I haven't sailed on a 15, 000 ton cargo ship.
The place to find this information is on a Classification Society Website, where you will find the rules that determine these things. If the plating is made of high tensile steel it will be thinner than if made of ordinary steel.
If you were looking for this on board a ship you would look at the Shell Plate expansion drawings.
Scantlings is a general term that covers the structural components of a ships structure, but is also used in reference to the thickness of these items. Very confusing if English is not your first language.
Any good Naval Architecture Text Book will clarify this.
I have only ever seen 1 steam steering gear and that was when I did time as a fitter's mate in John Readhead's shipyard in South Shields, as part of my pre Sea training. (1973)
That was on a wartime frigate (1944) with triple expansion engines that had been converted, either for cable laying, or Trinity House, I am not sure which, after all these years. I can not imagine any were built after about 1948.
Certainly I sailed on several ships built in 1953, some to designs that were first built in the 1930's and they all had electro hydraulic steering.
I do not think there will be any ships left afloat with a "steam tiller". As I recall there were heavy springs in the linkages between the steam engine and the tiller to act as shock absorbers and safety valves on the steam pipes.
Emergency steering was by a "relieving tackle" wooden pulleys and rope, attached from each side of the steering flat to the tiller.
You will have to look for a book on General Engineering Knowledge, dating back to the 40's of 50's for more information.
You are wandering a long way from Motor EK here!!
It is always better to ask a stupid question than to do a stupid thing.