Prevention and detection of fouling on ship hulls

Final Report Summary - CLEANSHIP (Prevention and detection of fouling on ship hulls)

Executive Summary:
Ships have to be frequently taken out of service to be cleaned due to the formation of hull fouling in the marine environment. As a consequence of fouling buildup, considerably more fuel is consumed thereby resulting in both an economic and environmental impact. The marine industry globally spends significant resources (equivalent to billions of euros) in addressing fouling using a variety of invasive cleaning techniques and prevention methods that can harm the environment.
The Cleanship project, proposes an effective non-invasive and non polluting solution, based on an ultrasonic approach, for improving the maintenance of ships. The solution is to deploy long range ultrasonic waves travelling throughout plates of a ship hull for, as much as possible both the prevention and detection of fouling.

In order to achieve this, the project has developed an integrated system which has shown promise in field trials. We believe that this work represents a major improvement in the shipping industry fouling prevention which can lead to an important fuel composition, reduce of production break downs and a reduction of CO2 emissions.

A multidisciplinary consortium consisting of both industrial and academic experts from across Europe collaborated in this project. It is anticipated that a functional prototype system for industrial validation will be available in due course. Updates are available via the Cleanship project website (www.cleanship-project.eu) and the project coordinator; Brunel Innovation Centre of Brunel University.

Cleanship prototype is expected to improve the prevention of biofouling in marine industry or in any other in which biofouling accumulation on metallic surfaces means a problem. The combination of the detection and prevention system provides a usefully tool to undertake biofouling accumulations. Cleanship prototype is expected to reduce visibly the accumulation of fouling in ship hulls.

Project Context and Objectives:
CleanShip is a project designed to prevent and detect fouling on ships, which frequently have to be taken out of service to be cleaned due to the formation of hull fouling from the marine environment. A consequence of hull fouling is that considerably more fuel is consumed as fouling accumulates, resulting in both an economic and environmental impact.

The marine industry globally spends significant resources (equivalent to billions of euros) in addressing fouling, using a variety of protection methods such as coatings, accompanied by periodic dry dock cleaning. The CleanShip project (www.cleanship-project.eu) a pan-European collaboration between organisations in the UK, France, The Netherlands, Spain, Greece and Turkey, coordinated by the Brunel Innovation Centre (BIC) based in Cambridge, England, UK has developed an effective non-invasive solution, using long range ultrasonic waves, both to reduce and detect fouling and thus improve improving the maintenance of ships.

Biofouling:

Biological fouling (biofouling) stems from the formation of organisms on a surface immersed in water. These deposits may consist of organic molecules (proteins, fatty acids, and carbohydrates), microorganisms (bacteria, protozoa, algae, fungi) and multicellular organisms (barnacles, colonial hydroids). This is a significant problem for all marine structures such as ships, offshore rigs, oceanographic sensors, etc.
After six months without protection against marine fouling deposits, biofouling growth increases the drag on a hull so much that a ship may have to use up to 40% more fuel and correspondingly produce 40% more CO2 emissions. The marine industry spends many billions of Euros worldwide on the prevention or removal of marine fouling, using a variety of biocidal coatings and cleaning tools in dock,. There are also serious health and safety issues associated with the widespread use of biocidal antifouling coatings, which harm marine life and enter the food chain. Clearly existing methods of fouling prevention and removal are in urgent need of improvement.
The CleanShip project had the objective of developing a novel, non-invasive and cost effective approach for fouling prevention without the need for taking a ship out of service.
The CleanShip approach deploys long range ultrasonic waves travelling throughout the entire ship’s hull below the water line These are used in two ways:
1. Leaky (Lamb wave mode) continuous waves prevent or slow down the accumulation of fouling by driving biomolecules away from the hull.
2. Continuous monitoring of the attenuation changes of pulsed waves caused by the growth of fouling in its early stages, allows earlier detection of biofouling accumulation.

Long range ultrasonic testing relies on the use of ultrasonic guided wave modes in the kilohertz range (typically between 20-300kHz) with relatively long ultrasonic wavelengths in comparison with conventional ultrasonic testing. These waves propagate with low attenuation in steel, covering a large distance from the ultrasonic source. For visualisation of ultrasonic waves travelling across a surface, a state of the art 3D laser scanning vibrometer from the BIC, housed at TWI’s Cambridge site was used to gain a better understanding of surface behaviour and material response to transduction.
The CleanShip project had two goals:

Fouling Prevention

The project aimed to permanently excite a ship’s hull with an ultrasonic wave of a frequency in the region of tens of kHz. Accordingly, the wave could be launched from a transducer at a single location on the ship and yet travel through the entire hull with very low power absorption in the hull itself.
With the CleanShip system, any fouling formation is subject to forces due to the vibration of the hull surface. These ultrasonically generated forces are expected to keep microorganisms away from the hull, discouraging any settlement. The CleanShip system can be operational whether a ship is moving at sea or is stationary in a port, as a result of careful design of the system.

Fouling Detection

Pulsed ultrasound of a similar frequency range to the ultrasonic waves used for fouling prevention is transmitted and detected from a single location after travelling up and down the entire length of a ship’s hull. As fouling builds up the received wave is attenuated. In order to compensate for spurious signal changes through eventual long-term instrument drift and temperature fluctuations, the received wave is compared with a second echo travelling through a fixed path in the hull. As hull fouling tends to occur over wide areas, a very high sensitivity allowing the detection of very thin layers of fouling build is possible.

The main advantages of CleanShip are therefore: use of preferably low frequency ultrasound in wave modes to provide total coverage of fouling prevention on a ship hull, from a transducer array location and at power levels much lower than those needed for industrial cleaning through cavitation for example.

1. Use of low frequency ultrasound in wave modes to provide total coverage for fouling identification on a ship’s hull, from an array of transducers.

2. Use of attenuation measurements for the detection of fouling build up on a ship’s hull.

3. Use of a comparator echo through appropriate signal processing algorithm(s).

4. An advanced signal processing algorithm for computing the long term attenuation changes due to fouling.

5. Optimal wave propagation scenarios through simulation for system design.

In order to achieve these CleanShip objectives, the project work was broken down into eight work packages consisting of five Research and Technology Development (RTD) work packages (WP), one Demonstration WP, and one other WP for dissemination and exploitation, and one work package, devoted to consortium management by BIC.
Future development of the Cleanship approach will include system optimisation to allow industrial realisation of the technology, coupled with studies of the long term effects of climate on fouling control: warm versus cold waters; North Sea versus Mediterranean Sea etc.

Project Results:
The initial phase of Cleanship project focused on the definition of the specifications of the requirements of the final prototype based on the demands of the shipping industry. This was done following terms specified by the End User, Lloyd’s Register. This focused the objectives of the project, including hull material, the thickness of the plates, and design features to be considered such as stiffeners, welds, joint designs and typical environmental conditions. These initial considerations also included other operational conditions for the Cleanship equipment including: portability, health and safety, user friendly interface, simple operational system, and component durability.

The key proposed operating system architecture uses a number of high power transducers attached to a ship hull. These transducers are excited with a portable high power signal generator, producing ultrasonic vibrations at resonance frequencies suitable for the prevention of biofouling. The wave traveling through the ship hull prevents the growth of fouling due to the leaking of the guided wave at the sea water interface. The equipment is intended to be employed from the very beginning of fouling creation in order to avoid problems associated with pre-existent biofouling.

The final Cleanship prototype includes an ultrasonic guided wave detection module for the location and measurement of fouling. Guided waves for detection systems are well known they can improve the performance of the final Cleanship prevention tool. The detection of any accumulation of biofouling provides information on the fouling growth, and therefore a increase or decrease of the prevention system power can be applied accordingly.

The combination of detection and prevention of biofouling with the same tool in the final Cleanship prototype provides a solution to the maintenance of ship hulls in a safe and productive manner for much longer than currently available methods.

The modelling of guided wave propagation through ship hull representative samples was performed by CERTH. These models were a key reference for the rest of the project and have given an important approach to the problem from a theoretical point of view. These studies showed that the higher the frequency of excitation in the two modes of vibration (Ao and So), the higher the acceleration hence the force produced by the vibration. These forces can be used for biofouling prevention. Also it was determined that the best mode of vibration for fouling prevention is the Ao due to the larger displacements and accelerations produced at the frequencies of excitation.

In parallel to the modelling experimentation, an analysis of the existing transducers of Shofchem was performed. An impedance analysis and 3D-vibromter analysis was carried out for each candidate high power transducer. This provided a better the understanding of the vibrating capabilities of the transducers and excitation parameters depending on their frequency. It was proved that transducers requiring higher levels of voltage for excitation can produce displacements large enough to be considered high power transducers.

Tecnalia designed the sensors for the biofouling detection. These sensors are capable of generating a guided wave in a ship hull. Following the results of the modelling performed by CERTH, the transducers were designed for the generation of Ao mode in the frequency range of 20 kHz to 100 kHz to avoid the generation of a number of higher frequency modes. The dispersion curves were calculated by BIC and used in different situations for the development of the final prototype.

Once the High power transducers had been analyzed, high power ultrasonic excitation trials were carried out with small lab samples. Candidate transducers were attached to plates with different design features including welds, stiffeners and curves. These were excited both in dry conditions and under water. The results were used to evaluate the capabilities of the transducers and study how the different features of a ship hull could affect high power guided wave excitation. The best frequencies for each transducer and the preliminary considerations for the transducer array were evaluated.

Since Cleanship’s aim is to cover an entire ship’s submerged hull with ultrasonic excitation, a transducer array to improve transduction was investigated and developed. Based on the modelling and previous laboratory results a new set of experiments were performed at BIC facilities. The location of each type of transducer in the transducer array was evaluated and an optimal array design produced. These results were presented in at the International Conference in Marine Technology (7th-9th July 2014 Glasgow), and were used for the field trials.

Tecnalia, has been the RTD responsible for biofouling detection developments and designed the detection array in parallel with the anti fouling work. The investigation established the optimal number of transducers and the distance between them based both in the laboratory experimentation and the modelling results. Tecnalia also developed the electronics for transducer excitation.

Laboratory experimentation was followed by field trials. BIC, in cooperation with WRS Marine performed two different sets of experiments. The first set established the best parameter for biofouling prevention in small plates. Previous to these experiments, BIC made a literature review of the effects of acoustic waves on marine life. This produced a Journal publication that is under review at the moment. With the information obtained in the literature review 13 plates were immersed in water using different excitation frequencies and powers. The results concluded that 23 kHz and 45 kHz are the optimal excitation frequencies.

Finally, based on all the previous experimentation, the field trials for fouling detection and prevention were performed. In order to evaluate the capabilities of the two systems two different locations were selected. Tecnalia performed their fouling detection experiments in Spanish waters, producing very promising results. The accumulation of fouling was detected due to the increase of signal amplitude because of reduced leakage of acoustic energy to the water. BIC, in cooperation with WRS Marine performed fouling prevention field trials in Holland. A 2x1m plate with the required specifications was immersed in sea water with the prevention system attached. Next to it, a reference plate was immersed with no prevention system but with the same design and same environmental conditions. The prevention system was energized to prevent the accumulation of fouling for one month and a half. Results of these trials indicated that Cleanship prevention system can reduce the accumulation of biofouling for more than 6 weeks. A video of these trials is also available from BIC.

Coordination and dissemination activities have been an important part of this work. A web site (https://arquivo.pt/wayback/20160314100914/http://cleanship-project.eu/) was created which covers the most important events and milestones of the project. A flyer was created at the very beginning of the project and is available in French Spanish and Turkish. This has been circulated at conferences and is available from December 2013

We believe that this work represents a major improvement in the shipping industry fouling prevention which can lead to an important fuel composition, reduce of production break downs and a reduction of CO2 production. Cleanship prototype is expected to improve the prevention of biofouling in marine industry or in any other in which biofouling accumulation on metallic surfaces is considered a problem. The combination of the detection and prevention system provides a usefully tool to undertake biofouling accumulations.

A detailed breakdown of the work performed and main results for each WP is shown in the following table (table 1).

1
Work package 1: system outline functional design, environmental specification and hull selection. established the functional design of the Cleanship prototype. The most significant result of this work package was the identification of the problem and the understanding of the environmental conditions in order to establish testplate designs and trial conditions. Hull and coating properties were defined. These were used during the rest of the project by the RTDs for their research.
D1.2 procured real samples for the RTDs for their development work and also established the locations for field trials.
WRS Marine and ENKON procured two sets of steel testpieces, both coated and uncoated, for the research, including different features; stiffeners, welds, curved plates. These replicated representative parts of a ship hull. These plates were used also for the field trials.
WRS Marine in Holland and Tecnalia in Spain procured the location for the field trials for the prevention and the detection system respectively.
2 Work package 2: Modeling and software for ultrasonic prevention and detection of fouling on ship hulls. The “Signal processing module” was produced to compare the amplitude of echo through the hull with the signals a reference signal obtained when no fouling is presented in the ship hull. The experiments performed by Tecnalia were shared with CERT who processed the data and designed the software for long term fouling detection.
3 Work Package 3: High power ultrasonic plate wave system for the prevention of fouling on ship hulls.
For the prevention of fouling in ship hulls, a transducer array was designed and optimized. The most important results of this optimization were presented in the “International Conference on Maritime Technology” Glasgow, UK, 7th–9th July 2014. This shows the analysis of the best locations of the high power transducers produced by Sofchem depending on the frequency and the ship’s hull properties.
The excitation of the transducers required the construction of a high voltage circuit. This circuit was designed to perform at the resonance frequency of the transducers for long periods. An important feature of the system is its capability for frequency shifting and frequency sweep, and the possibility of adjusting the power levels. Furthermore, it has a protection circuit to prevent damage of the system when subjected to high currents.
The system has been tested for long periods under real conditions with good results both in terms of fouling prevention the system durability.
It should be emphasized that the Cleanship system has been able to prevent the accumulation of fouling for at least one month and a half in a plate immersed in port environment conditions.
4 Work Package 4: Pulse ultrasonic plate wave for the detection of fouling on ship hulls included the design of an assembly of transducers for the detection of biofouling. This was tested during Work Package 5, following with a number of results obtained from laboratory trials.
The first deliverable from this work package showed the conceptual design of the detection system. This report included the preliminary ideas that could be used in the final prototype.
The workpackage concluded with an assessment of the system’s capability for measuring the accumulation of fouling.
It was found that that the accumulation of fouling decreased the leakage of sound into the water due to the higher difference in the acoustic impedance between the ship’s hull steel and the biofouling. This difference in acoustic impedance is less between water and the hull and therefore the acoustic energy can be transfer easily through the water.
5 Work Package 5: System validation through laboratory and port environment trials drew on experimental results and hull samples from earlier work packages for use in field trials which were performed in Holland for fouling prevention and in Spain for fouling detection. Both sets of field trials yielded good and promising results.
Cleanship system was tested for more than three months with continuous excitation and detection. This concluded with a working system that is expected to improve the biofouling prevention in the marine industry.
6 Work Package 6: Demonstration of the Cleanship system. A demonstration video with the research and development of the project has been created. This also contains brief presentations by the consortium members talking about the problem solved and the capabilities of the system. The final prototype and the results are also shown in this video, which is available from the 7th of November in Cleanship website (https://arquivo.pt/wayback/20160314100914/http://cleanship-project.eu/)
7 Work Package 7 (Dissemination, exploitation and training), has been a continuous task of the project. The project website (https://arquivo.pt/wayback/20160314100914/http://cleanship-project.eu/ covers technical and non-technical developments.
A flyer (available via the website) to publicize the project is available in English, Spanish, Turkish and French.
Other dissemination activities such as conferences, magazines and publications are listed below:
• Cleanship Web site, (http://cleanmine-project.com/)
• Cleanship flyer
• M. Legg, M.K. Y¨ucel, I. Garcia de Carellan, V. Kappatos, C. Selcuk, T.H. Gan “Acoustic Methods for Biofouling Control: A Review” Oceans Engineering Journal (Under review)
• Mathew Legg, Ignacio Garcia de Carellan, Vassilios Kappatos, Cem Selҫuk, Tat-Hean Gan from the Brunel Innovation Centre, Serafeim Moustakidis from the Centre for Research & Technology Hellas, Pierre Olivier Jost of SofChem and Teo Karayannis of Lloyd’s Register EMEA, “Detecting the sound of a Cleanship” The Royal Institution of Naval Architects, RSS News Feed, Magazine. February 2014.
• Serafeim Moustakidis, “Prevention and detection of fouling on ship hulls using advanced ultrasonic technology “ Industrial Technologies14. 9th-11th April 2014 Athens.
• “Cleanship Innovative Solution to Ship Hull Fouling”, Transport research arena, TRA conference 14th-17th April 2014 Paris.
• Ignacio Garcia De Carellan, Serafeim Moustakidis, Mathew Legg, Raghav Dave, Vassilios Kappatos, Cem Selcuk, Pierre-Oliver Jost, Hans Juerg Krause, Jan Seton, Tat-Hean Gan and Kostas Hrissagis, “Characterization of Ultrasounic Wave Propagation on the Application of Prevention of Fouling on Ship’s Hull” International Conference in Marine Technology. 7th-9th July 2014 Glasgow.
• Exhibitions stand at Shipbuilding Machinery and Marine ESS conference. 9th-12th September 2014, Hamburg, Germany.
• Exhibitions stand at “Offshore Energy 14” Exhibition & conference 28th-29th October 2014, Amsterdam, The Netherlands.
• Advert in Insider Marine (bi-monthly publication Targeting Marine Industry) to promote Cleanship. October 2014.
• Dialogs with Millenneium Integrated Projects L.L.C. Possibility of introducing Cleanship system in Middle East. June 2014-ongoing.
• Publishing Cleanship benefits and advances in LR’s internal as well as external media. In process.

8 Work package 8: Consortium management. Brunel University coordinated the project organizing meetings, teleconferences with all the partners to ensure that project producedsuccessful results.
Continuous communication between partners allowed parallel lines of investigations to be carried out by the three RTDs in the project.

Potential Impact:
It is anticipated that Cleanship system has the potential to significant change biofouling prevention and detection in ship hulls. Cleanship final prototype is applicable to the entire shipping industry worldwide. This will provide the industry with an environmental friendly method in comparison with the common chemical prevention methods. Cost reductions will be achievable also by significant reduction of fuel consumption, as compared to fouled hulls with an important reduction in their speed and therefore longer times for shipment. As result of these fuel economies there will be significant reductions of CO2 and particle emissions, further contributing to the environmentally sound profile of the Cleanship system.
The combination of prevention with hull fouling detection offers the significant advantage to permit ship operators to time their dry dock intervals. This has associated an important economical save and a better time for the shipping industry.
Cleanship system can also be applied in other offshore structures for the fouling prevention and detection. This would decrease the maintenance cost and increase the performance of this structures.

List of Websites:
The CleanShip project website is http://cleanship-project.eu
Please contact admin@cleanship-project.eu for private area access privileges.

Final Report Summary - CLEANSHIP (Prevention and detection of fouling on ship hulls)

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