Question 1

In BSafe Case Study 15, after the fixed CO2 system was released and visible smoke reduced, what did the crew believe, and what was actually still happening?

Accepted Answer

They believed the situation was stable, but the ammonium nitrate fertiliser's self-sustaining chemical decomposition was continuing regardless of the CO2 The crew believed the reduced smoke meant the situation was stable. Ammonium nitrate decomposition is a self-sustaining exothermic reaction that CO2 suppression, built for ordinary combustion, does not stop — the underlying hazard continued until the hold was later deliberately flooded.

Question 2

The yacht is loading additional stores and fuel before a long passage, raising the displacement significantly. What effect does this have on stability that you, as OOW, should be aware of?

Accepted Answer

Increased displacement generally raises the centre of gravity if weight is added high up, and free surface effects in partially-filled tanks can reduce the effective metacentric height (GM) Adding weight changes the vessel's centre of gravity depending on where it is stowed, and partially-filled tanks create free surface effects that reduce GM. OOWs should understand these basic stability principles even on smaller vessels without a dedicated loading computer.

Question 3

During a survey, watertight door seals in a transverse bulkhead below the waterline are found to be perished and not closing properly. As Master, what is the significance of this for the vessel's damage stability?

Accepted Answer

Significant — a failed watertight closure compromises the subdivision the vessel's damage stability calculations rely on, potentially allowing progressive flooding between compartments in the event of damage Damage stability calculations assume watertight subdivision functions as designed. A bulkhead door that cannot seal properly defeats that subdivision, allowing flooding to spread beyond the single compartment the design assumed — this must be rectified before further operation.