Interesting point, we have pitch shedding on the blades on our Voith tugs but haven’t considered what would happen on our ASDs. As it is 0730 on Sunday here, will spend the rest of the day resisting the urge to log into work and read the Rolls Royce manuals…
Most of my ships in the RAN were steam turbine and, as we never sailed at full power other than for trials for very short periods, there was always more readily available. The bridge ordered the revolutions and that was provided as ordered. Cruising speeds were usually well below 50% power for a destroyer or frigate 12 -16 knots. 50% power (one boiler connected, say) was sufficient for 24 knots. Double that power to get to 30.
I can’t say I ever noticed RPM variations from the bridge. There was no instrumentation for that anyway.
I can certainly vouch for the responsiveness of such steam plants. I was navigator of a destroyer where the Captain lost it a bit during berthing in Sydney. He had the con after I had set the ship up on a standard final approach. For reasons only he knew, he gave three “full” ie emergency engine orders in succession in a minute or two - full astern both, full ahead both and full astern both. I had never seen a “full” before and the first was impressive, the second absolutely spectacular stopping the ship in less than a quarter ship length from about 10 knots astern, and I reckon the third totally gob-smacking stopping the ship in 10 feet from about the same speed ahead and causing some sailors on deck (and probably below) to stumble. By the time I persuaded him to stop engines and settle down, all safeties were lifted, steam was screaming out and nobody could hear a thing, The stokers had the boilers at well over full power by the second manoeuvre and reaction time was instant.
Oh the joys of 50,000 shaft horsepower at the fingertips! Never seen it since unfortunately.
Having sailed through the different positions aboard steamships (and motorships for that matter), have had great occasion to experience different operational behaviors in heavy weather…
Of course I will be referring to only geared turbine vessels- it is largely dependent upon the type of turbine control system- the older, hand operated nozzle control valve systems operated with a maneuvering valve (normally opened wide at Departure) and the turbine controlled by the combination of nozzle control valves opened. This was basically a constant steam flow setting- the RPM would fluctuate according to loading, but the steam flow essentially remained constant… A speed limiting hydraulically actuated governor system through a series of hydraulic relays and control valves would close in on the throttle when a preset rpm was exceeded… Some (not all) incorporated an overspeed governor which would “trip” the throttle linkage when reaching a preset rpm (Shutte & Koerting) while others had a separate overspeed tripping device…
On GE ITC (Integrated Turbine Control) the control system would maintain the rpm set point according to either the Bridge or Engine Room control lever- and basically maintain that rpm (or attempt to) and thus constantly vary the steam flow. It was highly inadvisable to operate in heavy weather in Bridge Control…There was of course a “rough weather” setting (in the control cabinet originally) which would damper out the error signal and thus the system response- by offset and limiting functions; but it in real heavy weather we would usually be at full ahead maneuvering as opposed to above it… These systems were known to have electronic as well as mechanical overspeed shutdowns…
I have never sailed aboard a steamship with CPP…Would be very interesting to say the least!
good info here, great replies. I was reminded of cleaning the sight glasses, so old i had to make new gaskets out of something. Was also reminded of the Chernobyl disaster as I’ve just finished a well documented book about how that went down. quite the story!!
Thanks for your comments… I also have read extensively on this subject, especially careful reading of INSAG-1 and INSAG-7. The positive/negative void coefficients and quotients, also the “neutron poisoning”… The manual withdrawal of the control rods certainly didn’t help…Good reading… All about sufficient time for the emergency generators to start and come up to operating voltage…Poor procedures, non-existent safety culture, inherent design errors and massive complacency…
i was amazed at how fast the reactor went critical. they had only 2 or 3 rods in as I recall and producing a min. amount, like 200 i think? then BLAM, that was it!
Yes., Positive Void Coefficient- the RBMK direct transfer reactors were a nightmare- graphite moderator rods…
The whole thing was started because they wanted to find a way for the generator set to continue supplying power to the emergency coolant loop pumps after a turbine trip… back then the emergency generator startup, voltage buildup and on line timing for just the emergency services was too slow. First they changed out the rotary amplifier voltage regulators with static shunt inverters… still too slow, so they changed the exicters and upgraded the SSI’s…
The "final"test was supposed to take place in daytime- instead of on the Mid to Eight Watch… people weren’t following procedures and allowed the mW thermal to decay down to about 12%… In a panic they attempted to raise the output- by pulling 90% of the Control rods- including Manual rods which were NEVER supposed to be withdrawn… Couple this with the fact that the main coolant loop pumps were secured for the test… What essentially happened was a steam explosion which lifted and shattered the 1000 ton upper biological sheild… OUCH!
I have sailed on Steam Turbine Ships, Motor Ships, and a Gas Turbine Ship.
The Steam Turbine Ships were various types in the American Merchant Marine. All had manned engine rooms and never operated with Bridge Control. At sea, the steam flow was manually set to a desired set-point either with “Nozzles” or with the Main Throttle. In heavy weather, the RPMs went up and down according to the transient loads, but the steam flow was constant. Everything, except for the RPM, was steady-state.
The Slow Speed Motor Ships which I sailed on, were also US Flag, with unmanned engine rooms. They all operated with Bridge Control and speed control was set from the bridge. In heavy weather, as the RPM would drop from a transient load, the Governor would increase fuel delivery to try to maintain a constant RPM. The Governor and Fuel Pumps would be constantly hunting trying to maintain the set RPM. It would have been nice to put the Motor on Local Control and lock the Throttle in a fixed position, but that would of course required us to go on manned watches.
After a long ocean passage and approaching the first port, I saw it several times, a Third Mate unfamiliar with the ship, would do his arrival tests, including Steering Gear. On that ship, with its big rudder, putting the rudder over to 15° would overload the Motor (which was typically running at full sea speed). This would overload the Motor, causing high temps of the cooling water, and auto slow down, which would cause the Shaft Generator to disconnect and often cause a blackout if the Standby Generator could not connect fast enough. Great fun…
Well, you evidently didn’t know that most of the recent Main Propulsion Control Systems on Slow Speed Diesels incorporate a “rough sea” function as well as a command input limiting function which can in fact limit the speed set point irrespective of what the bridge control lever is set at. Also, you seem to be forgetting about the pre-set fuel limiters which will dial back the fuel control setting if scavenging air quantity (by dp of course) is insufficient. Even newer engines incorporate a control program which will not allow the speed setting to get to the left of the power/speed curve normal loaded propeller line…
I have had frequent occasion to have ran US Flag Steamships in manned engine room Bridge control- (cmakin- States Line Ro-Ro’s had this remember?) we used it often in convoys for the “stripes of shame”" (MSC)
Perhaps a bit overzealous, but my good engineers might have walked on water. Have not witnessed that, but worth their weight in gold. Treat them well, they will save your ass in tough times. Never forget that while driving the rig, The dudes below make your day positive.