Turbine engines

saber964 wrote: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.

While modern, real-world, systems are electric, there's no particular reason that a similar system couldn't be done with steam or Diesel power. It would be more prone to failure than electric propulser pods because of the need for mechanical linkages or high-pressure steam lines to each pod, but it could be done.

Weird Harold wrote:

saber964 wrote: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.

While modern, real-world, systems are electric, there's no particular reason that a similar system couldn't be done with steam or Diesel power. It would be more prone to failure than electric propulser pods because of the need for mechanical linkages or high-pressure steam lines to each pod, but it could be done.

It would have to be by mechanical linkage as the very last thing you ever want to do with steam is send it further than you strictly have to. Even with the best insulation in the world sending steam to outboard pods will cause massive loss of heat to the bloody cold water outside. Having the turbines themselves in the pods would also require the reduction gearing to be in the pods and these are huge. I would also mount the reduction gearing inside the ship because as mentioned above these things are massive. The obvious downside of this approach is a massive increase in mechanical complexity as you have to send power through several right angles within the hull of the ship in order to distribute it to all the pods, This will take up more space than the conventional linear layout and could well interfere with the positioning of the substructure of the main batteries and magazines.

Silverwall wrote:
It would have to be by mechanical linkage as the very last thing you ever want to do with steam is send it further than you strictly have to. Even with the best insulation in the world sending steam to outboard pods will cause massive loss of heat to the bloody cold water outside. Having the turbines themselves in the pods would also require the reduction gearing to be in the pods and these are huge. I would also mount the reduction gearing inside the ship because as mentioned above these things are massive. The obvious downside of this approach is a massive increase in mechanical complexity as you have to send power through several right angles within the hull of the ship in order to distribute it to all the pods, This will take up more space than the conventional linear layout and could well interfere with the positioning of the substructure of the main batteries and magazines.

Since they project from the hull, I would think it would also increase the minimum depth of water you could operate in.

Weird Harold wrote:

saber964 wrote: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.

While modern, real-world, systems are electric, there's no particular reason that a similar system couldn't be done with steam or Diesel power. It would be more prone to failure than electric propulser pods because of the need for mechanical linkages or high-pressure steam lines to each pod, but it could be done.

Or Hydraulic motors (which would be smaller than an equivalent power electric motor, and utterly unaffected by water leakage). Azimuth pods could be steerable at either front or rear but most marine captains seem to prefer rear steering rather than forward steering as the ship handles the same as one with rudders. That said a mechanical drive is also possible and sometimes done with small systems (Z-drives being an example). Thinking laterally is not a strong suit for a lot of marine engineers where conservative design being repeated ad nauseum is par for the course. (Repeats are cheap, dozens are cheaper still, which is how the Korean, Chinese and Japanese shipyards make a profit, by making small variations on a standard ship design (a bulk carrier, container ship and oil tanker are structurally interchangeable with minor differences and have almost identical machinery spaces and crew accommodation blocks)).

AirTech wrote:

Weird Harold wrote:""saber964"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."

While modern, real-world, systems are electric, there's no particular reason that a similar system couldn't be done with steam or Diesel power. It would be more prone to failure than electric propulser pods because of the need for mechanical linkages or high-pressure steam lines to each pod, but it could be done.

Or Hydraulic motors (which would be smaller than an equivalent power electric motor, and utterly unaffected by water leakage). Azimuth pods could be steerable at either front or rear but most marine captains seem to prefer rear steering rather than forward steering as the ship handles the same as one with rudders. That said a mechanical drive is also possible and sometimes done with small systems (Z-drives being an example). Thinking laterally is not a strong suit for a lot of marine engineers where conservative design being repeated ad nauseum is par for the course. (Repeats are cheap, dozens are cheaper still, which is how the Korean, Chinese and Japanese shipyards make a profit, by making small variations on a standard ship design (a bulk carrier, container ship and oil tanker are structurally interchangeable with minor differences and have almost identical machinery spaces and crew accommodation blocks)).

Minor notes: there were ads for a few hydraulic pumps and motors which are designed to use sea water as the fluid.

Pods can be in front, back, or sides, so they don't need to increase depth. There was also a design that built side-propulsion into the front and rear of the hull with reversible propellers and removable cover plates

DDHv wrote:
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Minor notes: there were ads for a few hydraulic pumps and motors which are designed to use sea water as the fluid.

Pods can be in front, back, or sides, so they don't need to increase depth. There was also a design that built side-propulsion into the front and rear of the hull with reversible propellers and removable cover plates

Fresh water works too... Hydraulic system pressures will keep leakage mostly in the outwards direction. Electric motors on the other hand really don't like, even small amounts of, salt water, and the HV ones used in azimuth drives like it even less.
Ducted propulsion would be another option (i.e. oversized jet boat) but most ships work in deep water anyway so having the pods clear of the hull improves efficiency significantly. (Of course shrouded props could be used too if sea floor impact is an issue but in really big sizes these can be com an issue on their own but are acoustically quieter than a conventional prop which is why most new submarine designs use them.

SNIP...

Weird Harold wrote:While modern, real-world, systems are electric, there's no particular reason that a similar system couldn't be done with steam or Diesel power. It would be more prone to failure than electric propulser pods because of the need for mechanical linkages or high-pressure steam lines to each pod, but it could be done.

I'm not sure I agree with your point about being more prone to failure, WH.

I'm an engineer by schooling, so theoretically I SHOULD try to make things as complicated as possible... BUT, I've also got a farming ancestry and everyone knows that farmers can simplify things like nobody's business.

I envision a shaft from the engine that has a bevel gear on the shaft to change direction 90 degrees (straight down into the "pod" in this case). In the pod itself, you've got a pretty simple set of roller bearings and a thrust bearing for a horizontal shaft that mounts the prop. also on the shaft is another bevel gear to receive power from the corresponding bevel gear at the bottom end of the vertical shaft. So now you've got a pod with a prop / shaft that can rotate.

As for changing direction, make the entire pod and pod mount (where it attaches to the ship) steerable. You'll need some strength here though - because if the vertical shaft "floats" (meaning that it just transfers rotational energy from the engine to the prop), then if you don't "fix" the pod in the desired position, then when you apply power to the vertical shaft, the entire pod will try to turn in the opposite direction!

Easy peasy lemon squeezy.

Very few components in the pod itself, and those that are are (IMHO) going to be relatively "robust" and not prone to failure unless you run aground or suffer some sort of battle damage.

Just a thought.

WeberFan wrote:I'm not sure I agree with your point about being more prone to failure, WH.

I'm an engineer by schooling, so theoretically I SHOULD try to make things as complicated as possible... BUT, I've also got a farming ancestry and everyone knows that farmers can simplify things like nobody's business.

As an engineer, you should know that moving parts are more prone to wear and/or failure than non-moving parts; there are fewer moving parts in a turbine-electric drive train than in a turbine-gear-train drive train.

A strictly mechanical drive train is certainly possible, but the various turbine-hydraulic or direct-steam would seem to satisfy the KISS principle better than any mechanical drive train; especially when a transmission gets involved.

Keith_w wrote:Since they project from the hull, I would think it would also increase the minimum depth of water you could operate in.

Yep. A ship with 'normally placed' external pods (aka under the bottom) is always going to need deeper water than a hypothetical sister ship with conventional shaft propulsion.

Not a big deal for modern cruise ships; since they can just lighter passengers ashore at the few stops that aren't willing to dredge deep enough channels or harbors for them. Bit more of an issue for a warship that might need the flexibility to use a smaller harbor (or even one captured during a war)

You could put them out to the sides; but that makes docking or underway replenishing more problematic; and you lose some of the maneuverability benefits of having a fully steerable pod. Plus IIRC screws work better when they're farther from the surface (more power before they start to cavitate) so you're potentially also losing some power or efficiency with a side-mounted pod.

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 separate "Astern" and/or "Manoeuvring" turbines.

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

In an old electrical engineering textbook (dated 1929) that I have at home there is a description of the Steam Turbine/Electrical drive systems for USN Capital ships.
I've looked up the list of these ships, as follows :-

BB-40 New Mexico

BB-43 Tennessee

BB-44 California

BB-45 Colorado

BB-46 Maryland

BB-48 West Virginia

CV-2 Lexington

CV-3 Saratoga