Why Two Types of Control Exist
Every vessel operates under two overlapping layers of authority. Flag State Control (FSC) is exercised by the state whose flag the vessel flies — for a British-flagged yacht, that is the MCA acting on behalf of the UK government. Port State Control (PSC) is exercised by the coastal state whose port the vessel enters. Both derive authority from UNCLOS and the major IMO conventions (SOLAS, MARPOL, MLC, STCW). The reason both layers exist is that flag states cannot realistically inspect every vessel every voyage, so port states act as a safety net, enforcing international standards on foreign-flagged vessels visiting their waters.
Flag State Obligations
The flag state issues statutory certificates — the Passenger Ship Safety Certificate, Cargo Ship Safety Construction Certificate, Load Line Certificate, IOPP Certificate, and so on — and sets the survey regime that keeps them valid. For a UK yacht, the MCA delivers this through the Red Ensign Group Yacht Code (REG YC Part A, which superseded LY3) or the Workboat Code as applicable, with MSN 1858 setting out the certification and manning requirements for vessels in this category. The flag state also approves the vessel's Safety Management System under ISM (where required) and issues the SMC and DOC.
As OOW, your practical obligation is to know which statutory certificates your vessel holds, when each expires, and where they are kept. A PSC officer will ask for them immediately. An expired or missing certificate triggers a more intensive inspection and risks detention.
Port State Control — How an Inspection Works
When a PSC officer boards, the sequence is deliberate. They first conduct an initial inspection: checking that required certificates are on board, valid, and carried in their correct form (originals, not copies, for most statutory certificates). They also assess the overall appearance of the vessel and the apparent competence of the crew they encounter. If this initial check raises concerns — deficiencies with the paperwork, visible unsafe conditions, a master unable to demonstrate familiarity with key procedures — the officer escalates to a more detailed inspection.
A more detailed inspection can cover any aspect of SOLAS, MARPOL, MLC, or STCW compliance: fire and LSA equipment, passage planning records, logbooks, crew work-and-rest hours, GMDSS equipment, garbage and oil record books, and the competency certificates of watchkeepers. The OOW should be prepared to demonstrate operation of fire detection systems, LSA, GMDSS, and to produce their own CoC.
If deficiencies are found, the PSC officer can issue a deficiency notice (rectify before next port), or, for serious deficiencies, detain the vessel until they are corrected. Detention is a significant commercial and reputational event and is published in the Paris or Tokyo MOU database — effectively a public record.
Paris MOU and Regional Regimes
Port states co-ordinate through regional MOUs. The Paris MOU covers European and North Atlantic waters; the Tokyo MOU covers the Asia-Pacific region; others exist for the Indian Ocean, Caribbean, and so on. These bodies maintain targeting systems that score each vessel by age, flag state performance, vessel type, and inspection history. A high-risk score means inspection at virtually every port call; a low-risk score earns reduced frequency. Maintaining clean inspection records directly benefits the vessel's targeting profile.