Pollution at sea and MARPOL on board

The lesson in plain words

1. Who Annex IV covers
   • MARPOL Annex IV covers international voyages by ships of 400 GT or more, or certified for more than 15 people.
   • GT means gross tonnage: enclosed volume, not weight.
   • Approved grinding and disinfection equipment permits discharge beyond 3 nautical miles (nm) from the nearest land.
   • Untreated sewage needs more than 12 nm.
   • Under these permissions, stored sewage must be released at an approved moderate rate while en route at 4 knots or more. Local bans still apply.
   • Small yachts usually follow national rules instead.
2. National and regional rules
   • Small boats are covered instead by the coastal state, and the rules differ widely.
   • Many ban toilet discharge in ports, marinas, bays and protected areas, and some ban it everywhere in their waters.
   • Before a cruise, look up the rules for each country and area: pilot books, the harbour office and national boating websites carry them.
3. Examples
   • Sweden has banned toilet discharge from all recreational boats, foreign ones included, in its waters out to 12 nautical miles since 1 April 2015.
   • In the United States, a boat with an installed toilet needs a certified marine sanitation device, and in a No Discharge Zone even treated sewage may not go overboard.
   • In the Baltic special area, passenger ships must retain sewage or use an approved treatment plant meeting its additional nutrient-removal standards.
4. Holding tanks
   • A holding tank keeps toilet waste on board until you reach a pump-out station.
   • Boats built under the current EU Recreational Craft Directive with a toilet must have a holding tank or a treatment system.
   • Where discharge is banned, secure the Y-valve, the selector for tank or sea, to the tank. See Ship for the plumbing.
5. Grey water
   • Grey water comes from sinks and showers.
   • Kept separate from sewage, it normally falls outside Annex IV.
   • Mixed with sewage, it follows sewage rules.
   • Local restrictions may also apply.
   • Keep oil and food scraps out: mixing them in does not bypass pollution rules.
   • Use little soap and scrape food into the bin; biodegradable soap can still harm marine life.

Key data

Key points

• Annex IV covers ships of 400 GT or more, or certified for over 15 people, on international voyages.
• Small boats follow national and regional sewage rules, which vary from country to country.
• Many areas ban toilet discharge in ports, bays and protected areas; some ban it completely.
• A holding tank keeps waste aboard until a pump-out station.

Check what you have read

True or false?

Practice case & exam keys

Exam keys

1. 1Annex IV: international voyages, 400 GT or more, or certified for over 15 people. Approved grinding and disinfection: >3 nm from nearest land; untreated: >12 nm. Stored sewage: approved moderate rate, en route at 4 knots or more. Local bans still apply.
2. 2Small boats: national rules apply; check each country and area before you go.
3. 3Holding tank and pump-out; in banned areas the Y-valve stays set to the tank.