HomeUnderwater Radiated Noise (URN) Tech Made Simple: 2026 Update
Underwater Radiated Noise (URN) Tech Made Simple: 2026 Update
December 29, 2025
Underwater Radiated Noise (URN) is quickly moving from “nice-to-have ESG” into something fleets will need to show work on with measurements, maintenance routines, and a simple management plan. The IMO’s revised guidelines are now in force, and the official experience-building phase runs through MEPC 85 in 2026, which is exactly when practical proof and repeatable methods start to matter most.
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What is it and Keep it Simple...
Underwater radiated noise is the sound energy a ship puts into the water while operating.
On many commercial vessels, the biggest contributors are the propeller (especially when it cavitates) and
vibration from onboard machinery that travels through the structure into the sea.
URN “tech” is usually not one gadget. It is a measure → reduce → verify approach:
capture a baseline, target the loudest sources on that vessel, and re-measure using a repeatable method.
The practical goal is operationally defensible improvement, not chasing a single perfect number.
In plain terms
Think of URN like “unwanted noise waste.” If the propeller is cavitating or vibration is being transmitted into the hull,
the vessel is converting energy into sound. Many practical reductions come from better prop condition, smoother inflow,
improved isolation, and targeted operating practices in sensitive areas.
Why 2026 matters
The IMO’s revised underwater noise guidance is in effect and the experience-building phase runs through MEPC 85 in 2026,
which keeps attention on what works in real operations. Measurement also gets more practical with standardized shallow-water
procedures, which helps vessels that rarely reach ideal deep-water test conditions.
What you are really buying
A repeatable baseline and re-check method you can run before and after changes
A prioritized “noise driver” list for that ship, so effort goes where it matters most
A simple management plan that links maintenance and operations to measurable evidence
An evidence pack you can show when stakeholders ask what you did and whether it worked
Underwater Radiated Noise (URN): Advantages and Disadvantages
Category
Advantages
Disadvantages
Notes / Considerations
Regulatory readiness
Aligns with the IMO revised guidelines and the current experience-building phase that runs through 2026, reducing “late scramble” risk.
Requirements are not “one size fits all,” and expectations can vary by region, customer, and sensitive operating areas.
Start with a lightweight plan: baseline, top drivers, actions, re-measure method, and recordkeeping.
Measurement and proof
Newer standardized approaches include shallow-water measurement procedures, making it easier to measure where ships actually operate.
URN is sensitive to speed, loading, sea state, and site acoustics, so inconsistent measurement setups can lead to disputed comparisons.
Use consistent speed points, comparable loading, and a documented procedure so “before vs after” is defensible.
Propeller and flow
Targeting cavitation and inflow quality can reduce URN at the main source, and often overlaps with smoother propulsion behavior.
Retrofits can require drydock time and engineering work, and gains vary by hull form, prop condition, and operating profile.
Propeller condition, polishing, and cavitation behavior are usually where the biggest practical wins start.
Maintenance routines
Makes noise reduction operational: cleanliness, prop condition, bearing health, and vibration checks become measurable KPIs.
Requires discipline to keep records and prevent “we fixed it once” drift over time.
Tie URN to existing maintenance workflows: docking reports, prop records, vibration trending, and hull performance logs.
Operational levers
Speed and operating mode changes can lower cavitation and noise quickly, sometimes with no hardware change.
Speed reductions can conflict with schedule, charter terms, and operational constraints.
Treat as “situational”: use on sensitive legs or specific conditions, not blanket slowdowns everywhere.
Commercial and ESG
Stronger stakeholder story in sensitive regions, plus clearer evidence for customers asking about biodiversity and impact.
If you cannot verify improvements, claims can become reputational risk.
A consistent measurement and reporting template lets you compare ships and prioritize capex where it pays off most.
Different hulls, prop types, trades, and ages can make fleet comparisons tricky without normalization.
Segment by vessel class and trade lane first, then benchmark within each segment.
Future-proofing
Active global initiatives running into late 2026 keep tools, training, and alignment moving, which helps owners avoid reinventing the wheel.
If industry adoption is weak, pressure for more formal requirements can increase later.
The lowest regret move is measurement plus a practical plan, even if you delay major retrofits.
Summary: URN programs tend to work best when they are treated like a measurable operational discipline:
establish a baseline, target the biggest source (often cavitation), document what changed, and re-measure with a repeatable method.
The main downside is proof complexity if measurement conditions are inconsistent, plus retrofit ROI variability by ship and trade.
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2026 URN Tech: What’s Really Working
1) Baselines that can be repeated
Programs that hold up in practice pick a repeatable setup: fixed speed points, clear loading assumptions,
and a documented method. The goal is not a perfect number. The goal is defensible before and after evidence.
2) Propeller-first reality
For many merchant ships, the loudest source is cavitation. The strongest early wins come from disciplined prop condition
(damage control, polishing strategy, and cavitation behavior awareness), then checking inflow issues that drive cavitation.
3) Measurement becomes more usable near where ships operate
A practical shift is that shallow-water measurement procedures are standardized, which matters because many vessels
rarely have access to ideal deep-water test areas. That makes routine baselining less painful.
4) “Quiet legs” beat blanket slowdowns
Operators see better results when they define specific legs and conditions where noise control matters most,
instead of adopting fleet-wide speed limits that break schedules. Think targeted operating practices, not permanent penalties.
5) URN management plans that stay lightweight
The plans that actually get used are short: baseline approach, target areas, top drivers, actions,
and how you will re-measure. If it feels like a research paper, it usually dies in operations.
6) Evidence packs are becoming the “currency”
What works commercially is simple proof: baseline record, what changed (maintenance or retrofit), and re-measure.
Owners that can show this tend to be more credible as stakeholder attention rises through the 2026 experience-building period.
Fast “is it working” test
If you can show (a) a repeatable baseline, (b) the top two noise drivers, (c) at least one improvement backed by a re-measure,
and (d) a plan to keep the gains through the next operating cycle, it is working. If you only have statements and no before and after evidence,
it is not working yet.
URN Program Value Estimator (measurement, maintenance, prop work, evidence)
Keep benefits capped. URN is often a proof and risk story, not a big fuel percent story.
Baseline and Finance
Effect Caps (to keep it realistic)
Program Costs and Expected Effects
Assumed Annual Effects (keep conservative)
One-time CAPEX
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Annual OPEX
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Annual fuel value
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Annual maintenance value
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Annual event value
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Incentives or commercial value
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Net annual benefit
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Payback (years, discounted)
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NPV / IRR
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URN programs win when they produce proof that holds up: baseline, actions, re-measure. Financial value is often indirect.
Use the incentives field only if you can defend it. Otherwise, keep it at zero and judge the program on risk reduction and stakeholder readiness.
In 2026, the URN winners are not the fleets chasing a perfect number. They are the fleets that can show repeatable baselines, practical prop and machinery actions, and a lightweight management plan that survives contact with operations. The IMO’s experience-building phase through MEPC 85 is essentially a global “proof period,” and measurement is getting more practical with standardized shallow-water procedures. If you can document baseline, actions, and re-measure results, you will be in a stronger position as stakeholder expectations keep rising through 2026.
