DWO Cargo Operations & Stability 3 — Questions and Answers
Question 1: During a heavy-lift operation, the cargo is considered to be transferred to the ship's crane when:
- The slings are attached to the cargo
- The cargo leaves the dock surface
- The hook takes the weight (cargo becomes weightless on the dock) (Correct answer)
- The cargo crosses the ship's rail
Correct answer: The hook takes the weight (cargo becomes weightless on the dock)
At the moment the crane takes the full weight of the lift, the cargo acts as if suspended from the hook—its center of gravity rises to the hook height regardless of the cargo's actual elevation.
Question 2: The 'solid waterplane area' is used in hydrostatic calculations to determine:
- Reserve buoyancy
- The metacentric radius BM (Correct answer)
- Draft at even keel
- Freeboard
Correct answer: The metacentric radius BM
BM = I/V, where I is the second moment of the waterplane area about the vessel's centerline; a larger waterplane area increases the metacentric radius.
Question 3: A ship's GM is found to be negative. The SAFEST immediate action is to:
- Increase speed to reduce rolling
- Lower the center of gravity by ballasting double-bottom tanks (Correct answer)
- Move ballast to the highest tanks
- Shift cargo toward the bow
Correct answer: Lower the center of gravity by ballasting double-bottom tanks
Adding ballast to double-bottom tanks lowers G, increasing GM from negative to positive and restoring transverse stability.
Question 4: Stowage factor is BEST defined as:
- The weight of cargo per cubic meter of hold
- The cubic volume (m³ or ft³) occupied by one tonne of cargo including dunnage (Correct answer)
- The ratio of cargo weight to ship displacement
- The number of packages per TEU
Correct answer: The cubic volume (m³ or ft³) occupied by one tonne of cargo including dunnage
Stowage factor expresses how many cubic meters (or cubic feet) one metric ton of a commodity occupies aboard ship, including necessary dunnage.
Question 5: The purpose of dunnage in cargo operations is to:
- Increase the weight of the cargo
- Protect cargo from moisture and provide ventilation between tiers (Correct answer)
- Mark dangerous goods stowage positions
- Secure hatch covers against weather
Correct answer: Protect cargo from moisture and provide ventilation between tiers
Dunnage (typically wooden boards or mats) is placed under and between cargo to prevent moisture damage, allow air circulation, and distribute load.
Question 6: A grain shipper is required to provide a declaration that the cargo's moisture content is below the:
- Flow moisture point (FMP)
- Transportable moisture limit (TML) (Correct answer)
- Equilibrium moisture content
- Critical moisture threshold
Correct answer: Transportable moisture limit (TML)
IMSBC Code requires bulk cargo that may liquefy to be shipped at or below its Transportable Moisture Limit, which is set at 90% of the Flow Moisture Point.
Question 7: When discharging ballast to compensate for cargo loaded on one side, the officer should ensure:
- Ballast is discharged faster than cargo is loaded
- The operation sequence minimizes list and maintains adequate GM throughout (Correct answer)
- All ballast tanks are emptied before loading begins
- Ballast is only discharged from the cargo-loaded side
Correct answer: The operation sequence minimizes list and maintains adequate GM throughout
A properly planned sequence prevents excessive list and dangerous reduction of GM at any intermediate stage of the operation.
DWO Cargo Operations & Stability 3
During a heavy-lift operation, the cargo is considered to be transferred to the ship's crane when: