Sunday, 8 November 2015

HEELING TEST.

Captain Ilbery, the commodore of the Blue Anchor fleet, and the holder of a certificate of competency as master, No. 24380, supervised the ship's construction in the later stages. When completed he was to take command of her. He was present on the 10th of October, 1908, when the ship was being prepared for the heeling experiment, but before the actual experiment was undertaken he went away. It was conducted by Mr. George Barrie, chief of the scientific department of Messrs. Barclay, Curle, & Co. 

Mr. Barrie gave an account of the way he performed the experiment, and the precautions he took to ensure its accuracy. From his account it would appear that all proper measures were adopted to obtain the correct vertical position of the centre of gravity of the vessel in her then condition. The vessel was about to go on trial and was practically complete, all refrigerating machinery on board, insulation finished, and boats in place. it was estimated that weights yet to be put into the ship amounted to 20 tons. The metacentric height was found to be .556 feet. From the curve of transverse metacentres the metacentre in this condition was ascertained to be 26.38 feet above the base line, the centre of gravity thus being 25.82 feet above the base. Calculations were made to find the effect on the centre of gravity of removing weights, including water ballast in Nos. 3 and 8 tanks, which were to come out of the ship, and of adding the 20 tons above referred to. The metacentric height of the ship in a light condition, viz., vessel empty except that 300 tons of fresh water, stores and crew were on board, was then shown to be .26 feet.

It remains a mystery why Captain Ilbery was not present for the heeling experiment. Surely it would have been important for the future commander of the Waratah to be present? No reason was given for his absence. Perhaps the exercise was routine and Captain Ilbery, having 'supervised the ship's construction in the later stages', had enough insight into the stability of the Waratah? The teething problems experienced on the maiden voyage with regard to cargo stowage and ballasting, suggest otherwise. Perhaps Captain Ilbery anticipated the short-comings and did not want to be part of the confirmatory heeling experiment. Makes one wonder how he felt about commanding the flagship....

The heeling experiment was revealing. In her initial condition, the Waratah was fully ballasted (assumed), weights added to represent the completed vessel, but without cargo and full component of coal. The GM of 0.556 ft. almost complied with the average GM for a cargo / passenger vessel of her size, deep, fully loaded and certainly greater than the figure quoted for light (without coal and cargo):  

In the following reference  (books.google.co.za/books?isbn=3861950936) metacentric heights are quoted for an ocean going steamer (525 ft in length) circa 1908:

- light                                                             0.4 ft

- loaded to lower deck                                     0.7 ft

- deep, fully loaded                                         0.62 ft
  

The heeling experiment then determined what the Waratah's GM would be with significant ballast water removed, and the figure of 0.26 ft. illustrated that in this condition, the Waratah was significantly less stable than the average figure of 0.4 ft. But we have to remember that the Waratah departed Durban with a GM of 1.5 ft. which is significantly greater than the quoted 0.7 ft.The secret of the Waratah's GM stability lay in the weight of cargo, deeply loaded. The impression of top heaviness was confirmed by the GM, in very light condition, but dispelled once the Waratah departed port with her full component of cargo and coal.



Note that in this diagram, a positive value is equated with stability. The Waratah never recorded a negative value, to my knowledge.

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