With PredictWind Weather Routing, you can set your Wave Polar not only to define the performance of your boat in various wave conditions but also to view the Roll, Vertical accelerations and Slamming Incidence that your boat will experience through the route.
Setting up the Wave polar can only be done on the PredictWind Website at https://forecast.predictwind.com; once set up, all the PredictWind Apps will use these settings saved on your account. The Apps (PredictWind App and Offshore App) cannot modify the Wave polar settings. They can only turn it ON or OFF.
To set up Wave polar:
Go to the weather routing page, then click Routing Preferences.
Press the Wave Polar button in the Routing Settings section
You will first need to turn ON Wave polar
Next, turn OFF Advanced Wave Polar (if it isn't already. We will explain Advanced Wave polar at the bottom of this article)
If you use a Predefined Polar, make sure the checkbox indicating "Use Predefined Boat Dimensions" is ticked. The boat dimensions of our Predefined Polars will be automatically defined using this setting, saving you the effort of looking them up.
If you're not using a Predefined Polar or think the values given are incorrect, uncheck the box, then fill out the fields, Displacement, LWL, Beam and Draught. If you're unsure what these values mean, click on the link: "What are Displacement, LWL, Beam and Draught?" The image below will be shown on screen.
The router will use these supplied dimensions to alter the performance of your boat based on the influence of wave conditions.
Set up Advanced Polar:
Although not recommended, it is possible not to use the automated Wave polar and instead define your own Wave polar Table.
Turn ON Advanced Wave Polar.
You will see a table of values as shown below:
Each cell defines the performance factor to be applied to your polar when your boat experiences the given wave conditions. E.g. the highlighted cell will define the factor applied to your polar when the wave conditions are 5m high, at an angle of 0 degrees to your boat (boat heading with the waves), while the TWS is 0 knots. 100 refers to 100%, so a reduction in performance is a number ranging from 1-99.
Roll, Vertical Acceleration & Slamming Incidence
(Only available on the Professional Subscription. Upgrade Here )
There are three new data points output by the router at each route point: Roll, Vertical Acceleration and Slamming Incidence.
Roll is the root-mean-square (RMS) roll amplitude in degrees. When roll motions are large, moving around the boat and performing tasks becomes difficult. Objects not strapped down are likely to move. A roll RMS limit of 4 degrees is often used for safely moving around the boat and completing tasks. Roll tends to be largest in beam seas.
Vertical acceleration is the root-mean-square vertical acceleration in 'g's' (1.0 = Earth's gravity 9.81 m/s^2) Vertical acceleration is a good indicator for the potential for the crew to get sea sick. The algorithm takes into account the primary, secondary and tertiary swells to calculate the overall vertical acceleration for the boat. The higher the acceleration, the more likely the crew will get sea sick.
Vertical acceleration limit of 0.2g are often used for safely performing tasks and avoiding seasickness.
Slamming Incidence is the likelihood of experiencing at least one slamming event in one minute. Slamming tends to be worst in head seas. Excessive slamming can cause hull damage and may result in injuries for people onboard.
There are three new graphs on the graphs tab of the route results, one for each new variable; the data is also given in a tabular format on the wave tab.