潜水艦ハンリー(Hunley)の保存処理

独立戦争時代の潜水艦、ハンリーが引き上げられてから6年が過ぎます。ハンリーは潜水艦としては初めて敵艦を沈めたことで有名です。引き上げられてから、潜水艦内の発掘や保存処理などが行われています。ほとんどの人は、水中遺跡が発掘(引き上げ)されれば後の仕事は楽なように思っているようですが、実は引き上げた後に本当の大変で大切な(また費用がかかる)仕事が始まるのです。
ハンリーの保存にはすでに日本円にして6億円かかっており、またこれから7-10年ほど保存処理に時間がかかります。この間、1年に1億円ほど費用を必要とします。このプロセスを早めるために新しい鉄の保存法などが開発されています。この方法とは、遺物を薬品と一緒にタンクの中にいれ加熱・加圧します。これにより鉄の中に溶け込んだ塩分が本体から外に溶け出すそうです。
どうして単なる潜水艦にこれだけのお金と時間をつぎ込むのかよく聞かれるそうですが、歴史上重要であった潜水艦であるため、それだけ費用を使ってでも完全に保存処理を行い、将来にまで伝えていく努力が必要とのこと。また、テキサスA&Mで保存処理を行っているベル号も10年以上時間をかけて保存を行っていきます。

Hunley preservation complex
Work on Civil War sub will also be costly, could take seven-10 more years
By JOHN MONK
jmonk@thestate.com

Although the Hunley was raised from the ocean almost six years ago, long-term preservation of its salt-infested iron hull isn’t expected to begin until later this year.

“The Hunley turned out to be a much bigger project than I anticipated,” said Robert Neyland, who directed the Hunley project from 1998 to 2001. Now head of underwater archaeology at the Naval Historical Center, Neyland is still involved with oversight of the Hunley project.

“I’m guessing you are probably looking at seven to 10 more years” before the work is completed, Neyland said.

Preserving sunken wrecks like the Hunley is complex, lengthy, costly and uncertain.

“This is why most underwater archaeologists insist that shipwrecks should be preserved in place rather than excavated, recovered and conserved,” Neyland wrote in a 2005 article.

In the Hunley’s case, scientists and politicians determined that if the Hunley were left in place, it might be looted by scavengers. Led by Sen. Glenn McConnell, R-Charleston, South Carolina assured federal officials the state would take care of the Hunley and eventually exhibit it.

Long-term preservation will remove salts from the hull and make the Hunley museum-ready. If the salts are not removed, they will combine with oxygen in the air and turn the Hunley into a pile of rust.

The Hunley sits in a North Charleston conservation laboratory, in a tank of cool water that retards the rusting process. The sub is exposed to air only in short bursts while scientists continue the final exams of its innards.

Originally, Hunley officials said excavating the sub’s inside would take 10 months — which turned out to be an optimistic prediction. The Hunley was not only filled with 10 tons of claylike silt, it contained skeletal remains of eight crewmen, as well as thousands of artifacts.

Thus, it was both a tomb and a wreck, said Hunley senior conservator Paul Mardikian, an internationally respected underwater scientist who has worked on the Hunley since it was raised.

Rarely, if ever, has such a combination tomb/intact wreck been lifted out of the sea, he said. Many wrecks aren’t intact, and few have preserved bodies.

Artifacts in the silt included more than 1,600 bones (from eight complete skeletons), 140 buttons, shoes, clothing, pieces of thread, leather, a watch and a gold coin — some 9,700 items in all, each of which was identified and labeled.

Each kind of material retrieved — bone, leather, cloth, wood and metal — had to be treated differently. Once in the fresh air, those items start to rot, rust or decay.

Most people think that once a wreck is brought up, the hard part is over, Neyland said. That’s when much of the work — and the expense — comes into play.

When the Hunley was raised in August 2000, McConnell already had helped arrange some $3 million in public and private money to ready the lab. It paid for cold-water tanks and an array of high-tech equipment, including a morgue for human remains. Raising the sub and readying the lab cost about $6 million in all.

Since 2000, Hunley work has cost about $1 million yearly. Long-term preservation is expected to cost about the same.

Shortcut possible?

The work has been both high-tech and low-tech. Scientists held the silt in their gloved hands, rinsing it with water to uncover the artifacts. But expensive computers with lasers were used to do three-dimensional mapping of each item before it was removed.

“The level of recording and documentation is exceptional,” Neyland said.

Scientists from many disciplines have participated — archaeologists, geologists, conservators, corrosion experts, mechanical engineers, ocean engineers, soil engineers, forensic anthropologists, physicists, DNA experts, genealogists, and computer and radiation experts.

The long-term preservation will be similar to treatments used for other wrecks. But there is a different recipe for each wreck, based on what the wreck is made of and its particular problems.

In November 2004, Hunley scientists submitted an initial 175-page long-term preservation plan to the U.S. Navy. Before preservation can begin, the U.S. Navy, which owns the Hunley even though South Carolina has custody, must approve the preservation process.

Since then, the Navy has circulated the proposal to 19 experts around the world for comment. This process, called “peer review,” is in its final stages. The Friends of the Hunley foundation declined to let The State see the document. It will be made public once the Navy approves the plan, a foundation spokeswoman said.

Meanwhile, professor Mike Drews of Clemson University, who has been working with Hunley scientists for five years, is experimenting with a new preservation process he hopes will cut years from the traditional process.

Essentially, Drews’ process involves putting the Hunley in a chemical solution in a big tank, pressuring the solution and heating it to more than 270 degrees Fahrenheit, while still under pressure. This will trigger the rapid release of salts, he said.

If it works — and it has worked in small tanks with small items, Drews said — the Hunley could be preserved in a matter of months.

But because it’s both expensive and experimental, Drews first must test his method on increasingly larger items — meaning he has to build two more intermediate-sized tanks — before finally getting to the Hunley. All this still would take years and would require the Navy’s approval.

OTHERS’ EXPERIENCES

The slow pace of preservation is typical of old wrecks.

In Virginia, museum officials said it will take 15 years to preserve the iron turret of the Monitor, a Union ship destined for a new $30 million wing of Mariners’ Museum in Newport News, Va.

In Texas, remains of a 1686 French wreck — La Belle, found in the Gulf of Mexico — are taking 10 years or more to preserve.

Scientists say it’s important to do this work correctly because the Hunley is one of a dozen or so world-class wrecks discovered in the 20th century.

“This has been a very hard project, very tough, because there is no textbook for it,” Mardikian said.

引用元:http://www.thestate.com/mld/thestate/14583036.htm

コメントを残す

メールアドレスが公開されることはありません。 * が付いている欄は必須項目です