Wednesday, 3 February 2016

CONDITION OF THE WARATAH WRECK?

What could one expect to find of the Waratah wreck more than 100 years on?

The preservation of steel wrecks depends on a number of factors:

  • the wreck becoming covered in sand or silt - tends to be preserved far better. There is a great deal of silt output by both the Umzimvubu and Nkadusweni Rivers. The challenge would be using a magnetometer or sub-bottom sonar imaging, effectively.
  • the salinity of the water the wreck is in - reduced salinity = reduced rusting. 
  • the level of destruction involved in the ship's loss - if there was indeed an explosion, this could have a significant impact on how much 'intact' wreckage lies on the sea floor and the extent of the scatter field.
  • whether the components or cargo of the wreck were salvaged - I cannot help wondering if the wreck has already been discovered and subjected to illegal salvage??
  • whether the wreck was demolished to clear a navigable channel - not applicable.
  • the depth of water at the wreck site - generally the deeper, the better the preservation due to decreased oxygen levels and temperature (exception: SS Yongala). Read further...
  • the strength of tidal currents or wave action at the wreck site - the waters off Cape Hermes are well known for powerful currents and wave action - detrimental to wreck preservation.
  • the exposure to surface weather conditions at the wreck site - not applicable.
  • the presence of marine animals that consume the ship's fabric - there is no doubt this is a significant factor, including shipworms, destroying wooden components.
  • temperature - warmer, less favourable.
  • the acidity (or pH), and other chemical characteristics of the water at the site - any information on this?

The above-mentioned, especially the stratification (silt/sand sediments piled up on the shipwrecks) and the damages caused by marine creatures is better described as "stratification and contamination" of shipwrecks. The stratification not only creates another challenge for marine archaeology but also a challenge to its primary state, the state that it had when it sank.
Stratification includes several different types of sand and/or silt, as well as tumulus and encrustations. These "sediments" are tightly linked to the type of currents, depth, and the type of water (salinity, pH, etc.), which implies any chemical reactions that would lead to affecting the hypothetical/possible main cargo (such as wine, olive oil, spices, etc.).
Besides this geological phenomenon, wrecks also face the damage of marine creatures that create a home out of them; primarily being octopuses and crustaceans. These creatures affect the primary state because they move, or break, any parts of the shipwreck that are in their way, thereby affecting the original condition of amphorae, for example, or any other hollow places. Finally, in addition to the slight or severe destruction marine animals can create, there are also "external" contaminants, such as modern-day commodities, or contemporary pollution in bodies of water, that as well severely affect shipwrecks by changing the chemical structures, or even destroying or devastating even more of what is left of a specific ship.
Steel and iron, depending on their thickness, may retain the ship's structure for decades. As corrosion takes place, sometimes helped by tides and weather, the structure collapses. Thick ferrous objects such as cannons, steam boilers or the pressure vessel of a submarine often survive well underwater in spite of corrosion.

This paragraph gives us an important clue. Steam boilers might be the only way of initially identifying the wreck of the Waratah. One assumes that the five boilers listed under specifications would be cut and dried. However, boilers might have exploded either on the surface or while going down, destroying identifiable integrity.

Propellerscondensershinges and port holes were often made from non-ferrous metals such as brass and phosphor bronze, which do not corrode easily.

These would certainly be Waratah-identifying objects to look for if an ROV were able to operate within the powerful Agulhas Current and turbidity off Cape Hermes.

  • Iron-based metals corrode much more quickly in seawater because of the dissolved salt present; the sodium and chloride ions chemically accelerate the process of metal oxidation which, in the case of ferrous metals, leads to rust. Such cases are prominent on deep-water shipwrecks, such as the RMS Titanic (which sank in 1912), RMSLusitania (which sank in 1915), and the Bismarck (which sank in 1941).[citation needed] However, there are some exceptions, the RMS Empress of Ireland lies in the saltwater portion of the St. Lawrence River, but is still in remarkably good conditions.[8]
  • Unprotected wood in seawater is rapidly consumed by shipworms and small wood-boring sea creatures.[9] Shipworms found in higher salinity waters, such as the Caribbean, are notorious for boring into wooden structures that are immersed in sea water and can completely destroy the hull of a wooden shipwreck (or the wooden (teak) trimmings of the upper decks).
  • Catastrophic explosion (e.g., HMS Hood), steamship boilers often explode when water covers them during the process of sinking.
  • Fire that burns for a long time before the ship sinks (e.g., MS Achille Lauro) - this is a very real consideration in the light of Captain Bruce's observation that the Waratah was on fire before she went down.
  • Foundering, i.e., taking in so much water that buoyancy is lost and the ship sinks (e.g., the RMS Titanic and the HMHS Britannic); some ships with a dense cargo (e.g., iron ore) may break up when sinking quickly and hitting a rocky seabed - one might be looking for an object 465 ft. in length, roughly 10 000 tons, when in point of fact one should be looking for sections of the 'broken up' ship.

On the seabed, wrecks are slowly broken up by the forces of wave action caused by the weather and currents caused by tides

There is no doubt of this factor off Cape Hermes.

Extreme cold (such as in a glacial-fed lake), Arctic waters, the Great Lakes, etc. slow the degradation of organic ship materials. Decay, corrosion and marine encrustation are inhibited or largely absent in cold waters.

Unfortunately this is not the case in the shallow waters off Cape Hermes. But all is not lost:

At depths less than 100 m off the Wild Coast in summer months, the predominant Agulhas Current is warm and the salinity significantly reduced (decreased rusting). The significant river runoff - Umzimvubu and Nkadusweni - contributes to the decreased salinity. There is, however, a high salinity tongue between 150 and 200 m. Generally speaking there is a tendency to lower salinity the closer one approaches shore. This body of water is also associated with a shallow oxygen minimum (equals reduced rusting). 

Although the water due to the Agulhas Current is relatively warm (17 degrees), there are daily variations up to 5 degrees due to shear-edge eddies relating to the Continental Shelf margin.Sediment bedforms show that the dominant direction of the water movement off Hermes at ocean floor level over the shelf is with the Agulhas Current (1 m/s). At least one would be dealing with only one direction current.  

Shipwrecks are a potential substrate for deep-water coral communities:

Recent studies suggest that deepwater reef ecosystems may have a diversity of species comparable to that of coral reefs in shallow waters, and have found deep water coral species on continental margins worldwide. One of the most conspicuous differences between shallow and deep water corals is that most shallow-water species have symbiotic algae (zooxanthellae) living inside the coral tissue, and these algae play an important part in reef-building and biological productivity (strengthening the overall structure)

• Galvanic exchange results from the presence of different metals in contact with seawater. Metals can be classified into an “Electromotive Series” according to the strength with which they “hold on” to their electrons. Metals higher in the Series tend to draw electrons away from metals that are lower in the Series. When two metals with different electromotive strengths are connected by an electrolyte (such as salt water), electrons will flow from the metal lower in the electromotive series, causing this metal to form oxides or other compounds in a process we know as corrosion (this is also the process through which batteries produce an electric current). Besides iron in the hull and elsewhere on the vessel, steel shipwrecks contain many other metals such as bronze and brass that are higher in the Electromotive Series than iron. 

As a result, the steel in the hull is degraded as iron is replaced by other compounds formed through galvanic exchange. The integrity of the hull structure can be preserved through this process.

 Rusting is an oxidation process whose primary product usually is Fe(OH)2 , but iron can react with oxygen and water to produce other products including Fe(OH)3 (hematite), Fe3O4 (magnetite), and Fe3O4•H2O (hydrated magnetite). Only iron and steel rust; other metals corrode.

Rusticles are structures produced by complex communities of bacteria and fungi that biodegrade shipwrecks. Rusticles superficially resemble icicles or stalactites, and are built up in ring structures that are highly porous with channels and reservoirs that allow water to flow through. Up to 35% of rusticles’ mass consists of iron compounds (iron oxides, iron carbonates, and iron hydroxides). The remainder is biomass of bacteria and fungi.

Rusticles grown in laboratories have been found to continuously release a red, powder-like material as well as a yellowish slime. The iron content of these materials is 20 ± 5% and 8 ± 3% respectively. Daily iron released from rusticles was between 0.02% and 0.03% of the rusticles’ biomass. So the amount of iron released by a rusticle biomass of 1,000 tons would be between 0.2 and 0.3 tons per day: 0.0002 • 1,000 tons = 0.2 tons per day 0.0003 • 1,000 tons = 0.3 tons per day So, to consume 40,000 tons of iron, a 1,000 ton biomass of rusticles would require between 365 and 548 years: (40,000 tons) ÷ (0.2 tons/day) = 200,000 days = 548 years (40,000 tons) ÷ (0.3 tons/day) = 133,333 days = 365 years

Rusticles are extremely delicate and can disintegrate on touch. If we are to apply this calculation to the Waratah wreck of some 10 000 tons, given the rusticle biomass example is 1000 tons, it would take about 114 years to consume all the steel. The Waratah has been missing for 106 years, which does not leave very much of the wreck. Rusticles form quicker in warmer waters which is a negative factor in the case of the Waratah wreck.

However, on a brighter note, The SS Yongala, steel steamship, foundered in 1911, off Cape Bowling Green, Australia, and lies in relatively shallow, warm waters:


SS Yongala
The Yongala lies in the central section of the Great Barrier Reef Marine Park, approximately 12 nautical miles east of Cape Bowling Green and 48 nautical miles south-east of Townsville.
The wreck sits intact and proud on the seabed, listing to starboard at an angle of 60 to 70 degrees. The upper sections of the wreck are approximately 16 metres below the surface with a site maximum depth of 30 meters.
The Yongala was an early 20th century interstate coastal steamer sunk during cyclonic weather in March 1911. It supplies a snapshot of Edwardian life in Australia and is now one of Australia's most highly regarded and popular wreck dives. It is a site of national significance and a substantial artificial reef that supports a great diversity of fish life with 122 recorded fish species in an established community around the wreck. The wreck is also the final resting place of the 122 passengers and crew who were aboard the Yongala on her 99th and final journey.

I am certainly no expert in the complicated field of wreck survival and preservation, but these extracts give us some insight into the subject and challenges that confront further searches for the wreck of the Waratah - particularly if she lies off Cape Hermes. I choose to hold onto the thought that she might be as well preserved as the SS Yongala.


Yongala wreck map.





Wikipedia and,
https://books.google.co.za/books?id=BRVGAAAAQBAJ&pg=PA106&lpg=PA106&dq=agulhas+current+salinity&source=bl&ots=rsdpK9K7MK&sig=vJF9Y1XgHxq8oOq9sPfhsDuseIU&hl=en&sa=X&ved=0ahUKEwid9NfclNvKAhVEaRQKHcbtAe0Q6AEINDAD#v=onepage&q=agulhas%20current%20salinity&f=false

oceanexplorer.noaa.gov/explorations/08lophelia/background/edu/media/eating.pdf

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