Nautical Institute Dynamic Positioning (DP) Revalidation and CPD Program Practice Exam

The correct factor that primarily influences the risk of cavitation in thrusters is the operating depth. Cavitation occurs when the pressure in the fluid around the thruster drops below the vapor pressure of the fluid, leading to the formation of vapor bubbles that can collapse and cause damage to the thruster and reduce efficiency.

At different operating depths, the ambient pressure varies significantly. In deeper waters, the increased pressure can help prevent cavitation as it raises the pressure on the thruster blades, while shallower depths can lead to lower ambient pressure, increasing the likelihood of cavitation occurring at given speeds and thrust levels. Therefore, the depth at which the thruster operates is a critical factor because it directly impacts the local hydrostatic pressure and the behavior of the fluid around the thruster.

While other factors like vessel speed and motor power rating can influence the overall performance and efficiency of the thruster system, it is primarily the operating depth that dictates whether the conditions will support or inhibit cavitation. Understanding this relationship is important for avoiding damage and ensuring optimal operation in various conditions.