Turbine engines

Read on. The thread eventually plays around with some really interesting designs. Some of which may appear while other will definitely not appear in the stories.

fallsfromtrees wrote:

PeterZ wrote:Textev is in LaMA, September YOG 896 chapter II almost at the end with Howsmyn, Rock Point, Pine Hollow and Ironhill discussing production plans.

http://forums.davidweber.net/viewtopic.php?f=7&t=4116&hilit=hms+shan+wei

Thank you for the link - it was from before my time here, and I had never seen it before - fascinating.

chrisd wrote:

Jonathan_S wrote:Also some other ships of the era, like the Buckley-class destroyer escorts, went with turbo-electric machinery as a different way to bypass that reduction gear manufacturing bottleneck.
Though that option isn't open to Safehold; not while the proscriptions hold.

There is also a benefit to "turbo-electric" propulsion in that you don't need "Aster" and/or "Manoeuvring" turbines.

The turbine being uni-rotational, the generator-motor combination gives speed control and reversing similar to a "Ward-Leonard Set"

Not sure if any did, but on ships with reduction gears between the turbines and the prop shafts I'd think you should be able to construct a reverse gear to let you apply the main propulsion turbines to spin the props backwards... (Though for torque reasons you probably need to bring the shaft to a stop before switching gears)

Obviously that's not a even an option on the older direct drive turbines.

Still, speed control and being able to go very quickly from full ahead to full astern is an advantage of turbo-electric propulsion. (Not to mention being able to just as easily reverse only half the props to yank the bow around from differential thrust)

Jonathan_S wrote:

chrisd wrote:quote="Jonathan_S"]Also some other ships of the era, like the Buckley-class destroyer escorts, went with turbo-electric machinery as a different way to bypass that reduction gear manufacturing bottleneck.
Though that option isn't open to Safehold; not while the proscriptions hold.

There is also a benefit to "turbo-electric" propulsion in that you don't need "Aster" and/or "Manoeuvring" turbines.

The turbine being uni-rotational, the generator-motor combination gives speed control and reversing similar to a "Ward-Leonard Set"

Not sure if any did, but on ships with reduction gears between the turbines and the prop shafts I'd think you should be able to construct a reverse gear to let you apply the main propulsion turbines to spin the props backwards... (Though for torque reasons you probably need to bring the shaft to a stop before switching gears)

Obviously that's not a even an option on the older direct drive turbines.

Still, speed control and being able to go very quickly from full ahead to full astern is an advantage of turbo-electric propulsion. (Not to mention being able to just as easily reverse only half the props to yank the bow around from differential thrust)[/quote]

There is a reverse gear so to speak, but you have to stop the engine completely first, which can take several minutes to initiate.

The astern turbine is designed to propel the ship in the astern direction. The concept is the same as in a car. A car is designed to go both forward and reverse. The designers could have designed the car with two totally separate transmissions, one for forward and one for reverse. Instead, they designed cars with one transmission capable of going both forward and reverse. The same concept exists on the ship's main engines. The ship is not designed with two engines per shaft. Rather, it is designed with one engine per shaft. In a car, the ability to go in reverse is contained within the transmission. On the ship's main engine, the ability to go astern is contained within the LP turbine. The astern turbine is designed as an integral part of the LP turbine rotor. On a double flow LP turbine, the ahead elements of the LP turbine are located towards the center of the LP turbine. The astern elements are located on the forward and after end of the LP turbine rotor. On a single flow LP turbine, the astern elements are located on the forward end of the LP turbine. The astern turbine is a single axial flow, velocity compounded, condensing impulse turbine consisting of one or two Curtis stages located on the forward and/or after end of the LP turbine.

And no, modern propulsion systems (gas turbines or combined systems like CODAG) simply used controllable reversible-pitch propellers (CRPP).

saber964 wrote:

Jonathan_S wrote:
snip

Still, speed control and being able to go very quickly from full ahead to full astern is an advantage of turbo-electric propulsion. (Not to mention being able to just as easily reverse only half the props to yank the bow around from differential thrust)

There is a reverse gear so to speak, but you have to stop the engine completely first, which can take several minutes to initiate.

Are there turbine speed hydraulic pump designs? What if a pneumatic design was made where the heat from the compressor goes immediately to the expander? Either would have more problems and lower efficiency than turbo-electric, but are they impossible

DDHv wrote:
Are there turbine speed hydraulic pump designs? What if a pneumatic design was made where the heat from the compressor goes immediately to the expander? Either would have more problems and lower efficiency than turbo-electric, but are they impossible

The closest I have found that does not use a reduction gear set would be the fuel pumps in rocket engines, which are direct drive turbine to centrifugal pumps. Some manufacturers (like Orbital)prefer piston engines and pumps for this service however. This would require low viscosity oil to work properly (similar to turbine lube oil).
One of the advantages of a non mechanical drive is the engines can be located anywhere and so can the props. Most modern cruise liners have gone to steerable pods as it eliminates the need for tugs when docking or moving through locks and you can free up space by putting the engines on the outside hull of the ship (easing maintenance and making the ship more stable).
For a warship this would also give propulsion redundancy and avoid the fate of the Bismark which lost its steering with one torpedo hit.

AirTech wrote:For a warship this would also give propulsion redundancy and avoid the fate of the Bismark which lost its steering with one torpedo hit.

Wouldn't external engine mounts be MORE vulnerable to things like torpedo hits?

evilauthor wrote:

AirTech wrote:For a warship this would also give propulsion redundancy and avoid the fate of the Bismark which lost its steering with one torpedo hit.

Wouldn't external engine mounts be MORE vulnerable to things like torpedo hits?

Well, Mk48 ADCAP has a 650 pounds PBX warhead - does it really matter? Torpedo Kill

evilauthor wrote:

AirTech wrote:For a warship this would also give propulsion redundancy and avoid the fate of the Bismark which lost its steering with one torpedo hit.

Wouldn't external engine mounts be MORE vulnerable to things like torpedo hits?

Yes but having six propellers with two in the stern, two in the bow and two amidships like some of the modern cruise ships as opposed to having your propellors and rudders clustered in the stern distributes the power well and you can stick your boilers anywhere on the ship, perhaps some forwards and some in the stern. This eliminates the weak spot under the engine room found in most ships where a large void space is present. You also have a ship that can turn in its own length and move sideways.

AirTech wrote:

evilauthor" quote="AirTech wrote:For a warship this would also give propulsion redundancy and avoid the fate of the Bismark which lost its steering with one torpedo hit.

Wouldn't external engine mounts be MORE vulnerable to things like torpedo hits?

Yes but having six propellers with two in the stern, two in the bow and two amidships like some of the modern cruise ships as opposed to having your propellors and rudders clustered in the stern distributes the power well and you can stick your boilers anywhere on the ship, perhaps some forwards and some in the stern. This eliminates the weak spot under the engine room found in most ships where a large void space is present. You also have a ship that can turn in its own length and move sideways.[/quote]
What you are describing are propulser pods they are electric driven. They are always mounted at the rear of the ship. There are however propulser mounted at the bow to help with docking and close quarter maneuvering.