Seakeeping - Loading Condition
- Last UpdatedDec 18, 2025
- 3 minute read
Seakeeping calculations are performed on a single loading condition. This condition may be one previously defined in Hydrostatics, or may be defined only for use in the seakeeping calculations.
Loading Data
The following is a brief description of each item in the grid control:
|
Condition |
By default, a User Defined condition is created, that is, it is independent of the Loading Conditions previously set up in Hydrostatics. However, each loading condition is included in the drop-down list, allowing you to easily perform seakeeping calculations on predefined loading conditions. Note: If a defined loading condition is selected, then you may not change the Name, Draughts or fields calculated automatically. |
|
Automatic Update |
Checking this button will automatically update certain fields by calculating the properties from the input weight distribution. The following values are calculated:
This item is only available for a User Defined condition, and if it is checked, and the User changes the weight distribution, then values are again automatically updated on the fly. Note: |
|
Name |
Condition Name. |
|
Draft Aft |
The draught at the aft perpendicular. Note: This value is only editable for a User Defined loading condition. |
|
Draft Fwd |
The draught at the forward perpendicular. Note: Again, this value is only editable for a User Defined loading condition. |
|
Mean Draft |
The draught at midships. Not editable. |
|
Trim |
Trim by the bow (Tf-Ta). Not editable. |
|
GM |
Fluid Metacentric height. |
|
LCG |
Longitudinal centre of gravity from the Aft Perpendicular. |
|
VCG |
Vertical centre of gravity (from the keel). |
|
Roll Gyradius |
kxx/Beam. |
|
Pitch Gyradius |
kyy/Lpp. |
|
Yaw Gyradius |
kzz/Lpp. |
Weights
A weight distribution is only required by the seakeeping module, and then, only if you require the calculation of dynamic loads.
If a User Defined loading condition has been defined, then you have the opportunity of entering the weight distribution in two formats:
|
Point weights |
The weights are entered in blocks with the centre of mass of each block at the same stations as defined on the Seakeeping - Hydrodynamics page. |
|
Weight Distribution |
The weight distribution is defined as in the rest of Hydrostatics. |
If a predefined loading condition is chosen, then the weight distribution has already been calculated and so this weight distribution is used. It cannot be edited.
Important: Note on the calculation of dynamic loads.
The calculation of the dynamic loads is based on the integration of four terms along
the vessel, from the aft end to the station of interest. These four components are
due to the inertia, restoring, hydrodynamic effects and wave forces/moments.
The weight distribution is required for the calculation of the inertia terms. However,
the motions are calculated using the total LCG, VCG and gyradii as specified in the
Loading Data grid.
At the aft end of the vessel, the loads should be zero (because there is no integration).
In addition, the loads at the forward end should also be zero. For this to be the
case, the four terms should sum to zero. However, each of these four terms can be
a very large value and very small differences in any one of these components can cause
large differences.
To ensure that these terms sum to zero, the weight distribution and the total weight,
LCG and gyradii must agree.
|
Open |
For a User Defined loading condition, the weight distribution may be entered. This may be entered directly into the grid control, or a previously saved file may be imported by clicking on this button. |
|
Save |
Once a weight distribution has been entered, this may, if required, be saved to a standard ASCII file by clicking on this button. |
The formats of the different weight files is described in Point Weight Data File Structure and Weight Distribution Data File Structure.