Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015 REVIEW OF LEGISLATION ON NOISE AND VIBRATION REGULATIONS IN


MERCHANT SHIPS (DOI No: 10.3940/rina.ijme.2015.a3.315)


R Hernández Molina, F Fernández Zacarías, F J Bermúdez, A Muñoz Rubio and J C Rasero, University of Cádiz, Marine Engineering Department, Spain SUMMARY


This paper aims to describe the evolution of noise regulations for merchant ships over the last four decades, analysing the most important aspects with respect to crew, passengers and exposed populations in cities, in line with the requirements of the European Union to reduce the environmental impact of transport. The paper also analyses the changes in regulations aimed at not only regulating noise and vibration inside the ship, but also noise emitted to the port and underwater radiated noise. We shall also include Classification Societies, given the importance of their standards in ensuring increasing levels of comfort on board ship.


1. INTRODUCTION


Previous strict specifications regarding the maximum levels of noise and vibration on board ship reflected the need for extremely careful planning from the early stages of ship design. This process involves detailed analysis of the different elements of the "acoustic transmission paths", identifying and characterizing the sources of noise on board, its receptors –situation and required limits– and the transmission paths linking the source with the receptors.


Two factors exist in the technological evolution of vessels that increase the problem of noise and vibration on board:


a) The reduction in scantlings in the structures that form the vessel leading to increased flexibility and a reduction in the typical vibration frequencies of individual elements as well as of assemblies of such elements.


b) Increased service speed and size respectively aimed at reducing transit time between ports and increasing capacity, which require the use of higher power propulsion engines and lead to increased rigidity in the shaft line.


To study noise and vibration on board ships, it is


necessary to consider the sources of excitation as well as the structures that may be exposed to this excitation. Once the sources and affected structures are known, resonance phenomena may be studied to avoid excessive dynamic amplification. It is maintain the different


therefore frequencies far foreseeable excitation frequencies.


Irrespective of the phenomenon of direct resonance between the sources of excitation and the structural elements of the assembly of the hull girder, some local structural assemblies may act as localized resonators capable of creating additional dynamic amplification of the stresses produced by the sources of excitation.


To further complicate the problem, the phenomenon of beats may cause resonance in structures whose actual frequencies are different from each of the excitation frequencies.


©2015: The Royal Institution of Naval Architects


advisable to from any


2. SOURCES OF NOISE ON SHIPS


The main vibration excitation sources (noise emission sources) in


ships are: the propellers, the


machinery, heating, ventilation and air (HVAC) systems, and exhaust gas systems.


primary conditioning


There are also secondary sources of noise, such as: auxiliary machinery, hydraulic systems, different types of pumps, and the effects of the sea, wind, etc.


2.1 THE PROPELLERS The propeller produces two types of excitation: ‐


Alternative thrust:


giving rise to longitudinal ‐


vibrations in the shaft and machinery, which depends on the blade step-frequency - propeller revolutions multiplied by the number of blades (rpm.N) -, and their harmonics. Vertical pressure forces in


propeller aperture:


causing vibration in the hull and superstructure induced by propeller cavitation.


Given the above, the propellers are often the main cause of the high noise levels that arise astern and most of the low frequency noise in remote spaces, which spread to distant spaces via induced vibrations through the shaft line and surrounding surfaces of the outer shell. Interaction between the propeller and the hull is normally responsible for low frequency noise between 1 Hz and 1 kHz


2.2 LOW SPEED MAIN DIESEL ENGINES


Although there are vessels with diesel-electric engine propulsion systems and, to a lesser extent, steam turbines, most ships employ reciprocating internal combustion engines (slow speed diesel engines) as their propulsion system. There are two different


types of


forces that may be associated with reciprocating internal combustion engines, namely: Pressure forces due to combustion contribute


processes, and inertial to the vibration occurring in the structure. However, their destructive potential lies in A-135


forces. Both engine

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