MCA Certificate of Competency Ship Stability and Trim Questions and Answers

Question 1

A vessel has a negative initial metacentric height (GM) when upright. What is the resulting condition of the vessel called?

Accepted Answer

Angle of loll

Answer

An angle of loll occurs when a vessel has a negative initial metacentric height (GM), making it unstable when upright. The vessel will heel to one side until the centre of buoyancy (B) moves outboard, increasing the KM and establishing a new, stable equilibrium at a certain angle of heel. This is different from an angle of list, which is caused by an unequal distribution of weight across the vessel.

Question 2

According to the MCA's interpretation of the International Load Line Convention, which of the following is a key intact stability requirement for a general cargo ship?

Accepted Answer

The area under the GZ curve up to 40° must be at least 0.09 metre-radians.

Answer

The UK's Maritime and Coastguard Agency (MCA) adheres to the Intact Stability (IS) Code, which specifies several criteria for intact stability. One of these is that the area under the righting lever (GZ) curve shall not be less than 0.09 metre-radians up to a 40° angle of heel or the angle of downflooding if this is less. The minimum initial GM for a general cargo ship is 0.15m.

Question 3

A ship is loading a timber deck cargo and intends to sail with a timber load line. Which of the following stability criteria is specifically required under UK regulations for this condition?

Accepted Answer

The maximum righting arm (GZ) must be at least 0.25m.

Answer

For ships loaded with timber deck cargoes making use of their timber load line, the MCA requires specific stability criteria to be met. One of these is that the maximum value of the righting lever (GZ) should be at least 0.25m. Another key requirement is that the metacentric height (GM) should not be less than 0.10m at all times during the voyage after corrections.

Question 4

A vessel has several slack double-bottom tanks. What is the primary effect of the free surface of the liquid in these tanks on the vessel's stability?

Accepted Answer

A reduction in the righting arm (GZ) at all angles of heel.

Answer

The free surface effect, caused by liquid moving in a partially filled tank, results in a virtual rise of the vessel's centre of gravity (G). This leads to a reduction in the effective metacentric height (GM) and consequently reduces the righting arm (GZ) at all angles of heel, thereby impairing the vessel's stability.

Question 5

When calculating a ship's trim, the Moment to Change Trim by one Centimetre (MCTC) is a critical value. Which of the following factors primarily determines the MCTC?

Accepted Answer

The vessel's displacement and longitudinal metacentric height (GML).

Answer

The Moment to Change Trim by one Centimetre (MCTC) is calculated using the formula: MCTC = (Displacement x GML) / (100 x L), where L is the length between perpendiculars. Therefore, it is primarily determined by the vessel's displacement and its longitudinal metacentric height (GML).

MCA CoC Practice Test

MCA CoC Practice Test

MCA Certificate of Competency Ship Stability and Trim Questions and Answers