ODST relies on advanced calculations based on the vessel's Response Amplitude Operator (RAO) and the forecasted 2D wave spectrum. This information enables us to predict the vessel's motions several days in advance for all degrees of freedom at various positions onboard the vessel.

The predicted motions are represented through statistical parameters, or more specifically the extreme value estimate of the vessel's motion probability distribution.

"Probability distributions are commonly used to describe real-world phenomena, from the roll of a dice to distribution of wave heights in a population"

Let's look at an example. The Most Probable Maximum (MPM) is one type of statistical parameter defining the highest expected motions that is likely to occur within a given time frame, based on a combination of vessel motion characteristics, environmental conditions, and mathematical modeling. Unlike the historical observed motions that you may extract from the vessel's motion response unit (MRU), the Most Probable Maximum is a forward-looking prediction. It provides a reliable estimate for planning purposes, as it considers a range of conditions and factors that influence vessel motion.

The thresholds for the maximum allowed vessel motions during operations are typically derived during the project planning phase. The preferred statistical parameter defining the operation may differ based on characteristics of the operation and associated risk.

To meet this, ODST caters for a range of different 3-hour statistical parameters for extreme motion estimation with the following being the most used ones:

An example is given in the illustration below for heave motions described by a Rayleigh probability distribution:

If you need a specific statistical parameter to define your operations, contact us at odstsupport@4subsea.com.