To people on shore, a ship can pass almost silently beyond the horizon. Underwater, its propeller, machinery and hull radiate sound across long distances. For whales, fish and other marine animals that use sound to navigate, communicate, feed and reproduce, the ocean is an acoustic habitat.
The International Maritime Organization has revised voluntary guidelines for reducing underwater radiated noise and is extending an experience-building phase through 2028. Its GloNoise work is helping pilot countries identify hotspots and apply a toolkit. The central challenge is turning awareness into measurements and choices that survive commercial pressure.
Noise is not one simple pollutant
Propeller cavitation, machinery vibration and flow around the hull contribute different frequencies and patterns. Effects depend on source level, distance, depth, background sound and the hearing of particular species. Chronic masking differs from an acute blast.
Policy needs both broad indicators and context. A global average cannot replace local protection around migration routes, breeding areas or quiet refuges.
Design is the cheapest moment to act
Hull form, propeller selection, machinery isolation and wake quality can reduce noise when considered during design. Retrofitting is harder, but maintenance can still matter: damaged propellers and fouled hulls increase turbulence, fuel use and sound.
Noise should be included in efficiency and maintenance decisions rather than treated as an exotic environmental add-on. Some measures can reduce emissions and operating cost as well.
Speed is powerful but context-dependent
Slower operation can reduce cavitation and noise for many ships, while also cutting fuel consumption. Yet the relationship is vessel-specific, and schedule changes can require more ships or shift traffic timing. Measures need route and fleet analysis.
Temporary speed reductions near sensitive habitat can be paired with routing and seasonal management. Compliance and safety must remain visible.
You cannot manage what you never measure
Ports and states need baselines: which ships, routes and conditions dominate the soundscape. Hydrophones, vessel data and modelling can identify hotspots, but measurement standards must allow comparison.
Ship-level noise plans should state a target, methods, maintenance checks and operational options. Publishing aggregated results would help distinguish genuine progress from isolated demonstrations.
Ports and charterers hold leverage
Owners make technical decisions, but charter contracts, arrival windows and port queues influence speed. Just-in-time arrival can reduce racing to wait at anchor. Ports can incorporate noise into incentives alongside air emissions.
Cargo owners and lenders can request performance information, creating demand before mandatory global limits exist. Care is needed so smaller operators receive technical support rather than only new paperwork.
Voluntary guidance is a beginning
IMO guidance creates a shared vocabulary and reduces uncertainty for early adopters. The experience-building phase can identify feasible measures across ship types and regions. But voluntary adoption may concentrate among modern fleets while the loudest vessels continue unchanged.
The next stage should consider measurable objectives, reporting and targeted mandatory measures where evidence supports them. Assistance for developing states is essential because marine habitat and shipping exposure do not follow administrative capacity.
Protecting acoustic habitat
Ocean planning routinely maps depth, traffic and biology; sound should join those layers. Quiet areas and seasonal protections can preserve communication space even when eliminating shipping noise is impossible.
The ocean supports trade and life at once. Treating it as silent infrastructure makes one use invisible to another. A serious policy listens, measures and then changes the ships and schedules producing the avoidable part of the noise.
