DWO Cargo Operations & Stability 2 — Questions and Answers
Question 1: A vessel's free surface effect is MOST critical when tanks are:
- Completely full
- Partially filled (Correct answer)
- Completely empty
- Fitted with baffles
Correct answer: Partially filled
Partially filled tanks allow liquid to shift transversely, reducing the effective metacentric height and worsening stability.
Question 2: The stability document that shows the maximum allowable KG at various displacements is called a:
- Trim and stability booklet
- Damage stability report
- Limiting KG curve (Correct answer)
- Hydrostatic table
Correct answer: Limiting KG curve
The limiting KG curve (or maximum KG curve) plots the highest permissible center of gravity for each displacement to ensure adequate GM.
Question 3: When loading heavy cargo on deck, the PRIMARY stability concern is:
- Increased draft
- Raised center of gravity reducing GM (Correct answer)
- Increased freeboard
- Reduced reserve buoyancy
Correct answer: Raised center of gravity reducing GM
Deck cargo raises the vessel's center of gravity, reducing GM and potentially making the ship tender or unstable.
Question 4: A vessel lists to starboard during loading operations. The BEST corrective action is to:
- Ballast the port double-bottom tank
- Shift cargo to port side
- Reduce loading rate
- Both A and B are correct (Correct answer)
Correct answer: Both A and B are correct
Either ballasting the low (port) side or shifting weight to the high (port) side will correct a starboard list; both methods are valid.
Question 5: The term 'angle of loll' refers to:
- The maximum angle before capsizing
- A stable equilibrium angle when GM is zero or negative (Correct answer)
- The designed heel for curved vessels
- The list caused by off-center loading
Correct answer: A stable equilibrium angle when GM is zero or negative
Angle of loll occurs when a vessel with negative or zero GM finds a new equilibrium position at a small angle of heel where GZ becomes positive.
Question 6: According to SOLAS, cargo securing arrangements must be documented in the:
- Ship's logbook only
- Cargo securing manual (Correct answer)
- Bill of lading
- Port state control certificate
Correct answer: Cargo securing manual
SOLAS II-1/45 and the CSS Code require every ship to have an approved Cargo Securing Manual detailing lashing and securing procedures.
Question 7: The 'virtual rise of GM' due to free surface effect is calculated using:
- The volume of liquid in the tank
- The second moment of area of the free surface divided by vessel displacement (Correct answer)
- Tank length multiplied by breadth
- The density ratio of liquid to seawater
Correct answer: The second moment of area of the free surface divided by vessel displacement
Free surface correction = i/V (second moment of free surface area ÷ vessel displacement volume), giving the virtual loss of GM.
DWO Cargo Operations & Stability 2
A vessel's free surface effect is MOST critical when tanks are: