The Finer Points of Ship Construction


Jan 5, 2001
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I thought that it would be interesting to start a thread here discussing various points of hull construction in large steamships of the Titanic’s era.

The first question I thought would be interesting is to do with a vessel’s scantlings — I personally had assumed that a vessel with heavier scantlings would be greater in strength than another vessel of lighter scantling, but this cannot be the full picture; for example, the Majestic II gives an impression of good solid materials in her design, and heavier scantlings than other vessels, but did that make her stronger?

Strength measured in inches cannot be just to do with heavy scantlings either, because ships have to flex and bend with the sea. Large vessels may have rode up and over the crest of a large wave compared to smaller ships, but the large ship would need to flex somewhat, otherwise she would just stick to her rigid shape and surely there would be no relief for the stresses she endured? Might that not lead to sudden, catastrophic failure such as the hull fracturing?

My initial belief with a vessel whose lower hull was very heavily-constructed was that the vessel would have much greater strength in the event of collision or accident, but surely then that needed to be balanced with the need for the structure to flex in heavy seas over a period of twenty-five or thirty years?

Expansion joints, as I understand it, were fitted in liners’ superstructure above the strength deck to allow the superstructure to flex even though it was not part of the structural hull, relieving the stresses on essentially lighter plating and construction when the superstructure is compared to the lower hull. Surely, then, lighter superstructure construction combined with two, three or even four expansion joints would be superior to a more heavily constructed superstructure that was hopelessly inflexible? Furthermore, lighter construction of the topsides adds to the ship’s stability and (I think) metacentric height, does it not?

I apologise if I am rabbitting on, but I did think this topic might prove interesting with some of the techies here.

Best regards,

Mark.
 

Erik Wood

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I sure am glad this thread was started. This is somewhere where we can all share our knowledge and stuff.

Mark said:
quote:

Expansion joints, as I understand it, were fitted in liners’ superstructure above the strength deck to allow the superstructure to flex even though it was not part of the structural hull, relieving the stresses on essentially lighter plating and construction when the superstructure is compared to the lower hull.

It's to bad that you won't be in Topeka. We will be discussing expansion joints and there relation to Titanic's foundering. It is my understanding (after conversations with H&W) that the way you have described them is dead on. Expansion joints are used today but in a entirely different manner then they where used then. For the most part the superstructure of a ship (the part that is about 30 feet and up from the water) is constructed of a much lighter material then the rest of the ship. This material is supposedly just as strong as the rest of the ship but the because of the weight and now the size of the ships today it makes it a neccessity. Otherwise ships would just roll over.

I don't know but I believe the Queen Mary was built using the same construction method as Titanic. Most of her superstructure is of the same steel grade and most of it, is connected to the hull of the ship. Is this right???

Mark aslo said:
quote:

Surely, then, lighter superstructure construction combined with two, three or even four expansion joints would be superior to a more heavily constructed superstructure that was hopelessly inflexible? Furthermore, lighter construction of the topsides adds to the ship’s stability and (I think) metacentric height, does it not?

Yep, that was my point earlier I just wrote it in the wrong spot.

quote:

My initial belief with a vessel whose lower hull was very heavily-constructed was that the vessel would have much greater strength in the event of collision or accident, but surely then that needed to be balanced with the need for the structure to flex in heavy seas over a period of twenty-five or thirty years?

The bigger they are the harder they fall. Strength in a collision is dependent on where the collision takes place, at what speed, sea state, and all kinds of other good things. If the hull is already under stress before the collision regardless of how it is built the ship will suffer some extreme amount of damage. Yet if the hull isn't under any stress and the collision is "light" then the ship won't sustain that bad of damage.

When we talk about collisions remember that one sort of damage leads to another sort of damage. An example would be in a collision that pokes a hole in a ship and breaks through the shell plating that isn't the only damage.

There is damage to the frames around the collision.

If the ship takes water unevenly there is undue and possibly harmful damage done to the keel.

etc etc etc....

I look forward to reading more on this thread.​
 
Jan 5, 2001
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Hi Erik!

I am glad that you responded to my post, I too hope that this thread will become a very interesting technical conversation. I know you and Mike are moderators of the other technical section, so perhaps this thread could be moved there depending on how it develops?


Erik wrote:
quote:

For the most part the superstructure of a ship (the part that is about 30 feet and up from the water) is constructed of a much lighter material then the rest of the ship. This material is supposedly just as strong as the rest of the ship but the because of the weight and now the size of the ships today it makes it a neccessity. Otherwise ships would just roll over.

I seem to remember that the QE2's superstructure is lightweight aluminum, with an 'expoxy-resin' [sic?] compound joining the lightweight material to the lower hull to prevent corrosion, which could weaken the material. I am not quite sure about the Queen Mary, but I know that the Board of Trade wanted to increase the thickness of her scantlings after the experiences of the Aquitania, Olympic and Imperator classes by 1931.

How exactly are expansion joints used today then, and are they a 'cut' in the ship's structure, covered by flexible material, if not leather?

quote:

When we talk about collisions remember that one sort of damage leads to another sort of damage. An example would be in a collision that pokes a hole in a ship and breaks through the shell plating that isn't the only damage.

So, say a strake of hull plates is distorted in a collision -- one plate is pierced and deformed, while those nearby are also deformed. Your point would be that rivets could also be 'popped' or loosened with the deformed plates, and even frames could be damaged, being warped, or cracked or whatever?

My thoughts about such a situation would initially be that it would be better to have thicker plates, stronger/thicker frames and quadruple rather than triple rivetting. But, then we'd still have problems; perhaps a hole in one plate with less deformation, and cracking near the rivets. Quadruple rivets would put more strength into holding the plates, but as some naval architects have said, that would lead to increased local stresses, possibly leading to cracking. The thin plating between rivets would have far higher local stresses and cracking would surely increase.

When Olympic had a new stern frame fitted after a collision, the original design for five rows of rivets to hold the frame to the hull plating was changed to three or four, presumably due to these worried, and because the rivets were all in the propeller slipstream and underwent massive vibrations.

Best regards,

Mark.​
 

Erik Wood

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Hey Mark,

This looks to be an interesting thread. I will send you an email about moving this thread.

Mark wrote:
quote:

How exactly are expansion joints used today then, and are they a 'cut' in the ship's structure, covered by flexible material, if not leather?

I am not exactly what you mean. Do you mean how are they connected to the internal workings of the ship??? Or do you mean what are they made of and how are they installed?? I will wait to answer your question until I understand it better.

quote:

Your point would be that rivets could also be 'popped' or loosened with the deformed plates, and even frames could be damaged, being warped, or cracked or whatever?

This is exactly what I mean. Damage to one plate could also mean damage to the nearby rivets structure, the frame and the plates on either side of it. That is one of the many things that I learned just recently while attending a Maritime Incident Invesitgator course.

This looks to be interesting.​
 
Jan 5, 2001
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Hi!

I'll be checking my e-mail this evening. I am glad that you have found this thread interesting Adam. Now, Erik, to deal with your point:

I wrote, and Erik replied:

quote:

How exactly are expansion joints used today then, and are they a 'cut' in the ship's structure, covered by flexible material, if not leather?
I am not exactly what you mean. Do you mean how are they connected to the internal workings of the ship??? Or do you mean what are they made of and how are they installed?? I will wait to answer your question until I understand it better.

Well, basically I am asking how they differ from the expansion joints used in Titanic's day, how they are connected to the ship internally and how they are installed. I know ship construction now has changed importantly, such as pre-fabricated interior spaces, 'blocks' of hull being lowered into a drydock and built up like a lego kit, and welding being employed rather than rivetting, for example, so assume that the design and construction of expansion joints has changed.

One further point to do with the topsides of liners. The lightly-constructed (scantlings) superstructure, complete with the appropriate number of expansion joints to allow the superstructure to flex, will serve the ship well, also contributing to stability, but what about transverse deck girders?

For example, to reduce racking stresses, heavy brackets were fitted on the Olympic around A deck and the public room areas; these, I understand, were transverse girders and as they were intended to prevent racking (maintaining the ship's width) in heavy seas and when the ship is rolling, it would surely have been good to have these brackets/girders as thicker scantling as possible. But, if I am right to assume that, would not it adversely stiffen the structure so that it cannot flex? Or, are there kind of three sections of the superstructure, that move like hinges at the two expansion joints? Olympic never suffered any problems from racking stresses so presumably these 'heavy brackets' did their job well.

<font color="ff6000">Under the superstructure, the strength deck, forming the top of the structural hull, or the bridge and shelter decks on the Olympic class, was of heavy scantling; plating was thicker, girders stronger [not sure on the girders], and doubling plates alongside the shell plating, combined with lots of hydraulic riveting, were all intended to make these decks a monument of strength as they experienced the vast bulk of the stresses that the lower hull endured. Doubled plating ensured that localised stresses were distributed among more material, reducing the stresses per inch and guarding better against fractures. However, while effort was made to make these decks so strong, they were right under the flexing superstructure and expansion joints, so surely they lacked an essential flexibility? (Or, more likely, my technical understanding or theory is seriously flawed here.)

Before I confuse myself, I will sign off this post. When I see it posted, it will probably look like a marathon. Or not...
wink.gif


Best regards,

Mark.​
 

Erik Wood

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The answer to this one is very complex. So I will do my best to answer it in a way as not to confuse me or anybody else.

Most ships that have a forward well deck area like the Olympic Class liners, the Aquitania and Mauretania etc. have a tendency to suffer small cracks around the bridge deck area. Most due to the transverse girders used to support not only the weight of the deck, but enhance it's ability to remain stable. During heavy weather this area took strain more so then the expansion joints do.

It is more often then not that transverse girders are put in place to serve a variety of purposes, overall structural stability and in other cases it is to hold the decks to together.

Expansion joints are in reality the weakest link in a big chain. If the bottom portion of the plating around, next to, whatever to, the expansion joint, the joint itself will most then likely give. Expansion joints are meant to take temporary mass amounts of strain. An example is when the bow plows down into a wave and then hits the ocean. The bow or first section supported by the expansion joint is forced up, while behind this joint is forced down. So at that second the joint is carrying the load of momentum from the ship and the weight of the ship behind it. It is only holding this load for a few seconds at best. Where as in a sinking scenrio (i.e. Titanic) the joint was forced to sustain the weight of the bow and the weight of the flooding compartments, plus gravity was forcing the stern section down at a straight angle. Eventually the joint gives because it can no longer support the weight.

Transverse girders serve as stability points, they are usually connected to the internal workings of the ship and the hull structure. Where as Expansion joints are connected loosely to the internal workings but mostly to the hull structure (by today's standard). To be honest I don't even think they call them expansion joints anymore. I know there is another fancy term for them.

If I recall rightly todays ships are built to withstand waves of a certain height. I think the superstructure has enough give in it to allow for that. On a side note it is fairly common for ships of the "Conquest Class" to avoid heavy weather at almost any cost. They ride horribly in bad weather and the sway of the ship made me want to loose my lunch.

Does this help any???
 

Erik Wood

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After rereading that last post I may have posted some things that confuse the issue on transverse girders. What I will do is look a few things up in my Naval Engineering books and post something a little bit more intelligent this weekend or first thing next week.

After reading accident reports all day my brain is pretty fried on techincal matters.
 

Noel F. Jones

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Scantlings & Expansion Joints:

Before the advent of Shaw Savill's "Southern Cross" in 1955 all passenger liners had cargo carrying capacity and the magnitude of scantlings was more a reflection of the vicissitudes of this attribute than any inherent need stemming from passenger carrying. Modern cruise vessels are relieved of this burden, hence their relative fragility.

I've always regarded heavy scantlings as a feature of such as heavily-worked general cargo vessels and heavy lift ships where liberties have to be taken with the static curve of loads and this situation has in turn to be routinely taken to sea. Bulk carriers also, must surely reflect the density of their cargoes and their large hatchway openings relative to ship size. It does not follow therefore that heavy scantlings necessarily confer excessive rigidity. They imply a high first cost – and have incidentally increased survivability in collisions with lesser ships!

This topic really requires the input of a qualified, practising and experienced naval architect. That's not to say we should not read up on the subject so's we can understand ships the better. I have ready access to Reed, Muckle and Munro-Smith via Attwood (contemporaneous with the Titanic); also Seaton on ship propulsion devices (late Victorian) has passed before me. Attwood I find particularly useful for historical work because all the units and formulae are pre-S.I.

It was the practise to gather longitudinal scantlings into a hypothetical 'equivalent girder' to which the requisite moduli were then applied. The elements of the 'equivalent girder' vary as to whether the vessel is hogging or sagging. The location of the neutral axis also varies, it being elevated in sagging mode. Whatever the mode, the girder properties have to be consistent above and below the neutral axis.

Regarding stability considerations, presumably any desired weight saving above the neutral axis would have to be achieved by a substitution of materials without compromising the constancy of the moduli. Such substitution would also have the effect of lowering the centre of gravity with a corresponding increase in the transverse metacentric height but this would tend towards a 'stiff' ship, susceptible to heavy weather damage and injurious to her complement.

Interestingly, according to Attwood the armour of warships was excluded from the 'equivalent girder'.

Regarding expansion joints, surely these are merely spaces between adjacent deck erections sufficient to allow their alternating longitudinal convergence and divergence in response to the flexing of the 'ship girder' upon which they stand. Their only discernible function is to remain of such magnitude, while the ship girder above the neutral axis is in compression, that the deck erections do not impinge on each other.

It's a while since I was in proximity to an expansion joint. To facilitate passage over decks and throughout the accommodation I assume they were bridged by narrow metal strips hinged on one side and sliding free on the other. I would conjecture that vertical partitions in way of expansion joints were of leather, rubber or plastic 'bellows' (much like the walkways between railroad cars) cosmetically masked on each side by a hanging panel free to work over the adjacent panels. Perhaps a trip to Long Beach would confirm.

The Queen Mary has (had?) three expansion joints, two abaft and one forward of her funnels. That uppermost of her decks which contributed to the strength of the ship girder was the promenade deck.

I would have thought trochoidal wave theory, only ever a working hypothesis both in its formulation and application, would have been superseded by now. There was a moderating formula postulated by the British naval architect W.E.Smith in 1883 (the Smith Correction) which computed the apparent head of water in a trochoidal wave, and therefore the pressure and therefore the buoyancy (I'm struggling now!) from still water level. Doubtless things have moved on, particularly with computerised stress analyses etc.

Furthermore, according to Muckle the ship girder in critical compression responds, inter alia, to Euler's formula. And if Euler (whose name, I am reliably informed, rhymes with 'boiler') is to be adduced here, you'll find me in the pub.

Noel
 
Aug 10, 2002
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Hello,
I'm new to this, so please indulge any errors I make. I believe LaDage "Modern Ships", or Baker "Introduction to Steel Shipbuilding" might be helpful. In general strength is directly related to Scantling (thickness) that is why they put Doubler Plates double thickness arround openings like sideports or hatchs. Also longitudinally framed hulls like tankers or bulker tend to be stronger than transversely framed ones like Titanic.
Regards
Charles Weeks
 

Erik Wood

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Noel is on a roll. This is the second post made by him that I actually understand and that I can actually partially agree with.

Mr. Weeks,

Are you a sailor? I knew a Chief Engineer named Charles Weeks. I was under the impression he was still underway but perhaps not. If so or not I am interested in exchanging emails on the subject if you are.
 
Jan 5, 2001
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Hi!

This thread is growing just like I hoped it would. I have some things to add later, but meanwhile welcome aboard Charles.

Could you answer a question for me please Charles (or anyone else)? On another forum I am being argued at by an 'author' who asserts that reciprocating engines 'shake a ship apart.' He seems to be exaggerating, but I'd be great for a second opinion! He mentioned Liberty ships, but weren't they built to last World War II, and otherwise dissimilar to liners of 1914?

Best regards,

Mark.
 
Aug 10, 2002
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Dear Mark,
There is no doubt recips. shake a lot. The faster they go the more they shake. One of the reasons turbines became so popular. One moving part rotational motion. Example reciprocating pumps are only good for about 32 double strokes per minute, above that and they start to self destruct. Think of the start, stop motion. The more cylinders an engine had the smoother it was, ie. V-12 or 16s, vice four bangers. Ultimately one rotating turbine is smoothest of all.
Liberties had three legged triple expanders, Titanic,s wing engines were four legged triple expanders. Instead of one extremely large LP Cylinder it had two smaller LPs.
Regards,
Charlie
 

Erik Wood

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I can already see that Charles is going to be a great addition to the techie group. Glad to have you again.

I would have to agree with what he already said.
 
Jan 5, 2001
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Hi Charles, Erik!

Thanks Charles for the information. I understand that reciprocating engines then are not as smooth as turbine engines (at least the engines themselves, not the propellers). But I can't seem to find anyone supporting the 'shake the ship apart' talk with regard to these engines -- I mean, there seems no reason why well-designed and balanced engines could 'shake a ship apart.'

I've also some thoughts on bulk carriers, Noel.

Best regards,

Mark.
 

Erik Wood

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I don't think they would shake the ship apart. But I think some loose engine bedding can be attributed to recip engines. Who, if you don't mind is saying the ship would be shaken apart???
 
Aug 10, 2002
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I don't think they'd actually shake the ship apart. But they could cause pipes to break (a frequent cause of engine room fires on new Diesel ships) or other parts to fail due to the vibration. I have read accounts of the German liners, pre-Imperator that had large recips and they were noted for the vibration and the discomfort to passengers and crew alike. The scene in the engine room in Cameron's movie shows the engines very nice and quiet, and at slow speed they are. But Hooked Up they're something else.
Charlie
 

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