Why is Icon underpowered when compared to Oasis?

[JP350]

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. 

[brillohead]

This would be a question for @chengkp75 ... he's acquainted with the technical side of things.

[Saab4444]

2 hours ago, 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. 

Many older ships have more power compared to newer once of similar size. One reason is more efficiency and environmental and fuel cost focus in the last years. Newer ships also have a lower top speed as the focus has shifted.

[Anton]

I’ve read a couple articles about this.  Icon has fuel cells that provide electricity for onboard services (we called it hotel load in the Navy) instead of traditional generators.  Another interesting fact is the elevators going down generate electricity that is used by those going up.  Waste heat and even losses from cooling are captured and reused in various ways.  

[twangster]

More efficient?

[dragontrainer]

As a point of reference, the captain of Harmony recently noted during his discussion that Harmony, built roughly six years after Allure, was 20% more efficient than Allure.

 

Efficiency can be measured in a myriad of ways, and he did not go into details of how he was defining "efficiency", but it is reasonable to me that another eight years (and two ships) of technology progression since Harmony could lead to reduced power needs even as the ship gets larger.

 

With that said, I will defer to the maritime experts for their experience/opinions.

[alfaeric]

Another factor is knowledge of the system.  Every time we've been able to visit the bridge or talk to the chief engineer, Oasis ships seem to run mostly on 3 of the 6 engines.  Which is one reason the Oasis got away with an empty engine for so very long (they had 5 out of 6 running engines for many years until there was a dry dock where they cut a hole in the ship to swap engines).  

 

All engines have a sweet spot for efficiency, too- so to maximize that, the "throttled" engine to make up the varying power requirements needs to be as small as possible and the rest of the engines need to run at peak efficiency all the time.  

 

So beyond the extra power generation systems, it's likely that time and engine efficiency has taught the designers a better understanding of the true needs of the power system.

 

I could be wrong about this- but it also seems that cruise ships rarely every use all of the power they have.  So there's not much need for that extra power an Oasis ship has over the Icon.

[pyrateslife4me84]

I heard a rumor that guests in the cheapest rooms down in Steerage are expected to take a row 8 hours each day, so this could explain the need for less power. 

[gmerick]

ICON runs on LP Gas, Oasis on diesel fuel.  LP gas doesn't produce as much energy.

[d9704011]

5 minutes ago, gmerick said:

ICON runs on LP Gas, Oasis on diesel fuel.  LP gas doesn't produce as much energy.

Pretty sure ICON uses Liquefied Natural Gas (LNG) in propulsion engines.

[gmerick]

LPG, LNG - same energy density -- 20% less than diesel fuel.

[alfaeric]

removed

 

Edited Monday at 04:59 PM by alfaeric

[alfaeric]

24 minutes ago, gmerick said:

LPG, LNG - same energy density -- 20% less than diesel fuel.

If they needed the power, they would have sized it up, but they didn't.

[twangster]

Conflicting information on Icon's engines.

 

One source claims 67,500 kW:

 

https://www.ship-technology.com/projects/icon-of-the-seas-cruise-ship-usa/

 

Other sources claims 89,310 kW:

 

https://www.bairdmaritime.com/passenger/cruise/vessel-review-icon-of-the-seas-royal-caribbeans-newest-lng-powered-ship-can-house-5600-guests

 

3 x 16,030 kW

3 x 13,740 kW

Total: 89,310 kW

 

Wikipedia:

 

3 × Wärtsilä 14V46DF, 16,030 kW (21,790 hp) each

3 × Wärtsilä 12V46DF, 13,740 kW (18,680 hp) each

Total: 89,310 kW

 

With more efficient lighting and other energy measures to reduce energy consumption it's possible they don't need as much production available.   Oasis was built before numerous energy conserving measures were readily available like they are today.

 

Compare Wonder to Utopia for a better LNG to HFO comparison.

 

Wonder:

4 × 14,400 kW (19,300 hp) Wärtsilä 12V46F

2 × 19,200 kW (25,700 hp) Wärtsilä 16V46F

2 × 2,070 kW (2,780 hp) MTU 16V4000

Total: 100,140 kW (134,290 hp)

 

Utopia:

6 x 16kW Wartsila 46TS-DF 

Total: 96,000 kW

 

Utopia has slightly lower energy production available.

 

55 minutes ago, gmerick said:

ICON runs on LP Gas, Oasis on diesel fuel.  LP gas doesn't produce as much energy.

 

Which is why they consume more LNG to create the equivalent energy output.   This causes them to have much larger LNG fuel tanks on board since they will consume more by volume to produce the same energy.

Edited Monday at 05:14 PM by twangster

[donsullivan]

According to the consoles in the engine control room we saw on the Behind the Scenes tour  on the 9/7 sailing, they are:

 

3 x 13,400kW

3 x 15,700kW

 

Operational at the time:

1 x 15,7000kW

2 x 13,400 kW

Generating 42.5 MW 

 

Not Operational at the time:

1 x 15,700 Shutdown

1 x 15,700 Ready and Remote

1 x 13,400 Ready and Remote

[gatour]

As some of the prior post have alighted to.  The so-called "engines" are actually generators of electricity.   The downstream "consumers" of the electricity uses it for various purposes.  Things like the electric motors that turn the screws that move the ship.  The bulbs that provide light for you to get around the ship etc.  As those devices become more efficient they require less electricity, so the generators don't have the need to provide as much electricity.  Think of when you switched from incandescent light bulbs to led light bulbs.  You went from using 100kw of electricity to 12-15 kw electricity.  So you are consuming less electricity.

 

I imagine the motors etc on the newest ships are more efficient than the motors on the now "older" ships so the generators (engines) can be "smaller". 

[CruseKrazy]

Interesting thread, thanks.

[twangster]

Perhaps they've come to realize that other mega ships are overpowered so they adjusted Icon down to something more appropriate.

 

A 300HP car and a 400HP car both can only go the speed limit on the interstate.  Having extra power is cool and comes in handy sometimes but may not be absolutely necessary to get the job done proficiently.  

 

There is a point of diminishing returns.

 

Probably some savings to be had by operating with less total potential power while still having ample power to get the job done.  

 

 

Edited Wednesday at 02:12 PM by twangster

[shof515]

another thing to consider is fuel consumption. a big overpower engine requires more fuel and a more lean sized appropriate smaller engine uses less fuel. 

 

less fuel that needs to be pumped into a ship, is money a cruise line is saving

 

its like having a car burning 20 miles per gallon and then switching to a hybrid car that gets like 50 miles per gallon 

[ONECRUISER]

On 9/30/2024 at 11:08 AM, donsullivan said:

According to the consoles in the engine control room we saw on the Behind the Scenes tour  on the 9/7 sailing, they are:

 

3 x 13,400kW

3 x 15,700kW

 

Operational at the time:

1 x 15,7000kW

2 x 13,400 kW

Generating 42.5 MW 

 

Not Operational at the time:

1 x 15,700 Shutdown

1 x 15,700 Ready and Remote

1 x 13,400 Ready and Remote

Yeah but which one is Fastest off the Line 0-60?  😁     ...Thanks for Posting

[chengkp75]

On 9/30/2024 at 10:49 AM, alfaeric said:

All engines have a sweet spot for efficiency, too- so to maximize that, the "throttled" engine to make up the varying power requirements needs to be as small as possible and the rest of the engines need to run at peak efficiency all the time. 

There is no "throttled" engine.  All the engines run at the same percentage of load, when connected together on the electrical system.  So, a smaller engine will produce less power than a larger engine, but they will both produce 80% of capacity, for example.  The optimum point for diesel engines is around 85% for best fuel efficiency, but this is also the point at which the automation will start another engine, to prevent possible overloads and blackouts.  So, they will usually run in the 75-85% range, if possible.  This is why most ships have two different sized engines, so the capacity can be tailored to meet the demand while maximizing the load percentage (so, sometimes 3 small and 1 large, sometimes 2 small and 2 large, etc)

 

On 9/30/2024 at 12:34 PM, gmerick said:

LPG, LNG - same energy density -- 20% less than diesel fuel.

This is correct, and is reflected in Wartsila's data for the 46 series engine, rated at 1250 kw/cylinder on liquid fuel (HFO, diesel, methanol) or 1145 kw/cylinder on LNG.

 

On 9/30/2024 at 7:25 AM, Anton said:

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

The fuel cells on Icon amount to about 10% of hotel load, or about 1Mw.

 

On 9/30/2024 at 1:09 PM, twangster said:

Conflicting information on Icon's engines.

Using Wartsila's datasheet on the 46 series engine, Icon should have the 89,310 kw figure, from 78 cylinders rated at 1145 kw/cylinder.

 

On 9/30/2024 at 1:09 PM, twangster said:

Utopia:

6 x 16kW Wartsila 46TS-DF 

Total: 96,000 kW

Not sure this is correct.  According to Wartsila, 96,000 kw from 6 engines is 16,000 kw per engine.  Now, the 46TS-DF engine has a 12 cylinder rated 15,600 kw or a 14 cylinder rated 18,200 kw.  The 16 cylinder is over 20,000 kw.  My guess is that the press releases state 96,000 which is the "normal" operating level, not the capacity, as this is about 87% of the rated capacity of 6 14 cylinder engines.

 

On 9/30/2024 at 2:08 PM, donsullivan said:

According to the consoles in the engine control room we saw on the Behind the Scenes tour  on the 9/7 sailing, they are:

 

3 x 13,400kW

3 x 15,700kW

This is about 97% of rated capacity, which is where the engineers start to pucker up, so that is where the operational "red line" is set.

 

5 hours ago, twangster said:

Perhaps they've come to realize that other mega ships are overpowered so they adjusted Icon down to something more appropriate.

I note that Oasis is designed for 24.5 knots, and Icon at 22 knots  Icon is 3 meters longer (not sure of the relative waterline lengths, which is really the criterion, but overall length is a fair comparison), so the "hull speed" (the most efficient speed to push the hull form (the underwater hull) through the water) would be very similar.  This tells me that the Oasis is pushing the ship faster than the hull speed, and therefore using a lot more power than is necessary.  As an example, the Oasis displaces (her actual weight) about 100,000 tons, and the SS United States weighs about half of that (47,000 tons), but Oasis needs only 60,000 kw (her three 20Mw azipods) to push twice the weight at 24 knots.  The SSUS, while reaching 38 knots on her sea trials, required a whopping 184Mw just on her propellers, or 3 times the power.  The SSUS at 38 knots was obviously operating well above her "hull speed".

 

Why does Icon have less installed power than Oasis?  A lower designed speed (probably close to hull speed) is the big factor.  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.  Another major factor is the "air lubrication" system, that spreads a layer of air bubbles over the entire underwater hull, reducing friction and drag.  Icon also has a built in hull cleaning system, that can be deployed whenever in port, to clean the hull, and not wait for a dry docking every 2.5 or 5 years.

[alfaeric]

1 hour ago, chengkp75 said:

There is no "throttled" engine.  All the engines run at the same percentage of load, when connected together on the electrical system.  So, a smaller engine will produce less power than a larger engine, but they will both produce 80% of capacity, for example.  The optimum point for diesel engines is around 85% for best fuel efficiency, but this is also the point at which the automation will start another engine, to prevent possible overloads and blackouts.  So, they will usually run in the 75-85% range, if possible.  This is why most ships have two different sized engines, so the capacity can be tailored to meet the demand while maximizing the load percentage (so, sometimes 3 small and 1 large, sometimes 2 small and 2 large, etc)

 

I very much respect your position, but one engine is going to be "throttled" as a diesel.  Load is never constant- there's enough variability that even if the ideal range is 75-85%, it's likely that it's going to have to dip to 65 at low times and maybe even 90 for brief times.  

 

Besides, ranging between 75-85% is throttling the output.

 

Run all but one at ideal output, the last will be close enough, but not perfect.  Meaning throttled, even a little bit.

[chengkp75]

35 minutes ago, alfaeric said:

Run all but one at ideal output, the last will be close enough, but not perfect.  Meaning throttled, even a little bit.

This can't happen.  When generators are connected in parallel on a distribution bus, as the diesel generators on a cruise ship are, they all run at the exact same speed, which keeps the frequency of the power constant (60 Hz).  It is as if they are all connected on the same solid shaft.  Yes, load is variable, but when an engine takes load, it wants to slow down, so the governor tells the fuel pumps to allow more fuel to the engine, to generate more, and maintain the constant speed.  Each engine will get this same signal (in minutely different amounts) so that the engines all run at the exact same speed.  So, while the load may vary from 25% to 85%, each engine puts out 25% or 85% of their capacity, exactly the same as the other engines on line.  As I said, a 15Mw generator will put out more actual power than a 13Mw generator, but each will be operating at the same percentage of power, there is no "one" generator that is kept at reduced load while others run at maximum.  Can't happen on a set of parallel generators.

 

And, when the load reaches 90% as you suggest, the automation will start another generator and add it's full capacity to the system, and it will then drop the percentage load on all engines, since the capacity has increased while the load is the same.

[alfaeric]

Lets not confuse throttling with engine speed, please.  Throttling effects engine output in all aspects,  so if the engine speed is forced to be constant, then the power output will go up or down based on the requirements.  

 

And varying the output of the engine, regardless of if it's speed, or power, or both- is throttling the output.  I've seen plenty of dyno testing where the intention was to keep the engine speed constant, but vary the load, so I know it's possible.  For a gas engine, the air flow is varied, for a diesel, the fuel flow is varied.  Both are throttling the output.  Basically, you are saying all of the engine outputs are throttled proportionally- so they are being throttled.

 

As for how they are run, the way you describe it to me makes no sense to do it that way.  Each engine has it's onw generator, right?  So as long as all of them are in phase with each other, they can each output different amounts of power.  As an engineer, it makes no sense to have all of the engines run out of their peak efficiency range when you can limit it to just one. Using one engine to fine tune the power output give the team much finer control over the total output.  

 

Maybe that's how it does, but I certainly would not run it that way.

Edited Wednesday at 11:51 PM by alfaeric

[brillohead]

4 hours ago, chengkp75 said:

There is no "throttled" engine.  All the engines run at the same percentage of load, when connected together on the electrical system.  So, a smaller engine will produce less power than a larger engine, but they will both produce 80% of capacity, for example.  The optimum point for diesel engines is around 85% for best fuel efficiency, but this is also the point at which the automation will start another engine, to prevent possible overloads and blackouts.  So, they will usually run in the 75-85% range, if possible.  This is why most ships have two different sized engines, so the capacity can be tailored to meet the demand while maximizing the load percentage (so, sometimes 3 small and 1 large, sometimes 2 small and 2 large, etc)

 

This is correct, and is reflected in Wartsila's data for the 46 series engine, rated at 1250 kw/cylinder on liquid fuel (HFO, diesel, methanol) or 1145 kw/cylinder on LNG.

 

The fuel cells on Icon amount to about 10% of hotel load, or about 1Mw.

 

Using Wartsila's datasheet on the 46 series engine, Icon should have the 89,310 kw figure, from 78 cylinders rated at 1145 kw/cylinder.

 

Not sure this is correct.  According to Wartsila, 96,000 kw from 6 engines is 16,000 kw per engine.  Now, the 46TS-DF engine has a 12 cylinder rated 15,600 kw or a 14 cylinder rated 18,200 kw.  The 16 cylinder is over 20,000 kw.  My guess is that the press releases state 96,000 which is the "normal" operating level, not the capacity, as this is about 87% of the rated capacity of 6 14 cylinder engines.

 

This is about 97% of rated capacity, which is where the engineers start to pucker up, so that is where the operational "red line" is set.

 

I note that Oasis is designed for 24.5 knots, and Icon at 22 knots  Icon is 3 meters longer (not sure of the relative waterline lengths, which is really the criterion, but overall length is a fair comparison), so the "hull speed" (the most efficient speed to push the hull form (the underwater hull) through the water) would be very similar.  This tells me that the Oasis is pushing the ship faster than the hull speed, and therefore using a lot more power than is necessary.  As an example, the Oasis displaces (her actual weight) about 100,000 tons, and the SS United States weighs about half of that (47,000 tons), but Oasis needs only 60,000 kw (her three 20Mw azipods) to push twice the weight at 24 knots.  The SSUS, while reaching 38 knots on her sea trials, required a whopping 184Mw just on her propellers, or 3 times the power.  The SSUS at 38 knots was obviously operating well above her "hull speed".

 

Why does Icon have less installed power than Oasis?  A lower designed speed (probably close to hull speed) is the big factor.  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.  Another major factor is the "air lubrication" system, that spreads a layer of air bubbles over the entire underwater hull, reducing friction and drag.  Icon also has a built in hull cleaning system, that can be deployed whenever in port, to clean the hull, and not wait for a dry docking every 2.5 or 5 years.

 

I just *knew* you'd be equipped to answer this technical stuff.  

Thanks for chiming in!