Hazard Unstable vessel
Knowledge and understanding
Understand all associated hazard knowledge
A vessel may become unstable due to events, including:
- Loading or unloading operations, including winching
- Refuelling the vessel, known as bunkering
- Placing heavy material, such as gravel, sand or iron in the bilge of a vessel to improve stability, known as ballasting
- Explosions or collisions, leading to water ingress
- Movement of passengers, especially on smaller vessels
- Movement of cargo or water, known as the free surface effect
- Taking heavy equipment, including that of the fire and rescue service, onto the vessel
Assessing the stability of a vessel, and the effects that fire and rescue service activity may have on it, requires complex calculations.
Free surface effect
Free flowing liquids or solids on the deck or in the tanks of a vessel can cause it to become unstable. A wave or firefighting water run-off on deck can introduce many tonnes of water; a strong rolling force, known as the free surface effect, could be added. The extra weight from this combined effect drastically raises the vessel’s centre of gravity. The water then shifts and tries to roll the vessel over.