Speed of new RN CVFs

[drjn]

First time post......hello one and all.

I've been doing a bit of reading about the new CVFs that the RN and French navy are getting and was somewhat surprised to note that the top speed is 25 knots. Now given the length of the vessel (as well as it mass) I would have expected to see 30 to 35 knots as its' top speed.
Thoughts anyone?

 

[Dr Phobus]

To be honest, a lot of nation give a generic top speed of 25-27Knots. Often real speeds are more classified. Loko at the speeds of the RN SSN's the information is somewhat vague, from different sources. Thats my perspective on it.

 

[Systems Adict]

As Dr P stated, Carriers are usually listed as somewhere between 20-30 kts.
(A quick google of various naval info sites will no doubt back this up with actual figures)

Additionally, Carriers are more usually A LOT bigger than the vessels that support them in a Carrier Battle Group (CBG), so it's important that the vessels in support are capable of a resonable speed to keep up.
Your average FFG or DDG is only capable of a maximum of 25-29 kts.

Finally, trying to make anything from 25,000 GRT - 75,000 GRT weight move above 25-30 kts consumes an awful lot of power.

If you were to look at an average ships Diesel engine power map, you would see that even with gearing, every knot above say 20 kts, can almost double the amount of fuel consumed per hour. On the 25-30 kt band it becomes a vertical line, that's why most navies around the world tend to pootle about in an "economic" fuel consumption mode (around 10 - 15 Kts).

Hope this helps....

Systems Adict

 

[Tasman]

Additionally, Carriers are more usually A LOT bigger than the vessels that support them in a Carrier Battle Group (CBG), so it's important that the vessels in support are capable of a resonable speed to keep up.
Your average FFG or DDG is only capable of a maximum of 25-29 kts.


Systems Adict

Whilst it may be true that the average DDG/FFG being built these days may have a top speed of less than 30 knots surely escort vessels should be built to meet the needs of the carrier and not the other way around.

Carriers need good acceleration and the ability to make good speed into the wind for launching and recovering aircraft. Powerful catapults can make up for some lack of speed but situations can arise in windless conditions when carriers with insufficient speed cannot operate their aircraft with satisfactory fuel and/or weapon load. The new RN carriers will rely on skijumps to launch their STOVL aircraft and speed will surely be important to enable them to operate efficiently.

The RAN often had problems with lack of speed over the deck in the 'good old days' when it operated light fleet carriers. These ships had a maximum speed listed in most sources as 24.5 knots but normal sea speed was somewhat less.

The USN seems to regard speeds well above 30 knots as essential even for their large carriers. IMO it would be even more important for a smaller vessel.

Cheers

 

[Sea Toby]

Navies around the world have converted from steam plants to diesel and/or gas turbines to provide propulsion for most of their ships. The US Navy has invested for nuclear propulsion of their aircraft carriers.

In the day of steam when fuel was cheap and plentiful huge ships went faster than 30 knots. In today's world when fuel is expensive and not plentiful huge ships go slower than 30 knots. I also don't think anyone has advanced nautical diesel technology to go 30 knots, if they have its too expensive to go much faster than 25-27 knots.

Only in exercises during peacetime do ships reach flank speed anyways. Most of the time they are happy to go 20 knots or less, using their most economical speed in crossing oceans. Even the US Navy's Nimitz class of aircraft carriers are limited, their nuclear fuel consumption is watched even though they can go faster than 30 knots. An aircraft carrier that runs out of nuclear fuel a month before its refueling is not of much worth.

I believe Princess built a few ships before Carnival bought them out with gas turbines. Why? Its cheaper in the long run to add gas turbines to increase the speed than building more or larger diesels. Princess did so for competitive reasons, attempting to go another 50-70 nautical miles between ports in the same amount of time overnight or to sail further in a similar intinerary.

 

[Ligreton]

The new spanish BPE (CV/LHD) has a top "maintained" speed of only 21kts...
savings in fuel

 

[contedicavour]

The new spanish BPE (CV/LHD) has a top "maintained" speed of only 21kts...
savings in fuel

The Mistrals have max speed of 19 or 20kts. It's a common characteristic of LHD/LPD/LST etc

cheers

 

[Distiller]

...

Only in exercises during peacetime do ships reach flank speed anyways. Most of the time they are happy to go 20 knots or less, using their most economical speed in crossing oceans. Even the US Navy's Nimitz class of aircraft carriers are limited, their nuclear fuel consumption is watched even though they can go faster than 30 knots. An aircraft carrier that runs out of nuclear fuel a month before its refueling is not of much worth.

...

Nuclear fuel "consumption" does not increase because of higher vessel speeds. Output from the atomic decaying process in a thermal fission reactor is always the same (well, decreasing over time), the reactors are moderated if less energy (steam) is needed.

Might be interesting: http://www.fas.org/man/gao/nsiad98001/index.html

 

[Sea Toby]

Yes, but an aircraft carrier does use up its fuel faster when its used more. For example, when the Nimitz was sent to the Arabian Sea during the Iranian hostage crisis, its deployment was extended, and it had to steam all the way around Africa. My brother was on the ship at the time, and he knows for a fact that Admiral Rickover put the Nimitz on rations, so that it could make it to the next refueling.

Newport News hasn't discovered how to do two aircraft carrier nuclear refuelings at the same time.

 

[alexsa]

I believe Princess built a few ships before Carnival bought them out with gas turbines. Why? Its cheaper in the long run to add gas turbines to increase the speed than building more or larger diesels. Princess did so for competitive reasons, attempting to go another 50-70 nautical miles between ports in the same amount of time overnight or to sail further in a similar intinerary.

A slow speed two stroke diesel will always be cheaper to run that a gas turbine as the slow speed can burn HFO where the gas turbine runs of gas oil or MDO anf generally has a higher consuption in respect of power output.

fuel prices are critical with HFO 380 at about half the prices of MDO or MGO

http://www.bunkerworld.com/markets/img/minicalcgraph.gif

However, for electic drive cruise vesel with high hotel loads the gas turbine makes sense as part of a combined cycles sytem where the waste heat is also employed. The other issue for comemrcila operators is the SOX and NOX air emmision restristictions coming into play with the adoptionsof annex VI of MARPOL. The gas turbine meets these requirement quite easilly while it is a bit of a challege for a slow speed burning HFO whihc, depending on the centrestoke, can be pretty crappy.

Finally, trying to make anything from 25,000 GRT - 75,000 GRT weight move above 25-30 kts consumes an awful lot of power.

If you were to look at an average ships Diesel engine power map, you would see that even with gearing, every knot above say 20 kts, can almost double the amount of fuel consumed per hour. On the 25-30 kt band it becomes a vertical line, that's why most navies around the world tend to pootle about in an "economic" fuel consumption mode (around 10 - 15 Kts)..

This is not striclty true for commercial vessel. Speed is driven by the trade and many 'main line' container vessel will be desinge for a speed of about 25knots.

If you look at the last generation (the lastest is shown below) of large box boats built by maersk you will see a vessel with a DWT of 107,000 tonnes dirved by a tsingle slow speed two stroke diesel burning HFO with a 'designed sustained operating speed' in the order of 25knots. This ship is a tad under 350m long and 43m wide. (The power output inthe attached spec appear a bit low to me.). This is pretty representative of the typical post panamax designe of box boat.

http://www.ship-technology.com/projects/clifford/

The problem is these types of low speed engines are huge and this drive the configuration of the ship. Gas turbine by contrast are quite compact even wiht the air ducting and exhaust. In addition the are not designed to provide spirited exeleration. What will happen is the engine will 'run up' over a matter of one or two hours and 'run down' in a similar manner at the end of the voyage. These hull types, in the support role, could keep up wiht most task groups, in fact the hard part is stopping them due the he ihg mass and low block coefficient.

If you think that is impreesive have a look at the biggest container ship in the world

http://www.jtashipphoto.dk/jtashipphoto.dk 1/Emma Maersk/Emma Maersk 15.jpg

http://en.wikipedia.org/wiki/Emma_Mærsk

The Emma Maersk is declared as have a capabiltiy in the order or 11500 TEU but AP Molar always understate and that is a homoginous capcaity based on 17 tonned boxes. The real capacity is in the order of 14500 TEU.

The main particulars are as follows:
Length o.a.​

​

. . . . . . . . . . . . . . . . . . . . . . . . . . . 397 metres
Beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 metres
Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 metres

and DWT 156,907 tonnes

The propulsion machinery is a 14-cylinder Wärtsilä diesel engine from Doosan Engine Co. developing 110,000 BHP or 80,000 kW at 102 revolutions per minute.

The ship si fitted wiht a hybrid drive system and speed is augmented by electric motors fitted to the propeller drive shaft. Five diesel generators with a combined power of 20,700 kW (all burning HFO) and one combined gas/steam turbine generator of 8,500 kW driven by the main engine exhaust are installed.

This ship is opperated by a core crew of 13 but has accomodation for 30.

So in summary noting the very competitive nature of shipping, depending of ship design, fuel used and type of operation a sustained speed of 25 knots is certainly achievable both practically and economically.
​

 

[drjn]

A slow speed two stroke diesel will always be cheaper to run that a gas turbine as the slow speed can burn HFO where the gas turbine runs of gas oil or MDO anf generally has a higher consuption in respect of power output.

fuel prices are critical with HFO 380 at about half the prices of MDO or MGO

http://www.bunkerworld.com/markets/img/minicalcgraph.gif

However, for electic drive cruise vesel with high hotel loads the gas turbine makes sense as part of a combined cycles sytem where the waste heat is also employed. The other issue for comemrcila operators is the SOX and NOX air emmision restristictions coming into play with the adoptionsof annex VI of MARPOL. The gas turbine meets these requirement quite easilly while it is a bit of a challege for a slow speed burning HFO whihc, depending on the centrestoke, can be pretty crappy.



This is not striclty true for commercial vessel. Speed is driven by the trade and many 'main line' container vessel will be desinge for a speed of about 25knots.

If you look at the last generation (the lastest is shown below) of large box boats built by maersk you will see a vessel with a DWT of 107,000 tonnes dirved by a tsingle slow speed two stroke diesel burning HFO with a 'designed sustained operating speed' in the order of 25knots. This ship is a tad under 350m long and 43m wide. (The power output inthe attached spec appear a bit low to me.). This is pretty representative of the typical post panamax designe of box boat.

http://www.ship-technology.com/projects/clifford/

The problem is these types of low speed engines are huge and this drive the configuration of the ship. Gas turbine by contrast are quite compact even wiht the air ducting and exhaust. In addition the are not designed to provide spirited exeleration. What will happen is the engine will 'run up' over a matter of one or two hours and 'run down' in a similar manner at the end of the voyage. These hull types, in the support role, could keep up wiht most task groups, in fact the hard part is stopping them due the he ihg mass and low block coefficient.

If you think that is impreesive have a look at the biggest container ship in the world

http://www.jtashipphoto.dk/jtashipphoto.dk 1/Emma Maersk/Emma Maersk 15.jpg

http://en.wikipedia.org/wiki/Emma_Mærsk

The Emma Maersk is declared as have a capabiltiy in the order or 11500 TEU but AP Molar always understate and that is a homoginous capcaity based on 17 tonned boxes. The real capacity is in the order of 14500 TEU.

The main particulars are as follows:
Length o.a.​

​

. . . . . . . . . . . . . . . . . . . . . . . . . . . 397 metres
Beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 metres
Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 metres

and DWT 156,907 tonnes

The propulsion machinery is a 14-cylinder Wärtsilä diesel engine from Doosan Engine Co. developing 110,000 BHP or 80,000 kW at 102 revolutions per minute.

The ship si fitted wiht a hybrid drive system and speed is augmented by electric motors fitted to the propeller drive shaft. Five diesel generators with a combined power of 20,700 kW (all burning HFO) and one combined gas/steam turbine generator of 8,500 kW driven by the main engine exhaust are installed.

This ship is opperated by a core crew of 13 but has accomodation for 30.

So in summary noting the very competitive nature of shipping, depending of ship design, fuel used and type of operation a sustained speed of 25 knots is certainly achievable both practically and economically.
​

Thanks alexsa, very interesting read. I seem to recall reading something about how it is not only the horsepower output that determines the speed of the vessel but also the length of the vessel is a major factor (as are such things as the type of hull) . Is anyone able to enlighten me on this?​

 

[alexsa]

Thanks alexsa, very interesting read. I seem to recall reading something about how it is not only the horsepower output that determines the speed of the vessel but also the length of the vessel is a major factor (as are such things as the type of hull) . Is anyone able to enlighten me on this?

There are a couple of issue that will limit hull speed. Lenght is one factor but more in reagrds to the directional stability of the vessel. The ratio of length to breadth at the water line (Coefficent of fineness or Cw), the waterline and underwater shape including the block coeficient (Cb) will have a greater impact as these factors will determine the amount of resistance the hull will experiance when it passes through the water.

If a vessel is very broad for its length (even if the block coeffecient is quite low) can suffer from directional instability and in such circumstances will tend to wiggle along, particualry where the vessel has a relatively low draft. This will have an adverse impact upon speed of advance and fuel economy. It will also push up the block coefficient in comparison to a ship with a lower length to breadth radio but will offer better transverse stability. Another impact of vesel with a high beam to length ratio and shallow draft is the increased potentail for cavitation around the propeller (particaurly in a swell) and difficulty in controlling the vesel in the turn when fully laden. This does not happen in all cases but is a trait.

The block coefficient is determined by the volume of the displacement at a given draft compared to a cube calculated from the length between perpendiculars, the molded beam and the draft. I low block coeffcient will not automatically give you a fast hull as the underwater shape is also critical.

The coeffcient of finess is calculated by the area of the waterplane at a give draft in realtion to the rectagle calculated from length between perpendiculars and the molded beam.

 

[Wooki]

If you think that is impressive have a look at the biggest container ship in the world

http://www.jtashipphoto.dk/jtashipphoto.dk 1/Emma Maersk/Emma Maersk 15.jpg

http://en.wikipedia.org/wiki/Emma_Mærsk

The Emma Maersk is declared as have a capabiltiy in the order or 11500 TEU but AP Molar always understate and that is a homoginous capcaity based on 17 tonned boxes. The real capacity is in the order of 14500 TEU.

The main particulars are as follows:
Length o.a.​

​

. . . . . . . . . . . . . . . . . . . . . . . . . . . 397 metres
Beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 metres
Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 metres

and DWT 156,907 tonnes

The propulsion machinery is a 14-cylinder Wärtsilä diesel engine from Doosan Engine Co. developing 110,000 BHP or 80,000 kW at 102 revolutions per minute.

The ship si fitted wiht a hybrid drive system and speed is augmented by electric motors fitted to the propeller drive shaft. Five diesel generators with a combined power of 20,700 kW (all burning HFO) and one combined gas/steam turbine generator of 8,500 kW driven by the main engine exhaust are installed.

This ship is opperated by a core crew of 13 but has accomodation for 30.

So in summary noting the very competitive nature of shipping, depending of ship design, fuel used and type of operation a sustained speed of 25 knots is certainly achievable both practically and economically.
​

What a thing of beauty.

Did you read this Alex, from your wiki reference?

...Instead of biocides, used by much of the industry to keep barnacles off of the hull, a special silicon-based paint is used[6]. This increases the ships efficiency by decreasing drag while also protecting the ocean from biocides that may leak into the ocean.

I wonder if she is using the air bubbler system and paint developed by Mitsui Heavy Industries in the late 80's ? That system increases speed by 5% using a silicon based paint to "form" air bubbles against the hull and thereby lower resistance.

24 knots x 1.05 = 25.2 knots...sweet

cheers


w​

 

[alexsa]

What a thing of beauty.

Did you read this Alex, from your wiki reference?

...Instead of biocides, used by much of the industry to keep barnacles off of the hull, a special silicon-based paint is used[6]. This increases the ships efficiency by decreasing drag while also protecting the ocean from biocides that may leak into the ocean.

I wonder if she is using the air bubbler system and paint developed by Mitsui Heavy Industries in the late 80's ? That system increases speed by 5% using a silicon based paint to "form" air bubbles against the hull and thereby lower resistance.

24 knots x 1.05 = 25.2 knots...sweet

cheers


w

Silicon paints or "Slipcoats" are getting much wider use but some brands have problems, and given the cost when it falls off or fails operators get very annoyed.

Slip coat is also being used for coating propellers giving a claimed 5% efficiency increase.

The only bubbler system I am aware of that is in use relates to ballast exchange as part of the new ballast water convention. This is intended to prevent transfer of marine organisms into other environments (like the crown of thorn star fish on the GBR). A number of options are being developed to get rid of the need ot carry out a ballast exhange which has a range of risks in respect of ship safety. These use systems employing the likes of UV, Ozone, chlorine from salt etc treatments. A number of these are quite mature and going into operational use.

In so far as using air rafting to reduce resistancxe this would be a massive system on such a hull and would add to mainteance complexity and cost. This is somenting most ship owners avoid like the plague. I would watch coating development over the next few yeard though, as it really has improved from the nasty toxic anti foul of old (some of which were outlawed by the TBT ban) to something that looks like it will provide and environentally friendly efficiency benifit to hull speed.

Cheers
Alex

Sorry one last thing

24 knots x 1.05 = 25.2 knots...sweet

You may not necesarily get an improvement in the max design speed but you will limit any likely reduction in speed through fouling and ensure you burn less fuel in achieving it. In commercial operations efficiency is generally measured in fuel burn against operational speed.

Cheers again
Alex

 

[Wooki]

Silicon paints or "Slipcoats" are getting much wider use but some brands have problems, and given the cost when it falls off or fails operators get very annoyed.

Slip coat is also being used for coating propellers giving a claimed 5% efficiency increase.

The only bubbler system I am aware of that is in use relates to ballast exchange as part of the new ballast water convention. This is intended to prevent transfer of marine organisms into other environments (like the crown of thorn star fish on the GBR). A number of options are being developed to get rid of the need ot carry out a ballast exhange which has a range of risks in respect of ship safety. These use systems employing the likes of UV, Ozone, chlorine from salt etc treatments. A number of these are quite mature and going into operational use.

In so far as using air rafting to reduce resistancxe this would be a massive system on such a hull and would add to mainteance complexity and cost. This is somenting most ship owners avoid like the plague. I would watch coating development over the next few yeard though, as it really has improved from the nasty toxic anti foul of old (some of which were outlawed by the TBT ban) to something that looks like it will provide and environentally friendly efficiency benifit to hull speed.

Cheers
Alex

Sorry one last thing



You may not necesarily get an improvement in the max design speed but you will limit any likely reduction in speed through fouling and ensure you burn less fuel in achieving it. In commercial operations efficiency is generally measured in fuel burn against operational speed.

Cheers again
Alex

um, we must be talking about different systems as it takes a 4HP compressor located at the bulbous bow. You can go with more if you like, but just the inclusion of air beneath the water line is enough for the O2 to start wanting to coalesce with the silicon, along the entire hull form. And that gives you the increase in performance, whether it is speed or increased fuel efficiency you are looking for.

Mitsui are the guys who made it. Also IIRC, fouling was a major problem with it. So the use of the word "anti-fouling" is what caught my eye.

cheers

w

 

[alexsa]

um, we must be talking about different systems as it takes a 4HP compressor located at the bulbous bow. You can go with more if you like, but just the inclusion of air beneath the water line is enough for the O2 to start wanting to coalesce with the silicon, along the entire hull form. And that gives you the increase in performance, whether it is speed or increased fuel efficiency you are looking for.

Mitsui are the guys who made it. Also IIRC, fouling was a major problem with it. So the use of the word "anti-fouling" is what caught my eye.

cheers

w

Nope, covered it in ...

In so far as using air rafting to reduce resistance this would be a massive system on such a hull and would add to mainteance complexity and cost. This is somenting most ship owners avoid like the plague. I would watch coating development over the next few yeard though, as it really has improved from the nasty toxic anti foul of old (some of which were outlawed by the TBT ban) to something that looks like it will provide and environentally friendly efficiency benifit to hull speed.

 

[Wooki]

:nutkick Well, I guess I am confused as the system I am speaking of is extremely simple to do and not:

...In so far as using air rafting to reduce resistance this would be a massive system on such a hull and would add to mainteance complexity and cost...

cheers

w

 

[Grand Danois]

Regarding Emma Mærsk and antifouling coatings/fouling release coatings. From what the Danish trade press suggests I gather this product was used:

Globic NCT/Nexus.

It's developed by Hempel.

Globic NCT is also being tested on the Thetis class frigate Vædderen on its year long voyage across the globe. Estimates are a 1-2% saving on fuel on a frigate sized vessel. The bottom of the hull except the part aft of the hangar has been painted with Globic NCT (see attachments). Savings should be greater on a Emma Mærsk sized vessel (5 ton of duel a day, 3-5%?).

Attachment: Vædderen in dock in Stavanger. Hull aft of hangar is Hempasil. Second attachment: Also Vædderen, Globic left and Hempasil right.

 

[alexsa]

Regarding Emma Mærsk and antifouling coatings/fouling release coatings. From what the Danish trade press suggests I gather this product was used:

Globic NCT/Nexus.

It's developed by Hempel.

Globic NCT is also being tested on the Thetis class frigate Vædderen on its year long voyage across the globe. Estimates are a 1-2% saving on fuel on a frigate sized vessel. The bottom of the hull except the part aft of the hangar has been painted with Global NCT (see attachments). Savings should be greater on a Emma Mærsk sized vessel (5 ton of duel a day, 3-5%?).

Attachment: Vædderen in dock in Stavanger. Hull aft of hangar is Hempasil. Second attachment: Also Vædderen, Globic left and Hempasil right.

All the large paint manufactures ahve a version of it. International call it intersleek, Sigma call it Lion etc.

Well, I guess I am confused as the system I am speaking of is extremely simple to do and not:.

Not really I just look at it from a differnet perspective. I don't dispute the principal is simple but there are issue with practicality,
i.e *the bublous bow form part of the fore peak tank and is fwd of the collision bulkhead. Access to a space here will have to be by trunking from the focsle.
* having sufficient output for a 350m hull probably means you need additional outlets alonmg the hull.
* the sytems still needs to be maintained and blockages avoided.

As noted below ship owners hate additional cost and complexity unless it is guarentted to provide an advantage and I have not seen such a system in a mature form for commercial use nor have I seen any reports of it.

The Japanese are quite innovative in reagrds to trying to produce a more fuel efficinet ship but many of the ideas do not make it past the proof of concept phase due to the cost and complexity involved. A prime example was the sail assisted general cargo ship using computer controlled rigid sail sections on masts. Worked a treat, complex as hell, cost a motza and was not picked up. Owners prefered to look at more efficient 2 strokes instead as it was unlikley they could recover the cost of the installation over the operating life of the vessel (many owners only hold on to a ship for 10 to 15 years adn then on sell it).

On a similar note it will be interesing to see Willhemsens new zero emmision car carrier concept ever gets built as the constructions cost will be frightening.

 

[Grand Danois]

All the large paint manufactures ahve a version of it. International call it intersleek, Sigma call it Lion etc.

Well, I did expect that to be the case. Just trying to do some input on what coating was used on Emma Mærsk.