The equipment on board SS Titanic (in 1912) had a nominal range of 250 nautical miles in daytime and up to 2000 nautical miles at night . The equipment was considered state of the art for the time . (http://marconigraph.com/titanic/wireless/mgy_wireless.html)

You specifically asked about ships but on shore installations had signalled the width of the atlantic ad early as 1901.