The outer harbour has granite quays and a protective outer mole which has been used for filming arrival and departure scenes. Ships can proceed, from the inner harbour (via the lock gates) to the outer harbour and from there to open waters for filming sea horizons, general views, sailing shots etc. 

As oppose to the inner harbour, the outer harbour is tidal experiencing both low and high tides twice in a 24 hr period.

The outer harbour is also home to the Roundhouse, an small octagonal single room built as a Harbour masters office in 1895. It affords views out over St Austell bay from its prominent position on the harbour wall.