SS Central America paddlewheel

Salvaging the wrecked 'Ship of Gold' using latest ROV technology

The doomed SS Central America, dubbed the ‘Ship of Gold’, had lain untouched for over two decades. Since April 2014, salvage experts have been retrieving its high-value cargo using the latest ROV and vessel technology. What secrets have they uncovered so far?

In September 1857, during a hurricane 160 miles off the coast of North Carolina, the 85m copper-sheathed paddlewheel steamship SS Central America foundered and sank 2,200m under the Atlantic Ocean. The wooden-hulled wreck, dubbed the ‘Ship of Gold’, was returning from one of many trips from Panama to New York picking up travellers from the Californian Gold Rush town of San Francisco. It was carrying many tonnes of gold; some reports say up to 21 tonnes of the precious metal, including a mysterious ‘secret’ army cache.

She sailed out of her last port of call in Havana with 578 passengers and crew on board, before running into a hurricane. The women and children were rescued, but some 426 remaining passengers and crew went down with the ship. So much gold was on-board that her sinking contributed to the first global financial crisis. Many New York banks collapsed following the loss of the shipped gold, with a ripple effect travelling around the global banking community.

The fugitive discoverer

The history of the wreck is fraught with financial and legal shenanigans. In a story with more twists and turns than a Hollywood movie plot, the original discoverer of the wreck, Tommy Thompson, raised over $12m in the mid-1980s from investors who were to share in the proceeds from the sale of the wreck’s gold.

The site of the wreck was originally discovered in 1988 using side scan sonar, with the ship’s paddle wheels showing clearly. Her identity was confirmed when the first coins and gold bars were raised to the surface. Thompson and his team salvaged almost three tonnes of gold from the legendary wreck on the site between 1988 and 1991. However, none of the value of the recovered treasure was returned to the original investors in the expedition.

In 2012, Thompson failed to make a court appearance and seemed to have vanished. He disappeared after selling gold bars and coins to a California mint for $52 million. His trail went cold in either a rented mansion, or a trailer park in Florida, depending on whose version of events is to be believed. The 61-year-old elusive entrepreneur and his girlfriend were sought by US Marshals for two years before being discovered in a Florida hotel suite only 80 miles from where they were last seen. The couple had been paying all their bills in cash.

Investors, including a Columbus Ohio newspaper magnate and a prominent car dealer, say they are due millions. Also pursuing the elusive Thompson through the courts are the unpaid crew and technicians from the expeditions.

Deep sea salvagers

After Thompson disappeared, a Columbus court appointed a receiver to act on behalf of the investors. Archaeological marine salvage experts Odyssey Marine Exploration were contracted to retrieve gold and other high-value cargo, plus remaining artefacts from the site. The second wave of recovery of material from the wreck, which had been unvisited since 1991, began in April 2014.

Andrew Craig is a senior project manager for Odyssey and former mechanical engineer. He says: “Working on shipwrecks is one of the most fascinating jobs around. Although it requires long hours and extended periods at sea, to be part of a team accomplishing things once thought impossible and seeing objects that have been lost for hundreds of years is very rewarding.”

The team work in two rotating 12-hour shifts when aboard the 76m dynamically positioned (DP) vessel, the Odyssey Explorer. She serves as the mothership for onsite salvage operations, hosting 42 crew including scientists, archaeologists and  technicians for missions of up to 60 days before she needs to return to port. “We can work up to sea state six with equipment in the water, though the thrusters struggle to maintain position above sea state five - up to 4m waves,” says Craig. “Positioning accuracy maintains us in a footprint of less than 50cm using a suite of equipment installed around the vessel, dynamic GPS, gyro compasses and anemometers all feeding into a state-of-the-art control system which sends commands out to the two azimuth thrusters and two tunnel thrusters.”

The eight-tonne ZEUS

Working at 2,200m and at enormous pressure, no human divers are used. The workhorse of the project is ZEUS, an eight-tonne remotely operated vehicle (ROV) highly customised for deep-sea shipwreck exploration.

ZEUS is controlled from the ship via an umbilical cable - containing multiple fibre-optic cables - that carries control instructions to the ROV’s lights, the crucial manipulator arms, the imagery from the HD cameras and the pilot’s eye subsurface. ZEUS’s two arms are seven-function manipulators capable of lifting the weight of an average man. Powerful HMI lights illuminate the pitch-black wreck site for the array of on-board cameras transmitting real-time images from the seabed. The ROV is made neutrally buoyant by stacking its hull with tiny glass globes embedded in non-compressible resin. This also allows the vehicle to withstand the extreme depth pressure.

Accurate navigation around the shipwreck site is critical, especially on such a fragile wooden wreck as the SS Central America. Eight hydraulic thrusters give the expert ROV pilots extremely fine control over the machine’s movements, and an acoustic positioning system, linked to seabed transponders, gives a precise location of the robot at all times.

ZEUS also has a silicon ‘sucker’, which picks up delicate objects such as gold coins, jewellery and even glass spectacles. Everything recovered from the seafloor is recorded into the DATA LOGGER proprietary software, tying items to live visual imagery of the recovery operation, geographical coordinates, and the ZEUS dive information. Very delicate items, such as glass photographic plates or gold jewellery, are placed by the limpet into a drawer on ZEUS containing a proprietary gel that protects from abrasion and any minute damage to surfaces on the way up to the Odyssey Explorer.

Conservation strategies

Each type of object will have a specific conservation plan. Belgian Frederick Van de Walle is director of conservation aboard the ship. He trained at the Royal Academy for Arts in Antwerp, then specialised in marine archaeological conservation.

Van de Walle’s input starts before anything is recovered and he must weigh up the importance of objects versus the cost of conservation. “The way we deal with gold is obviously quite different from textile pouches, a pipe or papers. Gold is the easiest to deal with since it does not degrade at all in salt water,” he explains.

“As soon as an artefact is brought to the surface, we begin conservation treatments to prevent any deterioration. It is important to remove salt and active corrosion products first and the use of cold plasma reduction is looking to be a promising technique.”

The most difficult to conserve are objects made of composite materials, which include leather satchels with metal buckles. “The treasure grabs the most headlines but, for me personally, the delicate glass ambrotype and daguerreotype photographs are the most fascinating finds so far,” Van de Walle adds.
Emergency ‘first aid’ conservation of all recovered artefacts takes place aboard the Odyssey, but final preservation prior to long-term display or sale takes place in a dedicated lab at the company’s headquarters back in Florida.

A large collection of rare ambrotype and daguerreotype photographs were discovered in the wreckage in April - perhaps the property of an early professional photographer returning from making his fortune in the Gold Rush.

Ambrotypes are a short-lived type of photography on glass plates that were only in popular production for about 10 years in the mid-19th century; the Central America plates include many rare images of gold miners. The plates were left undisturbed on the bottom until a safe conservation plan could be agreed, finally being raised in August 2014.

Other artefacts that have been recovered include the ship’s sextant along with articles of luggage, jewellery, a pistol, spectacles and a pocket watch.

Painting a picture

Two pilots drive the ROV - one operates the manipulator arms and the other ‘flies’ the robot, both under instruction from the project marine archaeologist, Neil Cunningham Dobson. “We start with a full pre-disturbance survey using still and video cameras to create a detailed high-resolution photomosaic that is a record of the shipwreck in situ similar to an aerial photograph,” he explains. “The mosaic is a key tool in determining archaeological and project strategies.”

At this early stage of exploration, a bathymetric survey is also carried out to show the underwater topography, and tools mounted on ZEUS’s arms, such as pulse-induction sub-bottom imaging sensors and ferrous anomaly detection equipment, show what lies hidden beneath the surface.

“During this pre-disturbance survey, we were aware of large amounts of coal covering the area. Our team is very nimble and able to adapt tools for specialised needs,” says Cunningham Dobson. “The engineers constructed a rake that helped to carefully relocate the coal into a hydraulically actuated auto-unloading platform on the ROV. When the platform is full, the pilots fly to a sterile area away from the wreck, activate the drawer and push the coal onto the seafloor. It wasn’t difficult to do but was one of the least exciting parts of the excavation.”

Safety and security

The ship’s safe has been located and opened and its contents raised to the surface, but many of the passengers aboard the Central America would have kept their own gold in the form of dust or nuggets in leather pouches.

Over the intervening century-and-a-half most of the containers have disintegrated on the seabed, leaving much sediment to be sifted.

With so much valuable gold and silver as nuggets, ingots and coins being recovered, security is tight aboard ship. Recovered treasure and artefacts are individually tracked and inventoried at all stages of the operation: from the seabed and secure storage aboard ship to final transportation and secure warehousing in Florida. During processing, there are at least two people always present and all of their activities are monitored and recorded by CCTV cameras.

The ‘Ship of Gold’ still holds an estimated $343,000 to $1.4m of gold in 1857 values, which is almost $100m at today’s gold prices. However, this does not represent the value of the rare gold coins and ingots to numismatists. One single coin - a rare $20 double eagle - was sold for $11,750 by Heritage Auctions in 2013. A rare ingot from the original excavations dubbed the ‘Eureka’ bar, cast by Gold Rush assayers Kellogg and Humbert and weighing in at almost 40kg, was sold for $8m in 2001.

Before the Central America discoveries, original Californian ingots were virtually unknown as almost all had been melted down and turned into coins. This year more than 45 further ingots have been recovered. Between April and August 2014, the salvors also raised more than 2,900 gold coins and over 11,500 silver coins.

Bob Evans served as chief scientist on the 1988-1991 expeditions to the SS Central America and later as curator for the treasure recovered. As one of the court’s representatives on the project, he has been aboard the Odyssey Explorer since operations began again in April 2014, cataloguing the gold as it is recovered. “The variety and quality of the coins being recovered is just astonishing,” says Evans. “Of course, there are spectacular $20 double eagles like we found back in the 1980s and 90s. But the wide variety of other denominations makes this year’s recoveries very different from the earlier finds. I have seen what I believe are several of the finest known examples so far. The coins date from 1823 to 1857 and represent a wonderful diversity of denominations and mints, a time capsule of virtually all the coins that were used in 1857.”

It will not be until Odyssey Marine’s archaeological excavations and salvage operations are completed in 2015 or 2016 that all of the secrets of the SS Central America will be revealed, and the final value of the ‘Ship of Gold’s’ cargo is determined. One thing is certain: without the recent developments in ROV and vessel technology, many of its secrets would have remained on the seabed. *

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