Seakeeper calculates the motions of the vessel for a specified sea condition given in terms of a wave spectrum.

The water density should be specified in this dialog. At present Seakeeper assumes deep water for all calculations.

The Inputs window allows you to define multiple speeds, headings and spectra for analysis.

Use the edit menu to add or delete items (or you can use the keyboard short-cuts of Ctrl+A and the Delete key respectively). New items are added below the currently selected row (multiple rows can be added at once by selecting the number of rows required, these are then added below the lowest selected row). To delete a row or rows, simply select the rows you wish to delete and choose Edit | Delete.

For easier identification, you may give a name to each condition. Headings are given in terms of the relative heading of the waves compared with that of the vessel track (head seas = 180º; following seas = 0º; starboard beam seas = 90º, port beam = 270º etc…).

When entering a vessel speed, the vessel Froude Number should also be considered. The results from Seakeeper are likely to become less reliable at high Froude Numbers since the vertical force due to forward motion is ignored by Seakeeper. Seakeeper has been found to produce useful results at Froude Numbers of up to around 0.6 – 0.7.

The “Analyse” column allows you to select which conditions to compute for the next analysis run.

All the locations, speeds, headings, spectra and other analysis options are saved when you save the Seakeeper data.

If no speeds, headings and spectra are selected for testing it is not possible to perform an analysis and the following warning dialog will be displayed:

The wave spectrum type may be selected from five different standard spectra. For each spectrum, different input data are required, this is summarised below:

It should be noted that, the ITTC, JONSWAP and DNV spectra are closely related, the only difference being the peak enhancement factor used. The ITTC always has a peak enhancement factor of 1.0, whilst the JONSWAP spectrum has a peak enhancement factor of 3.3. The DNV spectrum has a peak enhancement factor which varies from 1.0 to 5.0 depending on a relationship between period and wave height.

For spectra requiring a wave period to be entered, the user may enter the modal period (), the average period (), or the zero crossing period (). The corresponding values for the other periods and other related values will be estimated by Seakeeper.

The Pierson Moskowitz spectrum is based on wind speed. If this spectrum is selected then the other spectral parameters will be estimated from the wind speed entered.

Seakeeper automatically calculates the range of frequencies over which to predict the vessel's RAOs. However, the number of steps at which the RAOs are calculated may be specified by the user. A sufficient number of steps should be specified to obtain good definition of the RAO curves, depending on the speed of your computer, you may want to try a smaller number at first and verify that the calculations are preformed correctly then increase the number for the final calculations once all the parameters are set up correctly.