Mariners are requested to notify the National Hydrographic Office (NHO) via fax and/ or email on the relevant Hydrographic Notes (Form PH 102 and PH 102a as modified from UKHO forms), when new or suspected dangers to navigation are discovered, changes observed in aids to navigation, or corrections to publications seen to be necessary. The Mariner's Handbook (NP 100) Chapter 4 gives general instructions. Form PH-102a lists the information required for Admiralty Sailing Directions about ports and should be used as an aide memoir. Such information should be forwarded on Form PH-102a together with Form PH-102.

Various elements of Hydrographic Notes can be downloaded here