Sunday, 6 December 2015

LEAD CONCENTRATES OVER STRESSING THE HULL.

2. Possible change at Adelaide in the disposition of cargo loaded at other Australian ports. Alexander Inglis, harbour master, detaining officer, and shipwright surveyor, in the employ of the Marine Board at Adelaide, said in his deposition that he had known cargoes to be considerably altered there to make room for Adelaide freight, but had heard of nothing in this respect so far as the "Waratah" was concerned; no other deponent said anything on this point.

Further confirmation that the issue of cargo details and weights was a grey zone. 'Altered' could refer to discharging excess cargo or readjustment of stowage, allowing for heaviest component, lowest down. 

3. The absence of complete details as to the disposition of cargo, especially as to its height in the ship. The method adopted by Mr. Larcombe was, after obtaining the distribution of weight in the manner already described, to obtain the volume of each parcel of cargo by calculations based upon information collected from persons experienced in the Australian trade. This seems the only method available in the circumstances, but shows occasional discrepancies when its results are compared with the depositions. Such, for example, is the case with the concentrates loaded at Adelaide. Arthur James Fisher, the assistant manager of the stevedoring company there, deponed that the concentrates were 8 feet deep all over the hold, and this figure was corroborated by John McArthur, the foreman stevedore. If this were correct it would necessitate taking the concentrates higher than the position assumed by Mr. Larcombe, who took their density such that 1 ton would occupy 12 cubic feet, being supported in this by a statement of McArthur that they go 11 cubic feet to the ton. The two statements made by the latter are irreconcilable, and there is little doubt that the height of 8 feet is excessive.

Lead concentrates shifting, causing the Waratah to become unstable in a severe storm, 28 July, remains one of the prominent theories for the loss of the flagship. This paragraph seems convincing in a number of respects; we have three witnesses who claimed, under oath, that there was a significant component of lead concentrates on board. We have to take this as given. The concentrates were loaded presumably in the lowest level hold, 11 or 12 cubic feet to the ton, 8 feet high. This represents a very significant dead weight component, which contributed favourably to the overall GM of the Waratah.  

However, lead concentrates loaded as such (8 ft. deep), would have created its own set of problems:

Carrying solid bulk cargoes safely - Lloyd's Register

Distribution and stability You must also make sure that cargoes are properly distributed throughout the ship’s holds to provide adequate stability and ensure that the ship’s structure is never overstressed. Information can be found in the ship’s stability information booklet or you can use loading calculators if they are available. The Master will need to calculate the stability for the anticipated worst conditions during the voyage as well as for departure and demonstrate that the stability is adequate.

This very important first point alludes to stability and hull stress. One assumes, based on the fact that the Waratah left Durban without a list that the lead concentrates were evenly stowed. However, overstressing of the hull has never been far from my mind. I have no doubt the Waratah was too heavy, including this lead component. She had already been subjected to excessive forces when taking the ground at Port Adelaide and there was no comprehensive way of assessing hull damage at Adelaide and subsequently when the Waratah arrived at Durban. The large steamer astern of the Harlow disappeared very quickly and a plausible explanation points in the direction of an overstressed, and fire-damaged hull, failing.

What is liquefaction and how does it affect cargo? Liquefaction means that a cargo becomes fluid (liquefies). On ships, this happens when the cargo is compacted by the ship’s motion. Cargoes which are prone to liquefaction contain a certain quantity of moisture and small particles, although they may look relatively dry and granular when loaded. Liquefaction can lead to cargo shift and even to the capsize and total loss of the ship, and can occur even when cargoes are cohesive and trimmed level.

Lead concentrates, depending on retained moisture, can liquefy causing weight shift and destabilization. This remains a highly plausible explanation for the Waratah foundering, if she did not come about and instead, steamed into the storm of 'exceptional violence'.

To control the risks of liquefaction, Group A cargoes (including lead concentrates) are tested to determine their Transportable Moisture Limit (TML) and their actual moisture content before they can be shipped. The TML is the maximum moisture content considered safe for carriage. The actual moisture content of the cargo must be below the TML.

I doubt whether the technology existed in 1909 to assess the moisture content of lead concentrates, but there is no doubt in my mind that masters of vessels were aware of this problem and knew how to manage it. The liquefaction process was not likely to be homogenous, requiring regular monitoring of the holds in question. 






a





b



Do we know how fine the lead concentrates were? Liquefaction was more likely to have occurred with the concentrates in image a.




http://www.lr.org/en/_images/213-35783_IMSBC_Code_pocket_guide_final_web_tcm155-247233.pdf

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