"You had an interesting question regarding Locking the main shaft on the main engine] when underway.  I can recall when I was serving in USS Shangri-La CVA-38, way back in 1954 and I had reported to the Forward Engine room as a Fireman apprentice! 

Man, I was so dumb that it is fortunate for me that the 1st class didn't send me to mess-cooking right away! However, when serving in large ships such as an aircraft carrier, they didn't keelhaul you when you first reported aboard for duty! Ha... 

One day, late in the evening, when the ship was underway on local operations, the Engineering Officer of the watched contacted the bridge and requested that the engineering department would like to conduct some casualty control exercises on the Forward Engineering Plant! The after-plant would come later! 

So, one of the exercises was "stopping and locking" the main shaft on #1 and #4 main engines. Stopping and Locking the main shaft was quite an order! This meant that the ship should not be doing more than 12 knots. So, you must realize that if the ship is at 25 or 30 knots, that the Engineering Officer of the Watch has to slow the ships speed in order to have one of the shafts stopped and locked. It's almost impossible to do if you are over 18 knots speed, but it can be done. 

A problem that could occur would be dragging a boiler down and burning it or another boiler up. We didn't always steam with all eight boilers on the line. If we were crossing the Pacific and trying to do so at 22 knots, we could operate on two boilers in the forward plant and two boilers in the after plant! With eight boilers, the plant used a lot of feed water and that wasn't good. The Midway CVA 41 had 12 boilers!!! Generally, we would be at 12 to 14 knots when the exercises were started! Usually, the 1st class or someone would go back and, without warning, energize the Low Lube Oil Pressure Alarm/siren. Even though the gage indicated that the lube oil pressure was at 42 lbs [normal], we were to follow the sound of the Low Lube Oil Pressure Alarm and shut down the engine whether the gauge was correct or not. Usually, the top watch [a 1st or 2nd class] would quickly make his way back to the main jacking gear located on the after-side of the main reduction gear and at the same time, the throttle man would have already closed off the main ahead throttle and opened the astern throttle. The Chief BT of the watch had already ordered superheat lowered to 750 degrees or lower, and the main shaft was now being stopped by introducing steam into the LP Stern Turbine elements! 

We had painted a candy strip or candy cane [red and white] stripes on the main 16" shaft just back of the reduction gear and there was a mirror that was placed at an angle so that the throttle man could see the candy-striped shaft rotating and coming to a stop. The 1st or 2nd class machinist mate would post himself in the vicinity of the shaft jacking gear locking device and he would then make a motion with his thumb up if more steam need to be allowed in order to slow the shaft more! When the shaft had come to a stop, the 1st or 2nd class would grip both hands together which meant that the shaft had stopped and that the throttle man was to hold the shaft stopped with the steam pressure going to the astern turbine at whatever throttle steam pressure was required at the time. The 1st or 2nd class would then engage the shaft locking device and turn on the jacking motor and then make a motion of "cutting your throat" which meant to "secure the steam" to the turbine! At this time, the throttle man would look at the L.P. turbine steam chest pressure and take a mental note as to what the steam chest pressure was indicated when the shaft was locked! 

The reason the jacking motor is turned on is to keep the turbine blading from becoming warped! Even if there is no lube oil to the bearings, the 43 to 1 ratio of the turning gear would hardly do any damage, even without lube oil pressure flowing to the bearings! Loss of lube oil pressure, noise in the reduction gear, noise in the turbines, hot bearings, or smoking bearing, or water in the lube oil, or loss of a line shaft bearing or outboard strut, or damage to the main propeller would serve cause to stop and lock the main shaft for the afflicted engine! Under battle conditions, there are many other measures that can be taken before taking an engine off of the line! Usually heavy vibration would justify slowing an engine, but if the vibration didn't stop, then the engine would probably be shut down and the shaft locked and turning gear engaged and activated! To restore the casualty, the 1st or 2nd class would station themselves at the jacking gear and signal when they were ready to disengage. The throttle man with orders to proceed from the Engineering Officer of the Watch, would introduce steam to the astern turbine and match the steam pressure that he had mentally taken note of when stopping and locking the shaft! In the meantime, the 1st or 2nd class top watch back at the jacking gear, would attempt to disengage the jacking gear and if he could not, then he would motion with thumbs up or down for more or less steam pressure in order to be able to disengage the jacking gear! When the jacking gear has become disengaged, the 1st or 2nd class would make a swiping motion across the throat which mean to secure the astern steam. At this time, the shaft would have started rotating! With direction from the Engineering Officer of the watch, the throttle man would turn the Engine Order Telegraph to indicate 1/3rd speed. The bridge would then ring down 1/3rd speed. Then the throttle man would bring the engine up to 1/3rd speed. Then the throttle man would bring the engine back up to speed in increments to 2/3rds, and Standard speed until the engine was matching the Rpm's of the other three shafts! Then Engineering Officer of the Watch, would then have the 1JV phone talker notify the bridge that the casualty to #1 main engine had been restored and then he'd have the JV talker tell the bridge what speed was available. The BT Chief of the watch would then request that superheat be raised on the boilers supporting the engine that had been returned to service! Usually the ship would not proceed above 12 knots until the superheat was above 750 degrees Fahrenheit! Normal operation for superheat for a 600 lb. plant was 850 degrees. 

In ships with non-controllable super-heaters, and a 1200 lb. plant, the superheat usually ran at 950 degrees. The Hopewell had B & W "M" type express boilers with a super-heated side that allowed for control of the superheat up to 850 degrees! We didn't have too many problems with the boilers! We had some really good BT's. Noel, I've seen ships that have lost lube oil pressure to the main engine and they failed to stop and lock the shaft! No one said anything, but when the USS Samuel Moore arrived at Pearl Harbor in 1966, ships force had taken the main thrust from the kingsbury thrust bearing on the main reduction gear while maneuvering. Their readings were .048" thousands! The bearings were wiped! This means that the bearings were burnt up! When I heard what the readings were on the #2 main engine main thrust, the Chief Engineer of the USS Moore didn't even realize his own problem. When I told him that the ship was not going anywhere, he turned white. 

Noel, this is but a sample of what could happen in a 600 or 1200 lb. steam plant and Bob Jones and I lost a lot of sleep over all of the things that could have happened! You just can't imagine how dangerous your job was at the time! Being in a 2100 Fletcher Class Destroyer is no easy task and it is extremely dangerous! Yet, you guys came though and did your job and you did it well! Well, done!!! gotta go.... "

Thought for the Day: Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information? -T. S. Eliot (1888-1965)