Ref: RCD/BK - 4 July 2005
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TESTING & CERTIFICATION FOR EXHAUST EMISSIONS AND NOISE LEVELS
for
RECREATIONAL CRAFT

About the Author

The author is the founder and owner of Seaward Marine Ltd, a boat building company that has successfully traded for over 25 years. Details of the company and craft produced can be viewed on the internet at www.seawardboat.com

Prior to forming Seaward Marine the author worked in motor engineering before moving to a leading boat manufacturer in 1973 where he became responsible for all engineering matters, including the development of underwater exhaust systems for the Nelson motor yachts.

 

Forward

This paper is produced in response to a request made to the author by the DTI.

 

Some background to the RCD and ISO Standards

The Recreational Craft Directive was introduced, it is claimed, to provide common standards in the industry Europe- wide in order to make cross border trading easier.

The RCD in its original form gave a few very simple requirements for matters of 'safety' in terms of the construction and outfitting of 'recreational craft'. There were no prescribed methods for complying with the Essential Safety Requirements of the RCD, however the use of ISO standards was generally accepted as the easiest way of proving compliance in most cases. In every case compliance could be established before the boat was built.

Within the Amended RCD Directive there is a requirement to control both exhaust emissions and sound emissions from boats. There are two fundamental differences between the original RCD and its amended version, with respect to the sound emission testing and demonstration of compliance, the use of an ISO is mandatory and compliance cannot be established for certain craft until the boat is complete and can be tested. Both of these requirements are restrictive and place an enormous burden on the small to medium sized boatbuilder.

The methods being applied in the Directive to achieve the stated objectives of the regulation are badly flawed, these flaws will produce anomalies and in some cases will increase the exhaust emission levels and shorten engine life. This is an important factor from the boat customer's point of view.

The ISO 14509, which the RCD requires builders to use, in some cases, to prove compliance calls for a "pass by" test under the responsibility of notified body. The use of this is severely restricted by the small number of days per year that the weather conditions are suitable to carry out testing.

ISO 14509 is also unreliable to use as a tool for the purpose of regulation.

The Directive and the lack of flexibility particularly disadvantage the SME boatbuilders. There are sensible workable solutions available to achieve the stated objectives of the Directive. These will be explained in this paper.

This paper is aimed specifically at boats required to carry out the 14509 'pass by' test to comply with the regulation. Engines referred to in this paper are generally of the inboard diesel type.


References

RCD Sound Emission Assessment CD (BMF) (Includes Sound Boat presentation - London 2005)
RCD Programme Workshop manual and standards CD (BMF)
EU Commission's proposal for amending the Directive 94/25/EC as forwarded to the Author by Mr Johan Renders, European Commission on 8 Sept 2004
Sound compliance certificates issued by VTT
Caterpillar Marine Engine Installation Guide - Ventilation and Exhaust System
Principles of Good Regulation - Better Regulation Task Force
Bruel & Kjaer - Product Data sheet - Exhaust Noise Inspector Types 3638A and 3638B


1.0      Responsibilities for compliance with the Amended RCD

1.1      The exhaust emissions are the responsibility of the engine manufacturer and are to be measured at the engine manufacturers' test house and verified/ certified by an approved notified body for compliance. Once a pre-production engine model has been certified as compliant, then mass production can commence on type approval basis.

1.2      Meeting compliance for noise emissions from outboard motors and stern drives with integral exhausts is also the responsibility of the engine manufacturer on a type approval basis with testing carried out on a master boat.

1.3      For craft with inboard or stern drive engines without integral exhausts, compliance rests with the boatbuilder (or importer). Craft may be deemed compliant if the craft meets the specified criteria for 'Froude number' and Power displacement ratio' calculations.

1.4      For craft that are unable to comply under the 'Froude number' and Power displacement ratio' calculations there is currently only one option available to the boatbuilder (or importer), that is the full 'pass-by' test to ISO 14509 under the directions of a notified body.


2.0      Froude-Power/Displacement Calculation

2.1      It is generally thought the formulae for 'Froude number' and Power displacement ratio' calculations are not an appropriate or reliable method for the prediction of boat sound levels. Indeed it was confirmed in an answer to this very question by the then President of BMF at the London Boat Show presentation in 2005 that the flaws were well known and his predecessor had made this clear years ago but it had been ignored by Brussels.

2.2      By way of illustration, the first craft built by the author's company was a 40 ft boat fitted with twin inboard 2-stroke diesel engines of a heavy-duty type that were intrinsically noisy. The exhaust noise from this vessel was such that it could be heard from miles away - partly due to the very short exhaust pipe lengths resulting from the V drive installation. The craft is still in commercial use today - instantly recognisable whenever her engines are started up!

2.3      If a similar boat were built today to the same specification but for pleasure use, the craft would be treated as fully compliant under the noise directive. Why? Because with twin 250 hp engines, a top speed of 16 knots and a displacement of 16 tonnes the craft meets the criteria for compliance under the Froude Number-Power/Displacement calculation. This formula allows P/D ratio of up to 40 kw/tonne, the actual ratio for this very noisy craft is only 23.3kw/tonne. The Froude number for this vessel is 0.8, well below the 1.1 maximum. The Froude number is a value based on the water line length of the vessel and speed.

2.4      By comparison, one of the author's company's standard 29' boats with similar powered engines to the 40' boat described above was tested in August 2004 because it had a power/displacement ratio of 57.5 and a Froude number of 1.68. In this case the engines were a quieter model from a different manufacturer and the noise level was measured at 71.1dB

2.5      This is not an isolated result as shown from all three of the Seaward craft tested on the same day. Note the highest P/D ratio is actually the quietest boat.

2.6      Those who fully understand the exponential nature of the dB curve will realise that these vessels are in fact nowhere near the prescribed 78 dB noise limit permitted under the RCD for twin screw craft. Yet these are all required to be tested because of the flawed nature of the Froude Number Power/Displacement ratio calculation.

2.7      The application of power/displacement and Froude numbers has been proven to be unreliable as a means of determining which craft should be tested. It will allow some noisy boats to comply whilst forcing the builders of many of the quietest craft to undertake the onerous task of the ISO 14509 'pass by' test. The following quote comes from page 26 of the Directive proposal: 'The test conditions prescribed by ISO 14509 seldom exist in many localities in Europe, thereby making it difficult to perform 'pass-by' testing. However, it is now an established fact that stringent sound level limits for recreational craft require stringent controls on the test environment as described in ISO 14509' unquote.

2.8      It was obviously realised at an early stage that the ISO standard for noise measurement was going to be very difficult to use and in conjunction with the British Marine Federation the 'SOUNDBOAT PROJECT' was set up to investigate alternative methods to the 'pass by' test and a presentation was given at the London Boat Show.


3.0      The SoundBoat Project (Presentation at London Boat Show - January 2005)

3.1      The SoundBoat Programme was a two-year project, start date 1st Feb 2003. The project was to involve data collection, data analysis and development of alternative test methods, with validation by further testing.

3.2      The SoundBoat objectives are made clear. "To develop practical and innovative methods for demonstrating compliance with the forthcoming RCD noise limits." The achievement of the stated objective has failed, leaving the industry without a workable alternative to the 14509 pass-by test.

3.3      One useful thing that has come out of the sound boat project is confirmation that all boats tested over the limit were due to noisy exhausts. Under the heading 'Lessons Learnt regarding Exhaust Noise Control' (CD Slide Show) members of the audience were advised to:

These are mostly things that boat builders already know.

3.4      One of the SoundBoat presenters claimed to be able to predict noise levels from known parameters. The author was asked to provide some random data for him to demonstrate his theory to the audience. The 'random data' provided was of one of the Seaward boats that had already been tested at less than 71 dB by the Sound Boat team. Yet according to the presenter's calculations the prediction was that this boat would be over the limit!

3.5      An alternative method for determining boat noise seems more complicated than ISO 14509. It involves the taking of boat noise levels from no less than seven microphone positions from around the boat, predicting the exhaust noise contribution, predicting the water noise contribution from a few hull parameters, and then predicting what the pass-by noise will be at 25 metres. The speaker suggested if the result was not what you were hoping for then one could always carry out the full pass by test.

3.6      In the author's opinion, the SoundBoat team did not/do not have enough expertise in boats and marine exhaust systems to manage the task they had undertaken. They failed to take account of data that would have been available from the engine manufacturers to enable the team to come up with an alternative workable solution. This is a case where the most obvious was totally ignored, particularly the fact that it is the engines and their exhausts that make most of the noise, not the boats.


4.0      The Sound Buoy

4.1      One alternative method worked on by the SoundBoat team was a data collection buoy that could be used to make the 'pass by' test easier and safer to carry out.

4.2      The sound buoy has not so far lived up to the claims made earlier. Now on the Mk III version, the buoy has suffered technical problems and was still out of action up to a few weeks ago according to a BMF source.

4.3      As with the pass by test, the buoy if/when working will still require settled weather conditions.

4.4      It is not really necessary to dwell any further on the sound buoy as it is a variant of the ISO 14509 'pass by' test that is in itself unreliable and difficult to perform. Besides, not all notified bodies are prepared to accept the results from a sound buoy test for certification.


5.0      Marine Exhaust Systems

5.1      Marine engine exhaust systems fall into two main categories, wet and dry. Dry exhaust systems are used almost exclusively on ships and workboats and not considered in this paper as virtually all recreational craft use wet exhaust systems.

5.2      A wet exhaust system is where the exhaust outlet pipe is fitted to the hull and the engine cooling water is pumped out through the same outlet. The engine is normally connected to the outlet pipe by way of flexible reinforced rubber hose. The expelled engine cooling water is injected at the exhaust system near the engine. The advantage of this type of exhaust system is the exhaust pipe is cooled and the water in the exhaust pipe assists in the reduction of noise levels. It is essential the exhaust line is fitted in such a way that prevents cooling water entering the cylinders as this will cause severe engine damage.

5.3      The preferred location of the exhaust outlet/s will vary from boat to boat and each manufacturer. However, it is essential to understand from a sound testing perspective that when a craft is stationary, the exhaust outlet/s could be below the waterline, on the waterline or above the waterline. Those same outlets may change their relationship to the waterline when the craft is underway to the extent that a below waterline outlet may become an above waterline outlet and an above waterline outlet may become a below waterline outlet. A below waterline outlet may become an above waterline outlet when the steering wheel is moved and vice versa. We will come back to this later.

5.4      Other factors will apply, for example fuel load, water tanks, holding tanks, number of persons on board, where sitting, power trim, trim tab positions, etc., etc. Even taking the chain out of the chain locker for the pass by test could influence the results. For on board measurements, even the sound recorder person taking the on-board measurements over the transom will induce a stern heavy trim and alter the readings - the list could go on and on......

5.5      The reasons for the exhaust outlets changing their location will be more readily understood when we have dealt with hull types and their characteristics in the next section.

5.6      The problems associated with the exhaust outlet changing position relative to the waterline was highlighted by a comment made by a SoundBoat team member at the SoundBoat presentation in January 2004. He intimated that the test boat may have to use a 'professional helmsman' to hold the craft in a straight line through the pass by test zone.

5.7      What is the point of arranging a test procedure to validate the maximum noise levels of a craft, when the craft can only obtain compliant results when driven by a 'professional' in a perfectly straight line! To turn the craft causes it to heel into the turn and depending on the location of the exhaust outlet, it might be lifted clear of the water, thereby releasing noise levels over the permitted limit. If the legislation called for all boats to be driven in perfectly straight lines then the pass by test would gain merit. But we all know that boats are not driven in straight lines and neither is it practical to do so. So the test is nonsense on this aspect alone!


6.0      Hull shapes

6.1      Craft that fall into the category that will require the 14509 pass-by test will include mostly vessels with V shaped 'planing' hulls and semi-displacement vessels with round bilged or shallow chine hulls. There are other definable hull shapes but for the purposes of this paper these two well-defined hull forms will suffice, as their behavioural traits on the water are well known.

6.2      The planing hull, as the term describes, is designed to skim along the surface of the sea. Between rest and full hull speed the craft goes from being supported fully by its buoyancy to lifting bodily out of the water and planing over the surface to a greater or lesser degree. With the V shaped hull, the flotation line when on the plane will vary according to many factors including things like, crew position, location of stores, batteries, tools, fuel load, water load and the position of the trim tabs.

6.3      The last point is of great importance. For example, it was disclosed by an exhaust manufacturer at a trade meeting held at the 2004 Southampton boat show, that two identical craft on pass by-testing were measured with a 6dB difference in sound levels - this is a significant variation. They had been dumfounded by this but eventually decided that one of the helmsmen must have 'incorrectly adjusted the trim tabs.' What exactly is an incorrect adjustment of the trim tabs? They are fitted to adjust the vessel's trim when the craft is under way, not to adjust the boat's noise levels!

6.4      Even greater variations are included in the EU Commission's own proposal on page 26, quote: The use of ISO 14509 'During the Lake X test series it has been demonstrated that by changing just one of the test parameters that are not specified by ISO 2922 the pass-by sound level test was altered by as much as 12dBa.' Unquote. 12 dB is a massive variation and confirms the unreliability of pass-by testing. What is the point of setting stringent criteria, completely unrelated to how the craft will be used by its owner when in service?

6.5      The semi-displacement hull has different characteristics to the fully planing type in that between rest and full speed it does not lift bodily to anything like the same extent and the hull remains immersed in the water to a greater extent than the planing hull.

Refer to attached drawings SM-1 & SM-2


7.0      Exhaust Back Pressure and Exhaust Emissions

7.1      It is a confused regulation that requires certification for exhaust emissions and sound emissions but separates the responsibility for their compliance when the two are directly related.

7.2      As the exhaust gas moves through the exhaust system, it experiences frictional resistance - causing back pressure on the engine's turbocharger discharge. Excessive exhaust back pressure will cause harmful effects to the engine including shortening exhaust valve and turbocharger life. This in turn will increase emissions.

7.3      Guidance referred to from a major engine producer provides formulae to calculate the exhaust system pipe diameter which, when fabricated into an exhaust system, will give exhaust back pressure less than the appropriate limit. Having calculated the diameter using the formulae, the installer is instructed to choose the next larger commercially available pipe size. This advice makes good sense for back pressure but what about noise?

7.4      The lesson to be learnt here is that bigger bore, straight-through exhausts positioned well above the water ensure the low back pressure and emissions are maintained, but they make more noise. Systems such as underwater exhausts that 'stay underwater' reduce noise levels but are likely cause high back pressure and emissions.

7.5      Under the regulation as long as the boat builder deals with the noise emissions to get through the 'pass by' test to the satisfaction of the notified body, the exhaust emissions are ignored having already been certified earlier by another notified body before the engine left the maker's factory. This is nonsense.

7.6      The regulators may have to make a choice as to which element is the more desirable (or of greatest environmental priority) - reduction of the exhaust emissions or reduction of sound emissions. Given that exhaust emissions go into the atmosphere whether the vessel is inshore or mid ocean then the common sense choice must surely be to award the priority to exhaust emissions.


8.0      Exhaust Noise

8.1      In principle it is possible to reduce exhaust noise levels in a number of ways: -

8.2      For a certain result the boatbuilder could do all of these things and obtain the necessary certificate from the notified body. However we are already aware the silencing has to be done in such a way that the engine makers specified exhaust back pressure limits are not exceeded and this is where much of the trouble lies. The degree of silencing is under the ultimate control of the engine makers who specify the maximum permitted back pressure!


9.      The Practicalities of Compliance with ISO 14509

9.1      Boats are not generally mass-produced like cars or washing machines where pre-production models are tested and certified for compliance before production is commenced. In fact, the vast majority of boat builders build only a handful of craft per year and many of these are one off craft built to order.

9.2      Let us take a one off custom built craft as an example. It is normal for the contract to be arranged in such a way that the ownership of the craft remains with the customer throughout the build period and payments are made in a number of 'stages' determined in the contract. Indeed, this is exactly the situation with the boatbuilding contract sponsored jointly by BMF & RYA. As far as the standard BMF contract is concerned the customer is at liberty to take the craft away at any stage of construction if they so wish.

9.3      Even if the customer allows the craft to be pass-by tested (weather permitting and assuming the availability of a notified body) the customer is under no obligation to accept the results or await certification. In the event the craft is tested and found say 1dB over the specified limit, the owner may not be inclined to have their new craft taken apart for modification work. This may be modification work that will reduce noise to within limits but may result in an increase of the back pressure and shortened engine life etc.

9.4      The time to find out if engines will meet the noise requirements is before the engines have left the manufacturer, not after the engines have been installed and surrounded by expensive bespoke joinery work that has taken thousands of hours to fit!

9.5      The old days of inspection and rejection have been replaced by lean manufacturing and right first time quality control. For some companies, a boatbuilding project may be a whole year's work or more. On completion of the craft there are typically large final payments to be made upon acceptance by the owner. It is totally unacceptable to have to wait for one of the rarely suitable days in the UK weather for 'pass-by' testing, and then hope a notified body is available on the day to carry out the test. This regulation is being actively marketed as 'trade enabling' and not onerous or unduly expensive: clearly it fails in all these respects.

9.6      It is regulation that puts all our SME boatbuilders at a disadvantage, given that the testing criteria makes Britain just about the least favourable place in Europe to carry out testing due to our own adverse weather conditions. Even the SoundBoat team had to journey to Italy for more favourable test conditions and still had to wait a full week for suitable weather to carry out testing.

9.7      Whilst there may be some public or political opinion in favour of reducing emission pollutants into the atmosphere, there seems to be little evidence to suggest that the type of boats we are talking about here should be controlled on noise limits when most of the time they are out of hearing range or in areas where speed limits or other local restrictions apply, or should apply.

9.8      The pass by test is not a workable solution. The SoundBoat team were specifically tasked to find an alternative to the pass-by test but have totally failed.

9.9      The background and development of the ISO 14509 shows it was originally proposed for outboard motors only in the 1980's, but extended to include a pass-by test for all small craft in 1994. There have been arguments regarding the safety aspects of carrying out these tests and that boats will normally not be driven so fast so near (25 m) of the shore.


10.0      ISO 14509-2 Reference Boat Standard

10.1      The 'reference boat' standard is a key feature included in the EU Commission's proposal document as part of the Impact Assessment (pages 51-55) with special reference to small and medium-sized enterprises (SMEs). The Commission's idea is to provide a simplified system of certification without involving a third party.

10.2      Referring to page 23 of the EU Commission's own proposal.

Quote: 'First a list of reference boats must be established by running any normal production boat/engine combination through a full pass-by sound test (in accordance with ISO 14509). Providing the boat/engine combination passes the relevant sound level requirements for its engine size, as stipulated in the Directive, and the Notified Body involved is fully satisfied, the boat may then be CE marked and added to the list of Reference Boats. A master list of Reference Boats will be held centrally. Full details of this Reference Boat Master List will be available for consultation to all boat builders and/or engine manufacturers.' Unquote.

10-3      This 'Reference Boat' standard is very unlikely to be of assistance to the small and medium sized boatbuilders that it is designed to help. The standard is naive in thinking that the builders of craft that have already been proved to comply with the standard will pass on the details of design and construction of their craft, possibly to benefit their competitors. Yet the criteria in the ISO 14509-2 states that the craft must be very similar, going right down to details like: the height of the boarding platform above the water when under way must be the same, exhaust outlets also the same.

10.4      One would need a boat that was nearly identical to the reference boat to comply under the Reference Boat Standard, and of course another builder fool enough to pass on their details in the first place!

10.5      The reference boat master list does not yet exist with less than 6 months to go for the full implementation of the regulation. According to the figures on page 52 of the EU proposal document there are 14,373 recreational craft manufacturing units in the EU (3000 in UK) employing 90,502 persons. On average each manufacturer is employing less than seven persons. With such numbers and such diversity it must be clear the reference boat concept is not going to provide the simplified system of certification as envisaged in the EU Commissions proposal.


11.0      Workable solutions

11.1      It is a fundamental requirement for manufacturers of low volume products, like boats, to be able to build them 'right first time'. This is a basic principal of modern quality control and an essential part of running a successful business in a competitive market.

11.2      There are more practical solutions. Solutions that will enable craft to be not only certified as compliant but actually operating within prescribed limits on both exhaust emissions and exhaust noise levels and regardless of whether or not the boat is driven in a straight line.

11.3      The SoundBoat project has produced some useful information. Most significant is the formal discovery confirming all the boats tested over the prescribed sound limits were due to noisy exhaust

11.4      Having discovered what most people knew already, the SoundBoat project could and should have focused the collection of data on the boats engines and exhaust systems. There is no data available, or being made available so far to record the engines and exhaust systems that were measured over the prescribed noise limits, or indeed those that were measured under the limits.

11.5      The author's proposal for an alternative to 14509 is to recommend that the maximum noise emission levels are based on readings that will replicate an above waterline exhaust system measured at say 1m from the exhaust outlet. This would provide readings that were far more reliable than those taken on a 'pass by' test.

11.6      Most importantly, the testing for noise levels should be carried out by the engine manufacturer with certification that the exhaust system is compliant within the prescribed limits of the exhaust emissions and exhaust noise emissions providing certain types of exhaust system/silencer are fitted. A few 'type approved' variations of exhaust systems will be able to meet the needs of the vast majority of the boatbuilders.

11.7      The EU Commission's simplified system of certification for SMEs without involving a third party is achieved.

11.8      In recent weeks written confirmation has been received from two leading engine suppliers to confirm their willingness to test the exhaust systems as fitted to the author's craft. Confirmation has also been received from a leading marine exhaust manufacturer of their willingness to assist.


12.0      Conclusion.

11.1      This paper has demonstrated the lack of expertise applied to the formulation of the sound emission regulation for boats. That emissions, back pressure and exhaust noise are all closely related. Years of development and testing have been mainly wasted through misguidance. It is possible to set and control engine emissions and exhaust sound emissions but all factors need to be taken into account to ensure the end result achieves the objectives.

11.2      The regulation concerning sound emissions is too prescriptive and contradicts the 'Principles of Good Regulation'

11.3      It is absolutely essential that a solution be found whereby boats can be 'built right first time'.

11.4      The author's proposal if adopted will allow the possibility of right first time manufacture.

 

Written by:

Barry Kimber
Seaward Marine Ltd
admin@seawardboat.com

 

Notes on the attached drawings.

Drawing No. SM-1 shows a selection of typical exhaust outlet positions on boats with planing hull designs and how the exhaust outlet positions change in relationship to the waterline depending on the craft being stationary or at full speed.

Drawing No. SM-2 shows the same information as above but this time with the round bilge semi-displacement hull.

The two drawings illustrate the difficulty in obtaining reliable sound readings where the boat's exhaust system varies its location in relation to the waterline when under way as referred to in section 5.0

The advice given by 'the experts' is to ensure underwater exhaust outlets really are underwater. It can be seen from drawing SM-1 that outlet 4 will have to be positioned even further underwater to comply with such 'advice' This may indeed stifle some of the noise at high speed but the effects on back pressure will vary according to speed and load and in many cases will increase emissions.

Drawing No. SM-3 illustrates the preferred option to combine emissions and noise into a single test.
referred to in 11.5 ­ 11.8