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The Subject Of Ship Design  
User currently offlineDocLightning From United States of America, joined Nov 2005, 19944 posts, RR: 59
Posted (2 years 1 month 2 weeks 13 hours ago) and read 5413 times:

Living on the SF Bay, I've become increasingly interested in large ships. We have a lot of container carriers coming into Oakland and tankers going to points further inland, like Richmond.

A few things I wonder:

1) Passenger ships tend to place the bridge up front. Why do merchantmen tend to have rear-mounted bridges?

2) Passenger ships tend to have multiple screws. Merchantmen, even the biggest, newest. and fastest, tend to be single-screwed. Why?

3) Why does it seem like direct diesel drive gets used more for merchantmen than for passenger ships?

54 replies: All unread, showing first 25:
 
User currently offlineMir From United States of America, joined Jan 2004, 21680 posts, RR: 55
Reply 1, posted (2 years 1 month 2 weeks 12 hours ago) and read 5379 times:

Quoting DocLightning (Thread starter):
1) Passenger ships tend to place the bridge up front. Why do merchantmen tend to have rear-mounted bridges?

So that the crew can keep an eye on the cargo deck from the bridge, I'd imagine. It also puts the bridge closer to the engine room.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineBMI727 From United States of America, joined Feb 2009, 15781 posts, RR: 27
Reply 2, posted (2 years 1 month 2 weeks 12 hours ago) and read 5376 times:

Quoting DocLightning (Thread starter):
3) Why does it seem like direct diesel drive gets used more for merchantmen than for passenger ships?

Noise and vibration maybe? Or the much higher electrical loads demanded by passenger ships.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineSmittyOne From , joined Dec 1969, posts, RR:
Reply 3, posted (2 years 1 month 2 weeks 10 hours ago) and read 5323 times:

Step into to my office, Doc.

Quoting DocLightning (Thread starter):


1) Passenger ships tend to place the bridge up front. Why do merchantmen tend to have rear-mounted bridges?


Generally, placing the pilothouse somewhere between amidships and the pivot point (about 1/3 of the way aft from the bow) is ideal from a shiphandling perspective. You'll notice that a lot of your older, smaller cargo ships and tankers had this arrangement but they're just about all gone now, for a few reasons.

- from a regulatory standpoint you can't put the pilothouse over a flammable cargo.
- the midship superstructure interferes with long, uninterrupted cargo / container spaces, which are most efficient.
- It is cheaper and more compact to construct all of your accommodations/machinery spaces together - minimizes space not devoted to payload (as well as hogging forces caused by hanging weights at either end of a shell). Putting all of that stuff all the way forward would not be practical - so far from the propeller - and would also leave the bridge vulnerable to getting nailed by large waves. So you put it all aft.

Great Lakes freighters used to have their pilothouse on the bow (for visibility) and their machinery at the stern, but that has been superseded by the more efficient "everything aft" design. Of course in the Great Lakes you don't see the same wave heights that you see on the ocean (though it can be just as 'unpleasant' overall due to the short period).

Passenger ships really have nowhere else to put their pilothouse but well forward...if located aft it would be really tall and goofy to see over the passenger accommodations. Cruise ships are so tall that they can get away with putting it far forward from a seakeeping perspective.

Quoting DocLightning (Thread starter):


2) Passenger ships tend to have multiple screws. Merchantmen, even the biggest, newest. and fastest, tend to be single-screwed. Why?

3) Why does it seem like direct diesel drive gets used more for merchantmen than for passenger ships?

A large diesel engine turning one screw is the cheapest solution to install and is efficient. It is not very responsive (especially in a direct drive configuration) or maneuverable but those things are not as important as cost for merchantmen.

Multiple shafts turning controllable-pitch propellers offer a lot of benefits to maneuverability and redundancy that are important to cruise lines. If a passenger ship had a problem with its only engine/shaft/screw in heavy weather, that could be really bad for the human cargo. Likewise, controllable pitch propellers can be 'reversed' almost instantly, which increases safety and the ability to maneuver in tight spots.

Noise/vibration is a consideration but passenger electrical load is not an issue because the ship has auxiliary diesel generators specifically installed for that purpose.


User currently offlinekngkyle From United States of America, joined Dec 2006, 408 posts, RR: 1
Reply 4, posted (2 years 1 month 2 weeks 10 hours ago) and read 5300 times:
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I'm also fairly interested in ships, particularly in lake freighters. They are just so long and skinny, looks like they would just split in half in rough seas, which I know the great lakes get their fair share of.

http://4.bp.blogspot.com/-8eNNUO64hM4/UCsuPyzddCI/AAAAAAAAk1I/ujbYgkLMGq8/s1600/jbarker15.jpg

Cool video showing arrivals and departures from the Port of Duluth, Minnesota. (well cool to someone who finds ships interesting)
http://www.youtube.com/watch?v=YUyRfltyAwU


User currently offlineSmittyOne From , joined Dec 1969, posts, RR:
Reply 5, posted (2 years 1 month 2 weeks 9 hours ago) and read 5278 times:

Quoting kngkyle (Reply 4):

Awesome Kyle - I had the chance one time to sail GEORGE A. STINSON for an overnight trip...the captain took us down to the tunnel leading under the cargo holds running the length of the ship...he said that you could definitely see the hull flex in a storm.

But my favorite lakers are the old school:

http://www.boatnerd.com/pictures/images/ryerson-icerockcut-jb.jpg


User currently offlineKiwiRob From New Zealand, joined Jun 2005, 7563 posts, RR: 4
Reply 6, posted (2 years 1 month 2 weeks 7 hours ago) and read 5229 times:

Quoting DocLightning (Thread starter):


1) Passenger ships tend to place the bridge up front. Why do merchantmen tend to have rear-mounted bridges?

Ease of control, plus is cheaper to build them when the majority of electrical and mechanical systems are in a single location.

That said the new Maersk Tripple E class will have the bridge amidships, and will have twin engines. You won't see these in the US as they are too big for your ports.



CMA's Christopher Colomb class also have the bridge further forward. These vessels also have cabins for 10 passengers in very luxurious berths.

Quoting DocLightning (Thread starter):
2) Passenger ships tend to have multiple screws. Merchantmen, even the biggest, newest. and fastest, tend to be single-screwed. Why?

They also tend to be single engined, single engines are more efficient. There are exceptions, tankers which operate in Arctic regions have twin engines, this was one of the outcomes of the Exxon Valdise grounding along with double hulls.

Quoting DocLightning (Thread starter):

3) Why does it seem like direct diesel drive gets used more for merchantmen than for passenger ships?

Not so, most cruise ships burn bunker oil, it's cheap and helps keep costs down, converting to lighter grades of oil or gas will increase the price of your cruise holiday. Until the industry is forced to change ships will continue to be built burning bunker oil, the industry won't do it by themselves.


User currently offlinecomorin From United States of America, joined May 2005, 4900 posts, RR: 16
Reply 7, posted (2 years 1 month 2 weeks 7 hours ago) and read 5208 times:

Excellent thread with great, informative posts!

Q: In sailboats (non-planing), max speed is proportional to the square root of hull length. Is this true of large vessels also? Thanks.


User currently offlineDocLightning From United States of America, joined Nov 2005, 19944 posts, RR: 59
Reply 8, posted (2 years 1 month 2 weeks 4 hours ago) and read 5161 times:

Quoting SmittyOne (Reply 3):
A large diesel engine turning one screw is the cheapest solution to install and is efficient. It is not very responsive (especially in a direct drive configuration) or maneuverable but those things are not as important as cost for merchantmen.

Why not? They still have to go into port and dock, right?

Quoting SmittyOne (Reply 3):
Noise/vibration is a consideration but passenger electrical load is not an issue because the ship has auxiliary diesel generators specifically installed for that purpose.

So I was reading about this. On the newest ships, like QM2, there are a number of diesel engines that drive a single electric bus. The hotel and propulsion loads are then automatically separated from this single electric output. To me, this seems like the simplest systems architecture for such a design.

On merchantmen, there are dedicated propulsion engines and dedicated engines for ship's power. The reasoning I read is that this is easier to install and cheaper to design, but offers less flexibility and minute-to-minute response to changes in demand.

Quoting SmittyOne (Reply 5):
Awesome Kyle - I had the chance one time to sail GEORGE A. STINSON for an overnight trip...the captain took us down to the tunnel leading under the cargo holds running the length of the ship...he said that you could definitely see the hull flex in a storm.

I've been aboard Stinson myself as a boy. She shipped a lot of my father's company's steel.


User currently offlineKiwiRob From New Zealand, joined Jun 2005, 7563 posts, RR: 4
Reply 9, posted (2 years 1 month 2 weeks 3 hours ago) and read 5158 times:

Quoting SmittyOne (Reply 3):
the midship superstructure interferes with long, uninterrupted cargo / container spaces, which are most efficient.

Not true anymore the Maersk Tripple E class carries some 2500 TEU more than the previous E class, the ship is only 3 m longer and 4 m wider. With the twin engine design they can use smaller engines which in turn means less space taken up by machinery and more cargo capacity

Quoting SmittyOne (Reply 3):
Great Lakes freighters used to have their pilothouse on the bow (for visibility) and their machinery at the stern, but that has been superseded by the more efficient "everything aft" design.

A yard in Russia which I supply built a design called RSD44, this had a forward pilot house, the design was by all accounts a disaster, the ship had significant control problems over similar sized conventional vessels, it's much easier to see what's going on in front of you than what's happening behind.

Quoting SmittyOne (Reply 3):
Noise/vibration is a consideration but passenger electrical load is not an issue because the ship has auxiliary diesel generators specifically installed for that purpose.

On QM2 the 4 diesels also provide electrical power for the ship not just for propulsion. When higher speeds are required the 2 gas turbines are turned on to provide the extra go. From what I understand the QM2 drive train was considered by B.E.A. for the CVF project.


User currently offlineSmittyOne From , joined Dec 1969, posts, RR:
Reply 10, posted (2 years 1 month 1 week 6 days 22 hours ago) and read 5076 times:

Quoting comorin (Reply 7):
Excellent thread with great, informative posts!

Q: In sailboats (non-planing), max speed is proportional to the square root of hull length. Is this true of large vessels also? Thanks.

Yes - pretty much all displacement hulls.

Quoting DocLightning (Reply 8):
Why not? They still have to go into port and dock, right?

True, but ships of this size generally to use tugs alongside anyway (except the Jedi Master shiphandlers on the Great Lakes who generally don't unless they're being dragged backwards somewhere). I'm not up to speed on the docking procedures and use of tugs by cruise ships, so I'll have to punt on the question of why more maneuverability would appeal to them. The redundancy of multiple screws/azipods would have to be attractive, though. There is also the issue of hull design etc. that might make it hard to fit a big enough single screw under the transom of some ships.

Quoting DocLightning (Reply 8):
So I was reading about this. On the newest ships, like QM2, there are a number of diesel engines that drive a single electric bus. The hotel and propulsion loads are then automatically separated from this single electric output. To me, this seems like the simplest systems architecture for such a design.

My experience has been on diesel-electric buoy tenders and icebreakers, where two large diesels generated 440vDC power for the propulsion motor, and two much smaller diesels provided the ship's AC 'hotel' power. These were relatively small ships though (140' and 180'), so generating auxiliary power with a smaller diesel made much more sense when you weren't running the main engines. You don't want a diesel running with too little of a load - wasteful and not great for the engine long-term.A practical consideration since we often anchored (engines not running) or tied up somewhere that didn't have a shore tie plug for power. Either way, the electrical system was mechanical and incredibly simple. My guess is that QM2's system is not simple and is run by computers  
Quoting DocLightning (Reply 8):
On merchantmen, there are dedicated propulsion engines and dedicated engines for ship's power. The reasoning I read is that this is easier to install and cheaper to design, but offers less flexibility and minute-to-minute response to changes in demand.

I don't think ship's auxiliary power plays much into the decision on whether or not to use electric propulsion for merchant ships - the technology has advanced to the point where if you are going to opt for electric propulsion in the first place you might as well power the rest of the ship via an integrated system too. The lower cost and efficiency of the big diesel direct drive systems is probably still too compelling in a cargo application.

Quoting DocLightning (Reply 8):

I've been aboard Stinson myself as a boy. She shipped a lot of my father's company's steel.

Awesome - she's AMERICAN SPIRIT now!


User currently offlineKen777 From United States of America, joined Mar 2004, 8328 posts, RR: 9
Reply 11, posted (2 years 1 month 1 week 6 days 21 hours ago) and read 5053 times:

Quoting SmittyOne (Reply 5):
he said that you could definitely see the hull flex in a storm.

I was on the USS LONG BEACH (a cruiser) where there were flex points built in. I don't know how long a ship needs to be before benefitting from these points - the LONG BEACH was a long, thin design.


User currently offlineDarkSnowyNight From United States of America, joined Jan 2012, 1378 posts, RR: 3
Reply 12, posted (2 years 1 month 1 week 6 days 21 hours ago) and read 5040 times:

Quoting SmittyOne (Reply 10):
Awesome - she's AMERICAN SPIRIT now!

Did her lay-up last long? She looks like the same class of ship as Mesabi Miner, which is one I remember seeing in the locks way back when. Though I could be wrong about that classification...



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlineSmittyOne From , joined Dec 1969, posts, RR:
Reply 13, posted (2 years 1 month 1 week 6 days 1 hour ago) and read 4979 times:

Quoting DarkSnowyNight (Reply 12):
Did her lay-up last long? She looks like the same class of ship as Mesabi Miner, which is one I remember seeing in the locks way back when. Though I could be wrong about that classification...

I think they did the name change as part of her normal winter layup. (Btw I used to live in Sturgeon Bay, WI...so cool to watch the big ships come in for the winter.)

Mesabi Miner and Stinson were both built at American Shipbuilding in Lorain, OH (hulls 906 and 907).


User currently offlinerwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 14, posted (2 years 1 month 1 week 5 days 19 hours ago) and read 4941 times:
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Quoting SmittyOne (Reply 10):
I don't think ship's auxiliary power plays much into the decision on whether or not to use electric propulsion for merchant ships - the technology has advanced to the point where if you are going to opt for electric propulsion in the first place you might as well power the rest of the ship via an integrated system too.

On many modern large cruise ships* the power needed for the hotel load exceeds that needed for propulsion. Rather oversimplified, that makes the motivation to simply upsize the electrical plant a bit, and then do electric propulsion. That makes azipods particularly attractive (since you can do away with stern thrusters too).


*Excluding the liners like the QM2, which have rather higher speed requirements (consider the 30kt, 150,000ton, 1130ft, 117MW QM2, vs. the 22kt, 225,000ton, 1180ft, 96MW Oasis of the Seas - the Oasis normally sails with twice the passengers and crew of the QM2, and would have a substantially higher hotel load).

Quoting comorin (Reply 7):
Q: In sailboats (non-planing), max speed is proportional to the square root of hull length. Is this true of large vessels also? Thanks.

Approximately - you can always go faster with more power, but it's an exponential curve. So there's a practical speed limit for most of us, and a slightly higher one for the money-is-no-object folks like Navies and folks running luxury liners.


User currently offlinestealthz From Australia, joined Feb 2005, 5714 posts, RR: 44
Reply 15, posted (2 years 1 month 1 week 5 days 18 hours ago) and read 4923 times:
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Quoting SmittyOne (Reply 10):
so I'll have to punt on the question of why more maneuverability would appeal to them

Ships like the Emma Maersk and Christopher Columb only travel between major industrial scale ports with deep water, tugs and facilities geared for their operation.

Cruise liners often visit small ports or "hover" off shore at even smaller locations so maneuverability becomes much more important to them.



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlinerwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 16, posted (2 years 1 month 1 week 5 days 18 hours ago) and read 4906 times:
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Quoting stealthz (Reply 15):
Ships like the Emma Maersk and Christopher Columb only travel between major industrial scale ports with deep water, tugs and facilities geared for their operation.

Cruise liners often visit small ports or "hover" off shore at even smaller locations so maneuverability becomes much more important to them.

Not to mention that cruise ships typically dock at a different port approximately every day, getting in and out quick would be a big plus (and makes for a better passenger experience).


User currently offlinezkojq From New Zealand, joined Sep 2011, 1267 posts, RR: 1
Reply 17, posted (2 years 1 month 1 week 5 days 16 hours ago) and read 4873 times:

Just curious (because this seems like a good place to ask), is there is a maritime inequivalent of ETOPS, regulating how reliable a passenger-carrying ship's engines must be?

Quoting SmittyOne (Reply 5):
he said that you could definitely see the hull flex in a storm.

Just like in a Boeing 757-300 during turbulence! =D

Quoting rwessel (Reply 14):
That makes azipods particularly attractive (since you can do away with stern thrusters too).

Does anyone know if the Azipod manufacturers fixed the reliability issues that many operators were experiencing a few years back? I remember reading a piece in Ships Monthly magazine a few years ago that indicated a substantial number of cruise ships weren't happy with them due to reliability issues.

Quoting rwessel (Reply 16):
Not to mention that cruise ships typically dock at a different port approximately every day, getting in and out quick would be a big plus (and makes for a better passenger experience).

And no-doubt save the Cruise Line on tug fees.



Air New Zealand; first to fly the Boeing 787-9. ZK-NZE, NZ103 AKL-SYD, 2014/08/09. I was 83rd to board.
User currently offlinecomorin From United States of America, joined May 2005, 4900 posts, RR: 16
Reply 18, posted (2 years 1 month 1 week 5 days 15 hours ago) and read 4851 times:

Quoting SmittyOne (Reply 10):
Quoting comorin (Reply 7):
Excellent thread with great, informative posts!

Q: In sailboats (non-planing), max speed is proportional to the square root of hull length. Is this true of large vessels also? Thanks.

Yes - pretty much all displacement hulls.
Quoting rwessel (Reply 14):
Quoting comorin (Reply 7):
Q: In sailboats (non-planing), max speed is proportional to the square root of hull length. Is this true of large vessels also? Thanks.

Approximately - you can always go faster with more power, but it's an exponential curve. So there's a practical speed limit for most of us, and a slightly higher one for the money-is-no-object folks like Navies and folks running luxury liners.

Appreciate the replies, thank you. Now to try and understand why! Time for Cliffs notes on Hydrodynamics...


User currently offlineKiwiRob From New Zealand, joined Jun 2005, 7563 posts, RR: 4
Reply 19, posted (2 years 1 month 1 week 5 days 15 hours ago) and read 4845 times:

Quoting zkojq (Reply 17):
Just curious (because this seems like a good place to ask), is there is a maritime inequivalent of ETOPS, regulating how reliable a passenger-carrying ship's engines must be?

The closest thing would be the SOLAS regulations, I'm not sure if propulsion is covered.


User currently offlinestealthz From Australia, joined Feb 2005, 5714 posts, RR: 44
Reply 20, posted (2 years 1 month 1 week 5 days 14 hours ago) and read 4842 times:
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Quoting zkojq (Reply 17):
And no-doubt save the Cruise Line on tug fees.


I was at Sydney's Circular Quay one evening a few years back awaiting the departure of what was then the largest passenger ship seen in Sydney. As departure time approached I commented to a couple of crusty old shipwatchers about whether she would leave on time, they responded along the lines of " won't be going for a while yet, the tugs are not here yet to assist her out of her berth".
I should have taken photos of the expression on their faces as she blew her whistle, then quietly and serenely moved sideways from the quayside and backed out into the main channel, did a 360deg + pirouette giving all her passengers their last look at the Opera House and Harbour bridge and slipped silently away into the night... all totally unassisted.



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlineKen777 From United States of America, joined Mar 2004, 8328 posts, RR: 9
Reply 21, posted (2 years 1 month 1 week 5 days 6 hours ago) and read 4740 times:

The Queen Victoria has had a bit of a problem and will be heading to dry dock in Germany. Would really like to know what specifically is the problem with the propulsion unit as the ship is pretty new - delivered in 2007.

Quote:

Hundreds of people have had their holiday plans ruined after a Southampton, England-based cruise ship suffered a mechanical failure.

Cunard's Queen Victoria has suffered a problem with one of its propulsion units with hundreds of passengers on board and it cannot travel at its top speed.
http://travel.usatoday.com/cruises/s...fers-mechanical-failure/57743392/1


User currently offlineDocLightning From United States of America, joined Nov 2005, 19944 posts, RR: 59
Reply 22, posted (2 years 1 month 1 week 5 days 5 hours ago) and read 4736 times:

Quoting SmittyOne (Reply 3):
A large diesel engine turning one screw is the cheapest solution to install and is efficient. It is not very responsive (especially in a direct drive configuration) or maneuverable but those things are not as important as cost for merchantmen.

Why not? An azipod-driven ship with bow thrusters could dock without tugs, which would have to save some fees, no?

Quoting SmittyOne (Reply 3):
Multiple shafts turning controllable-pitch propellers offer a lot of benefits to maneuverability and redundancy that are important to cruise lines. If a passenger ship had a problem with its only engine/shaft/screw in heavy weather, that could be really bad for the human cargo. Likewise, controllable pitch propellers can be 'reversed' almost instantly, which increases safety and the ability to maneuver in tight spots.

As I understand it, relatively few cruise ships have variable-pitch props. Azipods have become more popular because they allow tugless docking procedures, but particularly with the electric drivetrains in use on most cruise ships, reversing the propeller is trivial.

Quoting stealthz (Reply 15):
Ships like the Emma Maersk and Christopher Columb only travel between major industrial scale ports with deep water, tugs and facilities geared for their operation.

Cruise liners often visit small ports or "hover" off shore at even smaller locations so maneuverability becomes much more important to them.

That does make sense. Still doesn't explain to me why even large and fast ships like Emma Maersk have single screw propulsion.


User currently offlineKiwiRob From New Zealand, joined Jun 2005, 7563 posts, RR: 4
Reply 23, posted (2 years 1 month 1 week 5 days 1 hour ago) and read 4698 times:

Quoting DocLightning (Reply 22):
Still doesn't explain to me why even large and fast ships like Emma Maersk have single screw propulsion.

Simple cost, one large engine uses less fuel than two smaller ones, it also costs less to install and to maintain, it's all a matter of economics.


User currently offlineSmittyOne From , joined Dec 1969, posts, RR:
Reply 24, posted (2 years 1 month 1 week 4 days 22 hours ago) and read 4658 times:

Quoting KiwiRob (Reply 9):
A yard in Russia which I supply built a design called RSD44, this had a forward pilot house, the design was by all accounts a disaster, the ship had significant control problems over similar sized conventional vessels, it's much easier to see what's going on in front of you than what's happening behind.

I don't know, my guess is that the Great Lakes forward pilothouse design must have been superior 100+ years ago when it became the rage. Of course these were much smaller ships without radar or VHF radios, operating in congested waters in the days before we had Vessel Traffic Services etc. I could see how putting the pilothouse forward would be useful in that situation. Especially in limited visibility, which happens a lot due to fog (or sea smoke during the ice season).

Quoting DocLightning (Reply 22):
Why not? An azipod-driven ship with bow thrusters could dock without tugs, which would have to save some fees, no?

I suppose that they crunched the numbers and found it cheaper overall in that application to just rely on tugs...which could very well be compulsory in a port for a large ship regardless of how maneuverable it is.

Quoting KiwiRob (Reply 9):
Not true anymore the Maersk Tripple E class carries some 2500 TEU more than the previous E class, the ship is only 3 m longer and 4 m wider. With the twin engine design they can use smaller engines which in turn means less space taken up by machinery and more cargo capacity

I was thinking more about the large self-unloading bulk carriers that they have on the Great Lakes - full-depth cargo holds feeding the long, continuous unloading belt are the most efficient way to handle coal/wheat/taconite etc.

But the container ship example you cited does show how each succeeding technological improvement makes previous design 'rules' less relevant than before!


25 DocLightning : I know that QM2 had problem with its RR-powered units when the thrust bearings kept wearing out in the pounding of the North Atlantic. I believe Cuna
26 stealthz : It is so much more efficient, Emma makes 16 port visits in a 3 month cycle between Gdansk, the far East and return, most of that 3 months is spent wi
27 Klaus : How is that power coupled into the shaft?
28 stealthz : Steam turbine alternators and electric motors geared onto the shaft
29 Klaus : Okay... are these electric motors capable of driving the shaft alone as well in an emergency (such as keeping the ship maneuverable in bad weather wh
30 DocLightning : So if single-screw propulsion is more efficient (and I believe her screw has six blades), why do cruise ships seem to have a minimum of two?
31 DocLightning : Since the steam for those turbines comes from the main engine exhaust, I'd say that a total main engine failure would lead to loss of that electricit
32 Klaus : I'd guess that it has to do with the cost of delays or interruptions of the voyage, among other things. A passenger cruise is much more time-critical
33 Klaus : Being without any propulsion in heavy weather can be dangerous as far as I know, so I would expect there to be at least some kind of backup for emerg
34 N766UA : They may appear so, but many Lakers are actually as wide or wider than their salty counterparts, excluding the big wide oil tankers and container shi
35 Post contains links zckls04 : Ever since I've lived in Alameda I've loved the port of Oakland, especially at night: http://viveier.com/photos/444564554_Nc5W8-XL.jpg I was sailing
36 LMP737 : The Great Lakes get some preety nasty storms, especially in the late fall and winter. Just look at the case of the Edmund Fitzgerald.
37 N766UA : Also, the lakes see very different kinds of waves than the ocean. In the open ocean, you get long, rolling waves going in a single direction. On the
38 DocLightning : How do they get to the Lakes? They aren't really designed to tolerate ocean swells and they're too big to fit throught he locks in the Welland canals
39 N766UA : I believe they are "seawaymax" size, meaning they will be able to enter the locks along the welland canal, and though not designed for oceans long-te
40 Post contains images DocLightning : You, sir... ...need to take me sailing.
41 KiwiRob : That's an unfair comment, the Chinese build better ships, faster and cheaper than yards anywhere else in the world. The US can't hold a candle to the
42 sprout5199 : You need to add "for the same cost". Its like having four wheel drive. If its not needed, then dont have it. A single screw has less hull penatration
43 LMP737 : On Lake Superior you'll get waves in rapid succession, referred to as "three sister waves". What's ends up happening is tons of water being dumped on
44 KiwiRob : Cruise lines wouldn't want to take the risk, especially in tort happy America. Not even for the same cost, simple fact is a Chinese shipyard is ligth
45 DocLightning : But they don't have redundant engine rooms. In the past several years, I've heard about several cruise ships losing all power due to engine room fire
46 KiwiRob : Some do.
47 kl671 : Great lake freighters are certainly capable of operating in ocean conditions. A large number (133 according to Veterens Affairs Canada) were used in
48 Post contains images stealthz : Apart from reliability and maneuverability aspects that are likely important to cruise and passenger ship operators, there are significant physical a
49 KiwiRob : They also have two smaller engines, this also enabled the height of the engine room to be reduced which in turn allowed for much great cargo capacity
50 Post contains links and images SmittyOne : Amen, brother - I've lost a couple of good meals over the side in Lake Superior. But the smaller overall wave height does allow you to get away with
51 Klaus : Thanks. The mass of those components technically wouldn't increase the energy required; It might just take longer to get them up to speed. But the we
52 johns624 : Canadian and American Great Lakes ship standards are different. Most American traffic is from the Lake Superior lakehead at Duluth/Superior to steel
53 stealthz : Quite right, I didn't write that very well, I had intended to illustrate the scale of the engineering rather than hinting at limitations to the elect
54 DocLightning : Ah! Now that DOES make sense!
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Pirates Hijack 300,000 Ton S. Korean Ship posted Sun Apr 4 2010 22:13:38 by flanker