Saturday, April 26, 2008

Bet You Didn't Know This

On every warship with a SQS-26 or -53 sonar, there were sailors who had to be medically qualified to be divers. They weren't divers, they had no training as divers, but they had to be medically qualified as though they were divers.

In an earlier post, there were pictures of one of those large sonars. The sonar domes had rubber windows on them, for tests had shown that a rubber window was a lot better at conducting acoustical signals than a steel dome was. "Better" means that you might track a target that you couldn't or detect a target that you might have missed. "Better" means that you kill a submarine, and that, Gentle Reader, is what it was all about.

What you had, therefore, was part of a very large rubber tire on the front and sides of the sonar dome. A cruiser or destroyer could push that very large sonar dome through the water at over thirty knots. To prevent the rubber window from being pushed in from that much force, the sonar dome was pressurized with water. Fresh water was used in order to prevent the corrosion that would have occurred from sea water. There were high and low alarm points on the pressurization system, the alarms rang in both Sonar Control and on the Bridge. The importance of keeping the sonar dome pressurized was such that the alarm box was placed right next to the Captain's chair on the Bridge.

In really heavy seas, the bow of the ship would come out of the water, sonar dome and all. When the bow came back down, that large sonar dome would slam into the sea; the entire ship would quiver from the force of the impact and then the bow would continue down until the ship started up the front of the next wave. Warships did best in heavy seas by sailing into the waves. (By 'heavy seas," I mean seas with wave heights of thirty feet or higher.) If you were on the Bridge while that was going on, you would hear the loud beeping of the alarm as the dome was slammed down into the sea, as that would briefly overpressurize the sonar dome.

It was sort of an informal gauge of how bad the seas were by the number of beeps you heard from the dome alarm each time the bow came back into the sea. It was not unheard-of for a ship to suffer enough damage to its sonar dome in really heavy seas that the ship would have to be drydocked for repairs. (I'll blog about that process another day.)

Back to the point: There were periodic checks that had to be done to the interior of the sonar dome. If a bad sonar transducer element was detected during a source level check, it might need to be replaced. The sonar was designed so that you could replace elements of the transducer without having to drydock the ship. But keep in mind that you have a large dome that is, at its base, over twenty feet under water. That is a lot of pressure on the rubber window. What was done was that the fresh water in the dome was pumped out and replaced with compressed air. There was an air lock in the access trunk to the sonar dome. (A "trunk" on a ship is a narrow vertical shaft that goes through one or more decks.) The sailors who would do the work inside the sonar dome had to have diver's physicals, since they would have to work in a pressurized area.

And that is why you had sailors who had to be medically qualified for diving duty on warships.

Tuesday, April 15, 2008

Dry Air

On something as complex as a warship, you can find things that hardly anyone has ever heard of, but are critical to the ship’s being able to do its mission. In that category were the air dehydrators. This is why:

For reasons probably understood by electrical engineers and physicists (of which I am neither), you cannot send radar signals from the transmitter to the antenna by a wire or a cable. You send the actual radar wave itself up a tube called a “waveguide,” which takes the signal from the transmitter to the antenna. The return signal also comes down the waveguide to the receiver. If you had a radio transmitter in your home, the waveguide is the equivalent to the cable running from the radio set to the antenna.

Radar signals are rather powerful, with air search radars having a lot more power than surface search radars. Fire control radars are the most powerful. There is a lot of energy going up those waveguides to the antennas. If there is any moisture inside the waveguides, there will be arcing and sparking inside the waveguides, which can burn holes in the waveguides and ruin them.

Ideally, the best thing to do would be to use an inert and dry gas to fill and pressurize the waveguides. That’s impractical on a ship, for the gas canisters would be another item that would have to be supplied to the ship. So what is done instead is to pressurize the waveguides with dry air.

By “dry air”, I mean really dry. The dryness of air is measured by dewpoint, the temperature at which the water in the air will condense out. You may know that when it is summer and the dewpoint is high, the air is muggy. In the winter, when the dewpoint is low, people complain about their sinuses drying out and many people use humidifiers. Those dewpoints are positively soggy and too high for a radar waveguide.

How dry? You need a dewpoint of probably around -40degF for a generic radar. For a high-powered radar, you need a dewpoint around -70degF or even lower. The dehydrators are operated and maintained by A-Gang and the dewpoint is measured with a special dewpoint tester that takes a sample from the supply line to the waveguides. If the dehydrators are out of spec, the radars are shut down and that makes the Captain very unhappy, especially if the ship’s mission is anti-air warfare. If the dewpoint tester breaks, the radars are shut down.

The damndest things are critical items.

Friday, April 4, 2008

Boomity, Boomity, Boomity

Everything you wanted to know about fire control (aiming the realllly big guns) but were afraid to ask. This was back in the days of gear-driven analog computers, nothing digital about this stuff.

Thursday, April 3, 2008

The Watch From Hell

One of the cardinal sins in the Navy is being outdoors without wearing a hat (Navy term- “cover”). The only exception is when something is going on that makes it unsafe to wear a cover, such as operating aircraft. If you go out on the weather decks, you wear a cover. The cover worn with the working uniform was a navy-blue ballcap with the ship’s name on it.

This story took place in Djibouti. Djibouti is in the horn of Africa, where the Red Sea and the Indian Ocean meet, a small flyspeck of a place neighbored by Ethiopia and Somalia and controlled, for all intents and purposes, by the French Foreign Legion. Both Somalia and Ethiopia at the time were more-or-less aligned with the Soviet Union, so Djibouti was the only friendly port within a long distance. Because Ethiopia and Somalia had simmering civil wars going on, Djibouti was full of people who were destitute. It was not a very nice or safe place to be. It was such a hardship post that when a Navy ship pulled in, the Americans at the local consulate would come on board and virtually strip the ship’s store of its stock of candybars, pre-recorded cassette tapes (this was in the pre-CD era) and other small consumer goods.

This story also took place in July. July in Djibouti was hot. The water in the harbor was well over 90degF. Ships air-condition their interior spaces with chilled-water heat-exchangers. The heat-exchangers use sea water to carry away the heat and when the sea water coming into the heat-exchangers is already hot, not a lot of extra heat can be carried away. So even though the interior of the ships were air-conditioned, those air-conditioners were barely keeping the ships cool.

So let’s set the Way-Back Machine to July in Djibouti, more than two decades ago. A Navy warship limped into Djibouti with a serious engineering problem. Parts and technicians had to be flown into Djibouti to fix the ship. The ship was there for at least two weeks at a time when no captain would have tarried in port for longer than it took to refuel and load supplies. The few crewmen who went ashore came back with stories of how bleak and nasty the city was. As a result, the ship’s company stayed on board and did things such as write letters home and catch up on their sleep.

The time is 1400 at the peak of the day’s heat. A young ensign, a graduate of the Naval Academy, was the OOD in port, also known as the Quarterdeck Watch Officer. From this young lad’s vantage point, you could see two French warships each the size of an American destroyer escort from the Second World War, a dumpster with a couple of emaciated dogs sleeping in the shade and one local man, wearing only a sarong, sharing the shade with the dogs. The man was there to sell t-shirts and souvenirs to the few sailors who were going ashore. The air was still, oppressively so.

A mess cook came up to the Quarterdeck with a dripping bag of garbage from the noon meal, which he intended to throw into the dumpster. He had forgotten his ballcap. The OOD didn’t want the mess cook to carry that dripping bag of garbage back down through the ship so the mess cook could get a cover, nor did he want to have the mss cook leave the bag of garbage on the Quarterdeck. So the OOD let him go off the ship to the dumpster sans cover.

That was when the Captain and the XO appeared on the Quarterdeck. They had a social engagement ashore. The Captain saw the bare-headed mess cook on the pier and promptly began to royally chew the ass of the unfortunate ensign with an obscenity-laced tirade. Peppered throughout the tirade were comments such as “hard to believe that you fucking graduated from the fucking Naval Academy.” The Captain ended his tirade with “you are on watch and you will remain on watch until my return.”

And so began the Watch From Hell. The other young officers on the ship took turns bringing him cool drinks. Every few hours, one of his roommates from the JO Locker (where the male junior officers slept) would bring him a fresh shirt, as the uniform of the day was Summer Whites. The OOD was relieved for the evening meal by the Chief Petty Officer who would have stood watch from 1600 to 2000, but other than that and a couple breaks to visit the head (bathroom), the ensign stood his watch. And the next one. And the next one.

The Captain and the XO, both of whom were three sheets to the wind, came back aboard around 0230 that night. When the Captain saw the ensign still standing his watch, he grunted “call your relief” and with that, the Captain stumbled off to his cabin. The ensign sent the messenger to get his relief (who was awake and reading a book in the Wardroom). The watch turnover took maybe 30 seconds and the ensign was on his way for a shower and some sleep.

Of all of the officers on that ship when this story happened, only that young ensign is still on active duty. He is a senior officer. I can only hope he has treated his young officers with more dignity and consideration than was shown to him.

But one cannot be sure, of course.