Although the majority of ships in the US Navy are made out of steel, some are still made from wood. As the USS Guardian showed, wooden warships are critical to modern warfare!
On January 17, 2013 tragedy struck the USS Guardian. The dedicated Avenger-class minesweeper had departed from the Filipino naval base at Subic Bay days before. From there she stuck close to the coast headed south on a course for Indonesia.
This would prove to be a tragic mistake as the navigation charts aboard the Guardian were off by as many as 8 kilometers. Early on the 17th, the ship ran nose-first into a local reef and found itself grounded. The bow of the ship was significantly damaged by the impact and the ship itself became stuck. That was bad enough, but in the subsequent hours, local currents pushed more of the Guardian onto the reef so that the majority of the ship was sitting on the obstruction by the next morning.
If it weren’t for the actions of Sailor Nick Martin and Marine Matthew Pekarcik, the Guardian would have likely sank on the reef, then either rolled over or broke in half. For hours Martin and Pekarcik reinforced the ship’s keel, its vital backbone, while battling cramped spaces and flooding. On the 18th, Martin and Peklarcik further played in instrumental roles assisting crewmen off the Guardian onto the reef while carefully avoiding the local shark population, where they were picked up by waiting rescue vessels.
But despite their heroic actions, the Guardian was a total write off. There was simply no way to pull the ship off the reef without breaking the ships “back” (the keel). This was because the Guardian, unlike almost every other ship in the Navy's inventory, was made not of iron and steel, but of fiberglass and wood.
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Why Wooden Ships are in the Modern Navy
When we think of modern warships, many imagine the dreadnoughts and battleships from the World Wars. These ships were, as historian Robert K. Massie aptly described, castles of steel. They were true testaments to the industrial age while wooden ships were relics that belonged to the past. The very idea of a wooden-hulled warship probably invokes the image of the Age of Sail, with ships like the HMS Victory plying the waters hunting for the French and hurling iron cannonballs from crude cannons. That vision of ship design would, on the surface, seem to have as much relevance to modern warfare as the sail and the cannonball. So, what's the deal with the wood and fiberglass hull of the Guardian and the other Avenger-class ships?
This kind of hull construction is not unique to these American ships, but is common across the minesweepers of most modern navies. The reason lies in their job and the threat they face in action, which is twofold. Modern mines can be sophisticated, with some featuring torpedo launchers and acoustic sensors. However, the most common and the cheapest types of mines remain the magnetic mine. These mines are usually moored to the floor of the sea and have simple magnetometers which track local magnetic conditions.
When a sufficiently large piece of iron passes nearby, say the hull of a warship, the magnetometer sets off a fuse and detonates the mine. Usually, this explosion does not occur while the mine is in direct contact with the hull the way a torpedo or contact mine would. Instead, the shockwave warps and ruptures the ship's hull, which causes the damage and flooding.
Modern minesweepers and their wooden hulls defeat magnetic mines in two ways. First, unlike most steel warships, their wooden hulls generate smaller magnetic fields and decrease the possibility of accidental detonations. Secondly, and perhaps more importantly, the ship's wooden hulls help them resist underwater detonations. In the event of an accidental detonation, the wooden minesweeper's hull can warp, compress, and absorb shocks much better than a more rigid steel one. While these hulls may not be useful in ship-to-ship combat operations, where guided missiles reign and the risk of fire is significant, they are optimized to perform the job of minesweeping.
Getting to Know Degaussing
The specialized nature of the Guardian's hull makes sense in relation to its specialized job. But the fact remains that most modern warships are made out of steel, and dedicated minesweeper vessels are not always available to clear the way for destroyers and carriers. At the same time, they must find ways to defeat magnetic mines.
While there is no hiding the signature of a steel-hulled, 8,000-ton Arleigh Burke-class destroyer, there are things that can be done to significantly reduce its magnetic signature. As warships travel the seas, especially as they cross the magnetic equator, they build up a residual magnetic charge within the iron of their hulls. Over time, this charge can become quite significant, altering the ship’s signature and making it easier to detect.
To counter this natural process, the ship undergoes a process known as degaussing or deperming. PC gamers from the 1990s might be familiar with the concept of degaussing, as many CRT monitors featured a giant “degauss” buttons on them that performed a similar process. The button reset the magnetic fields of the cathode tubes inside the monitor with a small electric charge. At sea, things are significantly scaled up with a specialized support ship or port facility drags an electric cable across the hull of the warship until its signature is reset. But this isn’t the only way to reduce a ships magnetic signature.
Hull Materials Matter
The Independence-class Littoral Combat Ship has been plagued by many design, development, and public relations failures over its troubled history. One of these failures was in the construction of its hull. Austal, the Australian shipbuilder that designed the Independence, lauded the innovative new hull construction the company had pioneered with its vessels.
While the trimaran design (which uses three hulls) is perhaps the ship’s most striking and obvious feature, the all-aluminum hull was another important innovation. This hull was considerably lighter than a steel one, which meant that the Independence could go further, faster, longer than her steel-hulled rival, the Freedom-class. Also, since aluminum lacks the magnetic properties of steel, the Independence could theoretically replace the Avengers in the minesweeping role, therefore increasing the ship's multi-mission capabilities.
However, this ultimately proved to be a very poor design choice. While it was lightweight, the aluminum in the hull was not as flexible as steel or wood. Where steel plates might dent or wood would bend, aluminum tends to crack and tear, which is a big problem for seaborne vessels! Worse yet, aluminum generally corrodes more quickly than treated steel, a problem not helped by cracks and fissures within the hull. Finally, and perhaps most damningly, aluminum has one major drawback that steel does not. The metal weakens and melts at around 1200° F while steel remains solid past 2500° F. Given the risk of fire at sea and during naval warfare, that difference could mean the difference between saving a ship and losing it. So, that is perhaps why steel and wood reign on Naval ships for now.