A little late for somebody to reply to your question but I do have some experience of expansion joints during my service in the Royal Navy. HMS Amazon was the first in the class of 8 type 21 frigates designed by Vosper Thornycroft for the Royal navy. In 1975 she made her first long trip to the West Indies and met very bad weather. The stress on the all aluminium rigid superstructure caused some alarming cracking, as the flexing of the steel hull was too much for the rigid aluminium superstructure to cope with.
My ship, the second in the class, was about to leave Yarrow shipyard in Glasgow in pristine condition when a team of workers came on board and literally cut the superstructure through the middle through all the compartments amidships. A rubber joint was inserted between both halves.It looked like the joint connecting two railway carriages together except it was only about an inch wide and it was quite amazing to watch the movement in rough seas, as it could stretch much wider and then close completely It was said that you could crack nuts in the joint. Of course being a war ship, there was no point in trying to hide it. We did have ongoing problems for a while as some cables - in particular thick aerial cables -became overstretched in heavy seas.
I watched the documentary on the television for the first time last night on the subject of the expansion joints, when the divers filmed the joint on the Britanic to compare with the original ship's drawings. I would imagine that Harland and Wolfe used some very clever screening to hide the joint.
I hope that this is of some interest to you Jeremy. Dave.
I suspect one of them is an error in the plans on the site. It happens. Keep in mind that the role of the expansion joint was as a stress relieving device. It allowed the superstructure to flex in a heavy sea without breaking.
>>It serve it's purpose in that way but when it comes to the crunch,in other ways it actually helps ships brake in half.<<
Not really. The expansion joints were in the superstructure and didn't penetrate into the hull girder itself. By the time there was any failure here, the breakup of the hull itself was already well advanced. You might want to check out Roy Mengot's outstanding website at http://home.flash.net/~rfm/ to get the details from an engineer's perspective.
>>I'm guessing expansion joints have improved alot since then on modern ships.<<
Uhhhhh...not by much, and they're rarely if ever used in shipbuilding today. Expansion joints have been out of favour for almost half a century.
>>Michael sir.I thought that welding is weaker than rivets?<<
It may have started out that way, but once welding came into use, it the technology improved so rapidly that it became the preferred way of doing it. Not only does welding make for a hull which is stronger, but one which is smoother and signifigently lighter.