Quick Answer The Stability Booklet (or Loading Manual) is an approved technical document specific to each ship that contains the vessel's stability data: lightship weight, hydrostatic curves, stability curves (GZ curves), and sample loading conditions. Officers use it to calculate the ship's GM (metacentric height) before and during loading to ensure the ship is stable for sea. It is required by SOLAS and must be kept onboard.
Stability Booklet: What It Means
Every ship is different. The same amount of cargo in the same holds will create different stability conditions depending on the ship’s dimensions, tank arrangement, and hull form. The stability booklet is the ship-specific reference that tells you exactly how your vessel behaves.
What It Contains (Simplified)
Lightship data:
- The ship’s weight when empty
- The height of the centre of gravity when empty
- Length-wise position of centre of gravity
Hydrostatic data:
- For each draft, the displacement, KB (keel to centre of buoyancy), BM (buoyancy moment), and KM (keel to metacentre)
- This allows calculation of GM = KM – KG
Tank calibration tables:
- For each tank, the volume at each sounding level
- The vertical centre of gravity at each fill level
- Used to calculate the effect of tank contents on KG and FSE (Free Surface Effect)
Sample loading conditions:
- Pre-calculated stable conditions for departure, arrival, and ballast
- These serve as reference points and safety checks
Stability criteria:
- Minimum GM required (typically 0.15m for cargo ships)
- Minimum GZ (righting arm) at 30°
- Area under GZ curve requirements
- Maximum KG allowed at each displacement
How Officers Use It
Before loading:
- Calculate the ship’s current KG from all weights onboard
- Determine the proposed loading (cargo quantities and positions)
- Calculate the new KG after loading
- From hydrostatic tables, determine KM at the loaded draft
- GM = KM – KG
- Check GM meets minimum criteria
- Confirm acceptable trim
Modern ships: Most have computerised loading calculators (LOADICATOR) connected to the stability booklet data. Officers input tank soundings and cargo weights — the program calculates stability instantly and checks against criteria.
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Frequently Asked Questions
What does a stability booklet contain?
A stability booklet contains: lightship particulars (displacement, KG, LCG), hydrostatic tables (displacement vs draft), tank capacities and KGs for all tanks, sample loading conditions (departure, arrival, ballast), stability criteria (minimum GM, minimum GZ), and instructions for the stability calculation system (if electronic).
Who uses the stability booklet and when?
The Chief Officer primarily uses the stability booklet for every voyage — when planning loading, when shifting ballast, when fuel is consumed, when cargo is discharged. The Master approves the loading plan based on stability calculations. In port, it's the basis for all cargo loading and stowage decisions.
What is an approved stability booklet?
An approved stability booklet has been reviewed and stamped by the ship's classification society (DNV, Lloyd's, Bureau Veritas, etc.) and the flag state administration. It is the definitive document for that vessel. Any modification to the ship that changes stability characteristics requires an updated approved stability booklet.
What happens if you load a ship without checking the stability booklet?
Loading without stability verification risks: insufficient initial stability (GM too small → ship rolls excessively or capsizes), excessive GM (GM too large → stiff ship with violent short-period rolling → structure damage), or trim outside permitted range (steering problems, propeller emergence). Many casualties have been traced to ignored stability calculations.