Maintenance of vessel stability Flashcards
Centre of gravity (G)
The geographical centre of the mass of an object, in this case a vessel and its contents of which the force of gravity acts on
Centre of buoyancy (B)
The point of which all buoyant forces are acting upon the vessel
List and heel
Hell:
-Angle of the vessel leaning under and external force such as wind
List:
-Angle of the vessel leaning under an internal influence within or upon the vessel
Metacentric height (GM)
Metacentric height is a measurement of initial static stability of a vessel, this is the distance between the centre of gravity (G) and its meta-centre.
A larger metacentric height indicated greater stability or the ability to right herself
Righting lever (GZ)
Buoyancy acts vertically up through the Centre of buoyance (B1). The horizontal distance that separates the center of gravity (G) to the vertical line from B1, this is the right lever.
this is measured in metres and referred to as GZ
Period of roll
The time period that the vessel takes from the upright position, rolling to an angle on the portside, rolling to the same angle on the starboard side and then returning back to the upright position.
Free surface effect
The behavior of liquid, or unbound aggregates of small objects which behave like a liquid, to move freely in response to the movement of the vessel.
This liquid having an effect, could be because of water flooding on the deck, in the bilge, in a slack tank (whereby a tank containing liquid, which is not pressed/ full and doesn’t contain baffles
Freeboard
The distance vertically between the waterline and the main watertight deck
Reserve buoyancy
The volume of a vessel above the waterplane, made watertight can increase the ships buoyancy
Watertight integrity
The ability for a vessel to prevent water entering itself .
compartmentation divides this internally into smaller spaces improving integrity if weathertightness of a compartment if it were to fail
Understands and explains that vessel stability depends on the interaction of the forces of gravity and buoyancy.
Gravity acts vertically downward upon the vessel and is a constant force, and is infect thought the vessels center of gravity.
Buoyancy is has the opposite effect acting upwards throughout the centre of buoyancy.
The stability of the vessel is determined form the balance between these two factors.
Knowledge of the practices and conditions that could result in loss of stability
- Poor/incorrect loading of cargo/passengers on the vessel.
- If you were to load a larger weight on one side of the vessel and not have it balanced out you would cause the boat to list.
- Even distribution of weight will keep the vessel from listing.
Knowledge of the risks resulting from an excessive reduction in freeboard, an excessive reduction in reserve buoyancy,
and loading a vessel to a trim for which it was not designed.
-Overloading/loading to the wrong trim for the vessel can reduce the freeboard to to dangerous level which could result in a capsize in the wrong conditions.
Examples of situations which may result in dangerous loss of freeboard and reserve buoyancy.
Loading a vessel past its Plimsoll line/ the vessels capabilities, this can compromise the watertight integrity Eg, hatches and doors not closed or in poor condition potentially causing downfolding.
Understanding of the need to use closing appliances efficiently to achieve watertight integrity.
To ensure all watertight doors, hatch’s and covers are closed and maintained and check for watertight integrity,
