Dynamic Positioning Data - Miscellaneous
- Last UpdatedDec 18, 2025
- 2 minute read
Other data may be set by using the Miscellaneous page as detailed below:
External Forces
These values allows for additional forces which could arise from moorings, towlines or tugs.
|
Longitudinal |
longitudinal force. |
|
Transverse |
transverse force. |
|
Yaw Moment |
yaw moment. |
Forward Speed
These values allows for result where a small constant velocity is required, rather than station keeping
|
Longitudinal |
longitudinal velocity (knots) (positive forward). |
|
Transverse |
transverse velocity (knots) (positive to starboard). |
Water Depth
The current forces are, by default, calculated in deep water. However, a shallow water correction may be applied to the current coefficients to allow the Dynamic Positioning calculations to be performed in shallow water. Details are given in Environmental Effects.
|
Shallow Water |
Check this box to perform the Dynamic Positioning calculations in shallow water. Note: |
|
Water Depth |
The water depth at which the calculations are to be performed. Note: |
Spectrum
In calculating the wave drift forces on the vessel, the wave coefficients are combined with a wave energy spectrum to calculate the mean wave drift force in a specified direction. Two wave energy spectra are available for Dynamic Positioning calculations:
|
ITTC |
ITTC spectrum. |
|
JONSWAP |
Joint North Sea Wave Project spectrum. |
Wind-Wave Relationship
The Dynamic Positioning calculations are performed by matching the forces and moments of the thrusters to the combined forces and moments due to wind, waves and current. The primary parameter is wind speed, and this is used to calculate the wind forces and moments. The wave drift forces are dependent on wave height and period. Therefore a relationship between the wind speed and wave height/period is required.
A default relationship is supplied, as given in the table below:
|
Wind Speed (knots) |
Significant Wave Height (m) |
Average Wave Period (secs) |
|---|---|---|
|
0 |
0.00 |
5.50 |
|
5 |
0.86 |
5.93 |
|
10 |
1.40 |
6.20 |
|
15 |
1.97 |
6.49 |
|
20 |
2.68 |
6.84 |
|
25 |
3.43 |
7.22 |
|
30 |
4.17 |
7.59 |
|
35 |
5.01 |
8.01 |
|
40 |
5.80 |
8.40 |
|
45 |
6.66 |
8.83 |
|
50 |
7.26 |
9.13 |
|
55 |
8.00 |
9.50 |
|
60 |
8.59 |
9.80 |
|
65 |
9.41 |
10.21 |
|
70 |
10.15 |
10.58 |
|
75 |
10.81 |
10.91 |
|
80 |
11.48 |
11.24 |
These default values can be overwritten:
You may add and delete values as required by using the Add and Delete buttons respectively. Wind speeds may be deleted by highlighting one or a number of rows. The Delete button will then be activated so that you can delete the data.
By clicking the Defaults button, values as supplied in the table above are used.