Stability Flashcards
Covers topics like Intact & Damaged Stability, Dry Docking and criteria
What is the stability information that should be available to the Master?
- General Particulars (info to authorities)
- General Arrangement plan (to locate & identify tanks, compartments etc.)
- Capacities & Centre of Gravity of compartments
- Estimated Weight & Disposition of Pax and Crew
- Estimated Weight & Disposition of Cargo
- Loadline and Deadweight
- Hydrostatic Particulars
- Free Surface Info
- KN Tables / Cross Curves
- Pre-worked Vessel Conditions
- Statement of Instructions
- Inclining Experiment Report
What is the contents on a vessel’s pre-worked condition?
- Profile Diagram
- Statements of Lightship, Deadweights, GM and Draughts & Trim
- Diagram of GZ’s (GZ Curve) with GM
- Statement of Comparison (to the IS Requirements)
- Free Surface Effect
- Warning to the Master (for not complying with IS Requirements)
What is the purpose of Stability Instruments?
A detailed, yet clear to understand display of the vessel’s present loading condition, to determine compliance
NOTE: it is NOT a substitute for the Stability Manual
What data inputs does Stability Instruments rely on?
- PASSIVE - manual entries in the system
- ACTIVE - sensors in tanks, compartments with AUTOMATIC & CONTINUOUS
NOTE: active must have ability to OVERRIDE by the user
What are the different types of software for Stability Instruments?
- Type 1 - for INTACT stability ONLY
- Type 2 - for INTACT & DAMAGE stability (based on limit curve)
- Type 3 - for INTACT & DAMAGE stability (direct pre-programming of various scenarios for each loading condition)
List the data that should be presented on Stability Instruments?
The following must be presented in a clear manner with units of measure identifiable and used consistently:
- Deadweight Data (KG, TCG, LCG, FSM if applicable)
- Trim & List
- Draughts - at the marks & perpendiculars
- Summary of Load Condition (Displacement, VCG, LCG, VCB, LCB, LCF, GM, GML)
- Table of GZ’s for a range of heel
- Angle of Flooding
- Compliance with IS Criteria
- Clear Warning if not in compliance
Stability Requirements - GENERAL
Minimum GM = 0.15m
Maximum GZ = at least 0.20m
Angle of Max GZ = at least 30 degrees
Max GZ to occur after = 25 degrees
Area under the Curve 0 - 30 = at least 0.055mr
Area under the Curve 0 - 40 (or angle flooding whichever less) = 0.09mr
Area under the Curve 30 - 40 (or angle flooding whichever less) = 0.03mr
Stability Requirements - GRAIN
Vessel upright upon completion of loading
Minimum GM = 0.30m
Angle of heel due to grain shift = 12 degrees or angle of DEI (whichever lesser)
Area under the Curve = 0.075mr (measured from either 40 degrees, angle of flooding or difference between the curves)
Stability Requirements - TIMBER
Minimum GM = 0.10m
Maximum GZ = at least 0.25m
Area under the Curve 0 - 40 degrees or angle of flooding = 0.08mr
Extra Criteria Exemption
The effects of beam wind and rolling = 80% of angle DEI may be ignored
Stability Requirements - PASSENGER
As well as complying with the General & Weather Criterion…
Angle of heel on turning = max 10 degrees
Angle of heel with pax on one side = max 10 degrees
Minimum weight of Pax = 75kg
Minimum height of Pax = 1.0m (standing), 0.3m (seating)
Location of Pax & Luggage = at spaces in their disposal
Stability Requirements - WIND CRITERION (Compliance)
Compliance:
Angle of heel under STEADY BEAM wind = 16 degrees or 0.8 x angle of DEI (whichever is lesser)
Area b to be EQUAL OR GREATER THAN area a
Stability Requirements - WIND CRITERION (Angles)
Angles:
ϕ0 = angle of heel under steady beam wind
ϕ1 = angle of roll to windward due to wave action (measured from ϕ0 to end of area a)
ϕ2 = angle of flooding, 50 degrees or ϕc (whichever lesser)
ϕc = angle of second intercept of lW2 on the GZ Curve
Stability Requirements - WIND CRITERION (Levers)
Levers:
lW1 (Wind Lever 1) = wind lever of a steady beam wind
lW2 (Wind Lever 2) = wind lever of wind gusts (50% more than lW1)
Define a Type A vessel
A vessel which is designed to carry LIQUID CARGOES IN BULK ONLY
Define a Type B Vessel
Any vessel OTHER THAN A TYPE A VESSEL
What are the characteristics of a Type A vessel?
High integrity
Small, watertight openings
Low permeability (less lost volume if bilged)
More subdivisions (less lost volume if bilged)
Need to remain afloat of flooding ANY compartment (permeability 0.95)
Machinery space is a FLOODABLE compartment (permeability 0.85)
What are the characteristics of a Type B vessel?
Larger access openings
Low integrity
Less subdivisions
Greater permeability in cargo spaces
OVERALL, they have a higher freeboard than Type A vessels
What corrections can affect the final assignment of freeboard?
- Vessel under 100m in length
- Block Coefficient
- Depth of the vessel
- Position of the Deck Line
- Sheer of the vessel
- Recess in the Freeboard Deck
- Superstructure
- Minimum Bow Height
How can a Type B vessel reduce it’s freeboard? (Type B-60)
As well as the Type B requirements…
OVER 100m in length
WEATHERTIGHT openings
Remain afloat any SINGLE compartment (permeability 0.95)
Machinery space = FLOODABLE (permeability 0.85)
How can a Type B vessel reduce it’s freeboard? (Type B-100)
As well as the Type B-60 requirements…
WATERTIGHT openings
Deck to Machinery space = PROTECTED by deckhouse
Access between poop & bridge = GANGWAY OR UNDER DECK PASSAGE
Lieu of the bulwarks = OPEN RAILS OVER HALF LENGTH of vessel
What is defined as the assumed damage of a Type A and B vessel?
VERTICAL = from keel upwards with no limit
TRANSVERSE = 20% beam or 11.5 metres (whichever less)
LONGITUDINAL = between transverse bulkheads (for B-100, to include one bulkhead other than machinery space bulkhead)
What is defined as the assumed damage for a passenger vessel?
VERTICAL = up to the summer draught + 12.5m
TRANSVERSE = 20% beam or 11.5 metres (whichever less)
LONGITUDINAL = between transverse bulkheads (for B-100, to include one bulkhead other than machinery space bulkhead)
What is the condition of equilibrium criteria of a vessel in a damaged condition? (Type A & B)
WATERLINE = below any openings
ANGLE OF HEEL = no more than 15 degrees (17 degrees if deck edge not immersed)
GM FLOODED = positive
If a compartment is flooded or margin of safety is in doubt, STABILITY TO BE ASSESSED
SUFFICIENT stability:
Positive range of stability = 20 degrees
Max GZ = at least 0.10m
Area under the Curve = at least 0.0175mr
How does Synchronous Rolling occur?
This occurs when the natural period of roll of the ship is the same as the apparent period of the waves.
Describe how following and quartering seas can cause extreme angles of heel?
The reason is due to Broaching - vessel not being able to maintain steady course even with maximum steering efforts
What are the dangers for the vessel if they start to experience Broaching?
- Large angles of heel
- Possible ingress of water
- Possible capsize
- Injury or fatality to crew and passengers
- Shift of deadweights, making condition worse
Describe what could happen if the vessel experiences variations of the righting lever?
Between large wave troughs and crests, may cause variations in the righting lever and therefore the vessel may experience parametric rolling or pure loss of stability or a combination
How does Parametric Rolling occur?
When the ship is pitching heavily and rolling due to waves from near ahead or astern of a similar length to the ship.
Also, where the relative wave period is either equal to about half the vessel’s natural rolling period
Describe the consequences of a vessel experiencing Parametric Rolling?
- Crest of wave at bow and stern = INCREASE WPA, BM, GM, GZ
- Crest of wave at amidships = DECREASE WPA, BM, GM, GZ
- Different vessel experiences from stiff to tender quickly
What are the dangers for the vessel if they start to experience Parametric or Synchronised Rolling?
- Cargo shift / damage
- Structural damage
- Personnel injury
- Downflooding
- Potentially capsizing
State the actions to take if the vessel starts to experience Parametric or Synchronised Rolling?
- ALTER COURSE; ideally towards the waves (shortens the apparent period of the waves)
- ALTER SPEED; if waves not on the beam
- ALTER VERTICAL DISTRIBUTION OF WEIGHT; so as to change the vessel’s GM
- ALTER TRANSVERSE DISTRIBUTION OF WEIGHT; change the vessel’s radius of gyration
If a vessel was to proceed to sea with minimum stability, and encounter rough seas, what could happen?
- LARGE ALTERATIONS of the righting lever (GZ) when wave crest moves along vessel length
Define “Gross Tonnage”…
The volume of all enclosed spaces on a vessel. This includes the Engine Room and other non-cargo spaces
Define “Net Tonnage”…
The volume of only the cargo-carrying spaces on the vessel. This is the tonnage that determines the earning capability of the vessel
Define “Deadweight”…
The total carrying capacity of your vessel. This includes cargo, fuel / bunkers, fresh water, ballast water, grey water, provisions, stores, passengers and crew. It can be described as the vessel’s displacement minus the lightship
Define “Deadweight Scale”…
A drawing used for estimating the additional load that can be added to the vessel when it is in a density of water less than salt water
What are the 5 types of load line that can be assigned to a ship?
- Type A
- Type B
- Type B with Decrease of Freeboard (B-60, B-100)
- Type B with Increase of Freeboard
- Type B with Timber Loadlines
What is the difference between Static & Dynamic Stability?
STATIC: shows “a snapshot in time” the maximum GZ values the vessel will reach at specific angles of heel
DYNAMIC: the ship’s ability to bring herself back to the upright position
What is the term “Progressive Flooding?”
Ingress of water to a compartment of a ship, even though that compartment is still intact
Actions if the vessel suddenly heels over unexpectedly…
- Alter course to put the ship’s head into the predominant waves
- Check any potential transverse or longitudinal damage (if it’s safe to do so)
- Check that port and starboard listing moments are the same
- Check slack tanks
- Take action to lower G
What information would be available on board with regards to Damage Stability?
- Damage Control Plans
- Damage Control Booklets
- Damage Stability Information
What jobs would you expect to carry out in a Dry Dock?
- Hull cleaning and surface prep
- Survey of ship’s bottom
- Anchors
- Chain Locker
- Sea valves & chests
- Anodes & sensors
- Inspection / overhaul of equipment
- Tank and hold inspections
What jobs will you be expected to complete before Dry Dock as a Chief Mate?
- Reduce FSM / FSE
- Adequate GM to be achieved
- Trim according to the dry docking plan
- Sound tanks and record
- Plugs: storage and placement before refloating
- Reference previous stability condition for assistance
What preparations would you consider before going to Dry Dock?
- Meeting with head of departments of the plan
- Equipment & handling gear stowed
- Fendering if required
- Restricted areas secured & tagged
- Safety & security notices posted
- Fire fighting appliances ready
- ER prep to transfer to shore power, water, sewage
What is the Critical Instant?
The point at which the vessel almost rests fully on the blocks throughout the whole length (i.e at forward end assuming aft touches blocks first)
What is the Critical Period?
The time at which the vessel first touches the blocks until she is fully rested throughout the entire length
What is P Force?
An upthrust force acting when the vessel rests on the blocks. This brings M down proportionally with the reduction of B force
What document you must receive before you can refloat the dock?
Certificate of Flooding
What checks will you make before refloating the vessel from dry dock?
- All work & surveys intended has been complete
- Plugs are fitted
- Sea chest covered are fitted
- Sensors, anodes etc fitted and covers removed
- External connections (water, power, sewage) removed
- Equipment used in the dry dock is removed
- Anchor back on board
- Stability of the ship
- Secure heavy objects
- Certificate of Flooding authorised
