Propeller Cavitation, Machinery Noise, Wake / Appendage Flow, Retrofit dB Reduction, Power Change, Fuel Cost, CAPEX & Lifecycle NPV

Ship Underwater Radiated Noise Retrofit & Energy Trade-Off Tool

Screen how a noise-control retrofit changes underwater radiated noise and ship energy demand at the same operating condition. Simple mode handles one overall retrofit. Advanced mode combines several URN source contributors in the linear acoustic domain, then attaches net power, CAPEX and annual O&M changes to each measure so acoustic improvement and energy efficiency can be reviewed together.

Data type
Currency
Currency selection changes display only. No exchange-rate conversion is performed.
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Need multiple noise sources and retrofit measures? Click Advanced above.Advanced converts each source level from dB to linear acoustic energy, applies that source's expected reduction, recombines the ship-level URN, and separately sums each measure's net power, CAPEX and annual O&M impact.

Fast URN Retrofit & Energy Screen

Baseline and post-retrofit dB must use the same measurement/model metric, frequency treatment and operating condition. Positive power change means an energy penalty; negative means a power saving.

dB on a consistent user-defined URN measurement/model basis.
dB.
kW at the evaluated operating condition.
h/year.
% of baseline power. Negative = saving; positive = penalty.
g/kWh.
Selected currency / t.
Positive = added annual cost; negative = annual saving.
years; Simple mode is undiscounted.

Operating & Economic Basis

kW at the evaluated URN operating condition.
h/year.
g/kWh.
Selected currency / t.
years.
%.
dB planning target on the same URN basis.
% of baseline power.

URN Source & Retrofit Register

All source levels must use the same dB reference, frequency/band treatment and operating point. The source-combination screen assumes the listed acoustic contributions can be treated as uncorrelated energy contributors.

Source / retrofit measureBaseline source level dBExpected source reduction dBNet power change kWRetrofit CAPEXAnnual O&M change

URN Retrofit Readiness

URN / energy planning screen only: this tool does not predict regulatory compliance, class notation, marine-life exposure, cavitation inception speed, broadband or one-third-octave spectrum performance, or actual post-retrofit noise. dB reductions are only meaningful when baseline/post values use the same acoustic basis and operating condition. Advanced source aggregation is a screening approximation for uncorrelated acoustic-energy contributions.
2026 URN context: IMO's MEPC.1/Circ.906/Rev.1 revised guidelines took effect on 1 December 2024 and encourage a URN management process covering baseline measurement/modeling, targets, technical and operational measures, monitoring and assessment. The guidelines explicitly call for consideration of interactions between URN reduction and energy efficiency, note that cavitation can dominate ship URN, and identify options for existing ships including propeller/wake improvements, machinery isolation, maintenance and operational measures. They also state that energy-efficiency and safety obligations should take precedence where a URN measure conflicts with them. DNV offers voluntary SILENT underwater-noise class notations for vessels requiring documented underwater-noise performance. IMO MEPC.1/Circ.906/Rev.1 · DNV SILENT Class
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