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100 years ago the Titanic sank, a triumph of profit over safety; and we still appear not to have learned lessons. Modern cruise ships are getting bigger, with higher centres of gravity and tall super-structures that act like sails. Double hulls to above the water line (which would have saved the Titanic) are still only used on tankers. Crews on liners, can consist of a high proportion of entertainers and service staff, without being trained mariners. Obviously I'll defer to Asp on this, but a land based holiday seems more likely this year! :( (Source: "why do ships sink" CH4 tonight).

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I think you have to be very careful about the profit/safety angle surrounding Titanic.At the time of building she was the best there was in terms of capacity, speed and indeed safety as laid down by International Regulations. Over half a century later the Herald of Free Enterprise (amongst several other passenger ferry incidents) showed that the safety regulations were insufficient. Ship stability is a very complex subject, and naval architects have to design ships with the current regulations in mind. The calculations involve not only the safety and stability of the vessel, but also her economics. Because the vessel has to pay Port Dues at every port visited and these dues are dependent on her tonnage, the naval architect has to factor in these costs when deciding on the design. As for the size of the liners these days, well they are reportedly a lot more stable than their smaller predecessors (and I for one would be very suprised if this wasn't the case given the international pressure on safety in recent years). The Titanic was a one off, being in the same part of the ocean at the same time as an iceberg that, at that time of year, shouldn't have been anywhere near.

All staff on passenger ships have to be trained in safety procedures, and this includes entertainers, bar staff, cooks etc. All seafarers have, by international law, to be certificated for safety training.

As for the Costa Concordia we have to wait for the enquiry but it would seem to me to be down to showing off. :wink: :wink:

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Wouldn't dare question a professional Asp; but there were some obvious questions of safety about the trend for building bigger super-liners (36 planned over the next 3 years), with larger passenger capacity (up to 6,000). The Costa Concordia scraped the rocks, just like the Titanic scraped the iceberg, and it's hull was peeled back, as if by a giant can opener. A double hull up to above the water line could have prevented sinking. The multi-storey super-structures can be affected by the wind, acting literally like sails, driving ships off course and on occasion, into collisions. There are questions of adequate foam provision for fire-fighting and fixed installations. I was surprised to learn that ships pump water in and out via ports in their hulls, which in one case, where a pump valve failed; sea water entered the ship via the plumbing system! Add to this human error or incompetance, and things arn't as safe as we might expect. :huh:

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Well if you think they are unsafe then don't go on them, simple. Personally I wouldn't go near one because I know I'd be itching to have a go at driving!! :D :grin: :D

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What's to stop a rock or an iceberg which is hit hard enough to rip open a single hull from also ripping open a second hull placed within?

 

Surely the trick is NOT to hit things solid enough to cause damage in the first place!!!!

 

We've seen 3 major cruise ship incidents recently, two big fires and a full blown capsize, involving many thousands of passengers, and the loss of life has been quite frankly minimal.

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Both Titanic and Costa Concordia suffered glancing impacts, which caused a tear along the side, compromising several water tight compartments. I suspect a double hull would have survived such, depending on the gap between the plates. "Minimal loss of life" is reassuring, providing one isn't part of the "minimal" :wink: !

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The enquiry into the Costa Concordia has hardly begun, but it would seem to be the case that it was caused, not by human error but, by human arrogance on behalf of the Master. I'm not sure if there would have been as much loss of life if the Master had given the order to abandon ship at anearlier stage when the ship was still upright and before the second grounding. I fact I think (although this is only an opinion without the detailed knowledge of her stability) she may have stayed upright and afloat had she not been grounded the second time.

 

As for the Titanic, well an unfortunate accident. There is a saying "If anything can go wrong, it will" and hands up anyone who has never had an accident that they could have avoided with the benefit of hindsight.

 

Anyway as I said before, if you don't think a means of transport is safe, then don't get on it. Personally I'd rather go on a ferry than a plane, but thats more from a comfort point of view. :wink: :wink:

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Bit of basic physics for you Obs, Archimedes would recognise this one.

 

If you put a double hull on a ship then the gap between the two will presumably be full of air. That'll cause the ship to ride MUCH higher in the water, and the greater the gap between the two hulls the bigger this effect will be. This will make the centre of gravity of the ship much higher, reducing it's stability in rough weather and making it much more prone to capsizing. Since it's higher out of the water it'll also be even more affected by winds, so even more at risk of being driven "off course and on occasion, into collisions".

 

There's no avoiding this because it would obviously be necessary to design the ship in such a way that the ship could remain afloat if the outer hull were holed and the space between the two was completely flooded - so the ship must be designed to ride sufficiently high in the water that it maintains a safe freeboard even if it loses all of the buoyancy provided by the air between the two hulls when completely fully laden.

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Inky, is this what you are saying - certain double-hull vessels might at times be less stable than single-hull vessels, such as when the outer hull is pierced, allowing the space between the hulls to flood with water, certain double hull tankers can become unstable during cargo and ballast operations, also due to an increased height of the

center of gravity and the large free surface effect. When sailing, this is less of a problem as the vessel is trimmed by pumping water either in or out of the vessel ballast tanks to aid stability. Double hulls are not used to prevent a vessel from sinking as a result of striking any underwater objects that resulted in ripping the hull open they are mainly used on oil tankers to prevent product spillage in that very situation.

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Regardless of the reasons, faults or failings by man or mother nature it was a tragedy and will always be seen as such.

 

My problem though is that everytime there is mention of the titanic all I can think of is this.... I'm so sorry :oops:

 

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If the Costa Concordia had a double hull then the loss of power may have been prevented, however there would have been stability implications with all the water ingress being on one side of the ship.

 

Double hulls for oil tankers were made compulsory to help prevent spillage of cargo due to grounding or collision. They also have the added advantage of being used for ballast when the cargo tanks are empty removing the need for carrying ballast in cargo tanks, which would have to be pumped ashore to prevent pollution. :wink: :wink:

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Ever heard of ballast Inky? :wink: :wink:

 

So you plan to increase the buoyancy of a ship by providing it with a double hull, then add a load of ballast weight to make it sit lower in the water.

 

So what happens when it's got ballast on board, so it's sitting nice and low in the water, and then the double hull gets holed and flooded? Even if the ballast just consists of water you can't rely on the pumps working in an emergency to pump it out.

 

As others have said, oil tankers have double hulls to keep the cargo IN not to keep the water OUT - and they have the advantage that the cargo is lighter than water and so provides buoyancy anyway.

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So you plan to increase the buoyancy of a ship by providing it with a double hull, then add a load of ballast weight to make it sit lower in the water.

 

So what happens when it's got ballast on board, so it's sitting nice and low in the water, and then the double hull gets holed and flooded? Even if the ballast just consists of water you can't rely on the pumps working in an emergency to pump it out.

 

As others have said, oil tankers have double hulls to keep the cargo IN not to keep the water OUT - and they have the advantage that the cargo is lighter than water and so provides buoyancy anyway.

Large vessels have back up pumps exactly the same as you have in industry, especially the heavy and petrochemical industries, if you relied entirely on one pump or did not carry spare generators or battery back up, rest to sure no large vessel would ever leave harbour. I don't think any master would set out to intentionally commit suicide!.

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I thought that one of the problems experienced on both of the cruise ships which had to be towed after suffering engine room fires recently was that both had lost ALL electrical power - so that there wasn't even power for cooking or lighting and the passengers had to camp out on the open decks.

 

Pumps big enough to rapidly shift the kind of tonnages of water we're talking about as ballast in a double hull ship would never be able to run from battery backups.

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I thought that one of the problems experienced on both of the cruise ships which had to be towed after suffering engine room fires recently was that both had lost ALL electrical power - so that there wasn't even power for cooking or lighting and the passengers had to camp out on the open decks.

 

Pumps big enough to rapidly shift the kind of tonnages of water we're talking about as ballast in a double hull ship would never be able to run from battery backups.

I am not saying that the auxiliary battery back up would drive machinery but would provide sufficient power to provide emergency lighting or temporary power for emergency control systems ie. start up emergency diesel or steam driven pumps.

This may help you to come to terms with the subject we are discussing:- :wink:

 

Bilge and ballast systems

 

Bilge systems consist of pumps, sometimes assisted by eductors, to remove water and other accumulated liquids from the engine room and other compartments in the ship, other than oil tanks. Where bilge water may be contaminated by oil, it is first pumped to a holding tank and discharged overboard slowly through an oil-and-water separator. Ballast systems comprise the pumps and piping used to fill and empty ballast tanks. (Ballast tanks are filled to improve the trim or stability of a ship which is not carrying cargo.) To reduce pollution, past practices of filling empty fuel and cargo tanks with ballast are no longer allowed. Bilge and ballast pumps are usually motor-driven centrifugal pumps, although steam-reciprocating pumps are sometimes fitted for bilge service, while tanker ballast pumps are often steam-turbine-driven centrifugal units. In smaller plants the bilge pump may be driven via a clutch from the propulsion engine, and may double as a fire pump.

 

Electric generating plant

 

The electric power required for all continuous or recurring purposes on a ship is about 5% of the propulsion power, when restricted to the supply of motor-driven auxiliaries, lighting, other hotel services including high-voltage alternating current and provision refrigeration, communication, navigation, and control equipment of simple cargo ships. Much higher percentages are required when such services as cargo refrigeration or cargo hold ventilation are provided. On passenger ships the electric load can rival or exceed the propulsion power. Peak power demand may occur intermittently if motor-driven thrusters are fitted for maneuvering.

Ocean-going ships are required to have a minimum of two generators, with either one capable of supporting the essential electrical load, but most ships have at least three in order to improve ship reliability. A ship with a high electrical load may have three or more generators, with two or more operated in parallel to support the load. In addition, most ships are required to have a separate emergency source, usually a diesel generator, located outside the engine room, for emergency lighting, communication, navigation and control services, fire fighting, and often, steering.

Power from the generators is distributed to motors, lighting, and other consumers through switchboards and distribution boards.

On steamships, at least one of the generators, acting as the normal electricity source, is driven by an independent turbine supplied with steam from the same source as the propulsion turbines, and at least one will be a diesel generator. Most diesel-driven ships have diesel generators, as do many gas turbine--driven ships, although others have gas turbogenerators. Many ships are fitted with a generator driven from the propulsion gearing or shafting as the normal electricity source. In many high-powered diesel-engine ships, sufficient waste heat can be recovered by an exhaust gas boiler to support a steam turbine, adequate for the normal load. Ships with alternating-current electric drive may take power for ship services from the propulsion generator.

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