I sure by now most of us have  looked at http://people.bath.ac.uk/ccsshb/12cyl/

I was looking at some documentation on the engine builders site and
came across this:
". The cylinder liner wear rates are in the region of 0.02–0.03 mm/
1000 hours maximum."

in the document:
http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/marine_news/2000_3/rta96c_powerful_success.pdf

That equates to about 1 thou in 42 days - I don't now much about
internal combustion engines but that seems quite high. Is it because
of the large bore of the cylinders that the rings can cope with a
relatively large amount of cylinder and ring wear ?

Regards
Tim