ShipRight Design and Construction

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1 ShipRight Design and Construction Additional Design Procedures Additional Design and Construction Procedure for the Determination of a Vessel s Underwater Radiated Noise February 2018 Working together for a safer world

2 Document History Date: Notes: 01/02/18 Initial Publication Lloyd's Register Group Limited All rights reserved. Except as permitted under current legislation no part of this work may be photocopied, stored in a retrieval system, published, performed in public, adapted, broadcast, transmitted, recorded or reproduced in any form or by any means, without the prior permission of the copyright owner. Enquiries should be addressed to Lloyd's Register Group Limited, 71 Fenchurch Street, London, EC3M 4BS.

3 Chapter 1 Underwater radiated noise from ships Section 1 General requirements 1.1 Scope This procedure defines the process and the criteria for the assessment of the underwater radiated noise from ships for assignment of LR s notations related to underwater radiated noise and is to be applied in addition to the other relevant requirements of the Rules and Regulations for the Classification of Ships (hereinafter referred to as the Rules for Ships) The requirements of this Chapter may be applied no other statutory requirements exist. Where statutory requirements do exist they will generally take precedence. 1.2 Class notations Where a vessel has had its underwater radiated noise measured and certified in accordance with LR s ShipRight Procedure Additional Design and Construction Procedure for the Determination of a Vessel s Underwater Radiated Noise the UWN-M notation will be assigned Where a vessel has had its underwater radiated noise measured and certified in accordance with LR s ShipRight Procedure Additional Design and Construction Procedure for the Determination of a Vessel s Underwater Radiated Noise and the underwater radiated noise level is found to be less than the limits contained in the ShipRight Procedure the UWN-L(XYY) notation will be assigned. The parentheses are to contain a capital letter (shown as X, see Ch 1, 2.1 Assessment criteria 2.1.2) referencing to the limit set in accordance with the ShipRight Procedure and listed therein, and a number (shown as YY) indicating the vessel speed in knots (STW), indicating the speed the criteria was met. Examples: UWN-L(T20) indicates the vessel is meeting the transit criteria at a speed of 20 knots (STW). A ship can have multiple UWN notations, i.e. a cruise ship can have UWN-L(T20), UWN-L(Q). 1.3 Definitions For general terminology reference is made to ISO and the standard series ISO Underwater acoustics - Quantities and procedures for description and measurement of underwater sound from ships. STW speed though water SOG speed over ground Shallow water water depth less than 150 m or 1,5x overall length of the ship under test, whichever is smaller Deep water water depth more than 150 m or 1,5x overall length of the ship under test, whichever is smaller Background noise noise from all sources (biotic and abiotic) other than the ship being measured, including selfnoise/instrument noise Closest point of approach (CPA) point the horizontal distance (during a test run) from the ship reference point of the ship under test to the hydrophone(s) is the smallest Source depth (d s) d s = 0,7Dt, Dt is the actual draught of the vessel. Underwater sound pressure level (L p) the root-mean-square sound pressure level measured with a hydrophone in db given as: p p rms L p = 20log db 0 p rms = the root-mean-square sound pressure and the reference value p 0 = 1 µpa. The underwater sound pressure level is determined in 1/3-octave bands (third octave band filters to comply with IEC 61260) in the frequency range Hz or higher. 1

4 Radiated noise level (L RN) level of the product of the distance from a ship reference point of a sound source, d, and the far field root-mean-square sound pressure, p rms(d), at that distance for a specified reference value p p + 20log d d rms L RN = 20log db 0 0 (d 0) = the reference value for distance,1 m, d = the slant range from the ships reference point to each hydrophone. The above formula is based on spherical spreading of sound energy. Source level (L S) the monopole radiated noise level at 1 m distance, corrected for water surface reflections (Lloyd s mirror effect) L = L ΔPL db S RN + ΔPL = the difference in db between the propagation loss PL, and the spherical the propagation loss (20log (d/d 0)), accounting for reflections from the sea surface and seabed. ΔPL is determined in 1/3-octave bands in the frequency range of interest (see Ch 1, 3.4 Deep water correction and Ch 1, 3.5 Shallow water correction for definitions). Note: L S is also referred as the monopole source level radiating in an infinite, homogeneous and lossless medium. Section 2 Assessment criteria 2.1 Assessment criteria Figure Assessment criteria Table Mathematical definition of the criteria curves TRANSIT QUIET -0Hz log(f/) log(f/) 0-00 Hz log(f/0) log(f/0) Hz log (f/00) log (f/00) RESEARCH -160Hz log(f/) Hz log(f/0) Hz log (f/00) 2

5 The criteria curves are indicated in Figure Assessment criteria and shall be assigned with the letters (T) for transit, (Q) for quiet and (R) for research The criteria curves are stated to the monopole source level, L S in 1/3-octave frequency bands. The measured monopole source level L S shall be below or equal to the relevant criteria curve in each 1/3-octave band Measurements which exceed the criteria curve in a single 1/3-octave band of maximum 3 db is acceptable. Measurements which exceed the criteria curve in more than one band is not acceptable The operation conditions shall be agreed with the client, including the applicable criteria and the speed this is to be obtained If the uncertainty on the declaration measurements is higher than that stated in ISO , the criteria curve (as illustrated in Figure Assessment criteria) will be lowered by the difference in the uncertainties, in order to account for possible error in the measurement results. Example: the uncertainty of ISO measurements is ±3 db ( Hz). If the measurements performed have an uncertainty of ±5 db, the criteria curves will be shifted down by 2 db (5 3 = 2 db) The application to various types of vessels and the operating conditions are stated below. The limits apply to the condition with the vessel sailing straight ahead at a constant speed. The stated operating conditions are the defaults values. 2.2 Commercial vessels The transit criteria apply for commercial vessels (container ships, tankers, bulk carriers, car carriers, anchor handling vessels, tugs, etc.) under normal transit condition, typically at 85 percent of the maximum continuous rating (MCR). 2.3 Cruise ships The transit criteria apply for cruise ships under normal transit condition, typically at 85 per cent MCR The quiet criteria are intended for cruise ships and other vessels operating, e.g. in environmentally sensitive areas, typically with a maximum speed of knots. 2.4 Leisure crafts and yachts The transit and quiet criteria apply to leisure crafts and motor yachts sailing at typical cruising speeds. The quiet criteria apply to vessels with a length equal to or under 50 m and the transit criteria for other vessels The operating conditions including cruising speed needs to be agreed with the client for the individual vessels. 2.5 Research vessels The research criteria apply to research vessels. The default test condition is sailing straight ahead at 11 knots A separate test can be performed with an agreed towing load Only the necessary equipment needed for achieving the test speed shall be in operation during the test, e.g. power generation and propulsion systems. 2.6 Seismic vessels The transit criteria apply for seismic vessels. The default test condition for a seismic vessels shall be 5 knots and with the designed normal towing load A separate test can be performed with for a free sailing condition (no towing load) The operating conditions needs to be agreed with the client for the individual vessels. 2.7 Fishing vessels The quiet criteria apply to fishing vessels sailing at typical cruising speeds (no trawling load). 2.8 Ferries and fast ferries The transit criteria apply to ferries and fast ferries under normal transit condition, typically at 85 per cent MCR. 2.9 Thruster operation The transit criteria apply to under water noise from transverse thrusters or dynamic positioning (DP) operations The test condition for vessels in DP mode or with thrusters operating shall be 40 per cent of the nominal load No other parts of the propulsion system, e.g. fixed propellers, shall be operated during test of thrusters and systems. 3

6 Section 3 Testing 3.1 Measurement procedures A measurement procedure document shall be created for each test before measurements are carried out. The procedure document shall as a minimum state the following information: Location for the test, map of test site. Water depth at test site. Description of planned test arrangement, including number of runs, speed and Closest Point of Approach (CPA). If the vessel is to be operated with a towing load, the intended load shall be stated (in tonnes). Instrumentation to be used, including number and depth of deployed hydrophones, recording instrumentation. Vessel conditions during test, i.e. speed (knots STW), propeller/thruster speed (rpm), pitch (per cent), propeller type and number of blades, number of propellers/thrusters, and vessel draught (fore and aft) during test (m). Speed (rpm), number of cylinders, and stroke of main engines, auxiliary engines and generator sets, information on gear speed and tooth frequencies. Description of methods used to log ship operation conditions during test, how distances and weather data (wind and sea state) will be logged. Potential deviation from the ISO standard procedure and this LR procedure. If measurements are performed in shallow water, a description on how the correction of the transmission loss will be done, i.e. by measurement or by calculation (see Ch 1, 3.5 Shallow water correction) If the transmission loss is measured, the test setup shall be described, including type of source (single airgun, explosives), number of shots, depth of source, depth of near-field hydrophone and distances to source, distance to receiver hydrophone array, potential measurement of water profile and salinity profile in order to determine the water sound speed profile, the method used to determine the correction ΔLM on the reference source. If available, information on expected underwater background noise levels The procedure, including any deviation from the ISO standard procedure, shall be approved by LR before measurements are initiated The uncertainty of the measurements shall be as stated in the ISO standards. If not available uncertainties shall be evaluated according Ch 1, 4.1 References Test conditions Test conditions shall be as specified in the standard ISO The vessel under test shall be fully outfitted with respect to all aspects relevant for the underwater noise test. All equipment normally in operation shall be in operation at their default load and speed The ship shall be ballasted to the designed draught If measurements are planned for a towing load, this must be provided for either via a towed body or a simulated load must be created by other means, such as paravanes or other methods of simulating an equivalent load For thruster operation at least two runs must be carried out with the thrusters operating in opposite directions during the two runs. The test shall start with the bow pointing towards the hydrophones For transverse thruster operation a test run shall include a turn of at least 90. For DP mode each measurement shall have a duration of at least 60 seconds The weather conditions during measurements shall be maximum Beaufort 4 and sea state 2 (WMO sea state code). Sea state 3 can be acceptable if it is ensured that the background noise level is not affecting the measurement results Measurements during rain should be avoided as rain increases the background noise level. If rain occurs during the measurements, this shall be stated in the test report Any deviations from normal operations shall be stated in the test report. 3.3 Post processing of results The measurements shall be post processed as described in the ISO standard series. The measurement results are to be converted to a source level (L S) the monopole radiated noise level at 1 meter distance, corrected for water surface reflections (Lloyd s mirror effect). 4

7 3.4 Deep water correction For measurements performed in deep waters according to ISO , ΔPL can be determined according to the below formula: 1 1 ΔPL = log k ds sin α db k = 2πf is the wavenumber, f = the frequency (Hz), d s (m) = the source depth α = the depression angle ( ). 3.5 Shallow water correction The shallow water measurements shall follow the same procedure as stated in the deep water test standard (ISO ) The minimum water depth (Z s) for measurements is the greater of either 60 m or 0,3v², v is the ship speed in m/s, or 3(B Dt) ½, B is the width of the vessel (m) and Dt the draft (m) The three hydrophones shall be placed in the following positions: Hydrophone 1: one tenth water depth (Z s/) below the sea surface Hydrophone 2: approx. at half water depth (Z s/2) Hydrophone 3: approx. 5 m above the seabed The determination of the underwater radiated noise level L RN shall be determined in the same way as for the deep water standard ISO Each hydrophone measurement is corrected by the following parameter. L h) = L ( h) + ΔPL ( ) db S, shallow ( RN shallow h h = hydrophone number. ΔPL shallow = correction which is to be determined at the 1/3-octave band centre frequencies. L S,shallow = The source level is calculated as the energy average for the three hydrophones as stated below: S,shallow = log LRN (h1) + LRN (h2) 3 + LRN (h3)/ L db The data for multiple runs are then arithmetically averaged to determine the final source level as for the deep water standard The correction ΔPL shallow(h) can be determined by either numerical calculations or by measurement on site Numerical calculation of ΔPL shallow(h) A 2D or 3D calculation model shall be prepared simulating the measurement situation. The predictions need to take into account the following parameters: Geometry (source/receiver depth, distance source receiver, water depth) Sound speed profile in the water Sea bottom, geoacoustic properties for each defined layer The calculations shall preferably be performed with the wavenumber integration method. This method is typically valid for frequencies below 00 Hz. Alternative methods can be used, i.e. low-frequency calculation models based on the parabolic equation formulation. Calculations at higher frequencies should be based on ray tracing models The calculation shall be based on input data representing the actual conditions on the test site. 5

8 3.5. ΔPL shallow(h) shall be calculated for three conditions with a variation in distance (d CPA, d CPA 5%, d CPA +5%) The correction shall be determined as follows: ΔPL shallow (, h) = L S,ref L p ( n, h) + 20log d( n, h) d0 n db L p(n,h) = the underwater sound pressure level of hydrophone h for calculation number n, L S,ref = the corrected monopole underwater noise source strength of the reference source (i.e. airgun) d(n,h) = the distance to hydrophone h during calculation number n The ΔPL shallow(n,h) are arithmetically averaged over the number of calculations to get ΔPL shallow(h) Measurement of ΔPL shallow(h) The ΔPL shallow(h) can be measured by the use of a transient reference source, i.e. an airgun or explosives. At the CPA the reference source is deployed to the source depth (d s) of the vessel under test The reference source should preferably be deployed from the vessel under test and located close to the propeller. Alternatively measurements can be performed from a smaller standby vessel A nearfield hydrophone is deployed close to the reference source (typically in a distance d near of 1 to 5 m) and at the same depth, d s, as the reference source. The distance between the reference source and the nearfield hydrophone should be determined with an accuracy of per cent The GPS position of the reference source shall be logged continuously during the measurements of the transmission loss, in order to take account of drifting Measurements are then performed simultaneously on the nearfield hydrophone and the three receiver hydrophones when firing the reference source at a distance corresponding to the CPA, d CPA Care should be taken to make sure the nearfield hydrophone and measurement chain is not overloaded due to the high acoustic energy levels Measurements shall be averaged over at least five shots. Some natural drift of the vessel will most likely occur during the measurements and will result in some averaging over distance Care should be taken to ensure the full frequency range is covered during the measurements, e.g.. by selecting the appropriate firing chamber volume on the airgun and considering the distance to the receiver hydrophones as well as the background noise levels The sound exposure level measured on the near field hydrophone L E,p,near(n) is corrected for the Lloyd s Mirror reflection from the sea surface ΔLM and to the reference distance of d 0 = 1 m. Hereby the reference source level is obtained. Note: sound exposure levels referred to 1 second are used for analysis of transient signals, see ISO d d near L S, E,ref ( n) = LE,p,near ( n) + LM + 20log db 0 n = shot number. L S,E,ref. = final source level obtained by the data for multiple shots which are arithmetically averaged, The correction is then determined as follows: ΔPL L d( n, h) d0 shallow ( n, h) = LS,E,ref E,p ( n, h) + 20log db L E,p(n,h) = the sound exposure level of hydrophone h = shot number n = reference source d(n,h) = is the distance to hydrophone h during shot number n Subsequently, the ΔPL shallow(n,h) is arithmetically averaged over the number of shots to calculate ΔPL shallow(h). 6

9 3.6 Approved technical organisation The measurements will be carried out by LR or by a company approved by LR for performing underwater noise measurements. If measurements are carried out by a company approved by LR, must LR witness the measurements. 3.7 Reporting The test report shall address the information required from the standard series ISO and documentation of the test conditions stated in the measurement procedure If the UWN-L notation is to be assigned, the report shall state a comparison between the measured data and the relevant criteria curve in 1/3-octave bands. For each set of data the vessel speed, the propeller speed (rpm) and pitch (per cent) for all propellers shall be stated The report shall further state the correction ΔPL and what method used to determine this Any deviations from the ISO standards or from the test procedure shall be stated in the test report. Section 4 References 4.1 References ISO 18405: Underwater acoustics - Terminology ISO Underwater acoustics - Quantities and procedures for description and measurement of underwater sound from ships all parts IEC :2016 Electroacoustics - Octave-band and fractional-octave-band filters all parts ISO/TC 43/SC 3 - N130 Approved resolutions TC43/SC3 Teddington 2016 ( ) D.G. Morgan, Comparison of ship monopole and dipole source levels. Technical note, University of Southampton, England (September 2015) M.A. Ainslie, Principles of sonar performance modelling, Springer-Praxis, Chichester (20) FP SONIC PROJECT. Suppression Of underwater Noise Induced by Cavitation FP7 - Collaborative Project , AQUO Achieve QUieter Oceans by shipping noise footprint reduction SILENV FP7, WP 5: GREEN LABEL PROPOSAL. Subtask 5.2: Noise and vibration label proposal (2012) ICES, Cooperative Research report No Underwater noise of research vessels (1995) JCGM 0:2008 (GUM 1995 with minor corrections) Evaluation of measurement data Guide to the expression of uncertainty in measurement 7

10 Lloyd s Register Group Limited 2018 Published by Lloyd s Register Group Limited Registered office (Reg. no ) 71 Fenchurch Street, London, EC3M 4BS United Kingdom Lloyd s Register and variants of it are trading names of Lloyd s Register Group Limited, its subsidiaries and affiliates. For further details please see Lloyd's Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as Lloyd's Register. Lloyd's Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Lloyd's Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract. Lloyd s Register, 2018