Wednesday, 9 March 2016

SUPERSTRUCTURE, FORECASTLE, POOP AND STRUCTURAL INTEGRITY.

She had three complete steel decks (lower, main, and spar), a plated bridge deck and forecastle, and a partly plated poop. There were in addition a promenade deck and a boat deck, of the same length as the bridge. The bridge house was 175 feet 6 inches long, the forecastle 84 feet 10 inches long, adapted for the accommodation of the crew, and the poop about 108 feet long. 


The poop was closed by a steel bulkhead at its forward end, with two watertight doors. The bridge had a steel bulkhead at the forward end.


The forecastle had a partial steel bulkhead at each side, with weather boards between these and the forward corners of the refrigerator house. The forward well was 73 feet in length, and had at its forward end a refrigerator house 28 feet long and 34 feet wide; the after well was 30 feet long. 



Superstructures are defined as those erections above the freeboard deck (spar) which extend to the ships's side. Referring to the bridge deck as bridge house implies that the bridge, promenade and boat decks were within the line of the Waratah's side. It is important to note that the bridge had a steel bulkhead at the forward to withstand forces of seas shipped. Of great structural importance is the strength of the vessel where superstructures and in particular the bridge deck terminates (non-continuous). One assumes that the plated bridge deck accounted for these structural needs, but I doubt it. 

The Waratah's superstructure which exceeded 15% of her length, extended within 50% of her length, amidships contributed significantly to structural strength ie scantlings consistent with the main hull strength members (hull plate thickness). If the plating quoted did not meet these requirements we have another area of compromised structural integrity. 

Waratah's superstructure accounted for 175.5 ft. which is 38% of her length. Ideally the superstructure should have equated to 50% (232.5 ft.) of length. Most of the steamers with significant top hampers at the time had superstructures equating with 50%. This reduced top hamper and the generous use of weather boards could have contributed to the reduced budget price of 139 900 pounds. Further to this if a longer superstructure had been fitted, stress distribution would have been linear contributing to the strength of the spar deck (which was already compromised). A longer superstructure component would also have contributed to buoyancy and compensated for a relatively low freeboard.

Waratah's forecastle was 84 ft. 10 in. (exceeded 7% of total length) and partially plated which is of significant concern. It should have been been plated aft instead of weather boarding. The forecastle length came to within 50% of Waratah's length amidships, suggesting that additional stiffening was required. 

The poop had the required steel bulkhead at its forward end. 

It is important to note that expansion joints (transverse cuts) should have been included in the superstructure decks to alleviate the hull bending stresses. Sometimes expansion joints could be the source from which cracks initiated. We know that boltheads broke and a ladder spanning three decks broke in two. This could have been a manifestation of lack of expansion joints or a reflection of the inadequacy of spar and bridge deck strength. I am inclined to believe the latter. 

Waratah was a flawed design compromised in terms of quality of construction, inadequate scantlings (my opinion), a controversial spar deck which I do not believe was the strength deck it should have been and a superstructure which should have spanned at least 50% of her length, amidships. 

I have selected a few steamer profiles illustrating significant top hampers which accounted for at least 50% of the total length - but not in the case of Waratah - note how proportionally excessive her forward well and forecastle were (157 ft. + / 34% of length). 














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