A bulk carrier can take on tens of thousands of tonnes of coal, ore, clinker or grain in a short time. High loading rates mean that a wrong sequence can overstress the hull within hours. In Indonesia the picture is varied: from berths with modern shiploaders to coal loaded off Kalimantan from barges using floating cranes or ship's gear. This guide explains how to put together a safe loading sequence.
The rules: IMSBC Code, SOLAS and the BLU Code
Solid bulk cargoes are governed by the IMSBC Code. Each cargo has a schedule describing its properties, hazards and carriage requirements, and cargoes broadly fall into:
- Group A: may liquefy if the moisture content exceeds the transportable moisture limit (TML), such as some nickel ores and concentrates.
- Group B: chemical hazards, such as coal that can give off methane or self-heat. Coal with a high share of fines may also show Group A properties.
- Group C: neither A nor B.
The shipper must declare the cargo before loading, including its stowage factor and, for Group A, the moisture content and TML certificates. SOLAS requires the master and the terminal representative to agree a loading or unloading plan in line with the Code of Practice for the Safe Loading and Unloading of Bulk Carriers (BLU Code), and SOLAS chapter XII adds measures for bulk carriers, including a loading instrument for ships of 150 m in length and above. Hold volume checks can be run with the stowage factor calculator.
Pours and hold order
The loading plan splits the final weight of each hold into several pours. The loader moves to another hold after each pour so the load builds up evenly along the ship. An illustrative five-hold bulk carrier loading 50,000 t of coal:
| Pour | Hold | Tonnes | Cumulative | Ballast note (illustrative) |
|---|---|---|---|---|
| 1 | H3 | 5,000 | 5,000 | Start deballasting midship double-bottom tanks |
| 2 | H1 | 4,500 | 9,500 | Deballast forward tanks, keep trim by the stern |
| 3 | H5 | 4,500 | 14,000 | Deballast aft tanks |
| 4 | H2 | 5,500 | 19,500 | Continue, check drafts against plan |
| 5 | H4 | 5,500 | 25,000 | Ballast hold (if any) now empty |
| 6 | H3 | 5,000 | 30,000 | Check shear force at H3 bulkheads |
| 7 | H1 | 4,000 | 34,000 | Remaining forward tanks |
| 8 | H5 | 4,000 | 38,000 | Remaining aft tanks, keep some for trim |
| 9 | H2 | 4,500 | 42,500 | Read drafts, update the loading instrument |
| 10 | H4 | 4,500 | 47,000 | Ballast nearly out |
| 11 | H3, H2, H4 | 2,000 | 49,000 | Trimming pour: H3 1,000, H2 and H4 500 each |
| 12 | H1, H5 | 1,000 | 50,000 | Final trimming pour, 500 t each for final trim |
Final weights: H1 9,000 t, H2 10,500 t, H3 11,000 t, H4 10,500 t, H5 9,000 t. The pattern is illustrative only; the valid sequence is the one calculated in the ship's loading instrument and approved by the master.
Deballasting in step
Ballast has to come out in step with the cargo going in. If the shiploader runs at 2,000 t/h but the ballast pumps can only manage about 1,500 t/h, the plan needs pauses or a lower loading rate. Points to watch:
- Tanks emptied during each pour should be near the hold being loaded, so bending moments do not build up.
- Unpumpable ballast left after stripping is included in the drafts and the final weight.
- Air draft under the shiploader and draft against berth depth are checked at each stage.
- Peak tanks are often emptied last to control trim.
Longitudinal strength at every stage
Every stage, not just the final condition, has to stay within the shear force and bending moment limits for harbour conditions, which are normally wider than the seagoing limits. This is checked with a loading instrument approved under class requirements, including IACS UR L5 for stability software. The concepts are explained in shear force and bending moment.
Local strength is limited as well: the loading manual lists the maximum cargo mass per hold and per two adjacent holds as a function of draft.
- Alternate hold loading: heavy cargo in alternate holds (say H1, H3, H5) with the rest empty. Only for ships designed and approved for it, such as those with the BC-A notation.
- Block loading: two adjacent holds full with the neighbouring holds empty. Only where the condition is in the loading manual.
- Multi-port loading: part-loaded conditions between ports must also be approved.
Trimming and final draft
The trimming pours at the end set the final draft and trim. The loading rate is reduced and drafts are read again before the last tonnes go in. The cargo must also be trimmed reasonably level to the hold boundaries so it does not shift and does not form steep slopes, especially for cargoes with a low angle of repose. Trim can be checked with the draft and trim calculator and the guide on ship trim and draft.
Draft survey
Bulk cargo weight is usually established by a draft survey before and after loading. The surveyor reads the six draft marks, measures water density and applies corrections:
- draft mark corrections to the perpendiculars,
- hull deflection (hog or sag) using a weighted average, the quarter mean,
- first and second trim corrections, and the density correction,
- deductions for ballast, fresh water, bunkers and the ship's constant.
The difference in net displacement before and after loading is the cargo weight. Walk through the steps with the draft survey calculator.
Group A cargoes in Indonesia
Nickel ore and some other ores shipped between islands to smelter areas are often stockpiled in the open and exposed to rain. For Group A cargoes, the actual moisture content must be below the TML according to a valid certificate. The chief officer can run a simple can test on board from cargo samples as an additional check; if a sample looks wet or forms a fluid surface, stop loading and ask for retesting. A can test does not replace the laboratory certificate.
Common mistakes
- Checking only the final condition, when limits are most often exceeded in the middle stages.
- Using the nominal loading rate without allowing for the real capacity of the ballast pumps.
- Changing the hold order without recalculating because the shiploader or crane moves faster.
- Forgetting cargo still on the barge or conveyor when working out what is left for the trimming pours.
Communication with the terminal
The loading plan is signed with the terminal representative before loading starts. It covers loading rates, the pour sequence, stop points for draft readings, deballasting times and how to stop loading in an emergency. Every change, such as switching holds because of a breakdown, is recorded and recalculated. When loading from barges, rates are uneven and the weight per barge should be logged to track what is left for each hold.
Shore-side planners can use STOWAGE.ID Vessel Stowage and the bulk stowage page to prepare a draft pour sequence and compare scenarios. That draft is decision support: the ship's class-approved loading instrument and stability booklet remain the official reference, and the final plan is approved by the master and chief officer.