The Problem Statement describes the problem that needs to be solved. This includes the magnitude, the scope of the problem and the impact on the ship. A problem could consist of a gap between the current performance and the desired performance.
To make this more concrete; when your performance is below the current standard you can identify this as a problem. For example, when the quality level of our tank cleaning reduces over time this is a problem we need to address. You can identify these problems by analysing your performance.

Besides analysing your performance you will encounter many issues during your day-to-day operations. These issues can be addressed as problems as well. Examples are 'corrosion in the cargo hot water heating system', 'not having the right PPE on board', etcetera.
Tools and tips
Key to defining a good problem statement is to make it concrete and measurable. The 5W2H questions can help you to make a problem statement concrete. Answer these questions and use them to formulate the statement.
The second question (Why is the problem) relates to the impact of the problem. This is not about finding the root cause but about making sure that you have a clear understanding why it is important to solve the problem. By defining the impact you create understanding about what happens when the problem occurs.
Problem statements often include solutions, which might lead you into a direction that will not help you to solve the real problem. Therefore, don't include any solutions in the problem statement