However , in the centre section of the bridge ( the `` high girders '' ) the bridge girders ran as through trusses above the pier tops ( with the railway inside them ) in order to give the required clearance to allow passage of sailing ships to Perth .
However , in the centre section of the bridge ( the `` high girders '' ) the railway ran inside the bridge girder , which could then run above the pier tops to give the required clearance to allow passage of sailing ships upriver ( e.g. to Perth ) .