and a Reynolds number dependent component – viscous resistance (friction resistance).

The bracketed names give an alternative breakdown:

Total resistance = Wave + Viscous = Residuary + Friction

Typically the friction resistance is predicted using the ITTC’57 ship-model correlation line or some similar formulation.

The viscous resistance includes a form effect applied to the friction resistance thus:

Viscous resistance = (1 + k) Friction resistance

, where (1 + k) is the form factor.

Where possible, Hullspeed calculates all the components of resistance and these may be plotted and tabulated separately.

In some cases the regression method predicts residuary resistance and no form factor. In these cases, it is not possible to calculate the wave resistance.