Chapter 8 fixed the deepest draught she may have. This chapter is about the five or six hours in which she gets there.
9.1 Why the bulk carrier has a chapter of her own
Nothing else in the merchant fleet combines a very dense cargo, a very large single compartment, and a shore installation capable of delivering thousands of tonnes an hour. A container goes aboard in one lift of forty tonnes. Iron ore goes aboard in a stream, and six thousand tonnes can be in one hold before anybody has had time to think about it.
The losses of the early 1990s, many of them with all hands, made the point, and the answer came in three parts. The enhanced survey programme (resolution A.744(18), 1993, since replaced by the 2011 ESP Code) deals with the steel; SOLAS chapter XII, adopted by the SOLAS Conference of November 1997, deals with the ship; and the BLU Code, adopted the same month by resolution A.862(20), deals with the operation. This chapter is about the last one, because it is the one a deck officer works to.
9.2 The cargo information, and the interface
SOLAS chapter VI requires the shipper to give the master the cargo name and description, the stowage factor, the angle of repose, the trimming procedures, and whether the cargo is liable to shift or to liquefy. The IMSBC Code then places it in Group A, cargoes which may liquefy; Group B, cargoes with a chemical hazard; or Group C, cargoes which do neither. None of the arithmetic below can be done without the stowage factor, and none of it is worth doing if the moisture declaration is wrong.
Three things in the BLU Code matter more than the rest. The terminal must nominate a terminal representative, by name. The master and that representative must agree a loading plan in writing before cargo handling begins, and any change to it that affects safety must be agreed in writing before it is made. And the plan must keep the ship inside her approved stress limits at any stage of the operation. Not at the end of it. At any stage of it.
9.3 Loading MV Ninja
She arrives with 6009 tonnes of ballast, 11668 tonnes displacement at 4.019 m, trimmed 2.90 m by the stern, with a fluid GM of 8.017 m. She is to load 24797 tonnes at a stowage factor of 1.30, which fills all five holds and takes her to 9.600 m, the departure condition of Chapter 1. Every tonne of cargo goes in while every tonne of ballast comes out.
The figures that follow are worked on her data booklet, as the printed book works them: light ship 4950 t at 8.86 m and 66.31 m from aft; the consumables of the departure condition, 709 t with 815.2 t m of free surface, aboard throughout; a partly filled hold treated as a prism standing on the 2.20 m floor of the illustrative subdivision, so that a stow holding a fraction f of the hold has its centre at 2.20 + f(Kgfull − 2.20) m; the water in a slack ballast tank at the tabulated centre, with a free surface moment of i × 1.025; port and starboard tanks pumped together; and the hydrostatic table read by straight line interpolation.
| pour | cargo t | ballast t | displacement t | draught m | fwd m | aft m | trim m | fluid GM m |
|---|---|---|---|---|---|---|---|---|
| on arrival, in ballast | 0 | 6009 | 11668 | 4.019 | 2.659 | 5.564 | -2.90 | 8.017 |
| 1, No.1 to 35% | 1576 | 5627 | 12862 | 4.396 | 4.277 | 4.529 | -0.25 | 6.916 |
| 2, No.3 to 35% | 3339 | 5199 | 14197 | 4.814 | 4.754 | 4.880 | -0.13 | 6.361 |
| 3, No.3 to 70% | 5103 | 4772 | 15534 | 5.227 | 5.118 | 5.347 | -0.23 | 5.479 |
| 4, No.3 to 100% | 6614 | 4406 | 16679 | 5.579 | 5.405 | 5.766 | -0.36 | 4.540 |
| 5, No.2 to 35% | 8472 | 3956 | 18087 | 6.007 | 6.535 | 5.448 | +1.09 | 4.341 |
| 6, No.4 to 35% | 10330 | 3505 | 19494 | 6.430 | 6.554 | 6.301 | +0.25 | 4.195 |
| 7, No.4 to 70% | 12188 | 3055 | 20902 | 6.848 | 6.494 | 7.210 | -0.72 | 3.829 |
| 8, No.2 to 70% | 14046 | 2605 | 22310 | 7.263 | 7.358 | 7.168 | +0.19 | 3.464 |
| 9, No.4 to 100% | 15638 | 2219 | 23516 | 7.615 | 7.248 | 7.975 | -0.73 | 3.016 |
| 10, No.2 to 100% | 17230 | 1834 | 24723 | 7.963 | 8.481 | 7.461 | +1.02 | 2.588 |
| 11, No.5 to 35% | 18854 | 1440 | 25953 | 8.317 | 8.184 | 8.445 | -0.26 | 2.713 |
| 12, No.1 to 70% | 20430 | 1058 | 27147 | 8.659 | 9.317 | 8.030 | +1.29 | 2.616 |
| 13, No.5 to 70% | 22054 | 665 | 28378 | 9.010 | 8.478 | 9.515 | -1.04 | 2.532 |
| 14, No.1 to 100% | 23405 | 337 | 29401 | 9.301 | 9.769 | 8.857 | +0.91 | 2.251 |
| 15, No.5 to 100% | 24797 | 0 | 30456 | 9.600 | 9.673 | 9.531 | +0.14 | 2.218 |
The trim never exceeds 1.29 m, the draught never passes the summer marks, and the fluid metacentric height never falls below 2.22 m. Notice what happens to the GM: it starts at 8.02 m in ballast and finishes at 2.22 m, falling almost the whole way; the one small recovery, at pour 11, is the slack No.5 double bottom pair being emptied. Cargo goes in above the ballast that comes out, and a ship gets tenderer as she loads.
9.4 What the terminal would rather do
A terminal has one loader on a rail, and its preference is always to work along the ship once: fill No.1, shift, fill No.2, and so on. Here is the same cargo, the same ship and the same total, in that order.
| pour | cargo t | ballast t | draught m | fwd m | aft m | trim m | fluid GM m |
|---|---|---|---|---|---|---|---|
| on arrival, in ballast | 0 | 6009 | 4.019 | 2.659 | 5.564 | -2.90 | 8.017 |
| 1, No.1 filled | 4503 | 4917 | 5.087 | 7.113 | 2.866 | +4.25 | 4.924 |
| 2, No.2 filled | 9811 | 3631 | 6.312 | 10.202 | 2.246 | +7.96 | 3.294 |
| 3, No.3 filled | 14849 | 2410 | 7.441 | 11.084 | 3.833 | +7.25 | 2.515 |
| 4, No.4 filled | 20157 | 1124 | 8.600 | 11.134 | 6.178 | +4.96 | 2.203 |
| 5, No.5 filled | 24797 | 0 | 9.600 | 9.673 | 9.531 | +0.14 | 2.218 |
At the second pour she is trimmed +7.96 m by the head, with the bow at 10.202 m and the stern at 2.246. At an after draught of 2.25 m the propeller and the rudder are largely out of the water. She cannot be shifted along the berth under her own power. The cargo is identical. Only the order has changed.
And this is the part the arithmetic here does not show
Trim is the visible symptom. The invisible one is the bending moment. A ship trimmed eight metres by the head with ten thousand tonnes in her two forward holds, her machinery aft and three empty holds between them is hogging hard, beyond her permissible bending moment, and that figure is on none of these tables. It is on the loading instrument, and Chapter 10 is about how the instrument arrives at it.
9.5 The deballasting race
Behind every loading plan is an arithmetic with nothing to do with stability. She must shed 5862 m³ of ballast while taking 24797 tonnes of cargo: 0.2364 m³ a tonne, fixed by the ship and not by the terminal. Divide her pump capacity by it and the answer is the fastest loading rate she can keep up with.
| loading rate, t/h | ballast to be shed, m3/h | can she keep up? | behind by the end | ballast aboard at the end |
|---|---|---|---|---|
| 1500 | 355 | yes | — | — |
| 2500 | 591 | yes | — | — |
| 3500 | 827 | yes | — | — |
| 4230 | 1000 | just | — | — |
| 5000 | 1182 | short by 182 m3/h | 903 m3 | 925 t |
| 6000 | 1418 | short by 418 m3/h | 1729 m3 | 1772 t |
A modern iron ore berth loads at six thousand tonnes an hour and thinks nothing of it. At that rate this ship falls 418 m³ an hour behind, and by the end she would have 1772 tonnes of ballast still aboard and float at 10.100 m, 50 cm over her marks. The remedy is a line in the agreed plan saying the loading rate shall not exceed 4200 tonnes an hour, and a master who enforces it.
9.6 One pump gone
Take the agreed plan, which is sound, and lose one ballast pump at the start while the terminal loads at 3000 tonnes an hour, well inside the limit for two. The order of the pours is unchanged; only the rate the ballast leaves has halved. She crosses her summer marks at pour 14, No.1 to 100 per cent, 17 cm over, with 2010 tonnes of ballast still aboard. Nothing about the plan was wrong. The plan assumed two pumps.
9.7 Alternate hold loading
A dense cargo creates a problem that looks like the opposite of the usual one. Put 24797 tonnes of iron ore at a stowage factor of 0.40 into all five holds and it occupies 1984 m³ in each, a stow whose surface is only 6.09 m above the keel in No.1 and lower in the others: a fluid GM of 5.368 m. She is not unstable. She is violently stiff, and in a seaway that is dangerous to the cargo, to the lashings and to the people aboard.
Loading No.1, No.3 and No.5 only puts 8266 tonnes in each, stowed to 8.68 m in No.1, raising the centre of gravity by 1.087 m and bringing the GM down from 5.368 to 4.281 m. That is the whole purpose of the practice. And there is the price: the load on the tank top of No.1 goes from 10.0 to 16.6 tonnes on every square metre, and a full hold next to an empty one produces a shear force at the bulkhead between them that a homogeneous loading never approaches. The permitted patterns are in the loading manual, not in anybody’s judgement.
9.8 SOLAS chapter XII, and what reaches a ship of 148 metres
Chapter XII is written mostly for bulk carriers of 150 metres and upwards, and she is 148.
| regulation | what it requires | to whom | does it reach her? |
|---|---|---|---|
| 4 | damage stability, flooding of any one hold | 150 m and upwards, dense cargoes | no |
| 5 | structural strength | 150 m and upwards | no |
| 6 | structural and other requirements | 150 m and upwards | no |
| 7 | survey and maintenance | 150 m and upwards, single side skin | no |
| 11 | loading instrument | 150 m and upwards; under 150 m if built on or after 1 July 2006 (intact stability) | if built on or after 1 July 2006 |
| 12 | hold, ballast and dry space water level detectors | all bulk carriers | yes |
| 13 | availability of pumping systems | all bulk carriers | yes |
| 14 | restrictions from sailing with any hold empty | single side skin, 150 m and upwards, dense cargoes | no |
So what reaches her is regulation 11, a loading instrument giving her intact stability, if she was built on or after 1 July 2006; regulation 12, water level detectors with audible and visual alarms in every cargo hold and in the spaces forward, fitted at the aft end of the holds; and regulation 13, the availability of pumping systems for those forward spaces.
Regulation 12 is the direct descendant of Chapter 5. The casualty that chapter worked through was No.1 hold flooding and the ship going down by the head, and the arithmetic showed her stability all but untouched while it happened. Nothing on the bridge would have told anybody. The water level detector exists because there is no other way to know.
9.9 The master’s authority
The terminal representative is responsible for the terminal’s side of the operation. The master is responsible for the ship, for the loading plan and for the safety of the operation as it affects her, and he may stop it at any time, for any reason, without arguing about it first. There is no provision anywhere in the Code for a master who is overruled. What there is, and what makes the authority usable, is a requirement that the means of stopping be agreed before the operation begins and that it work.
Chapter 9 in seven lines
- The enhanced survey programme (1993) deals with the steel, SOLAS chapter XII (November 1997) with the ship and the BLU Code (the same month) with the operation.
- The shipper must supply the cargo information required by SOLAS chapter VI before loading.
- The plan is agreed in writing before cargo handling begins and must keep her inside her stress limits at every stage, not only at the end.
- Sequence matters as much as tonnage: the agreed plan keeps the trim inside 1.29 m, loading one hold at a time from forward reaches +7.96 m.
- She sheds 0.2364 m³ of ballast a tonne, so with 1000 m³ an hour of pumps she can take no more than 4230 tonnes an hour.
- Alternate hold loading raises the KG deliberately, here by 1.087 m, and is paid for in tank top loading and shear force at the bulkheads.
- The master may stop the operation at any time. The Code makes no provision for his being overruled.
Test yourself
Questions
- State the three instruments adopted in 1997 in response to the bulk carrier losses, and what each of them addresses.
- State the information a shipper must supply to the master before a solid bulk cargo is loaded, and explain the significance of the IMSBC Code groups A, B and C.
- Describe the loading plan required by the BLU Code: who prepares it, who agrees it, what it must contain and what happens when it needs to be changed.
- Explain what is meant by the requirement that the plan must keep the ship within her approved stress limits at any stage of the operation, and why the words at any stage are the important ones.
- MV Ninja loads 24797 t of cargo while shedding 5862 m3 of ballast, with pumps delivering 1000 m3 an hour. Calculate the maximum loading rate she can sustain and explain what should appear in the loading plan as a result.
- A terminal proposes to load a five hold bulk carrier one hold at a time working aft from No.1. State the objections to this and describe the consequences for trim, for the ship’s ability to shift along the berth, and for the hull.
- Explain why a ship becomes tenderer as she loads a homogeneous cargo and deballasts, and why this makes the last pours of a sequence the most important to get right.
- Explain the purpose of alternate hold loading with a dense cargo, and state two penalties that are incurred by adopting it.
- State which regulations of SOLAS chapter XII apply to a bulk carrier of less than 150 metres in length, and describe what regulation 12 requires and why.
- A ballast pump fails midway through an agreed loading plan. State what the master should do and what the BLU Code requires before loading may continue.
Looking ahead
Every table in this chapter has a column that was not printed. Against each of those fifteen pours there is a shear force and a bending moment, and it is those, not the trim, that decide whether a sequence is safe. Chapter 10 builds them: the weight at every point along her length, the buoyancy at every point along her length, the difference integrated once to give the shear force and again to give the bending moment, and the two limit curves, harbour and sea, the answer must stay inside. It is the calculation the loading instrument does, and doing it once by hand is the only way to know what the instrument is telling you.