Seakeeper may be used to calculate the motions at the centre of gravity of the vessel and also at specified positions on the hull away from the centre of gravity. These positions are known as remote locations. This may be useful for determining if a slam is likely to occur; what accelerations are likely to be experienced in the bridge or accommodation areas, etc.
Seakeeper will calculate the absolute and relative (to wave surface) vertical motion, velocity and acceleration and MSI at the specified remote locations.
You may specify as many remote locations as you like and they are referred to by name. Remote locations are specified in the Input table:
The first column is used to specify a label or name for the remote location. The next three columns give the remote location's position relative to the zero point. The next three give the location relative to the vessel's centre of gravity; you may use which ever is most convenient using the following coordinate system: longitudinal, positive forward; transverse, positive to starboard; and vertical, positive up. The centre of gravity will be computed from the vessel's hydrostatics and will be positioned such that its longitudinal and transverse positions coincide with those of the centre of buoyancy. The VCG is specified by the user, see the section on Setting Mass Distribution, above. Note that the vessel's hydrostatics will not be computed until the hull has been measured. To do this, select Measure Hull or Solve Seakeeping Analysis from the Analysis menu.
The last three columns are used to specify the coefficients to be used when calculating motion induced interruptions (MII) at the remote location. Standard sliding and tipping coefficients are:
MII coefficients for different events
|
Incident |
Coefficient |
|
Personnel |
|
|
Fore-and-aft tipping |
0.17 |
|
Side-to-side tipping |
0.25 |
|
Sliding on dry deck |
0.70 |
|
Equipment |
|
|
Sliding of chair on linoleum floor |
0.19 |
|
Sliding of helicopters, typical minimum |
0.20 |
|
Sliding of helicopters, typical maximum |
0.80 |
Source: Standard material requirements for RAN ships and submarines, vol 3, part 6.
Seakeeper calculates the MSI according to the McCauley et al. 1976 formulation which includes an exposure time. This is the only place where the MSI exposure time for the remote location is used.
The exposure time can be specified for each remote location (you can define multiple remote locations at the same point on the vessel and give them different exposure times if you wish).
Specification of exposure time for each remote location for the MSI 1976 calculation
See: Calculation of Subjective Magnitude and Motion Sickness Incidence on page 69 for details of the calculations performed.
The remote locations and centre of gravity will be displayed in the Design view as small crosses.
Use the Analysis | Add Remote Locations menu item to add remote locations. This will add remote locations below the currently selected row in the Remote Locations table. The number of remote locations inserted is the same as the number of rows selected.
To delete remote locations, select the rows of the remote locations you wish to delete, and then select Delete Remote Locations from the Analysis menu. (You must click in the numbered grey cell on the left to high light the entire row.)
Seakeeping results at remote locations are summarised in the Summary table in the Results window. For each remote location, the absolute and relative (to the wavy surface) motions, velocities and accelerations are calculated:
