Sea Stories: Deperming

[Gunboat1]

Sea Stories: #46 - Deperming

 

One of the more unique, albeit infrequent evolutions that a ship must undergo is called “Deperming.” Ever since man realized that a metal object disturbs the earth's magnetic field (and some time afterward determined that this was a dandy way to get a torpedo or mine to explode near a ship without having to make physical contact with it ), taking steps to minimize that metal ship's own magnetic field has been considered important. Deperming is that process; reducing to the maximum extent possible the ship's permanent magnetic signature.

When the ship was built, it was in a building dock aligned at a certain angle with the local magnetic field. The process of welding everything together permanently induced a magnetic field onto the ship itself. It is this field that we want to minimize. So after major structural work is done, a ship travels to a purpose-built facility called a Deperming Crib. The ship moors in the Crib. The crew then takes hold of messenger cables on both sides of the ship and uses them to pull large electrical cables which were resting on the bottom of the harbor onto and over the ship. This results in the ship being wrapped in dozens of slimy, muddy cables like being wound in a cocoon. Sensitive electronics have to be protected. And when all is ready, the cables are energized with a very high-voltage electrical current. This turns the ship into a huge electromagnet and permanently realigns its magnetic field to minimum configuration. (A separate Degaussing System built into the ship further reduces this signature when the ship operates day-to-day.)

I got a humorous exposure to the process of Deperming on my First Class Midshipman's Cruise aboard USS McINERNEY (FFG-8) in 1981. The ship had recently had some work done, so was ordered to deperm, and transited to Norfolk, Virginia where a Deperming Facility is located. We pulled in and before long, were treading gingerly over, under and around muddy, slimy, barnacle-encrusted cables fresh off the bottom of the Elizabeth River. The ship was a filthy shambles topside.

Just then, the telephone rang. It was Commander, Naval Surface Forces Atlantic (SURFLANT) calling. (My Captain's bosses' bosses' boss – a three-star admiral. Well, okay, it wasn't actually the Admiral on the phone, it was one of his underlings.) The situation was this. USS McINERNEY was the second ship of what eventually became a large class of guided missile frigates. But she was the shiny new frigate on the block. And the US Navy was hoping to market the ship's design to a number of other allied navies, including the perennially well-heeled Kingdom of Saudi Arabia. A delegation of Saudi naval officers happened to be visiting Norfolk that day, and SURFLANT “wondered if it would be convenient for them to visit McINERNEY – right now, today.” And this wasn't a request.

So of course, amidst all the work, the ship had to plan a semi-diplomatic VIP visit. The Chief Petty Officer in charge of the Officer's Wardroom mess pulled together a quick set of refreshments and hors d'oeuvres to be served in the Wardroom. (This polite Filipino gentleman initially planned to present “a nice ham”, but the ship's Supply Officer caught wind in time to have this religious faux pas avoided and shrimp cocktail was served instead.) And in about half an hour, here came a small boat with the Saudi delegation embarked. IN DRESS WHITE UNIFORMS AND SHOES.

We ushered the officers aboard with due traditional ceremonies, and set about showing them the ship. It was hysterical, watching them try to avoid touching ANYTHING as they were shown the various corners of the ship, attempting to keep their pristine uniforms clean. And it became pretty apparent that the Saudis weren't particularly interested In the ship. They had plenty of money to afford any of a dozen larger, more capable and more expensive ships if they wanted them. They were simply humoring the USN's request that they give the ship and class a look and consideration. They didn't want to be there, and we didn't want to have them there! They came, they saw, they ate shrimp and they departed dirtier than they arrived. Diplomacy had been served.

And then we got on with the business of deperming.

[aomagrat]

All of the cathode ray tube TV's and computer monitors would be screwed, colors out of whack, screen distorted etc. until a degaussing ring could be passed over them.  I don't know how flat screen monitors and TV's would react.  We didn't have those back then.