Wednesday, 4 September 2013

Waratah - stability and ballast.

Ballast is material (coal or water in this case) used to provide stability for a ship.  Ballast remains below the water line in order to counter-balance the weight of the vessel above the waterline.Too much ballast and the operation costs for the ship mount. Not enough ballast  increases the probability of listing (heeling) over too far, the vessel struggling to right herself, and in extreme cases, capsizing.
The Board of Trade Inquiry took particular interest in the question of ballast and the Waratah.

The following is an extract:

'Clause 5 of the specification contained the following provisions: "Vessel to be able to stand and shift without any ballast, and to be designed, if possible, to go to sea with permanent coal and water ballast only."

'Stand and shift' without ballast applies to movement within the harbour environment with the assistance of a tug boat.  Permanent coal and water ballast implies that the water and coal used for ballast would thus be unavailable for other uses.  Cargo can form part of ballast and the design request in the case of the Waratah was that it not be a necessity.'

The inquiry went of further to say:

'Considerable confusion was introduced into the discussion of this clause, and the correspondence upon it by a loose use of the phrase "in a light condition," or of the word "light." Sometimes it was used as referring to the first limb of the foregoing provision, i.e., "vessel to be able to stand and shift without any ballast," and sometimes as referring to the second condition, i.e., going "to sea with permanent coal and water ballast only." Mr. F. W. Lund unhappily introduced a further complication by using the expression as meaning "with water ballast but without coal"; and Mr. Barrie in his evidence referred to "a" light condition, which meant vessel empty, except that 300 tons of fresh water, stores, and crew were on board.'

This paragraph is loaded (excuse the pun).  The Waratah was regarded by many, those who sailed in her and those who observed her, to be top heavy (unstable) and inclined to have a slow roll with a significant list and longer than expected time to right herself again.

These accusations blatantly contradicted Lloyd's of London, who gave her the classification "+100 A1" – their top rating, granted only to ships Lloyd's had inspected and assessed throughout the design, construction, fitting out and sea trials, over and above the two valuations and inspections. however, there is far more to this issue than meets the eye. I shall return to these details and the controversy.

Of note in the confusion surrounding the definition of 'light' and its implications in the context of stability, the primary stakeholders (Mr Lund and Mr Barrie) contradicted one another in terms of the general definition of 'light'.

It seems to me that by implying that the Waratah could still remain stable without the prerequisite coal ballast component and Mr Barrie went on to state that the Waratah would remain stable even with 300 tons of water, stores and crew, attempts were made to convince the court that stability was not an inherent problem of the Waratah. The Waratah was fully loaded and ballasted for her final voyage which renders the nit-picking regarding various conditions of loading irrelevant to the issue at hand.

However, the Inquiry took charge of the issue:

'To avoid continual repetition, the court, throughout this report, will speak of the ship when without coal or water ballast as "in the extreme light condition," and when with permanent coal and water ballast as "light." If occasion arises to deal with other light conditions, they will be set out in detail.'

'It seems that the owners desired the ship to be capable of going to sea light. But they were also desirous of having provided a space on the spar deck which could be used as a bunker, or for the provision of temporary accommodation when conveying emigrants or troops, or for any other purpose to which it might be desired to put it. As a matter of fact the space is included in all the plans as a permanent bunker, and it is to be understood that in this report it is always so included, unless the contrary is stated.'

'Having the additional bunker space in mind, the builders are of opinion that they could not guarantee the ship should go to sea with water ballast and permanent coal only, that is if they were to fulfil all the other conditions as to dead weight capacity, dimensions, and general accommodation; and they would not accept the paragraph providing for the ship going to sea light without the insertion of the words "if possible."

'Correspondence which passed in August, 1907, shows that the question of sending the ship to sea light was then under discussion, and there are indications in other letters that the matter had received attention at a still earlier date. The genesis of this condition will be dealt with at a later stage of the report.'

These paragraphs of the inquiry raise a very significant issue with regard to the Waratah's stability and reputation for being 'top heavy'. The bunker in question located on the spar deck if loaded with either passengers or coal would potentially and significantly impact on the weight of the vessel above the waterline, thus contributing to the allegations of her being 'top heavy' and unstable. This vital piece of information was further fleshed out in the inquiry as follows:

'3. When loaded to capacity with cargo of 40 cubic feet to the ton in holds, and 80 cubic feet to the ton in 'tween decks, ship (Waratah) has a G.M. of about 4 1/2 inches. This is increased to 10 inches by burning out the 614 tons of coal in bridge.'

G.M. is, as I have mentioned, the metacentric height between the centre of gravity and the metacentre.  The metacentre is calculated by the intersection of the two vertical lines: a line through the centre of buoyancy when the ship is in equilibrium (upright) and a line through the centre of buoyancy when the ship is listing to one side. The distance of this intersection above the centre of gravity of the ship is an indication of its stability.

This is made simpler for us by the Inquiry statement that the GM increased by as much as five and a half inches (stability improved) once the coal in the spar deck was burned.  If one interprets this in terms of percentage, the implication is very significant indeed.  Coal loaded to capacity in the spar deck bunker could decrease the stability of the Waratah significantly.

290 tons were allegedly loaded in the spar deck bunker at Durban on 26 July, 1909, thus reducing the stability of the Waratah by a significant factor, one which will be explored in detail in future posts.
This vital section of the inquiry concluded with the following two paragraphs:

'4. When loading and coaling at the same time, tanks must be full and all coal except bridge space and trunk may be filled; but before the bridge space may be filled the 1,200 tons cargo mentioned in (2) must be shipped. After this point the tanks may be gradually emptied as the remaining cargo goes aboard.'

'5. It is strongly recommended that vessel should have a G.M. of 10 inches when going to sea'

The Waratah was fully loaded with cargo (roughly 9 000 tons, although officially quoted as about 6 400 tons) at Durban and her metacentric height was at least .75 ft, which is stable.

The techno-buffs are welcome to have fun with this diagram showing the various vertical lines at stake in the calculation of the metacentric height.

For the rest of us, let's take a break for now...

This post is an oversimplification of the factors surrounding Waratah's stability in various conditions of lading. These factors are explored in far more detail in future posts.

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