WO2006045161A1

WO2006045161A1 - Marine anti-fouling system using ultrasonics

Info

Publication number: WO2006045161A1
Application number: PCT/AU2005/001676
Authority: WO
Inventors: Gary Arthur Stutt; Philip Henry Jones
Original assignee: Watertech Holdings Ltd
Priority date: 2004-10-29
Filing date: 2005-10-31
Publication date: 2006-05-04

Abstract

A marine anti-fouling system for a marine surface (11) such as a boat hull, marine vessels or underwater structures. The system includes at least one ultrasonic generation and transmission means, the system also includes a transducer (10) with at least partially magnetic operation. The transducer has a polar axis and is attached to the surface so that the polar axis is parallel to the surface. The transducer (10) includes a rod (14) of magneto strictive material, usually wood, about which two aerials (13) are wound to form a coil. The rod is positioned using a support structure of a base plate (15) and a pair of upstanding arm members (16). Power is supplied by cables (12) to create a modulating ultrasonic field around the aerials (13) and the ultrasonic field ranging in frequency from 50 to 80000 hertz.

Description

MARINE ANTI-FOULING SYSTEM USING ULTRASONICS

Field of the Invention.

The present invention relates to anti-fouling systems and particularly those used to prevent scale and biological buildup on marine vessels or underwater structures.

Background Art.

Ultrasonics have been used in the past to clean surfaces, remove existing scale, prevent scale formation and to prevent biological build-up or animal growth by helping to break down the protective shell of most common parasitic organisms. These organisms typically include barnacles, mussels, marine worms, corals, anemones, sponges and algae which attach themselves to any exposed surface of boats, ships, docks and other submerged or partially submerged structures. When these organisms attach themselves to the hulls of ships or boats, their presence hastens the breakdown of the outer finish of the hull as well as detracting from the performance of the affected vessel. Ultrasonic transducers convert electrical energy into vibrational mechanical energy, often sound or ultrasound, that is used to perform the cleaning task.

The simplest manner of removing this build-up in the past has been by employing divers to scrape the surface of the structure or vessel clean of the build-up. Other more complex and user-friendly methods have been developed as the diver- assisted removal is time-consuming and can be expensive.

Ultrasonic cleaning is a result of sound waves introduced into water flowing through a conduit or pipe by means of a series of coils wrapped around a pipe. The sound travels through the pipe carrying the water and creates waves of compression and expansion in the liquid. Ih the compression wave, the molecules of the fluid are compressed together tightly. Conversely, in the expansion wave, the molecules are forced apart, creating microscopic bubbles. The bubbles only exist for a split second and contain a partial vacuum while they exist.

As the pressure of the bubbles increases, the fluid around the bubble rushes in, collapsing the bubbles rapidly. When this occurs, a jet of liquid is created that may travel very quickly. They rise in temperature to as high as 5000 degrees

Celsius. This extreme temperature, combined with the velocity of the liquid jet, provides an intense cleaning action in a minute area. Due to the very short duration of the bubble expansion and collapse cycle, the liquid surrounding the bubble quickly absorbs the heat and the area cools quickly.

As stated above, there are quite a number of devices available that purport to effectively prevent the fouling of a marine hull or structure. One such known system uses external electrodes on the hull to produce poisonous chemicals by electrolysis of seawater. However, the practice of poisoning the organisms is not considered environmentally responsible, especially since other marine life may be unintentionally harmed.

Other methods such as methods of hull manufacture, in which wire mesh is embedded in the fibreglass, are known. This wire mesh conducts a sonic signal from the generator to the hull exterior which has metallic plates interspersed on its exterior surface. The sonic signal emanates from each of the metallic plates to provide a plurality of sonic emitters.

Other methods such as systems which rely upon low frequency vibration to cause water movement near the hull exterior to inhibit attachment of marine organisms have been used. In order to provide the necessary field of vibration, the transducers must be arranged on the inside of the hull in pairs. These pairs of transducers must be spaced on either side of a nodal line at a pre-determined distance.

Such precise placement of the transducers, in many vessels, would be impossible due to the structure of the hull and the placement of bulkheads.

It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

Summary of the Invention. The present invention is directed to a marine anti-fouling system, which may at least partially overcome the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

In one form, the invention resides in a marine anti-fouling system for a marine surface, the system including at least one ultrasonic generation means and at least one ultrasonic transmission means, the system including a transducer with at least partially magnetic operation, the transducer having a polar axis, the transducer attached with the polar axis parallel to the surface.

The system finds application where a surface is the subject of scale formation or biological build-up or animal growth by helping to break down the protective shell of most common parasitic organisms. These organisms typically include barnacles, mussels, marine worms, corals, anemones, sponges and algae, which attach themselves to any exposed surface of boats, ships, docks and other submerged or partially submerged structures. The system is particularly well adapted to treat boat hulls, pier footings and any underwater structure or surface.

According to a particularly preferred embodiment, the ultrasonic generation means may comprise a power supply connected to a power source. The power supply is preferably linked to the transducer via supply cables. The transducer will typically be a magnetostrictive transducer.

The system may further comprise a transducer having at least one and typically two aerials. Each of the aerials may take the form of elongate members or wires. The aerials may preferably be wires approximately 2.5 mm in diameter.

The transducer may suitably include a rod of magnetostrictive material, preferably wood, about which the aerials may be wound. The rod may take any shape and be of any length although it will typically be approximately 20 to 80 cm in length and approximately 5 cm in diameter.

The rod will suitably be held in position using a support structure. The support structure may include a base plate and at least one, but preferably a pair of upstanding arm members extending approximately perpendicular from the base plate. All portions of the support structure may suitably be manufactured from a conductive material in order to transmit the sound waves from the transducer to the surface effectively. Typically, the support structure will be manufactured from wood. Other materials may be used, and the material used may be chosen depending upon the surface to be anti-fouled. Where wood is used, typically the more dense the wood, the better.

Generally, the ends of the rod may engage the upstanding arm members of the support structure in a mortise and tenon attachment. The rod may be removable from the arms but preferably will be securely attached thereto. The base plate will typically be securely fastened relative to the surface to be treated. This fastening may typically be such that the rod with the attendant aerials will extend in a configuration which is parallel to the surface to be treated. For instance, when treating a boat hull, the transducer may be fitted beneath the floor of the boat adjacent the keel of the boat.

The aerials may each preferably form a coil. Each coil, when electrified, preferably produces an alternating magnetic field which in turn induces mechanical vibrations at an ultrasonic frequency in resonant magnetostrictive material which is attached relative to the surface to be vibrated.

The aerials are suitably wrapped about the rod. The two aerials may be wound about the rod starting from the same point on the rod. Generally a minimum of seven revolutions may be required for the ultrasonic means to function optimally. It is preferred that each of the aerials revolve in opposed directions about the rod, one in a clockwise direction and one in a counter-clockwise direction. The coils will typically be separated from one another and the distance between each coil may suitably be approximately 75 mm.

The aerials are typically separable from the supply cables. Any means of attachment of the aerials to the cables may be used and typically the attachment means will allow transmission of an electrical and/or an ultrasonic signal to the transducer.

As the coils are preferably wrapped about the same rod, the polar axis of the coils will be coaxial. The current applied to each of the coils may differ in such aspects as the level of current, the direction in which the current is applied thus changing the direction of the polar axis when the charge is applied to the coils and the frequencies of each of the coils maybe offset.

The power supply preferably creates a modulating ultrasonic field around the aerials, the field ranging in frequency from 50 to 80000 hertz. According to a particularly preferred embodiment, the power supply supplies a signal at a variable frequency (or sweeping frequency) to each of the aerials. Preferably, the signal frequency starts at approximately 15 kilohertz and increases by 2 kilohertz over each two minute period. When a frequency of 71 kilohertz is reached, the frequency drops to 15 kilohertz and repeats the above process. In the past, magnetostrictive systems have not moved to a sweep frequency system. The reason is that the magnetostrictive transducer generally has such a large inertial mass that it is difficult to shift the frequency as rapidly as is required to get good sweep frequency. By sweeping the frequency at two minute intervals, this problem is at least partially overcome. The use of deliberate frequency sweeping and multiple frequencies may avoid localized hot spots in the fluid surrounding or adjacent the surface to be treated which are generally caused from standing wave formation. The ultrasonic frequency generated by the transducer is typically dependent on the length of the transducer with higher frequency requiring a shorter length. The use of a pair of coils may also assist with the production of standing wave formation

The ultrasonic frequency impacts the diameter of the cavitation event. Low frequencies generally result in large diameter cavitations and higher frequencies result in small diameter cavitations. The energy per cavitation follows the same trend. However, the number of cavitations per unit volume is high with high frequency systems and low with low frequency systems. The combination of energy per cavitation and number of cavitations is total energy and this is approximately equal for most frequencies. A graphical representation of the relationship between frequency and number and energy of the cavitation is illustrated in Figure 1. By inducing a frequency sweep between 15 kHz and 71 kHz, the surface to be treated may be subjected to both large diameter cavitations and small diameter cavitations as well as higher and lower energy cavitations. The combination of all of these preferably results in improved cleaning performance and a reduction in the number of transducers required to accomplish an effective cleaning of the surface. Control means may also be provided for the system. It is preferred that the operation of the system, including its start and finish time (if any), be controlled by the system control means. The control means may initiate a cleaning cycle, time the cycle, and shut down the system at the completion of the cleaning cycle.

The system may operate continuously. One or more timers may also be provided.

One major difference between the transducer of the present invention and those of the prior art is the orientation of the polar axis of the transducer. In the prior art magnetostrictive transducers, the polar axis is oriented perpendicular to the surface to be treated. According to a preferred embodiment of the present invention, the polar axis of the transducer is oriented substantially parallel with the surface to be treated.

Brief Description of the Drawings. Various embodiments of the invention will be described with reference to the following drawings, in which:

Figure 1 illustrates a graphical representation of the relationship between ultrasonic frequency and the number and energy of the cavitations.

Figure 2 is a top view of a transducer according to a preferred embodiment of the present invention.

Figure 3 is a perspective view of the transducer illustrated in Figure 2. Figure 4 is a schematic representation of a prior art magnetostrictive transducer.

Detailed Description of the Invention. According to an embodiment of the invention, a marine anti-fouling system is provided.

The system is used to treat a marine surface 11, generally a submerged surface. The system includes an ultrasonic generation means and a magnetostrictive transducer 10 having a polar axis. The transducer 10 is attached relative to the surface to be treated 11 with its polar axis parallel to the surface. When the surface to be treated 11 is a boat hull or similar, the transducer 10 is attached on the interior of the boat hull as seen in Figures 2 and 3.

According to a particularly preferred embodiment, the ultrasonic generation means may comprise a power supply connected to power source. The power supply is linked to the transducer 10 via supply cables 12.

The system includes a transducer 10 having two aerials 13. Each of the aerials of the preferred embodiment is in the form of elongate members or wires. The aerials are approximately 2.5 mm in diameter.

The transducer 10 includes a rod 14 of magnetostrictive material, usually wood, about which the aerials 13 are wound. The rod 14 illustrated in figures 2 and 3 is approximately 50 cm in length and approximately 5 cm in diameter.

The rod 14 is held in position using a support structure. The support structure includes a base plate 15 and a pair of upstanding arm members 16 extending approximately perpendicular from the base plate 15. All portions of the support structure are manufactured from a conductive material in order to transmit the sound waves from the transducer 10 to the surface 11 effectively. The support structure illustrated in Figures 2 and 3 is manufactured from wood.

The ends of the rod 14 engage the upstanding arm members 16 of the support structure in a mortise and tenon attachment.

The base plate 15 is securely fastened relative to the surface 11 to be treated. This fastening is such that the rod 14 with the attendant aerials 13 extends in a configuration which is parallel to the surface 11 to be treated. For instance, when treating a boat hull, the transducer 10 is fitted beneath the floor of the boat adjacent the keel of the boat.

The aerials 13 are each formed into a coil about the rod 14. Each coil, when electrified, produces a magnetic field which in turn induces mechanical vibrations at an ultrasonic frequency in resonant magnetostrictive material which is attached relative to the surface 11 to be vibrated.

The aerials 13 are wrapped about the rod 14. The two aerials 13 are wound about the rod 14 starting from the same point on the rod 14. A minimum of seven revolutions may be required for the ultrasonic means to function optimally. It is preferred that each of the aerials 13 revolve in opposed directions about the rod 14, one in a clockwise direction and one in a counter-clockwise direction. The aerials 13 are separated from one another and the distance between the aerials 13 is approximately 75 mm.

The aerials 13 are typically separable from the supply cables 12. Typically, an attachment means 17 is provided and the attachment means 17 allows transmission of an electrical and/or an ultrasonic signal to the transducer 10.

As the aerials 13 are wrapped about the same rod 14, the polar axis of the coils will be coaxial.

The power supply creates a modulating ultrasonic field around the aerials 13, the field ranging in frequency from 50 to 80000 hertz. According to a particularly preferred embodiment, the power supply supplies a signal at a variable frequency (or sweeping frequency) to each of the aerials 13. The signal frequency starts at approximately 15 kilohertz and increases by 2 kilohertz over each two minute period. When a frequency of 71 kilohertz is reached, the frequency drops to 15 kilohertz and repeats the above process. Because magnetostrictive materials behave identically to a magnetic field of either polarity, the frequency of the electrical energy applied to the transducer is approximately 1/2 of the desired output frequency.

In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated i integers but does not exclude the inclusion of one or more further integers.

Claims

Claims:

1. A marine anti-fouling system for a marine surface, the system including at least one ultrasonic generation and transmission means, the system including a transducer with at least partially magnetic operation, the transducer having a polar axis, the transducer attached with the polar axis parallel to the surface.

2. A marine anti-fouling system for a marine surface according to claim 1, wherein the transducer is a magnetostrictive transducer having a polar axis, the transducer attached with the polar axis parallel to the surface.

3. A marine anti-fouling system for a marine surface according to claim 1, wherein the transducer has at least one elongate aerial.

4. A marine anti-fouling system for a marine surface according to claim 3, wherein the transducer includes a rod of magnetostrictive material about which the at least one aerial is wound.

5. A marine anti-fouling system for a marine surface according to claim 4, wherein the rod is mounted relative to the marine surface using a support structure including a base plate and at least one upstanding arm member extending approximately perpendicular from the base plate to space the rod from the marine surface.

6. A marine anti-fouling system for a marine surface according to claim 4, wherein a pair of aerials are provided and the aerials are wound in counter rotating directions about the rod to each form a coil.

7. A marine anti-fouling system for a marine surface according to claim 6, wherein the aerials are wound about the rod starting from a central longitudinal location, the coils separated from one another and each extends outwardly in a different direction.

8. A marine anti-fouling system for a marine surface according to claim 1, wherein one ultrasonic generation and transmission means creates a modulating ultrasonic field, the field ranging in frequency from 50 to 80000 hertz.

9. A marine anti-fouling system for a marine surface according to claim 8, wherein a frequency sweep is used, the frequency initiating at approximately 15 kilohertz and increasing by 2 kilohertz over successive two minute periods until a frequency of 71 kilohertz is reached, the frequency sweep then repeating.

10. A marine anti-fouling system for a marine surface according to claim 1, used to treat a marine vessel hull, the transducer mounted adjacent the keel of the boat.