Joined: 8:22 PM - Mar 16, 2017

7:23 PM - Feb 03, 2018 #11

I've been thinking about this also, especially in regard to the FFG(X) design.  I think this is a big benefit of at least partial electric propulsion, most likely some sort of CODLAG arrangment.  Have one set of diesel gensets forward, one aft, have the GT and it's transmission amidships, keep at least one compartment between each one.  I'm also toying with the idea of a large amount of battery storage distributed around the ship for instantly available backup power.
Quote
Like
Share

Joined: 9:15 AM - Aug 30, 2005

7:48 PM - Feb 03, 2018 #12

You are more or less describing a diesel electric submarine. Think about how much battery they need to get the equivalent of a running for a couple of hours on the diesels.
"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)
Quote
Like
Share

Joined: 8:22 PM - Mar 16, 2017

9:30 PM - Feb 07, 2018 #13

WarshipAdmin wrote: You are more or less describing a diesel electric submarine. Think about how much battery they need to get the equivalent of a running for a couple of hours on the diesels.
That's not the purpose of the battery in this application.  The idea would never be running for hours on battery power.  

The use of the battery would be to cover short term spikes in use or to provide instant redundant power if a generator goes down.  The idea would never be to drain the battery for more than 15-20 minutes.

In a ship set up as I describe, only enough generators would run to cover the average constant draw.  In many cases, this would be only one genset.  But if you get a spike that's greater than that genset can cover, or that genset drops out, you have a problem.  In may take several minutes to get another genset spun up.  Because of this, procedure would be to have an extra gen set spun up and idling or to run multiple gensets at partial output.  Both of these are highly inefficient.  With the battery capacity available, the ship could run just the optimal number of gensets necessary to keep them running at their most efficient (which is near max output), and if more short term electrical power is needed suck it from the battery.  If that draw looks like it's going to continue, then spin up another genset to cover it (and recharge the battery.)  If the running genset dies, let the battery cover the full draw (shedding load gracefully if necessary), until generator power is recovered.
Quote
Like
Share

Joined: 9:49 PM - Jan 06, 2014

7:46 PM - Aug 07, 2018 #14

Numerous smaller items are generally much less space/weight efficient than fewer larger units. Certainly could be made to work, but how much it's worth the cost is another question. You also have to account for maintenance, operation, additional cabling/switching, additional services, etc etc. All of these are going to be significantly harder with additional distribution of powerplants. Further, you need a certain minimum access space, so the growth in volume (and hence weight) is quite a bit more than just the increase from the additional units. Likewise you need to allow for rigging paths for maintenance, intake/exhaust, vents, etc.... more volume loss. Also need to account for intake a exhaust paths - either you have long trunk runs to get to a central stack or lots of smaller stacks spread all over... not exactly optimal either way. 

Having the engineering plant low and centrally located also helps with stability - having them distributed instead would almost certainly mean they move up in the hull - so you're removing good weight and adding bad weight (from a stability point of view). Further, what do you do with the vacated space? Nothing I can think of that wouldn't be suboptimal somehow (for instance, consolidating all berthing there) and nothing that would help the stability problem either. So you're going to be carrying ballast or widening the hull. 

Beyond that, IMHO you're really not gaining much. CG/DDG and larger ship already have a pretty well distributed engineering plant. Not sure about the arrangement on LCS and smaller ships. If the entire plant is damaged with the current setup you've probably got enough damage to the ship as a whole that it's highly questionable if it's going to survive anyway.... at that point a more distributed plant is useless.
Quote
Like
Share

Joined: 9:49 PM - Jan 06, 2014

7:55 PM - Aug 07, 2018 #15

BBMW wrote:
That's not the purpose of the battery in this application.  The idea would never be running for hours on battery power.  


The use of the battery would be to cover short term spikes in use or to provide instant redundant power if a generator goes down.  The idea would never be to drain the battery for more than 15-20 minutes.

In a ship set up as I describe, only enough generators would run to cover the average constant draw.  In many cases, this would be only one genset.  But if you get a spike that's greater than that genset can cover, or that genset drops out, you have a problem.  In may take several minutes to get another genset spun up.  Because of this, procedure would be to have an extra gen set spun up and idling or to run multiple gensets at partial output.  Both of these are highly inefficient.  With the battery capacity available, the ship could run just the optimal number of gensets necessary to keep them running at their most efficient (which is near max output), and if more short term electrical power is needed suck it from the battery.  If that draw looks like it's going to continue, then spin up another genset to cover it (and recharge the battery.)  If the running genset dies, let the battery cover the full draw (shedding load gracefully if necessary), until generator power is recovered.
A high rate short duration load like that is quite hard on lead acid batteries and the power density is much worse at those rates than at longer duration loads. Other battery chemistry are more forgiving, but there's serious technical challenges to work through with any of them. 

A typical CG/DDG runs around 3 MW electrical plant load. That's a lot of power to get out of a battery, and means you'd need a pretty huge battery and equally large and complex power conversion equipment. Ballpark estimate I'd say you're looking at 500 tons at a minimum, possibly into the thousands of tons of growth on a DDG. (including increased hull size, larger structure, more power to compensate for speed loss, increased auxiliary service, etc etc). Lots of additional maintenance too. Based on sub experience, I'd expect a lifetime of a couple of years, and a fair bit of work to replace it.... not cheap. 
Quote
Like
Share

XV
Joined: 4:33 AM - Jun 29, 2014

7:21 AM - Aug 11, 2018 #16

Simply put, batteries have worse power/weight than gas turbines. If you can afford the room for a battery, you probably can for a turbine.

Spikes are not currently the top problem for ship power sources, the turbine temporarily acts as a flywheel to provide for the spike. Distribution systems are more vulnerable. Spikes are much less of a problem for IFEP - there, the majority of power goes to propulsion, so when there's a spike, everyone shares the drop in voltage. Since propulsion doesn't spike. Emergency batteries are already available.

That said, since electric aircraft are a thing now, some very high-density systems are now being designed to a reasonable set of standards. With high power requirements and strict weight constraints, aeroderivative systems will have the technical specs to be a net gain for shipboard applications. There will be a price in complexity and maintenance, however (the question is mostly which superconducting architecture to use rather than whether), so the business case for them will need to be stronger than "just in case".

skipper101 wrote:Could we also have multiple fuel tanks to go with each engine? this would also help with survivability and redundancy.
This has been the norm pretty much forever.

For a modern warship, further separation of power systems is largely redundant. Note the term - redundancy in general is a negative; it's only good to have redundancy in critical systems. The most critical subsystem in a modern warship is C4I, or simply put sensors and computers. It depends on electrical power to function, but a coupled failure mode between the two is acceptable - if you lose control, you don't need power.

It's unlikely that a failure would affect all three GTG but not C4I. Note that the 51's designers considered it unnecessary to fit the turbines with shaft motor-generators to share propulsion and hotel power, a lot of power redundancy for very little cost. The recent retrofit has to do with efficiency rather than survivability.
Quote
Like
Share

Joined: 8:22 PM - Mar 16, 2017

4:19 PM - Aug 14, 2018 #17

sdmuleman wrote:
BBMW wrote:
That's not the purpose of the battery in this application.  The idea would never be running for hours on battery power.  


The use of the battery would be to cover short term spikes in use or to provide instant redundant power if a generator goes down.  The idea would never be to drain the battery for more than 15-20 minutes.

In a ship set up as I describe, only enough generators would run to cover the average constant draw.  In many cases, this would be only one genset.  But if you get a spike that's greater than that genset can cover, or that genset drops out, you have a problem.  In may take several minutes to get another genset spun up.  Because of this, procedure would be to have an extra gen set spun up and idling or to run multiple gensets at partial output.  Both of these are highly inefficient.  With the battery capacity available, the ship could run just the optimal number of gensets necessary to keep them running at their most efficient (which is near max output), and if more short term electrical power is needed suck it from the battery.  If that draw looks like it's going to continue, then spin up another genset to cover it (and recharge the battery.)  If the running genset dies, let the battery cover the full draw (shedding load gracefully if necessary), until generator power is recovered.
A high rate short duration load like that is quite hard on lead acid batteries and the power density is much worse at those rates than at longer duration loads. Other battery chemistry are more forgiving, but there's serious technical challenges to work through with any of them. 

A typical CG/DDG runs around 3 MW electrical plant load. That's a lot of power to get out of a battery, and means you'd need a pretty huge battery and equally large and complex power conversion equipment. Ballpark estimate I'd say you're looking at 500 tons at a minimum, possibly into the thousands of tons of growth on a DDG. (including increased hull size, larger structure, more power to compensate for speed loss, increased auxiliary service, etc etc). Lots of additional maintenance too. Based on sub experience, I'd expect a lifetime of a couple of years, and a fair bit of work to replace it.... not cheap. 
This isn't 1973.  Lead acid batteries wouldn't be used.  If it was done today, it would likely be lithium Ion, in another 5-10 years, other battery types may be available (Aluminum Ion?.)  

There are now utility scale lithium Ion arrays being used for solar (and other renewable) storage, in a similar (but not exact) way I'd be using them on a ship.  A lot of these are packaged into shipping containers.  A 40' container can hold a 2.8 MW/h array and output up to 2.8MW.  That's with an array that's set up for utility work.  I have to think that the array could be wired in such a way as to have higher output for a shorter period.  

As far as weight, you're right if you include the enclosure and environmental systems.  But in a ship, the enclosure (shipping container) wouldn't be necessary, and the enviromental systems could be part of the shipwide systems.  Expanding those would likely be lighter and smaller than completely separate systems.  

The battery racks also wouldn't need to be centrally located.  They could be placed around the ship where there is available space.

Here's a link to one brand of these systems.  It links to other pages with more info: https://www.neces.com/products-services ... 5654296875
Quote
Like
Share

Joined: 8:22 PM - Mar 16, 2017

4:57 PM - Aug 14, 2018 #18

XV wrote: Simply put, batteries have worse power/weight than gas turbines. If you can afford the room for a battery, you probably can for a turbine.

Spikes are not currently the top problem for ship power sources, the turbine temporarily acts as a flywheel to provide for the spike. Distribution systems are more vulnerable. Spikes are much less of a problem for IFEP - there, the majority of power goes to propulsion, so when there's a spike, everyone shares the drop in voltage. Since propulsion doesn't spike. Emergency batteries are already available.

That said, since electric aircraft are a thing now, some very high-density systems are now being designed to a reasonable set of standards. With high power requirements and strict weight constraints, aeroderivative systems will have the technical specs to be a net gain for shipboard applications. There will be a price in complexity and maintenance, however (the question is mostly which superconducting architecture to use rather than whether), so the business case for them will need to be stronger than "just in case".
Yes, but they have much more flexibility.  Gas turbines are only really efficient at one power level (near their maximium output) and they take some time to spin up.  We've been down the road of all GT (the Burkes), and it's proven effective, but hideously inefficient.  GTs are great for constant base load generation, but that's the exact opposite of what I'm planning on using the batteries before.  The idea of the batteries is to keep as many of the gensets shut down, until/unless they're needed for constant output operation.
The weakness of GT was shown by the abortive attempt to backfit some COGLAG capability to the Burkes.  They could fit electric motor,s and they had the generating capacity to power them.  But in order to guarantee power availability to the electric motors if a GT genset went down, they had to keep a spare genset up and idling, which is inefficient.  If they had the type of battery array I'm talking about, they could run on only the one genset, and depend on the battery to provide power for the time it would take to spin up another genset.
Quote
Like
Share

Joined: 12:26 AM - Feb 13, 2014

7:29 PM - Aug 14, 2018 #19

sdmuleman wrote: Numerous smaller items are generally much less space/weight efficient than fewer larger units. Certainly could be made to work, but how much it's worth the cost is another question. You also have to account for maintenance, operation, additional cabling/switching, additional services, etc etc. All of these are going to be significantly harder with additional distribution of powerplants. Further, you need a certain minimum access space, so the growth in volume (and hence weight) is quite a bit more than just the increase from the additional units. Likewise you need to allow for rigging paths for maintenance, intake/exhaust, vents, etc.... more volume loss. Also need to account for intake a exhaust paths - either you have long trunk runs to get to a central stack or lots of smaller stacks spread all over... not exactly optimal either way. 

Having the engineering plant low and centrally located also helps with stability - having them distributed instead would almost certainly mean they move up in the hull - so you're removing good weight and adding bad weight (from a stability point of view). Further, what do you do with the vacated space? Nothing I can think of that wouldn't be suboptimal somehow (for instance, consolidating all berthing there) and nothing that would help the stability problem either. So you're going to be carrying ballast or widening the hull. 

Beyond that, IMHO you're really not gaining much. CG/DDG and larger ship already have a pretty well distributed engineering plant. Not sure about the arrangement on LCS and smaller ships. If the entire plant is damaged with the current setup you've probably got enough damage to the ship as a whole that it's highly questionable if it's going to survive anyway.... at that point a more distributed plant is useless.
Not a design engineer by trade, but it makes sense that you'd have to worry about the placement -- although I would imagine any vertical movement may not be too much, & could potentially be offset by moving other heavy equipment further "down" in the hull to compensate.

What would worry me, however, is then having to redistribute where the rest of the equipment & systems go...like the weapon systems, CIC, magazines, etc.  And I can think of 1 major issue that would mean a significant increase in a support system for those diesels:  intakes/exhaust.  Centralized engine rooms is why you only see large numbers of stacks on larger vessels, with most destroyers & smaller vessels only needing 1 or 2 (or at least able to combine them in to a pair of stacks).  But just imagine, though, if you installed 8 separate diesels in a new destroyer design, & each one had its own separate stack coming out of the deck -- say, 1 just aft of the bow, 1 on the fantail right behind your helipad, etc. -- or worse, you have to run extra, super-hot exhaust lines all through your ship (or possibly even bulkier, because of all of the extra insulation you need to keep your sailors from burning themselves).  And all of that is extra space that you can't use for other things:  lighting, power, water, HVAC, sensors, etc.  
Quote
Like
Share

Joined: 8:22 PM - Mar 16, 2017

9:42 PM - Aug 14, 2018 #20

Whipped4073 wrote:
sdmuleman wrote: Numerous smaller items are generally much less space/weight efficient than fewer larger units. Certainly could be made to work, but how much it's worth the cost is another question. You also have to account for maintenance, operation, additional cabling/switching, additional services, etc etc. All of these are going to be significantly harder with additional distribution of powerplants. Further, you need a certain minimum access space, so the growth in volume (and hence weight) is quite a bit more than just the increase from the additional units. Likewise you need to allow for rigging paths for maintenance, intake/exhaust, vents, etc.... more volume loss. Also need to account for intake a exhaust paths - either you have long trunk runs to get to a central stack or lots of smaller stacks spread all over... not exactly optimal either way. 

Having the engineering plant low and centrally located also helps with stability - having them distributed instead would almost certainly mean they move up in the hull - so you're removing good weight and adding bad weight (from a stability point of view). Further, what do you do with the vacated space? Nothing I can think of that wouldn't be suboptimal somehow (for instance, consolidating all berthing there) and nothing that would help the stability problem either. So you're going to be carrying ballast or widening the hull. 

Beyond that, IMHO you're really not gaining much. CG/DDG and larger ship already have a pretty well distributed engineering plant. Not sure about the arrangement on LCS and smaller ships. If the entire plant is damaged with the current setup you've probably got enough damage to the ship as a whole that it's highly questionable if it's going to survive anyway.... at that point a more distributed plant is useless.
Not a design engineer by trade, but it makes sense that you'd have to worry about the placement -- although I would imagine any vertical movement may not be too much, & could potentially be offset by moving other heavy equipment further "down" in the hull to compensate.

What would worry me, however, is then having to redistribute where the rest of the equipment & systems go...like the weapon systems, CIC, magazines, etc.  And I can think of 1 major issue that would mean a significant increase in a support system for those diesels:  intakes/exhaust.  Centralized engine rooms is why you only see large numbers of stacks on larger vessels, with most destroyers & smaller vessels only needing 1 or 2 (or at least able to combine them in to a pair of stacks).  But just imagine, though, if you installed 8 separate diesels in a new destroyer design, & each one had its own separate stack coming out of the deck -- say, 1 just aft of the bow, 1 on the fantail right behind your helipad, etc. -- or worse, you have to run extra, super-hot exhaust lines all through your ship (or possibly even bulkier, because of all of the extra insulation you need to keep your sailors from burning themselves).  And all of that is extra space that you can't use for other things:  lighting, power, water, HVAC, sensors, etc.  
By combining diesel gensets for both propulsion and service generation, you can end up with a smaller number prime movers.  AFAIK the F100 design (at least the bigger versions) have eight prime movers, 2 GTs, 2 propulsion diesels and 4 ships service generators.  For a frigate, I'd try to use 4 prime movers, 1 GT and 3 diesel gensets.  I'd use diesels of different outputs, but of the same basic design and cylinder module.  In addition, I'd have two electric motors of about 4KW output each, and 2.5-3MW/h of battery storage.  The only items that need fixed placements are the GT and EMs, since they're directly attached to the shaft lines and/or transmission.  Everything else can be positioned where it makes the most sense for stability, redundancy, damage resistance, service accessability, etc..  

I'm not worried about exhaust.  Look at how the FREMMs handle exhaust.  There are lots of options in there to place the exhausts (buried in the radar mast, in the hull at the water line.)  

Between the different combinations of diesels, and the GT, with the option of using the GT alone, generating electrical power running motive power into the EMs and using them as generators, the design would have a lot of combinations of power output where the running prime movers are running at their most efficient power output.
Quote
Like
Share