Admiralty Sailing Directions dating to 1870 note that St Tudwalls Sound 'is a safe channel for vessels entering or quitting St Tudwall roads, it being clear on both sides, with a depth of 6 or 7 fathoms in it. The tides, however are strong, and when opposed by the wind, cause a short cross sea.' The current sets south through St. Tudwals Sound rounds Trywn Cilan and sets northwest into Porth Neigwel.

Sources include:
Admiralty, 1870, Sailing Directions for the West Coast of England from Milford Haven to the Mull of Galloway including the Isle of Man, pg62
Historic Admiralty Chart 1412-A7, RCAHMW Digital Collections sourced from UK Hydrographic Office (published 1842)

Maritime Officer, RCAHMW, September 2014.