Intact Stability

Question 1

The area under the righting lever curve (GZ curve) should not be less than…………….. up to 30° angle of heel.

Answer 1

0.055 metre-radians

Question 2

The area under the righting lever curve (GZ curve) should not be less than ……………. up to 40° angle of heel or the angle of downflooding if this is less than 40°

Answer 2

0.09 metre-radians

Question 3

The area under the righting curve between the angles of heel of 30° and 40° or between 30° and the angle of downflooding if this angle is less than 40°, should not be less than ………………..

Answer 3

0.03 metre-radians

Question 4

The righting lever GZ should be at least ……………….. at an angle of heel equal to or greater than 30°

Answer 4

0.20 m

Question 5

The maximum righting arm should occur at an angle of heel preferably exceeding …………… but not less than …………..

Answer 5

30° & 25°

Question 6

The initial metacentric height GM should not be less than ……………..

Answer 6

0.15 m

Question 7

Severe wind and rolling criterion (weather criterion)

Answer 7

In addition to the criteria described above, ships covered by the 2008 IS Code should meet a weather criterion that considers the effect of strong beam wind and waves applied when the vessel is in dead ship condition.

Question 8

Who does the intact stability code apply to?

Answer 8

Cargo ships, passenger vessels over 24m

Question 9

Where might a vessel experience parametric rolling or pure loss of stability?

Answer 9

Vessel with a large righting lever between wave trough and wave crest variations

Question 10

What is dynamic stability phenomena in waves?

Answer 10

Certain vessel types are at risk of encountering critical stability situations in waves. As the ride over the top of waves the buoyancy of the water is not distributed evenly allong the vessels hull.

Question 11

When might a ship experience resonant rolling?

Answer 11

When drifting freely beam on to the waves

Question 12

What is broaching?

Answer 12

Ships in a following sea or sea on quarter may not be able to keep a constant course, the ship can “broach” turn beam on to the swell, loose stability and may lead to extreme angles of heel

Question 13

What is contained withing the vessel stability booklet?

Answer 13

In the working language of the vessel, enough information as regquired by the flag state to ensure the Master has enough information to make a quick assessment of the stability condition of the vessel.

General description of vessel

Instructions how to use the booklet

General arrangement plan, showing water tight compartments, closures vents, downflooding angles, permanent ballast, allowable deck loadings and freeboard diagrams

Hydrostatic curves or tables of cross curve stability calculated on a free trimming basis, for the range of displacement and trim anticipated in normal operating conditions

Capacity plan or tables showing capacities and CoG for each cargo space

Tank sounding tables show capacities, CoG and free surface data for each tank

Information on loading restrictions such as Maximum KG or minimum GM curve or table that can be used to determine compliance with the applicable stability criteria

standard operating conditions and acceptable examples for developing other acceptable loading conditions

A brief description of the stability calculations done including assumptions

general precautions for preventing unintentional flooding

information concerning the use of cross flooding fittings with descriptions of damage conditions which may require cross flooding

any other necessary guidance for the safe operation of the ship under normal and emergency conditions

inclining test report

recommendation for determining ships stability by means of inclination test

Question 14

What is “progressive flooding”

Answer 14

Ingress of water to compartments assumed to be intact

Such additional floodings may occur through internal openings or through non watertight external openings and pipes if they are located below the waterline after damage

The possibility of progressive flooding through ballast piping passing through the assumed extent of damage, where positive action valves are not fitted to the ballast system at the open ends of pipes in the tanks serverd, is to be considered

Question 15

What is “down flooding”

Answer 15

The angle of flooding or down flooding angle related to intact stability is the angle of heel at which the lower edge of opennings in the hull or superstructure or deckhouses can not be closed weather tight immerse

Air inlets to the engine roo must always remain open and the downflooding angle for the intact stability shall be calculated taking into account these openings

Some types of dangerous cargos require continuous ventilation, in such cases it is necessary to check down flooding angle also for hold ventilation opennings

Question 16

What does the curve of statical stability represent?

Answer 16

The ability of the ship to return to the upright position when heeled over by an external force

Question 17

What does the GZ value represent?

Answer 17

The GZ value represents the horizontal distance from CoG to CoB

Question 18

As the ship heels over what will happen to the righting lever? GZ

Answer 18

As the ship heels the righting lever will heel to it’s maximum (around 40 degs) and then decrease until it becomes a capsizing lever (negative GZ)

Question 19

What is dynamic stability?

Answer 19

Dynamic stability is the work required by an external force to heel the ship to that angle of heel

It is the area under the GZ curve, as it represents the sum of the righting moments an external force has to overcome if it wants to heel the vessel over to that angle.

Question 20

What is the effect of a beam wind on your ship?

Answer 20

Reduced dynamic stability as a result of the wind righting lever

Question 21

What consideration would you take if there was a strong wind on the beam and what actions will you take?

Answer 21

A strong wind on the beam will result in a wind heeling moment affecting the ship and a loss in dynamic stability.

I would be aware of the affect of gusting wind and take action to alter my course.

Question 22

What action would you take if the vessel heeled over unexpectedly? Loll?

Answer 22

Raise the alarm and muster the crew as the vessel is in potentially a very dangerous situation.

Alter course to put the ships head in predominent waves - we want to stay lolled one side and this will help prevent rolling across to the opposite side.

Check that port and starboard listing moments are the same - If we can determine whether listing moments exist for example a shift in cargo, we can determine whether the unexpected inclination has been caused by a list or by a rise in CoG. If no listing moments, we are dealing with an angle of loll.

Check for slack tanks - free surface moments in tanks may cause a loss of GM which is enough to make the vessel unstable

Take action to lower G and reduce KG - either by pumping out ballast in high sided tanks or by ballasting double bottom tanks, ideally on the low side until positive GM is established

Question 23

What is an angle of loll

Answer 23

An angle of loll occurs when the centre of gravity moves above the metacentric height causing an unstable stability condition

Question 24

Why are timber ships susceptable to an angle of loll?

Answer 24

They have a small GM when completing loading and if the cargo absorbs water during the passage the centre of gravity will rise above M.
Any external force will cause the ship to list and rest at an angle of loll.
It would be important at this stage to lower the centre of gravity of the vessel.

Question 25

What is an angle of list?

Answer 25

An angle of list is generally caused by the transverse movement of weights within the vessel. It is not easy to determine if the vessels is inclined due to a list or loll.

Question 26

Grain stability requirements

Answer 26

Angle of heel due to shift in grain not less than 12degrees or the angle of deck edge immersion, (which ever is less)

Residual area between the heeling arm and the curve and the righting arm curve to be not less than 0.075 m-r

Initial GM is not less than 0.3m (to account for decreased GM due to cargo shift) (normally 0.15m)