How does the Ultrasound protection system work?

Ultrasound and growths

Every spring in the winter yacht berths one can observe the same picture: with the first warm rays of the sun and the retreat of cold weather, yacht owners scurry around their charges, rushing around with colorful buckets and covering the hull with antifouling paint. Depending on the care and quality of the paint used, after eight years it will still be necessary to clean the hull to the ground, which involves removing the multi-millimeter layer of build-up, which often consists of crater-like particles. This is a very difficult and painstaking job, and therefore many owners prefer to hand over their yacht for such cleaning to a service center, while laying out a round sum of money. How convenient, healthy and economical in time and money it would be if there were another, durable and reliable method against the annoying build-up on the case!

Firm Impacttec / Hughesin particular her dealer Stefan Sheeb, have such a system in their range - and in this case, ultrasound is the lifesaver that all yachtsmen would like to have.

Operating principle: A specially developed scheme of ultrasonic vibrations with a frequency of 27 to 48 kHz, which are sent by means of ultrasonic transmitters mounted on the hull to the boat's hull, as well as to the outer surface of the underwater part of the hull. This special ultrasonic circuit, which does not have any negative effect on the function of the sonar transducer, must destroy certain components of the algae, which leads to their death. The ultrasound circuitry is sent digitally, and the human ear does not pick up any sounds from the black box, which can be equipped with different frequency sequences specifically to prevent the build-up of various organisms in the underwater world. However, it should be borne in mind that, according to biologist Dr. Ralph Sonntag from International Fund for the Protection of Animals (IFAW) in Hamburg, these frequencies harm small toothed whales such as guinea pigs, as these animals hear them especially well and, therefore, it drives them out of the area.

How does the process of formation of a build-up on the body take place? First, microscopic algae settle on the surface of the underwater part of the boat, forming a microscopic growth at the molecular level, which is a good basis for attaching other representatives of the living marine world. Then filamentous algae, mussels or other mollusks have the opportunity to gain a foothold on the body. Accordingly, if the formation of the first microscopic layer on the body is prevented, the possibility of the formation of a base for the formation of the main build-up can be excluded. The problem will be solved, only a thin, brown layer of mucus will remain - a fantastic idea.

Installing the ultrasound system

The set consists of a black box, two ultrasonic transmitters and two cables

Individual ultrasound circuit is saved and reproduced in the black box

Before gluing the transmitter, the sanded surface must be carefully treated with acetone.

The top layer of the housing surface must be sanded in the form of a circlip to fiberglass

The surface of the transmitter must be sanded with a sander

The transmitter can be easily installed near the echo sounder sensor

Transmitter operation is verified by an underwater microphone

The measuring device shows that even at a distance of 25 meters there is a clear received signal

To test the promised effect, we had to look well for a like-minded partner, because in the editorial office, none of the yacht owners wanted to sacrifice their boat for this experiment with an uncertain outcome. Of course, no one wanted to accept the possible prospect of getting a lushly overgrown underwater part of the hull at the exit. In addition, for the objectivity and purity of the experiment, it was necessary to completely remove the previously existing coatings. In the end, we were lucky enough to find a brand new boat. Varianta 44, the owner of which agreed to participate in the experiment.

a protective barrier for a 13m boat, a total of four ultrasonic transmitters must be installed. For small boats up to 9 meters, it is sufficient to install a system with a so-called "converter", for yachts with a length of 912 meters, two transmitters must be provided, and if the length exceeds 12 meters, at least three. We have installed four transmitters on the VA44 body.

The system is powered via the on-board network or connected to an onshore power source. It is possible to combine both methods, so that, for example, the system automatically connects to the battery in the event of a power outage on the shore.

The cable between the black box and the transducer is about five meters long. According to Stefan Sheba, it is especially important to choose the installation location carefully. Since the ultrasonic transmitter must be directly adjacent to the outer wall for maximum loss-free frequency transmission into the material, it must not be installed on the inner wall. It would absorb too much ultrasound, and there would be too little effect on the body. Less ultrasound also passes through sandwich laminates due to their massiveness. Once a suitable location has been found, the transmitter must be attached with screws. To do this, sand the top cover from the inside and attach the nut with which the transmitter is fixed. A special gel is applied between the fiberglass and the transducer for good ultrasound transmission.

In the Varianta 44, it was difficult to find a suitable location for the ultrasound system and cable routing. Throughout the day, we unscrewed the floorboards, sanded them, glued them on, pulled our ears through the too narrow and winding cable tunnels, swore and sweated. But it was not the ultrasonic system, but the special design of a modern yacht. The same problems would probably also be the case for yachts built in other large-scale shipyards.

Ultimately, four transmitters were installed fore and aft on the starboard side under the berth, on the port side in the middle of the boat by the table, on the starboard side in front of the galley and on the port side in the aft cabin. Two rather small controls were installed under the bunk boards in the aft cabin on the port side.

When the device was turned on, almost silent sounds of chirping, squeaking and whistling could be heard. Not everyone would be able to hear these sounds on board, but one of the owners, who had a particularly sensitive hearing, said that he felt like in a tropical bird park.

After installing the transmitters, we checked the operation of the system using an ultrasonic microphone, which we lowered into the water in the immediate vicinity of the case. Signals need to come from four different locations, which should be displayed on the meter with an increasing number of red and green LEDs illuminated. Near the hull, the readings were in order, and we could receive various signals within a radius of 30 meters. The installation was done correctly and in the right places.

The system worked all the time throughout the season and theoretically should have worked.

During the first control rise on July 7, that is, about seven weeks after the installation of the system, a sobering picture appeared before us: the entire surface of the hull was completely overgrown with branching bryozoans and tiny mussels, forming a layer of growth of 10 centimeters, and only the zones of the motor, steering wheel, and also side inlets and logs, which were originally treated with antifouling paint, were least affected by vegetation. Unfortunately, from the side of the German distributor of the ultrasound system, not a single employee came to the site, despite the timely notification.

In mid-August, about five weeks after a follow-up inspection, the dealer stated that the threaded rings glued to the body could be removed without effort. He also said that at this time it was no longer possible to achieve perfect ultrasound transmission. He attached the threaded rings with another glue and turned on the ultrasonic transmitters the next day. From this point on, the case was not monitored, but apparently showed only a very slight build-up.

Five weeks later, a second test lift of the boat took place and again no effect. The underwater part of the hull is completely overgrown with mussels and large colonies of gelatinous animals to areas treated with antifouling paint. The build-up layer thickness was about 15 to 20 millimeters.

The ultrasound system failed. None of the claimed effects have been confirmed. When asked what we might have done wrong, a colleague of the dealer who was present at this climb, replied: "Nothing!"

Proof test I

Seven weeks after the installation of the system, eagerly awaiting the first intermediate result, on July 7, we lifted VA 44. Until then, the yacht had been practically motionless at Sonwik Marina in Flensburg Fjord. The picture before our eyes was very sobering: with the exception of the areas treated with antifouling paint (steering wheel, engine), the underwater part of the hull was densely and evenly covered with a fluffy layer of growth, about ten centimeters wide. Among other representatives of the marine world, young mussels (2-5 mm long) and branching bryozoans were also found.

Proof test II

Nine weeks later, on September 16th, we made the second ascent of the yacht. Before that, the ultrasonic transmitters were re-glued, and the yacht was used for a vacation trip to the coast of Denmark. The second ascent of the yacht once again showed owners, who complained about a significant decrease in performance, an eerie picture: again the entire surface of the hull was covered with a thick layer of growth, this time with almost adult shells and mussels, as well as a large colony of rather colorful gelatinous animals, the so-called ascidians. The engine and rudder areas did not have any build-up, as on the first day.

Ultrasonic systems market overview

There are many suppliers of ultrasound systems in Europe that work on a similar principle: Transmitters that are attached internally or externally to the enclosure using glue or screws send out a specific ultrasonic circuit that propagates through the enclosure. This ultrasound must either destroy algae, which serve as the basis for further growth, or, through the formation of microscopic air bubbles, prevent vegetation from attaching. The transmitted ultrasonic frequencies range from about 20 to 50 kHz. It is possible that one or the other system, under different conditions, one way or another would show an effect that failed during the test, which, in turn, was not carried out to expose manufacturers or dealers of products.

Text: Gerald Sinshek

03.06.2014