Stability Flashcards
what are the 6 degrees of freedom
surge sway heave roll pitch yaw
What is vessel displacement
the amount of water that the vessel displaces due to its weight
what are some of the preparations you would make for heavy weather
Ensure pre departure checklist was completed thoroughly, heavy weather checklist, stowed cargo, freeing ports clear, water holds (Pools etc) and bilges empty, sounding tank levels and checking stability calcs.
what is free surface effect and where can it occur
When a compartment is not completely filled with liquid so it is able to move and thus move the G of the vessel. It can occur in bilges, tanks, pools, on deck.
what determines acceptable stability
MNZ rule 47. IMO requires 6 criteria:
- GM of at least 0.15m (0.35m for FV)
- Max GZ must be at least 0.2m
- Angle of max GZ must exceed 30*
- Area under GZ curve to 30* must be at least 0.055mRads
- Area under GZ curve to 40* must be at least 0.090mRads
- Area under GZ curve from 30-40 must be at least 0.03mRads
Draw an angle of loll diagram
As per notes
What is gross tonnage and net tonnage.
GT- overall volume of the interior of the vessel. NT- overall volume of cargo space.
what is the minimum legal GM before departure.
When GM is more than 0.15m (0.35m for FV)
what defines a stable and unstable vessel?
Stable is when G is below M. Unstable is when G is above M
If G was at M what would be occurring and what would be your action.
Angle of loll. Move weight to lowest point to lower G.
Draw a FSE diagram.
See notes
Draw an unstable vessel diagram
See notes
Draw a stable vessel diagram
See notes
Draw a diagram for a vessel at a angle of list
See notes
Explain the main points of a load line and reference a diagram
See notes
What is the difference between heel and list
Heel is due to external circumstances, a righting lever is trying to right the vessel
List is due to internal circumstances such as loading. The G of the vessel has moved and thus there is no righting lever.
State what the major risks in dry docking are with regards to stability. And discuss the precautions that would be taken.
As the vessels stern touches down (point loading), you theoretically loose weight (🔺) from the keel, this causes the position of G to move away from the area of weight loss (upthrust of P). As the rest of the vessel touches down, the area under the water starts to decrease, this brings ‘B’ down which in turn drags ‘M’ down, thus reducing GM.(potential for -GM)
Stability book and dry docking plan needs to be referenced.
The required GM for dry docking needs to be larger than when at sea.
When DEPARTING from the dry dock, you must ensure the vessel is the same condition as when it entered.
Define Stability.
A vessels ability to keep itself upright.
What is the metacenter of a vessel?
It is the point intersection of the B and the centreline of the vessel
What is the angle of inflection on a GZ curve.
The change of direction on the first part of the curve. It is the point where the deck edge of the vessel goes underwater.
Briefly describe the relationship between roll period and GM.
As the roll period increases, GM decreases.
Who determines the rules and regulations with regards to stability.
ICLL and SOLAS determine the rules and regulations around stability. These get written into flag state rules, such as the large yacht code, or MNZ rule 47.
Define freeboard
The distance from the watertight deck edge to the water level. It is also known as reserve buoyancy.
What is the benefits of fore/aft trim
trimmed to the aft= more manoeuvrability
Trimmed forward = more efficiency
