Nuclear power in Russian ships

Most propulsion systems use direct drive... which means the propeller is attached to a huge long shaft that is attached to a gearbox that has driveshafts to the engines which use gas turbines or diesel engines or steam boilers to turn the shaft.

Most have electric motors connected to them that are basically used as generators so the engines turn the electric motors to produce electric current to run all the electronic items on the ship.

Think of it like a petrol or diesel engine driven car... you need to connect the wheels to the engine to make it work... you need a differential to make sure when you turn that the wheels on one side are moving at a different speed to the wheels on the other side so they maintain grip and traction.

You need a drive shaft and gearbox and transmission etc etc.

With an electric drive car you have one electric motor for each wheel and then perhaps a small motor with an electric motor attached to that plus lots of batteries.

The small motor connected to the electric motor uses that electric motor as a dynamo to generate electric current that can be used to power each wheel individually or charge the batteries if they are getting low.

All the electrics on the car like lights and heater and entertainment system all run off the battery now and so do the wheels but add a computer and you can be smart... when going down hills all four wheel mounted motors will create electricity... not a huge amount but instead of draining the batteries they will be adding to the batteries.

With ships it means instead of transmissions and gearboxes and enormous heavy drive shafts you can have small pods mounted under the hull that can turn 360 degrees to manouver the ship even in very tight places. Power generation could become like batteries, so a nuclear power pod could be designed that you plug in to a ship and when it is spent unplug it and remove it and replace it with a new one with no need to open it and replace the active chemicals like they do now.

You could also place the reactors in areas where you would normally put ballast to balance the ship so instead of dead weight it is actually useful.

You could have four or six per ship and space them well apart so battle damage is unlikely to take out all your power...

In fact a big ship like a helicopter carrier might have 8 battery locations... four might be nuclear batteries and the other four might be conventional batteries that the nuclear batteries could charge up. Once they are charged up you could power down your reactors to extend their life and run off the conventional batteries till they get down a bit and then power up one or two reactors to run things and charge the batteries up again.

When you need lots of power bring them all online...

Singular_Transform wrote:

mnztr wrote:

I seriously doubt the Russian have yet developed large electric drive motors yet, not seen any evidence of it, let alone back in the day when Kirovs were built. I have seen pics of a Kirov class at full speed blowing some serious smoke.. It is a straight steam turbine shaft drive.

I did wonder about the reactors being Sub based, but they seem unique based on designation, however who the heck knows. It should not really be that hard to add multiple sub reactors, but maybe space becomes a problem. In any case, maybe they are able to fix the reactors with the upgrade. The Helo carriers will be in service for 30 years + so builiding them Nuclear with the plan to build Nuclear Leider class will make sense. Of course a helo carrier is not a CVN, but its also used in emegencies so transit time with or without escorts is useful. Plus as I said a Kazan or Oscar class can always be lurking around to launch missiles at any targets designated by drones, helos or radar from the Helo carrier. Having to do under way replinishment for one Gorshkov vs both ships also makes a BIG difference in transit time and logstics.

Electric motors aren't the hight tech at all.

Main reason why everyone avoid them on warship is beacuse they consume space and weight from weapon systems.

They don't increase the max speed, but weight more than a conventional turbine-gear combination.

Basic electric motors are not high tech, but state of the art tubine electric drives become pretty high tech. If you look at all the various combinations its quite complex. Turbines - do you use energy recapture and how?  Combined cycle or heat recuperator. Then there is the electrical grid, back up diesels etc. Yes the generators are sometimes run of the main turbine and sometimes they seperate them and sometimes both. Integrated is the most difficult. Then you can also add batteries to the mix. And then you can go with motor, turbine, gearbox to shaft in a mix (diesel genset turns motors to drive ship at slow speeds) or  you can go with Azipod type which improves manuverabilty and puts the drive outside the ship freeing up space. Also there have been huge advances on electric motors so yeah, they become pretty high tech as well, especially when you need to house them in an azipod as it needs to be very powerful and compact. Also it opens up all kinds of packaging options. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. Some of the newer RR marine turbines have 40% thermal efficiency, which is pretty damn impressive!!!

mnztr wrote:

Basic electric motors are not high tech, but state of the art tubine electric drives become pretty high tech. If you look at all the various combinations its quite complex. Turbines - do you use energy recapture and how?  Combined cycle or heat recuperator. Then there is the electrical grid, back up diesels etc. Yes the generators are sometimes run of the main turbine and sometimes they seperate them and sometimes both. Integrated is the most difficult. Then you can also add batteries to the mix. And then you can go with motor, turbine, gearbox to shaft in a mix (diesel genset turns motors to drive ship at slow speeds) or  you can go with Azipod type which improves manuverabilty and puts the drive outside the ship freeing up space. Also there have been huge advances on electric motors so yeah, they become pretty high tech as well, especially when you need to house them in an azipod as it needs to be very powerful and compact. Also it opens up all kinds of packaging options. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. Some of the newer RR marine turbines have 40% thermal efficiency, which is pretty damn impressive!!!

So , NO turbines-generator-electric drive is NO high tech, that is something used in the 2nd WW on battleships .


The math is simple : gas turbine + gearbox wieght less than gas turbine+generator+motor.

Because of this the great military minds tried to find a purpose , and they tried to push for rail guns, lasers and so on.


Azipod is fine, if the ship has to keep position , or manouvre  preciselly.

But useless if the ship needs speed, like a warship.


Put a generator and a turbine above waterline is interesting idea, considering it will push up the centre of gravity ,and makes the ship instable.OR heavy.Or both.

Singular_Transform wrote:

mnztr wrote:

Basic electric motors are not high tech, but state of the art tubine electric drives become pretty high tech. If you look at all the various combinations its quite complex. Turbines - do you use energy recapture and how?  Combined cycle or heat recuperator. Then there is the electrical grid, back up diesels etc. Yes the generators are sometimes run of the main turbine and sometimes they seperate them and sometimes both. Integrated is the most difficult. Then you can also add batteries to the mix. And then you can go with motor, turbine, gearbox to shaft in a mix (diesel genset turns motors to drive ship at slow speeds) or  you can go with Azipod type which improves manuverabilty and puts the drive outside the ship freeing up space. Also there have been huge advances on electric motors so yeah, they become pretty high tech as well, especially when you need to house them in an azipod as it needs to be very powerful and compact. Also it opens up all kinds of packaging options. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. As garry says it also opens up packaging options, You can place the engine room in the center of the ship. Put a backup genset with its own fuel system somewhere else so you have some electric power if the ship is hit. You can place the turbines above the waterline so the ship still has power and engine room is not the first thing that floods. etc etc. Some of the newer RR marine turbines have 40% thermal efficiency, which is pretty damn impressive!!!

So , NO turbines-generator-electric drive is NO high tech, that is something used in the 2nd WW on battleships .


The math is simple : gas turbine + gearbox wieght less than gas turbine+generator+motor.

Because of this the great military minds tried to find a purpose , and they tried to push for rail guns, lasers and so on.


Azipod is fine, if the ship has to keep position , or manouvre  preciselly.

But useless if the ship needs speed, like a warship.


Put a generator and a turbine above waterline is interesting idea, considering it will push up the centre of gravity ,and makes the ship instable.OR heavy.Or both.

I never said it was I said INTEGRATED electrical propulsion can be high tech and motors used today are much more advnaced then those of WWII. Azipods are used in Queen Mary II and the large ship has a top speed of 30 knots. As for the CG of the ship, there are a lot of things that weigh a lot, the gas turbines are not that heavy each 45K HP GE LM 2500 weighs about 22T, so we are talking 66T for 150K hp, 2x for the gensets. You can then put each genset in 3 different locations as well. Weight is not really a big consideration on ship powerplants. Packaging and efficiency are more important. But of course it depends on the ship. In a small corvette or sub - very important, in a large carrier like this, much less importance.

The math is simple : gas turbine + gearbox wieght less than gas turbine+generator+motor.

On a very small ship you are sort of right, except a gas turbine plus gearbox/transmission will have a generator attached to power the electrical things on the ship too and a gas turbine attached to an electric motor means the electric motor is the generator which generates the electricity so all you then need is an electric motor or two to drive the propellers...

On a large ship the drive shafts alone are metres thick and hundreds of tons in weight... and a 200 ton nuclear power plant is relatively light compared with the thousands of tonnes of fuel you would need to carry in bunkerage for a large ship.

Electric motors can also be stopped and reversed fairly easily and quickly. Gas Turbines require gearing and transmissions where the GT is stopped and reverse gear is selected with a stationary gear box (the ship might still be moving but the engine and prop need to stop before they can be put in reverse)... Often with marine diesel engines they can be stopped and then restarted in reverse so your forward gears now work in reverse with no need or capacity to use actual reverse gears if you understand what I mean.

On a very large ship ballast low down in the ship is a good thing but if your propulsion requirements mean it can't be located where you need it then something else has to be put there that can't be used or moved. You can't use ship or aviation fuel for ballast because on some operation you might need to use it up which would make the ship terribly vulnerable to overturning.

Having batteries there or backup diesel engines is ideal but if it can't be anything else then lead or mild steel ballast is used which is just weight you carry around with you that keeps you upright.

When they were experimenting with new thermal imagers for helicopter in the 1990s and 00s one of their options had a big huge thermal imager on the front of the Hind. Its location meant a 60kg ballast weight had to be placed in the tail to keep the trim right... it was just a weight so it could not be taken out and used for anything so flight performance was slightly reduced by having to carry around half a person just to balance this new thermal sight in the nose.

Personally I thought putting a turret mounted gatling gun like a 12.7mm gatling facing rearward with an optical sight and ammo in the main cabin would be more practical and useful... design it so it weighs about 60kgs without the ammo which could be in the main cabin on the cg so as you fly over targets they often pop up and shoot at you... this tail gun could be used to catch those targets unaware... they had designs for tail guns for the Hinds for a long time... this was a chance to try it.

It all came to nothing because modern thermals got much lighter and much more capable and also cheaper the old sight they used was big and bulky and heavy and expensive too. The current GOES systems are much better...

Regarding the speed issue you could have semi retractable pods that can lower and rotate 360 degrees for manouvering and low speed operations and semi retract with fixed rear facing motorised props in the usual position for high speed use... they could even use a planing hull to reduce drag in which case propellers that could turn horizontally 360 degrees could also be made to elevate up and down say 40 degrees (20 degrees up and 20 degrees down) to allow the ship to be trimmed for efficient high speed operations with a planing hull where at speed it lifts out of the water reducing drag and increasing speed..... perhaps it could even pitch down to pull the ship down in to the water to improve stability in rough weather to reduce rolling and pitching movements... active fin structures could be used to reduce roll or raise the hull out of the water when useful to provide higher speeds and better stability to the flight deck.


I have been requested to transfer this thread back to the universal landing ship thread for the moment.... any objections before I do because once moved it will be tricky to undo because all these posts will become intermeshed with the posts in the other thread... I personally think it makes sense to have one thread about ULS for Russia... when we see the final design we might split out the new design from the general thread about these types of ships if necessary...

So two days for objections and if none are received I will move this thread to the Universal Landing Ships thread.

I would add that super conducting materials created for EMALS and the electric power technology needed to make EMALS work is not only useful for EM guns, but also electric motors and electricity control... batteries and capacitor banks etc etc....

And an electric generator is essentially a manually spun electric motor so improvements in performance and efficiency in those will have effects across a wide range of technology areas from new fighters needing more powerful electrical power generators to power AESA radars, to electric trains and trucks and tanks and aircraft and ships and subs... both diesel electric and nukes...

Electric helicopters wont need complex heavy gearboxes...

mnztr wrote:

I never said it was I said INTEGRATED electrical propulsion can be high tech and motors used today are much more advnaced then those of WWII. Azipods are used in Queen Mary II and the large ship has a top speed of 30 knots. As for the CG of the ship, there are a lot of things that weigh a lot, the gas turbines are not that heavy each 45K HP GE LM 2500 weighs about 22T, so we are talking 66T for 150K hp, 2x for the gensets. You can then put each genset in 3 different locations as well. Weight is not really a big consideration on ship powerplants. Packaging and efficiency are more important. But of course it depends on the ship. In a small corvette or sub - very important, in a large carrier like this, much less importance.

So, just quick calculation : )


A 20 MW azipod weight 125 tons, generator additional 20 tons.

Means a Burke class destroyer would need +600 tons for full electric propulsion.

It increase the ship weight by 7-10%,and the cost of hull by 10-15% without increase the combat capabilities - all that it does is slightly reduce the fuel consumption .

Singular_Transform wrote:

So, just quick calculation : )


A 20 MW azipod weight 125 tons, generator additional 20 tons.

Means a Burke class destroyer would need +600 tons for full electric propulsion.

It increase the ship weight by 7-10%,and the cost of hull by 10-15% without increase the combat capabilities - all that it does is slightly reduce the fuel consumption .

What is the savings from gearbox and shafts?  What about elimination of rudder mechanism. What about reduced fuel tankage, What about making the ship smaller because a big chunk of its propulsion is now in the water and the hull can be smaller ....thats the problem with quick math, its often WRONG.

Modifying an existing type might lead to weight increases and inefficiencies, but ships designed from the outset as all electric drive can be made much much better.... or as we have seen with the Zumwalt and LCS much worse...

Lessons need to be learned...

The future of electric drive ships is looking good and is rather an important step forward and the application of the technologies in other areas is huge... but still very young.

I would add that gearboxes and transmissions are complex and expensive... it was technically a gearbox and transmission that cost Russia a Flanker and a Fulcrum in Syria when the landing arrester gear failed leading to the cables snapping instead of absorbing the energy of the landing aircraft.

GarryB wrote:Modifying an existing type might lead to weight increases and inefficiencies, but ships designed from the outset as all electric drive can be made much much better.... or as we have seen with the Zumwalt and LCS much worse...

Lessons need to be learned...

The future of electric drive ships is looking good and is rather an important step forward and the application of the technologies in other areas is huge... but still very young.

I would add that gearboxes and transmissions are complex and expensive... it was technically a gearbox and transmission that cost Russia a Flanker and a Fulcrum in Syria when the landing arrester gear failed leading to the cables snapping instead of absorbing the energy of the landing aircraft.

The shaft electric drive contain gearbox usually.


Problem is the power of electric motor/generator proportinal to its rpm.

Means a 200 tons generator on 3000 RPM has a capacity of 220 MW, but on 150 it has ony 11 MW .

So, it needs gearbox, or the mass will escallate very quick.

On the turbine side it helps , because the gas turbine rotate 6000-10000 rpm the above generator power will be over 400 MW on this RPM.


The Azipods has 200 tons weight for a 20 MW for motor unit only on 150 rpm.

The matching generator for that motor could be only 5-10 tons.


So, it is quite easy to attach an extra ,cheap and light generator to the turbine to feed all fancy laser, but hard to make electric propulsion.

If it was easy it would be in service already.

The problems of making it more efficient are there, but they can be solved as I mentioned with research into new materials etc etc.

Electric cars are as old as petrol driven cars, but there has been nothing like the investment in them as in petroleum powered vehicles and the planet has suffered because of this.

I remember Jeremy Clarkson in the 1990s say if an electric car could beat a petrol one in acceleration he would eat his hat and at the time with pathetic electric cars of the time that seemed like a very safe bet.

But with investment and work electric cars now accelerate much faster than internal combustion driven vehicles do and they are only going to be much much better.

We are at the peak of performance for diesel and petrol engines for ground vehicles... there is plenty of scope for growth for electric motors... essentially they have only just started....

GarryB wrote:If it was easy it would be in service already.

The problems of making it more efficient are there, but they can be solved as I mentioned with research into new materials etc etc.

Electric cars are as old as petrol driven cars, but there has been nothing like the investment in them as in petroleum powered vehicles and the planet has suffered because of this.

I remember Jeremy Clarkson in the 1990s say if an electric car could beat a petrol one in acceleration he would eat his hat and at the time with pathetic electric cars of the time that seemed like a very safe bet.

But with investment and work electric cars now accelerate much faster than internal combustion driven vehicles do and they are only going to be much much better.

We are at the peak of performance for diesel and petrol engines for ground vehicles... there is plenty of scope for growth for electric motors... essentially they have only just started....

You can't do anything about the generator / motor equations.

The enabler of electrical cars is the cheap lithium ion technology ,that in turn was enabled and financed by the prolifilation of the mobile devices .
prior of that everyone was forced to use lead batteries, and that is very heavy , negating all benefit of electrical propulsion .


In the case of electric propulsion a military ship, that needs to be fast and small doesn't benefit anything from it.

For a comerciall ship, that has to go with fuell efficient speed, docking frequently and needs expensive tugs to dock the podded propulsion could give operational savings, mainly from faster docking and less tugboat fee.


For a landing dock it could be beneficial as well, maybe. I have no clue about how they operate, but I presume they have to keep position to allow the ships to dock, so the pod could be beneficiall for them .

I forgot to mention, but the Zumwalt used the AMSC high temperature superconductor rotor motors.

https://www.amsc.com/wp-content/uploads/HTSGen_Bro_0312_forweb.pdf

The first page is a picture of the Zumwalt motor on testbench (I presume)

Considering that this company doesn't offer this type of motor for ships, only for wind turbines, and there is not so much talk about this motors in other naval ships I think it is safe to say the technology doesn't performed as it expected.

High temperature means liquid nitrogen cooling, just to make it clear. Low temperature is the helium cooled superconductor : D

The enabler of electrical cars is the cheap lithium ion technology ,that in turn was enabled and financed by the prolifilation of the mobile devices .
prior of that everyone was forced to use lead batteries, and that is very heavy , negating all benefit of electrical propulsion .

I don't think you understand what I am talking about... just because I am talking about an electric vehicle does not mean it is battery powered.

An electric car can use a motor to generate power... and the issues with battery performance can be overcome.

One of the biggest problems with solar power and wind power and hydro electric power is that they are unreliable.... clouds and night time for solar, lack of wind for wind power and lack of rainfall for hydro electric means that the power is not always available when you need it... you need some way of storing power so that when you need it it is ready.

One way is batteries... use solar and wind to charge up batteries... during the day the solar power can go straight to the grid and excess power can charge up batteries as well so when the sun is not available you can use the batteries to continue supplying power. For wind you do pretty much the same... have capacity to supply power when it is windy and also charge batteries so the batteries can be used when it is not windy enough or at all. And of course manage your hydro lakes and keep an eye on the weather forecast so you generate enough electricity without lowering the lake too much so even if you get a bit of heavy rain you can cope but also cope with a lack of rain for a while too.

The problem is that batteries are not 100% efficient and add weight and are bulky and difficult to transfer... also their characteristics are so variable it becomes a problem. Say I spend a fortune and get amazing top quality batteries for my bike or car... when I am driving around town I don't want to swap my flat batteries for some fully charged batteries because I might get much cheaper batteries in return for my high performance ones, so I have to charge which might take one hour... but it might also take 6 hours.

If my car has fuel cells on board instead of charging I could buy Hydrogen gas in bottles... hydrogen gas is cheap to make... if I have a fuel cell in my car I can make my own with water and an electrical current... so over night I could charge up the batteries in my car from a wall socket but also run water backwards through my fuel cell to create hydrogen gas to fill up tanks on board my car. When my batteries get low during the day I can switch to hydrogen... the byproduct of hydrogen going through my fuel cell is water which I can store. If the roof of my car has a solar panel I can be converting water back in to hydrogen while it is parked during the day in the sun.

The point is that an electric vehicle can use a variety of power sources and power storage options.... in 100 years time you might get a nuclear battery like those used in the Terminator films that powers the car for 5 years... and once depleted send it back to the factory to be recharged in a breeder reactor so it can be sold again... true recycling... true green...

Zumwalt was an attempt to be revolutionary at everything and they were too ambitious... it is not that the technology wont work... it is that they haven't got it working now/yet.

Electric is certainly the way forward.

Look at the Su-57... replacing hydraulic powered control surfaces with electric... lighter cheaper more responsive less vulnerable to battle damage because there is no high pressure liquid pipes to move the control surfaces...

If there is no battery then the generator-motor is a transmission only.


And for that purpose the mechanical, gear based transmission way cheaper, lighter and they more efficient.

Each gear cost 5% of performance, planetary gear cost 3%, electrical motor or generator cose 3-5%, so if there is a transmission-generator-motor-trnsmission then the losses will be very high.

An electric drive ship would have electric motors as close as possible to the propellers... separating the propellers from the propulsion system means you need big heavy drive shafts.

By attaching the electric motors to the propellers you eliminate the drive shafts and transmission.

You could use a gearbox or you could simply vary the current to change the RPM of the prop...

On a car you have one electric motor per wheel.

The Russians have trucks with the electric motor inside the wheel...

GarryB wrote:An electric drive ship would have electric motors as close as possible to the propellers... separating the propellers from the propulsion system means you need big heavy drive shafts.

By attaching the electric motors to the propellers you eliminate the drive shafts and transmission.

You could use a gearbox or you could simply vary the current to change the RPM of the prop...

On a car you have one electric motor per wheel.

The Russians have trucks with the electric motor inside the wheel...

It is about mechanical equations.

Power=torque*speed_of_rotation

The weight of shaft depends on the torque.


The electromagnetic field gives a small amount ot forque, so to make it powerfull the rpm has to be high.

The shift shaft rotate very slowly, means the electrical motor is not a good fit for that job. Can be used , but it will be very heavy.


As a matter of fact, if the issue is the length of shaft then the steam turbine (or even the gas) can be installed into a pod.
PRoblem of course is it can't be removed /disassembled from that point of time.

But the weight of the shaft can be decreased by increasing the rpm of it, to the gas turbine.


That proportionally decrease the weight of shaft.

The electromagnetic field gives a small amount ot forque, so to make it powerfull the rpm has to be high.

Electric cars can be made with better acceleration than any fuel driven motor... EM guns are being researched because they offer more power and speed than conventional propellants/explosives can achieve...

The shift shaft rotate very slowly, means the electrical motor is not a good fit for that job. Can be used , but it will be very heavy.

With Azipods the screw is attached directly to the electric motor contained in an external pod that can swivel 360 degrees...

As a matter of fact, if the issue is the length of shaft then the steam turbine (or even the gas) can be installed into a pod.
PRoblem of course is it can't be removed /disassembled from that point of time.

As ships get bigger the problem gets worse in terms of shaft weight and size... the whole problem is bypassed with electric motors.

Singular_Transform wrote:

GarryB wrote:An electric drive ship would have electric motors as close as possible to the propellers... separating the propellers from the propulsion system means you need big heavy drive shafts.

By attaching the electric motors to the propellers you eliminate the drive shafts and transmission.

You could use a gearbox or you could simply vary the current to change the RPM of the prop...

On a car you have one electric motor per wheel.

The Russians have trucks with the electric motor inside the wheel...

It is about mechanical equations.

Power=torque*speed_of_rotation

The weight of shaft depends on the torque.


The electromagnetic field gives a small amount ot forque, so to make it powerfull the rpm has to be high.

The shift shaft rotate very slowly, means the electrical motor is not a good fit for that job. Can be used , but it will be very heavy.


As a matter of fact, if the issue is the length of shaft then the steam turbine (or even the gas) can be installed into a pod.
PRoblem of course is it can't be removed /disassembled from that point of time.

But the weight of the shaft can be decreased by increasing the rpm of it, to the gas turbine.


That proportionally decrease the weight of shaft.

I don't get what you are saying. Electric motors are known for having max torque at 0 rpm. For example my car has a fixed ratio and revs up to 11K rpm. Turbines need to spin fast even at idle, and to produce power they need to turn really fast, thus they need a big reducer AND reverse gear. Diesels can sometimes be stopped and started in reverse (quite often) . Packaging rarely allows the final reduction to be close to the prop, so you really have no choice but to have long, heavy shafts.

GarryB wrote:An electric drive ship would have electric motors as close as possible to the propellers... separating the propellers from the propulsion system means you need big heavy drive shafts.

By attaching the electric motors to the propellers you eliminate the drive shafts and transmission.

You could use a gearbox or you could simply vary the current to change the RPM of the prop...

On a car you have one electric motor per wheel.

The Russians have trucks with the electric motor inside the wheel...

varying the current results in a huge loss of efficiency. Most electric motor control today is done thorugh pulse with modulation. i.e you supply the same volts and amps, but deliver it in varied pulses to achieve the actual KWH output or RPM you want.

mnztr wrote:

I don't get what you are saying. Electric motors are known for having max torque at 0 rpm. For example my car has a fixed ratio and revs up to 11K rpm. Turbines need to spin fast even at idle, and to produce power they need to turn really fast, thus they need a big reducer AND reverse gear. Diesels can sometimes be stopped and started in reverse (quite often) . Packaging rarely allows the final reduction to be close to the prop, so you really have no choice but to have long, heavy shafts.

Electric motor characteristic :



As visible the torque is constant over all RPM, and the power increase lineary by RPM.

Gas turbine :

The power decrease lineary by RPM, and there is a torque peak .


Diesel engine :



There is a peak power and peak torque.

The shaft is less massive as it seems, it is most likely a hollow tube on the ships.

The mass of it in the ship most likelly neglible, to insert the gearbox at the wall of the ship is most likely governed by the available reosurces.


To ballance out a long, high RPM shaft is not a trivial job, most likelly it has to spin thorught several critical resonant rpm during start.

So, if the overal saving is few tons then no one really bother to risk a long, expensive ballancing just to decrease the ship weight by 0.01%.

It is quite common to use this type of gear assembly , example the good quality heavy duty axles has planetry gear in the wheel hub, so the overal shaft mass can be decreased .

Of course it sacrafice 3% of power on the gear assembly : ), but the engine need transmission anyway.

So I don't see why you can't see why electric drive is so desireable. Turbines have to operate in a very tight range to be efficient and poweful which is why there is CODAG commonly used or COGOG so different engines can be set up at different speeds to optimize efficiency/power depending on their role. With eletric final drive they can just pick a ratio + variable pitch allows them to do just about everything without such complexity.

mnztr wrote:So I don't see why you can't see why electric drive is so desireable. Turbines have to operate in a very tight range to be efficient and poweful which is why there is CODAG commonly used or COGOG so different engines can be set up at different speeds to optimize efficiency/power depending on their role. With eletric final drive they can just pick a ratio + variable pitch allows them to do just about everything without such complexity.

Due to the mass.


The ABB likes so much the AZIPOD because for a small, 20 MW power it has to contain a 200+ ton motor.

So, they can sell for a crouse ship the same stuff that can work in a 1000 MW + power plant.

I mean, a power plant generator with 220 MVA ( MW) rating weight around 250 tons , strictly only the starot+rotor assembly.



Actually, the ABB most likelly charge way more for the azipods with 100 MW sum capacity than for a whole 2000 MW power plant electrical works.


On a crusie ship it worth it, considering they saving time with the docking, passanger comfort, less thug fee and so on, but in a warship it doesn't have too much value.

Ships need eletricity anyway, and more and more of it. I am not sure what a COGOG gearbox weighs but it can't be light. Also with an effcient electric drive you can carry less fuel.

mnztr wrote:Ships need eletricity anyway, and more and more of it. I am not sure what a COGOG gearbox weighs but it can't be light. Also with an effcient electric drive you can carry less fuel.

Let check the Ford carrier example.

It has close to 200 MW shaft power, means with a podded full electric propulsion it would nee 2000-3000 tons of electrical motors.

It could increase the ship weight by 2-3%, and what savings are on the other side ?


And the Ford actually has 200 MW generating capacity, because the high RPM generators weight so small it doesn't affect the ship weight by measurable ways.