Deballasting recommendations

(Based on Capt. J. Isbester, Bulk Carrier Practice, Ch.7 Ballast Management, The Nautical Institute, 1993)

1. Opening of Airpipe Cowls

Before commencing deballasting, all ballast tank airpipes must be opened.

Failure to do so may result in:

• Ballast pumps labouring while trying to remove water from a sealed tank;

• Structural damage due to vacuum formation inside the tank.

Always verify air ingress at the airpipe once pumping begins.

2. Keeping the Ship Upright

If the vessel develops a list during loading and deballasting, possible causes include:

• Uneven cargo distribution;

• Unequal discharge from paired ballast tanks.

Ballast discharge must be monitored to ensure symmetrical emptying of tanks.

3. Optimum Trim and List for Effective Stripping

Effective ballast discharge requires:

• Competence and organization;

• Understanding of suction and sounding pipe locations.

DBT Suction Position

In most bulk carriers, ballast suctions in Double Bottom Tanks (DBT) are located in the inboard after corner.

To maximize stripping efficiency:

• Trim vessel by stern;

• List vessel 2–3° toward the opposite side of the tank being stripped.

Example:
To strip No.2 DBT starboard:

• Trim by stern;

• List 2–3° to port.

This directs residual ballast toward the suction.

Inform the loading foreman before listing the vessel to ensure cargo is poured on centerline.

4. Final Stripping Considerations

• Stripping takes time and should not be rushed.

• It cannot be effectively completed when vessel is even keel.

• Residual water will continue to trickle through floors and girders.

• Final stripping often cannot remove 100% of water.

5. Preventing Ballast Pump Tripping

Monitoring Pump Load

• Monitor pump amperage every 30 minutes.

• Adjust discharge valve to maintain manufacturer’s recommended load.

When Water Depth Reaches 15–20 cm

• Water flow becomes intermittent.

• Pump may begin drawing air-water mixture.

Modern pumps:

• Equipped with automatic degassing systems.

Older pumps:

• May race and trip when air enters.

6. Sediment Blocking Suction

Mud accumulation can block ballast suction.

Indications:

• Mud visible on sounding rod.

• Slow discharge.

Temporary solution:

• Flood tank from another tank or sea.

• Sudden inflow washes sediment from suction.

This is only temporary. Proper tank cleaning is required.

7. Leaking Ballast Line

If leak exists:

• System works normally while hole remains submerged.

• Once water level drops below leak, air enters system.

• Pump may gas up and trip.

Signs of leak:

• Difficulty pumping last 0.5–1.0 m.

• Abnormal sounding changes in adjacent tanks.

Detection:

• Inspect ballast line while tank is pressurized from another full tank.

• Leak will visibly spray water.

Temporary repair:

• Tighten expansion joint bolts.

• Wrap joint with plastic sheeting.

8. Deballasting Problems – Case Example

On a minibulker:

• Pump lost suction at 40 cm sounding.

• Engineers suspected blocked drainage holes.

• Actual cause: pump emptied suction bay faster than water could replenish.

Solution:

• Reduce pumping rate.

Lesson:
Pump capacity must match internal tank drainage capability.

9. Precautions When Using Dump Valves

Topside tanks may discharge through dump valves.

Risk:
Crew may forget to close dump valves after discharge.

Recommendation:

• Close immediately after completion.

• Record closure in logbook.

10. Importance of Records and Methodical Approach

• Record all soundings.

• Log stages of deballasting.

• Recheck “empty” tanks later, preferably with stern trim.

• Confirm air intake through airpipe during pumping.

11. Typical Ballast Residues (Laden Condition)

Approximate residual ballast quantities:

Proper maintenance reduces sediment accumulation and operational problems.

1. Cleaning Methods

• Manual mud removal (shovel and bucket);

• Hosing of topside and forepeak tanks;

• Hosing of double-bottom tanks;

• High-pressure washing;

• Use of sediment remover chemicals.

2. Structural Maintenance

• Removal of scale;

• Patching leaks;

• Maintenance of protective coatings;

• Regular inspection of ballast tanks.

Efficient deballasting depends on:

• Proper trim and list;

• Controlled pumping rates;

• Clean tank structures;

• Functional ballast lines;

• Accurate record keeping.

A thorough, methodical approach significantly reduces operational delays and equipment damage.