Why MARPOL Exists
The oceans are a shared global resource. Routine operational discharges — bilge water, garbage, sewage, exhaust gases — were historically released without restriction, causing measurable harm to marine ecosystems. MARPOL 73/78 (the International Convention for the Prevention of Pollution from Ships) establishes the legal framework that converts this harm into enforceable prohibition. For an OOW, understanding why these rules exist makes compliance instinctive rather than procedural.
Structure: The Six Annexes
Each annex addresses a distinct pollutant category. A yacht under 3000 GT will most commonly engage with:
- Annex I – Oil (bilge water, fuel residues)
- Annex IV – Sewage
- Annex V – Garbage
- Annex VI – Air pollution (SOx, NOx, ODS)
Annex II (noxious liquid substances) and Annex III (harmful packaged substances) are rarely directly relevant to a private or charter yacht in normal operation but remain technically applicable.
Special Areas
Certain sea areas, by reason of their oceanographic and ecological conditions and their sea traffic, require special mandatory discharge controls. MARPOL designates these formally; examples include the Mediterranean Sea, Baltic Sea, North Sea, and Antarctic Area. Within Special Areas, discharge restrictions are generally more stringent — in some cases amounting to a near-total prohibition. An OOW must know the vessel's current operating area and verify which Special Area regime applies before any planned discharge.
Note that Special Area designations vary by Annex — a sea area may be a Special Area under one Annex but not another. The Baltic Sea is the only Special Area under Annex IV (sewage). The Mediterranean Sea is a Special Area under Annex I (oil) and Annex V (garbage), but is not an Annex IV sewage Special Area. The Red Sea Annex V Special Area came into effect on 1 January 2025.
Key Discharge Standards on Board a Yacht
Annex I (Oil): Oily bilge water may only be discharged outside Special Areas when the oil content does not exceed 15 ppm, the ship is underway, and an approved oily water separator (OWS) with oil-content meter is in use. Discharge in a Special Area is prohibited unless specific conditions are met. Oil Record Book Part I must be maintained.
Annex V (Garbage): Plastics discharge is prohibited everywhere. Food waste discharge rules are as follows:
- Outside Special Areas: comminuted or ground food waste (passed through a 25 mm screen) may be discharged at 3 nm or more from the nearest land; unprocessed food waste requires 12 nm or more from the nearest land. The vessel must be en route.
- Inside Special Areas: only comminuted or ground food waste (25 mm screen) may be discharged, and only at 12 nm or more from the nearest land. Unprocessed food waste discharge is prohibited within a Special Area regardless of distance.
A Garbage Management Plan and Garbage Record Book are required for vessels of 100 GT and above making international voyages, or certified to carry 15 or more persons. Note: this threshold was reduced from 400 GT to 100 GT on 1 May 2024 — older textbooks and some revision materials still quote 400 GT, and examiners are aware of the change.
Annex IV (Sewage): The following distance and treatment rules apply:
- Comminuted and disinfected sewage: may be discharged at more than 3 nm from the nearest land.
- Untreated sewage: may only be discharged at 12 nm or more from the nearest land, whilst the vessel is en route at not less than 4 knots, and at an approved rate.
- Vessels fitted with an approved sewage treatment plant meeting MEPC.227(64): discharge is permitted at any distance, provided there are no visible floating solids or discolouration of the surrounding water.
- The Baltic Sea is the only Annex IV Special Area; additional restrictions apply there.
Annex VI (Air): Global fuel sulphur content is limited to 0.50% m/m (since 1 January 2020). Within Sulphur Emission Control Areas (ECAs), the limit is 0.10% m/m. The established SOx ECAs are the Baltic Sea, North Sea, North American area, United States Caribbean Sea area, and — from 1 May 2025 — the Mediterranean Sea, which became the fifth SOx ECA. For vessels regularly operating in the Mediterranean, this is a significant practical development: bunker arrangements and fuel change-over procedures must account for the 0.10% m/m limit throughout those waters. The Mediterranean is therefore subject to MARPOL controls under three separate Annexes — Annex I, Annex V, and now Annex VI — making it one of the most comprehensively regulated sea areas in the world. Compliance with the sulphur limit can also be demonstrated by use of an approved equivalent arrangement such as an exhaust gas cleaning system.
From Regulation to the Deck
As OOW your practical duties are:
- Know which Special Area or ECA you are in or approaching.
- Ensure no overboard discharge occurs without verifying compliance.
- Ensure all record books (Oil Record Book, Garbage Record Book) are correctly completed at the time of the operation.
- Report any pollution incident to the Master immediately; the Master is responsible for reporting to the coastal state.