Question on gas turbine powered ships and blade count

[Bubblehead Nuke]

As I understand it, on gas turbine powered ships the screw is turning at a constant speed until you max the pitch out. In other words, at you move the throttle quadrant forward, you are only increasing blade pitch until you max the pitch out THEN you actually start to increase engine RPM's. Thus the bladecount is the same at ALL STOP up to a certain ship speed. At that speed you stop increasing blade pitch and actually start to increase engine RPM's. In essence you can not tell if the target guy is just sitting there or moving at ## knots.

Can any of you skimmer types on here confirm this?

[compressioncut]

It depends on the ship, but yes, variable pitch screws can give inconsistent and variable TPK readings.

Pitch also has an influence on cavitation inception speed, obviously.

[MaHuJa]

I do not think this is simulated in the game, though.

[Bubblehead Nuke]

I do not think this is simulated in the game, though.

I noticed that. I ran a quick mission and basically ran next to a Tico and watched his bladerate go up and down with speed. I was bummed out.

I think that it would be a worthwhile addition. It would just add another factor into the equation, particularly when it is another human at the helm. You have to look as the OTHER persons tactical situation and think more of what he may or may bit be doing, rather then just playing a numbers game.

I know that this would probably have to be done by SCS.

[Bubblehead Nuke]

Another thing that would be nice about a gas turbine ship would be its ability to sprint, come to a stop somewhere, and TURN OFF ITS ENGINE (TURBINE). That would kill a HUGE amount of noise and make the thing REALLY hard to detect. Then as soon as as they want, refire the engine and spring again.

Think that would make life hard on the bubbleheads??? You betcha.

Yes, I know that this is a game, but still.. I like a challenge. Give the suface guys the tools that they would have in real life as well.

[MaHuJa]

Another thing that would be nice about a gas turbine ship would be its ability to sprint, come to a stop somewhere, and TURN OFF ITS ENGINE (TURBINE). That would kill a HUGE amount of noise and make the thing REALLY hard to detect. Then as soon as as they want, refire the engine and spring again.

Think that would make life hard on the bubbleheads??? You betcha.

Yes, I know that this is a game, but still.. I like a challenge. Give the suface guys the tools that they would have in real life as well.

I heard a turbine ship (like the perry) has a startup-time of 5 minutes before they can get underway, as opposed to 30 minutes for dieselships. And numerous hours for nuclear-powered.

So it's not quite that simple. Being adrift like that puts you in a non-defensible position.

Plus, it's the power plant, as in electric power; they would have power concerns on top of it all. How much batteries do they have?

[Kazuaki Shimazaki II]

Actually, if you right-drag, you COULD disconnect the RPM with the pitch rate. The only thing is, you immediately find out the game doesn't simulate it - at all.

[Doc Savage]

I heard a turbine ship (like the perry) has a startup-time of 5 minutes before they can get underway, as opposed to 30 minutes for dieselships. And numerous hours for nuclear-powered.


Shouldn't it be the other way round?
A gas turbine needs a boiler which I assume would take time to develop the pressure needed to run the turbine.
A diesel, if it's anything like a car diesel, should start up faster as long as it's hot enough...

[Bubblehead Nuke]

I heard a turbine ship (like the perry) has a startup-time of 5 minutes before they can get underway, as opposed to 30 minutes for dieselships. And numerous hours for nuclear-powered.
From what training I had in the Navy, gas turbines plants can go from cold iron to underway in less than 8 minutes. I presume, that with the plant already hot and everything ready to go, all you have to do is hit the starter button. Once you are lit off, you are ready to rock. Only question how fast can it come up to minimum operating speed. A jet airplane can do it in less than a minute on a hot pad standby. Why should the same turbine, adapted to a ship, be significantly slower?

Personnal experience here:
When Hurricane Hugo was in the Atlantic they decided to sortie the fleet out of Norfolk. I was standing on the tender waiting for something when the message hit (the tender announced it over the 1MC that emergency sailing orders had just come down). I heard a Tico on the next pier over anncounce an immediate ships muster. They singled up lines and I heard the induction WHOOSH about 3-5 minutes later. Them as pretty as you please, with NO TUGS, they pulled in lines and the brow, and left. Watched them do a thruster turn to starboard and away they went. I remember because I was in awe at the time, it was less than 10 minutes from when I heard the announcement. I KNEW I had a pre-crit to do and these SOB's were already gone. Second Tico left about 3 minutes later.

Then all hell broke loose and just about every ship in port was working there butts off to get underway. All the gas turbine ships were LONG gone. The conventional ships were leaving in about 5 or 6 hours and us nukes.. it took us about 8 hours. We had no pre-crit done at the time, nor had any other boat on piers 22 & 23. Even the carriers got caught by suprise.

Wanna know the real funny thing? They would not let us go. We had our dive certificate pulled due to a few things and they made us tie up triple lined and rigged for dive right next to the pier.

There were a LOT of P.O'd sailors that day. Just that morning they had come out and stated that nobody would be leaving because the storm was going in WAY south of us. Everyone had relaxed and nobody had done any 'got to go honey', park the car somewhere safe and all that pre-underway stuff. If you were on the boat (ship) you were not allowed to leave due to the frantic 'we gotta GO' mentality that was there that day. We thought the storm had shifted north and was going to hit near us.

BTW: a Nuc boat can get fired up and underway in less than 1 hour if needed. Trust me, I know. But it has to be an emergency and you break a lot of rules to do it.

So it's not quite that simple. Being adrift like that puts you in a non-defensible position.
It also puts you in a position that makes it hard as heck for a sub to find you unless he goes active or looks out the 'scope. I can think of a lot of pro's and con's on it.

Plus, it's the power plant, as in electric power; they would have power concerns on top of it all. How much batteries do they have?
Gas turbine ships have either seperate gas turbines to power the electrical generation gear or they use backup diesels. These items would be heavily rafted to not transmit sound. The screw turning, even when making no way on the ship, would be significantly louder. Remember, a gas turbine is going to have a minimum speed that it has to maintain in order to operate. It is like a jet engine. There is a minimum alpha speed and that will be the slowest RPM that the screw can turn at (even with a reduction gear) and you have to zero the pitch out so that you do not make way on the ship.

[Wildcat]

if the boilers are hot then starting the turbine is a click-to-start affair and the ship will go whenever you want it to. Well, the engine will take approximately 30 seconds to a minute to spool up barring a hot start but after that it's good to go.

[Bubblehead Nuke]

Boilers??? Gas turbine ships are driven by what is basically a jet engine.

Boilers are used in steam powered ships. Those I understand all too well being an ex-machinst mate. That is a whole different animal.

[Doc Savage]

Hmm...
I assumed the ship turbines would be running off boilers - something like a conventional coal powerplant or a PWR nuke reactor
i.e. some thing (oil/diesel/U235) heats water (in the case of the PWR it would be the reactor fuel), water builds up pressure, runs though a turbine which is coupled to a shaft which in turn is coupled to the ship's screw or to a turbo electric generator.

The jet engines turbine would be different because the aviation fuel is burnt directly and run through the turbines.

From what you described above it seems the ship turbines are more like the latter case.

[compressioncut]

Hmm...
I assumed the ship turbines would be running off boilers - something like a conventional coal powerplant or a PWR nuke reactor
i.e. some thing (oil/diesel/U235) heats water (in the case of the PWR it would be the reactor fuel), water builds up pressure, runs though a turbine which is coupled to a shaft which in turn is coupled to the ship's screw or to a turbo electric generator.

The jet engines turbine would be different because the aviation fuel is burnt directly and run through the turbines.

From what you described above it seems the ship turbines are more like the latter case.

It's exactly like the latter case. They're just marine versions of aircraft jet engines. They don't run on avgas, but diesel fuel oil, although they can run on a mix if necessary (we had to mix it with helo fuel when we almost ran out halfway between Hawaii and Japan, one time).

An idling GT in a properly enclosed and damped space will not be detected by anyone outside of very close range. Even at speed, particularly below cavitation speed, modern ASW ships resemble a nuclear submarine on a gram. Operated carefully, they can be very hard to find.

[Bubblehead Nuke]

Actually, if you right-drag, you COULD disconnect the RPM with the pitch rate. The only thing is, you immediately find out the game doesn't simulate it - at all.

Thanks for the heads up on the right click thingie. I did not know you could do that. It made for some interesting experiments.

One thing I was playing with was, while answering a full bell, right click the thottles and slam full reverse pitch on. I dunno about you, but it stopped pretty dang quick.

Once I had decreased to 0 knots I took the pitch to 0 and sat there, dead in the water with the left hand quadrant STILL at Ahead Full.

It seems you CAN independently control pitch and engine RPM.. I was doing all kinds of weird throttle/pitch commands and the ship would move accordingly. Ahead 1/3 and then move the pitch to 100% and accelerate.

I do not have another computer here that I can run tests on this. Has anyone else tried this and see what happens to the blade rate and such?? It seems silly to model accuate ship helms controls and not model the cooresponding sound ques in a sonar profile.

[MaHuJa]

esp in as "sonar-heavy" sim as this.

I'll fire up my laptop now, but I expect *only* the speed is transmitted from one computer to another.

[Bubblehead Nuke]

esp in as "sonar-heavy" sim as this.

I'll fire up my laptop now, but I expect *only* the speed is transmitted from one computer to another.

That was my original question to begin with. If you can decouple bladerate to actual ships speed it makes for a more interesting tactical situation. It takes a preset matchimatical equation and trashes it.

I do not like to give any 'gimme's' in a game and any trick, tactic or subterfuge that is NOT a cheat I am open to and willing to use. I like to make the other side think. All's fair in love and war.

[Linton]

Just a quick question,do you have fadecs on the gas turbines you operate at sea or any other power management device?The 1980s cfm powered 737 had pmc's which were basically fuel trimmers.The later Trent engine from Rolls Royce has a fadec-it is really easy to start and operate.

[compressioncut]

Just a quick question,do you have fadecs on the gas turbines you operate at sea or any other power management device?The 1980s cfm powered 737 had pmc's which were basically fuel trimmers.The later Trent engine from Rolls Royce has a fadec-it is really easy to start and operate.

I do not know as I`m not an engineering type, but the most common naval marine gas turbine is the GE LM2500 (Perry, Burke, Tico, Canadian Patrol Frigate, etc). You might be able to find out more from there.

http://www.geae.com/engines/marine/lm2500.html

http://www.fas.org/man/dod-101/sys/ship/eng/lm2500.htm

http://www.fas.org/man/dod-101/navy/docs/swos/eng/62n-116.htm

They don't take much time at all to fire up, though.

[NastyHyena]

GE's propoganda on the first link indicates 'Intigrated Electronic Control', which sounds like a similar animal to a FADEC.

As for start stop time, you need to remember these are turboshaft engines... Or if you want to be very creative, turboprops with the prop submerged in water. They may fire up quick (inside 20 seconds between engaging starters and the engine lighting off), but then you need a few minutes for the engine to stabilize or you risk breaking things.