Why is Icon underpowered when compared to Oasis?

[steamboats]

On 9/30/2024 at 1:25 PM, Anton said:

Icon has fuel cells that provide electricity for onboard services (we called it hotel load in the Navy) instead of traditional generators.   

 

Currently there are no fuel cells onboard Icon. Icon and Silver Nova were supposed to have fuel cells but so far there´s still a part "not working". The so called reformer which is responsible to convert LNG to hydrogen is still not as efficient as it should be. So both ships are ready to use it but it doesn´t work yet. So far both ships have a reserved space and piping but no fuel cell installed.

 

steamboats

[chengkp75]

8 hours ago, alfaeric said:

So as long as all of them are in phase with each other, they can each output different amounts of power.

What you are describing would mean that the control system would have to instantaneously and constantly be monitoring the load, and adjusting the several engines you want to operate at maximum efficiency to maintain a constant load, while adjusting the one engine to a varying load, every second.  While possible, it would be costly, and also subject to failure, as engines do not react as quickly as the generator, meaning that when load increases, the generator can supply the power immediately, but the engine takes time to build up the power (seconds), causing a bog, or slowing of the speed, until the more fuel brings speed back up.  So, when a large load fluctuation happens, like going from full ahead to half ahead, you run the risk of the "controlled" engine loosing load too quickly, overspeeding, and tripping off line, or being "motorized" (essentially driven by the other generators) when the power drops and current flows from the highly loaded generators to the lower powered generator, reversing the current to be into the generator, at which time the "reverse power" relay will trip the generator off line, or with a load increase, it may bog too much, drop the frequency, and trip off line.  Also, when you have one or more generators operating at constant load, and one generator operating at fluctuating load, you tend to generate eddy currents that flow between the generators, and this leads to inefficient power factors, and higher than  needed current (and current is power in a fixed voltage system, so more fuel).

 

Every marine diesel generator has a reverse power relay, and we test them regularly, doing just this.  We have two generators running online, both at constant, equal, speed, and equal load.  We then reduce the governor setting on one engine, which remains running at the same speed, but produces less power.  When the power reaches zero on that generator, the relay trips it off line protectively to keep it from being motorized.  The same can happen if we were to be operating that generator at low load, and the load demand suddenly decreases, and the load on the lesser loaded engine becomes zero.  A motorized generator can drive the diesel engine to overspeed and damage.

[chengkp75]

3 hours ago, steamboats said:

 

Currently there are no fuel cells onboard Icon. Icon and Silver Nova were supposed to have fuel cells but so far there´s still a part "not working". The so called reformer which is responsible to convert LNG to hydrogen is still not as efficient as it should be. So both ships are ready to use it but it doesn´t work yet. So far both ships have a reserved space and piping but no fuel cell installed.

 

steamboats

So, they are using steam reforming of LNG to produce hydrogen, so this is not a truly "green" source of power.  Interesting.

[steamboats]

25 minutes ago, chengkp75 said:

So, they are using steam reforming of LNG to produce hydrogen, so this is not a truly "green" source of power.  Interesting.

 

I don't have a clue how the reforming process works. But I haven't read anything about steam connected with this. I only know that the reformer still doesn't work. The RCG confirmed this just recently. They are thinking about bunkering a small amount of hydrogen but so far it's still to complicated to have hydrogen onboard and "store" it.

 

steamboats 

[chengkp75]

3 hours ago, steamboats said:

 

I don't have a clue how the reforming process works. But I haven't read anything about steam connected with this. I only know that the reformer still doesn't work. The RCG confirmed this just recently. They are thinking about bunkering a small amount of hydrogen but so far it's still to complicated to have hydrogen onboard and "store" it.

 

steamboats 

Steam reforming is how you generate hydrogen from natural gas.  Methane (natural gas) is mixed with steam under about 20 bar pressure, and it generates hydrogen, carbon monoxide, and carbon dioxide.  The carbon monoxide is then mixed further with steam to generate more hydrogen, and carbon dioxide.  So, the main byproduct of this operation is CO2, a greenhouse gas.

 

And, yes, if they are not planning on using hydrogen as a fuel, just generating enough to keep the fuel cells running, then they won't have storage tanks, which are cryogenic tanks even colder than the LNG tanks.

[alfaeric]

4 hours ago, chengkp75 said:

What you are describing would mean that the control system would have to instantaneously and constantly be monitoring the load, and adjusting the several engines you want to operate at maximum efficiency to maintain a constant load, while adjusting the one engine to a varying load, every second.  While possible, it would be costly, and also subject to failure, as engines do not react as quickly as the generator, meaning that when load increases, the generator can supply the power immediately, but the engine takes time to build up the power (seconds), causing a bog, or slowing of the speed, until the more fuel brings speed back up.  So, when a large load fluctuation happens, like going from full ahead to half ahead, you run the risk of the "controlled" engine loosing load too quickly, overspeeding, and tripping off line, or being "motorized" (essentially driven by the other generators) when the power drops and current flows from the highly loaded generators to the lower powered generator, reversing the current to be into the generator, at which time the "reverse power" relay will trip the generator off line, or with a load increase, it may bog too much, drop the frequency, and trip off line.  Also, when you have one or more generators operating at constant load, and one generator operating at fluctuating load, you tend to generate eddy currents that flow between the generators, and this leads to inefficient power factors, and higher than  needed current (and current is power in a fixed voltage system, so more fuel).

 

Every marine diesel generator has a reverse power relay, and we test them regularly, doing just this.  We have two generators running online, both at constant, equal, speed, and equal load.  We then reduce the governor setting on one engine, which remains running at the same speed, but produces less power.  When the power reaches zero on that generator, the relay trips it off line protectively to keep it from being motorized.  The same can happen if we were to be operating that generator at low load, and the load demand suddenly decreases, and the load on the lesser loaded engine becomes zero.  A motorized generator can drive the diesel engine to overspeed and damage.

I'm confused.  

 

You just explained that it's hard for the engines to constantly follow the power output requirements for the ship.  Fair enough.  I don't really get that part of engine to electrical generation.  

 

But before that, you said that all the engines vary the same percentage to deal with the variable output.  If it is so difficult and complex and slow and coarse, why have all of the running engines do it when you can do it with just one?  Then you deal with the inertia of one engine as opposed to all of them, and if you do it on the "smaller" one, it's a little quicker to react.  Sure, there are possible times where there could be dramatic changes in requirements, but most changes are not really that- trimming the power to keep constant speed, lights, HVAC, galley power, etc.  Over all of the time we've cruised, I don't recall a time where the ship suddenly slowed after cruising at 17knt- that's something you would notice.  The largest immediate change I can recall experiencing is docking where the motors driving the azipods and bow thrusters are on and off to glide into the dock.

 

Still, to deal with the variable power requirements, the engine are throttling, as you have posted.  You may not call it throttling, but the fuel flow is varied (aka throttled) to best match the power requirements with the power generation.

 

[alfaeric]

4 hours ago, chengkp75 said:

So, they are using steam reforming of LNG to produce hydrogen, so this is not a truly "green" source of power.  Interesting.

Maybe they are planning for a day that H2 is available in a better way???  Otherwise, it's a lot of money to invest in fuel cells (which are considerably more expensive than a similar sized ICE) to generate power.  It would be interesting to know the size of the fuel cells, as a SI engine could make the same power with almost no additional emissions- NG emissions are really, really easy to deal with- they were some of the first PZEV vehicles on the market almost 25 years ago.

[dragontrainer]

56 minutes ago, chengkp75 said:

Steam reforming is how you generate hydrogen from natural gas.  Methane (natural gas) is mixed with steam under about 20 bar pressure, and it generates hydrogen, carbon monoxide, and carbon dioxide.  The carbon monoxide is then mixed further with steam to generate more hydrogen, and carbon dioxide.  So, the main byproduct of this operation is CO2, a greenhouse gas.

 

And, yes, if they are not planning on using hydrogen as a fuel, just generating enough to keep the fuel cells running, then they won't have storage tanks, which are cryogenic tanks even colder than the LNG tanks.

Would it be a given they would use LH2 tanks on a cruise ship, or for the above scenario would pressurized gaseous H2 tanks be a consideration to avoid the issues with cryogenic hydrogen?  Maybe asked another way, are there restrictions on pressurized gas storage on cruise ships? 

 

I have not run the numbers on the amount of LH2 that would need to be available, but there aren't a lot of hydrogen liquefiers in the US and LH2 sells at a premium, while steam methane reformers (SMRs) are far more plentiful (and in many cases are the hydrogen source for the liquefiers).

 

I understand why LH2 over pressurized gaseous hydrogen is preferred from a density standpoint.  For road trucking there are both LH2 tankers and pressurized hydrogen tankers depending on customer.  I don't have enough insight to maritime regulations to know if either are an option, at which point it becomes an economic optimization (unless safety rules prohibit pressurized H2 tanks/tubes aboard ship).

[broberts]

23 minutes ago, alfaeric said:

... Over all of the time we've cruised, I don't recall a time where the ship suddenly slowed after cruising at 17knt- that's something you would notice.  The largest immediate change I can recall experiencing is docking where the motors driving the azipods and bow thrusters are on and off to glide into the dock.

...

 

System designs have to take into account edge conditions. While you may not have experienced a particular situation you can't say that it has not and will never happen. 

 

In my (unrelated) experience, the most reliable systems are rarely the most complex.

[steamboats]

@dragontrainer remember the beginnings of LNG... The first two ships were by AIDA. They were able to burn LNG but did not have any tanks onboard as there were no regulations yet. So first they only used it in port with trucks with LNG standing next to the ship.Those were the first experiments with LNG on a cruise ship. It was said that it´s way too dangerous to bunker LNG while passengers are onboard. Well, now we do that. Plus in the beginning LNG was hardly available in any port. For AIDA the trucks had to go to Rotterdam and get the LNG there. Not just because it wasn´t available in Hamburg but also because there were no regulations in Germany by that time.

 

Same with hydrogen. There are no experiences with that onboard a cruise ship yet. Those fuel cells which were supposed to be installed on Icon and Silver Nova were to try out this fuel. Therefore they decided to reform LNG to hydrogen as so far there aren´t final regulations yet for bunkering hydrogen onboard a cruise ship. Plus hydrogen is not available everywhere. So it´s easier for those trial fuel cells to reform LNG to hydrogen.

 

steamboats

[steamboats]

On 9/30/2024 at 5:28 AM, JP350 said:

If underpowered is the wrong term forgive me, but I was reading on Icon's power plant today, and noticed that the diesel generators she's equipped with can output a maximum of 89,000 kw (Running three 14 Cylinder and three 12 Cylinder) at peak capacity. Oasis on the other hand can output 96,000kw (Running two 16 cylinder and four 12 cylinder), at peak capacity. Since Icon is larger in terms of gross tonnage, I became curious as to why Icon would have less powerful engines. 

 

First of all each generation of ships is more energy efficent than the last one. So usually you need 20% less energy for a ship built 5 years later. Between Oasis and Icon are 15 years. Better compare Utopia and Icon. Both are using LNG as fuel. Both are the same "age". Then compare Utopia and Oasis as both are the same class. You may see a difference... That´s evolution.

 

steamboats

[alfaeric]

5 minutes ago, broberts said:

 

System designs have to take into account edge conditions. While you may not have experienced a particular situation you can't say that it has not and will never happen. 

 

In my (unrelated) experience, the most reliable systems are rarely the most complex.

I didn't say it would never happen, I said that it's really rare and the rest of the time the motors have to match relatively small power requirement changes.  And *most* of the time, the larger requirement changes are during docking when motors are turned on and off regularly to position the ship.

Edited Thursday at 02:10 PM by alfaeric

[dragontrainer]

4 minutes ago, steamboats said:

@dragontrainer remember the beginnings of LNG... The first two ships were by AIDA. They were able to burn LNG but did not have any tanks onboard as there were no regulations yet. So first they only used it in port with trucks with LNG standing next to the ship.Those were the first experiments with LNG on a cruise ship. It was said that it´s way too dangerous to bunker LNG while passengers are onboard. Well, now we do that. Plus in the beginning LNG was hardly available in any port. For AIDA the trucks had to go to Rotterdam and get the LNG there. Not just because it wasn´t available in Hamburg but also because there were no regulations in Germany by that time.

 

Same with hydrogen. There are no experiences with that onboard a cruise ship yet. Those fuel cells which were supposed to be installed on Icon and Silver Nova were to try out this fuel. Therefore they decided to reform LNG to hydrogen as so far there aren´t final regulations yet for bunkering hydrogen onboard a cruise ship. Plus hydrogen is not available everywhere. So it´s easier for those trial fuel cells to reform LNG to hydrogen.

 

steamboats

Thanks.  There is a lot of talk about the potential of LH2 (and other "green*" options) for maritime/shipping and it's good to hear the current status for ship-based storage. 

 

Proof of concept via reforming makes sense from a technology demonstration standpoint.

 

*I specifically put green in quotes as today there is very little green (or even blue) liquid hydrogen available.

[chengkp75]

2 hours ago, dragontrainer said:

Would it be a given they would use LH2 tanks on a cruise ship, or for the above scenario would pressurized gaseous H2 tanks be a consideration to avoid the issues with cryogenic hydrogen?  Maybe asked another way, are there restrictions on pressurized gas storage on cruise ships? 

I haven't read up on the class rules for pressurized hydrogen, but ships that use pressurized LNG tanks (like your barbeque), the tank has to be outside on deck.  Not a good look for a cruise ship.  The class societies have pretty much ruled out pure hydrogen for ocean-going ship fuel, due to the low energy density (you gotta store a whole lot to get the same energy as other fuels).

 

2 hours ago, dragontrainer said:

I have not run the numbers on the amount of LH2 that would need to be available, but there aren't a lot of hydrogen liquefiers in the US and LH2 sells at a premium, while steam methane reformers (SMRs) are far more plentiful (and in many cases are the hydrogen source for the liquefiers).

As noted above, the big problem is the low energy density of hydrogen, so its use will always be limited to perhaps generating enough electricity in a fuel cell to charge batteries to provide hotel load in port.  That is still a lot of power, as most cruise ships use about 8-12Mw of hotel power.

 

2 hours ago, dragontrainer said:

I don't have enough insight to maritime regulations to know if either are an option, at which point it becomes an economic optimization (unless safety rules prohibit pressurized H2 tanks/tubes aboard ship).

As noted above, pressurized tanks have to be on deck, while cryogenic tanks, like LNG, can be located under the engineering spaces in the "double bottom", though there are restrictions there as well, to prevent damage to the tanks in case of grounding or allision.  Cryogenic tanks also require "boil off" usage, or re-liquification and reinjection into the tank, and an inert gas generator to fill the atmosphere of the tank.

[chengkp75]

2 hours ago, alfaeric said:

Over all of the time we've cruised, I don't recall a time where the ship suddenly slowed after cruising at 17knt- that's something you would notice.

I'll drop this after this post.  The ship doesn't "suddenly slow" because of inertia, when something is moving that weighs tens of thousands of tons, it takes a while for the thing to slow down.  But, when the Captain moves the telegraph from "full ahead" to "half ahead", you instantaneously drop the power going to the propellers by 40-60% (or about 30,000 kw power reduction).  And, given the amount of power used by propulsion, compared to the hotel load, this is a significant power reduction that happens within seconds.  If you put a frequency meter on the AC in your cabin, when the load comes off the engines that way, you will see a 0.5-1.0 Hz swing and oscillation.  That's about a 15 rpm swing for an engine running at 900 rpm, with a 990 rpm overspeed trip level.  The oscillation will typically take a few seconds to level out.

 

3 hours ago, alfaeric said:

Still, to deal with the variable power requirements, the engine are throttling, as you have posted.  You may not call it throttling, but the fuel flow is varied (aka throttled) to best match the power requirements with the power generation.

No, I was arguing that you could not, as you stated, "throttle" one engine while keeping the others running constantly at maximum efficiency.

 

But, let's agree to disagree, since this seems to be going nowhere.

[chengkp75]

2 hours ago, dragontrainer said:

Thanks.  There is a lot of talk about the potential of LH2 (and other "green*" options) for maritime/shipping and it's good to hear the current status for ship-based storage. 

 

Proof of concept via reforming makes sense from a technology demonstration standpoint.

 

*I specifically put green in quotes as today there is very little green (or even blue) liquid hydrogen available.

Even LNG is not as green as the environmentalists would have you believe.  Yes, if looked at from the viewpoint of the ship alone, it is greener than liquid fuels.  However, looking at both fuels from a "wellhead to combustion" viewpoint, LNG has significant drawbacks in the amount of methane slip involved in producing and transporting it, and methane is far more destructive as a greenhouse gas than CO2.

[dragontrainer]

58 minutes ago, chengkp75 said:

Even LNG is not as green as the environmentalists would have you believe.  Yes, if looked at from the viewpoint of the ship alone, it is greener than liquid fuels.  However, looking at both fuels from a "wellhead to combustion" viewpoint, LNG has significant drawbacks in the amount of methane slip involved in producing and transporting it, and methane is far more destructive as a greenhouse gas than CO2.

Yep, I 100% agree and am more than a little surprised that regulations tend to view LNG as "clean", but it's all a matter of degrees.

For clarity, I'm in no way attempting to argue any of the points discussed above, my questions really were out of curiosity of the current state of acceptable storage and technology.  I have a good feel for land-based energy (e.g., hydrogen, natural gas, ammonia, methanol, etc.) but find the insights of maritime experts extremely valuable; thanks again for all of your thoughts/comments!

[alfaeric]

1 hour ago, chengkp75 said:

I'll drop this after this post.  The ship doesn't "suddenly slow" because of inertia, when something is moving that weighs tens of thousands of tons, it takes a while for the thing to slow down.  But, when the Captain moves the telegraph from "full ahead" to "half ahead", you instantaneously drop the power going to the propellers by 40-60% (or about 30,000 kw power reduction).  And, given the amount of power used by propulsion, compared to the hotel load, this is a significant power reduction that happens within seconds.  If you put a frequency meter on the AC in your cabin, when the load comes off the engines that way, you will see a 0.5-1.0 Hz swing and oscillation.  That's about a 15 rpm swing for an engine running at 900 rpm, with a 990 rpm overspeed trip level.  The oscillation will typically take a few seconds to level out.

 

No, I was arguing that you could not, as you stated, "throttle" one engine while keeping the others running constantly at maximum efficiency.

 

But, let's agree to disagree, since this seems to be going nowhere.

Fair enough.

 

But the ship is travelling at a steady state that nobody notices the motion, you don't think people would notice if the thrust cut in half immediately?   Not sure how you would not notice that- the ship would be decelerating, regardless of how much.  I remember being woken up when it was clear the ship was turning when it should not be, because the ship was rescuing stranded fishermen.

 

And I will think it's dumb to throttle all of the engines instead of one.  Makes no sense to compromise all of the engines when you just would need one for a nominal power requirement fluctuation.  Especially when you can do it to the smaller one.

Edited Thursday at 06:06 PM by alfaeric

[chengkp75]

12 minutes ago, alfaeric said:

But the ship is travelling at a steady state that nobody notices the motion, you don't think people would notice if the thrust cut in half immediately?

Okay, since this isn't about the engine control, I'll take this.  Considering that going from the propellers at full speed ahead, and you move the telegraph to "full astern", or a crash stop, it takes over a mile to stop, so just reducing power to the propellers is not going to cut the speed (and also remember that speed and propeller power are an exponential relationship, so cutting half the power might only reduce speed by a quarter) for quite a distance.  If you move the telegraph to "half ahead" (remember, there are discrete stops on the engine order telegraph (stop, dead slow, slow, half, full, sea), not only do you cut the power by half or more, but the windmilling propellers actually take even less power than if you were going up to half ahead from slow, since the control looks at propeller speed and not power.  Also, the windmilling propellers will not slow the ship, but actually make it take longer to slow than if the propeller stopped completely.

 

And, I didn't say the "thrust" would be cut in half, but the power.  Too very different things when it comes to propellers.  Propeller thrust is based on the propeller speed, for a fixed pitch propeller.  However, the power required to move that propeller at a given speed is based on the propeller diameter, and is exponential to the speed.

[chengkp75]

27 minutes ago, alfaeric said:

And I will think it's dumb to throttle all of the engines instead of one. 

I'll just give you a pointer to where to look at this problem, since I believe you said you weren't well versed on the engine/generator interface.  What you are asking for is a plant that has multiple isochronous governors and one generator operating in droop mode.  This is considered to be an unstable condition, and will cause even more frequency fluctuations as the plant attempts to load share when load changes.  There are plenty of sites to explain about governor modes (isochronous, droop).  Apologies if you know about this.

[amindu]

On 10/2/2024 at 3:08 PM, chengkp75 said:

 

 Then, as others have noted, things like bottom paint has improved since Oasis was built, she went in for a dry dock a few years ago, and got the new teflon paint, so she probably needs less power than originally.  

 

Curious, I know nothing about the topic being discussed but how does paint help with power?

[d9704011]

14 minutes ago, amindu said:

 

Curious, I know nothing about the topic being discussed but how does paint help with power?

Nothing, but it does impact the resistance to movement by reducing friction at the hull/water interface meaning less power is used for non-productive purposes.

[DrProfessor]

13 minutes ago, amindu said:

 

Curious, I know nothing about the topic being discussed but how does paint help with power?

I'm sure others can chime in, but I am guessing that improvements in teflon paint reduce the friction between the ship and the water, thus making it easier (less power needed) to overcome friction to move the boat forward.

I'm more impressed with the ability to distribute a bubble "air shield" along the bottom of the ship to reduce friction. Didn't even know that was a thing, but ... cool.

[chengkp75]

21 minutes ago, amindu said:

 

Curious, I know nothing about the topic being discussed but how does paint help with power?

 

5 minutes ago, d9704011 said:

Nothing, but it does impact the resistance to movement by reducing friction at the hull/water interface meaning less power is used for non-productive purposes.

The teflon paint has a hard, slick surface that marine life cannot attach to, so by reducing the amount of fouling, you reduce the amount of "drag" that also increases the power needed to move the ship.  The slick surface also does as noted above, in reducing friction between the water and the hull, so less power is needed to move the ship at the same speed.  Same with the onboard hull cleaning machine that will remove the slime that gets on the hull creating more drag.

[not-enough-cruising]

45 minutes ago, d9704011 said:

Nothing, but it does impact the resistance to movement by reducing friction at the hull/water interface meaning less power is used for non-productive purposes.

Don't forget the micro bubbles.............