Posted by: Rob Viens | July 18, 2013

Hidden Ballast and Transatlantic Stowaways

By mid July the work on the Unicorn had been completed and the name was officially changed to the Adventure – after the command vessel that the Beagle sailed with on its first voyage (see The First Voyage of the Beagle). This milestone must have been exciting for Darwin, since it meant that he would soon be able to leave Uruguay and have a chance to explore new terrain.  On the 17th he wrote:

“The Schooners name has been changed into that of “Adventure”, in commemoration of the Corvette employed in the former voyage with the Beagle, & likewise as being the name of one of Captain Cooks ships & therefore classical to all Surveying vessels.” (July 15/16/17)

An interesting little side story occurred as the new ship acquired the iron ballast that was left behind on the last voyage by the Adventure.  Darwin tells the story:

“All hands have been employed in getting her masts in & bringing on board her iron ballast. — There is a curious little history attached to this ballast. — the old Adventure having too much buried 30 tuns in the Island of Guritti. The Brazilians when they were in possession, had heard of it & made great efforts to find the spot.— The sepulcre was close to the well; so public a place having been chosen quite baffled the Brazilians; So that the ballast remained to be very serviceable to the young Adventure.” (July 15/16/17)

Ballast is the material generally placed in the lower section of a ship to provide stability.  Imagine a paper boat floating on the water.  Now add a little gravel to the boat – the extra weight forces the boat to ride a little deeper in the water and makes it less likely to roll or tip over.  The same concept applies to a large ship. The cargo in a cargo ship can serve the role of ballast, but once it is offloaded the ship must take on ballast to maintain that stability.  In this way, a lot of water and stone have been shipped around the world. Ballast is not only carried by ships – hot air balloons and submarines use the additional and removal of weight to add stability and to control the elevation of the balloon/sub in the air/water.

Ship expelling ballast water (from MIT Sea Grant page, photo by David Smith)

ballast water

Historically ships used sand, rock or other heavy substances (such as iron) as ballast.  In modern times most ships use seawater as ballast, since it is easy to pump it in or drain it back out.  On the surface this seems innocent enough – carrying seawater from one part of the world to another (after all it is all one big ocean). But it is important to remember that the seawater is often taken from and discharged in shallow coastal waters or inland seas. Ultimately, this has led to the introduction of many very aggressive invasive species, which normally would not have been able to cross the open ocean.  For example, comb jellies (Mnemiopsis leidyi) expelled in the ballast water of cargo ships in the Black Sea have quickly taken over the ecosystem.  Within about 15 years they accounted for over 90% of the biomass in the Black Sea – leading to the loss of many of the native species.  In exchange, ballast water from the Black Sea and Caspian Sea carried zebra mussel larva to the Great Lakes.  Since they were introduced in 1988 they have quickly taken over the lakes and moved into waterways across the United States.

Zebra mussels distribution in 2010 (Click the map to see the spread animated over about 20 years) – From the NationalAtlas.gov:

zebra mussel map

The US Fish and Wildlife Agency estimates the economic coast of the introduction of zebra mussels alone has been in the range of $5 billion. Invasive species are annually a multibillion dollar expense for the US alone. Estimates for annual global costs fall in the trillion dollar range and above – far exceeding the total global coast of natural disasters.

The concept of ballast is not isolated to human engineering – you can also find examples in the animal kingdom.  For example, the chambered nautilus (a cephalopod) controls it buoyancy by alternatively pumping water or air into its spiraled “chambers” within the shell.  Adding water (as a form of ballast) will cause the nautilus to dive, while replacing the water with air (removing ballast) will cause it to rise.

Chambered nautilus (from the Monterey Bay Aquarium)

chambered nautilus

I can only speculate as to why the original HMS Adventure left its ballast behind (a more nautical minded reader should  feel free to pipe in).  I would suspect that it was either because (a) the ship was carrying a lot of cargo/extra weight on the way back and did not need it or (b) the ballast served a more important role while surveying the coast, and was not needed when the ship crossed back across the Atlantic. In any case, the iron was certainly of some value, so it was hidden rather than just randomly dumped.  In the end, it made for an interesting link between the two Adventures. (RJV)

PS – The ballast was hidden on Gorriti Island – more on that tomorrow…

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