No Noise is Good Noise

Noise pollution is slowly becoming an acknowledged problem in the maritime industry. Technologies exist to greatly mitigate this problem, but it is unlikely to come from fleet and ship operators because of the added expense involved. In the same way that pollution and safety are addressed by bodies such as IMO (The International Maritime Organization is a specialized agency of the United Nations), then noise mitigation will also require a comprehensive regulatory framework for shipping.

Introduction

The modern marine diesel engine is essentially a dinosaur dressed in a tuxedo – a large reciprocating engine running on the gloop left over after the refineries have taken the good stuff and dressed with turbochargers, sensors, microprocessors, control systems and various heat exchangers. These reciprocating behemoths are surprisingly inefficient with only 25 to 33% of their output being useful. Some engine manufacturers claim 50% but that involves process integration which can only be achieved on certain trading vessels.

The wasted energy is mostly generated heat that is removed through the stack and through the cooling system. However, up to 7% of the wasted energy manifests itself as vibration and noise and this is the subject of this blog. Some small power is lost as the shaft goes through the stern tube and shaft seal but the next large drop in efficiency is at the propeller which operates at between 60-80% efficiency.

The Scale of the Maritime Noise Problem

GESAMP (The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection) is an advisory body consisting of specialised experts nominated by the Sponsoring Agencies (IMO, FAO, UNESCO-IOC, UNIDO, WMO, IAEA, UN, UNEP) whose principal task is to provide scientific advice. A 2007 GESAMP report estimated that the total commercial maritime industry power use was 251 gigawatts (although the minimum deadweight they used was not shown) which is a bit more than the entire generating capacity of Germany and four times as much as the UK.

In early 2021, UNCTAD reported that the world fleet totalled 99,800 ships of 100 gross tons and above with an average dead-weight tonnage of 21,355 which would need a 6 MW engine (roughly), so 600 gigawatts. Both these figures are estimates but seem to give a likely range. Losing 50% of this is mind-boggling and wasting even 7% on the production of noise and vibration seems less than wise. Of course, this comment has the benefit of a hindsight not available during the development of maritime commerce.

Marine diesel engines are reciprocating engines and, as any fule kno, when you reciprocate you vibrate. When you vibrate, there is noise. This noise comes from the engine and from the propeller. There are solutions but they all lead to more expensive ships while, seemingly contributing little to the bottom line. To rephrase this – the increase in cost versus the decrease in energy wastage maybe worthwhile on an industry-wide basis but is less appealing when viewed by a ship-by-ship basis. This is why it must be down to the regulators and industry bodies to work on this problem.

The Effect of the Maritime Noise Problem

In seawater, noise is louder under the sea. A supertanker generating 128dB in air is equivalent to 190 dB below the surface which is loud enough to rupture eardrums. Noise travels faster underwater, more than four times as fast. Furthermore, because of temperature differences between deep water (below 1000m) and shallow water which create a sort of barrier, sound trapped below can travel very long distances.

Studies have shown that the oceans are naturally noisy places. A study in the Ionian Sea in 2004 shows that, at 500Hz, 60% of noise is wind generated, 30% wave generated and 10% comes from shipping. Shipping noise tends to dominate in the lower frequencies around 50Hz which are the frequencies used by whales, sea lions and dolphins. In the grand scheme of things and in the deep ocean, this is less of a problem. Close to shore, however, troubles arise. It turns out many fish species make noises to communicate shoaling behaviour, territorial possession and mating requirements – think piscatorial birdsong. Most fish, both in freshwater and salt, detect sound from 40Hz up to 1,000Hz (though some, like salmon, only hear to about 400Hz, while others, such as herrings, can hear to over 3,000Hz). This covers pelagic fish which live in the ocean being neither close to the bottom nor near the shore and demersal fish that live on or near the bottom, also reef fish. This means there is a lot of traffic on a relatively small frequency band.

While the reduction in fish stocks has been largely attributed to overfishing, loss of habitat, pollution and poor techniques such as industrial trawling, there remains the suspicion that noise from marine traffic might hinder successful breeding.

The two main areas of concern are therefore wasted energy and damage to marine fauna. It is worth noting at this point the increase in speed at which humanity has been able to identify existential threats (excluding the four horsemen). It took several hundred years to identify the problem of deforestation, a hundred to identify the greenhouse gas problem, only sixty years to spot the ozone depleters and currently bio-technology and AI are under constant scrutiny. Catastrophes, however, generally come from where we least expect them and we definitely don’t expect the racket that humanity makes to destroy our greatest resource which is the oceans and the aquatic life therein.

Solutions and the Problems of Implementation

Technological solutions for noisy ships abound but they are all more expensive than the existing systems. Alternative fuels which use the same type of engine are more expensive than marine diesels, alternative power trains using turbine technology are more expensive, propeller de-cavitation technology requires additions which add to the cost.

In general, it takes 20-30 years for new technologies to percolate through the entire merchant fleet as newer ships are passed down the merchant fleet companies. Normally, older technologies are protected by ‘grandfather’ clauses which exempt older vessels from being penalised by new legislation and guidance which is not applied retrospectively. However, there appears to be a change of heart. Two major conventions adopted under the auspices of the IMO, the United Nations agency concerned with maritime safety and pollution prevention, have been amended specifically to make major changes retroactive. The treaties are the International Convention for the Safety of Life at Sea (SOLAS), 1974, and the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 (MARPOL 73/78). There is an 11 year grace period to implement compliance.

Maritime industries are intensely competitive so extra cost is not welcome thus external regulation appears to be the most likely solution to the problem of noise control. In the same way that air and sea pollution and safety have been developed, then a similar approach to noise abatement is required. It is only for the legislators to appreciate the scale of the problem.

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