Test af mekanisk rensning af skibsbunde og antibegroningsmidler med reduceret miljøbelastning

English summary

During the 1998 yacht season, the Danish Sailing Association and Hempel carried out parts of the present project: "Practical testing of biocide-free paints in combination with mechanical cleaning and practical tests with paints containing biocides with an expected reduced impact to the aquatic environment". Apart from these practical tests the Danish Sailing Association made a general search on available methods for mechanical cleaning.

Besides the above investigations, in this project, VKI has carried out ecotoxicological assessments of Sea-Nine and Zinc Pyrithione, which, according to project 385/98 [1], potentially possess better environmental profiles compared with those of Irgarol and Diuron. Until now the latter two biocides have been used commercially in biocide-containing antifoulings on the Danish yacht market. Furthermore, VKI has worked out risk assessments for the two biocides and for copper. They have also carried out ecotoxicological assessments of the biocide-free bottom paints, which were tested during the practical part of the project. VKI will report all their evaluations and investigations separately. The following contains conclusions from the Danish Sailing Association and Hempel.

Boat washers and methods

This project identified three boat washers (Stark Boatwasher, KBK Boatcleaner and Marina-tec), a boat lift system (Magnum boat Lift), a high-pressure washing system (Rule) and a concept in which divers and remote-controlled brushes are meant to remove fouling (IMS). Stark, Rule and Magnum Boat Lift are commercially available.

According to the Danish Sailing Association's information, none of the investigated boat washers have been able to solve the problems of handling different hull shapes and cleaning of boats mooring in salt water.

It is to be expected that all the boat washers and the alternative methods identified will create both logistic (placing, capacity, preference of times), economic and environmental (disposal of removed fouling) problems.

Manual cleaning of biocide free bottom paints

A number of the participating boat-owners painted epoxy on one side of their yacht and an experimental silicone paint 86330 on the other. When inspecting the boats a substantial amount of fouling was observed on both paints. The most sedentary fouling was observed on the epoxy-side, where especially the basal plates of barnacles could not be removed. Because of the amount of accumulated fouling on the experimental silicone paint, it was necessary to use harder sponges for cleaning than expected since the silicone paint film was damaged during cleaning, facilitating settlement of fouling organisms. Silicone paints are by nature mechanically weaker than the conventional types of bottom paint.

Inspection intervals and cleaning

The boats were hauled ashore, inspected and cleaned four times during the project. The intervals between the inspections were:

The boats were most heavily fouled at the second inspection. The period between the first and second inspection was the longest and also the period in which the fouling was intensified. Therefore, it was concluded that the interval between the first and second inspection was too long. This project did not identify how often the boats should be hauled ashore and cleaned to keep the bottoms fouling-free, since that was not the purpose of the project. However, based on the results from the project it can be concluded that the period between the cleanings depends very much on the fouling intensity in the specific harbour and how clean the yacht owner wants to keep his boat.

Questionnaire

A questionnaire was handed out at each inspection and 57 out of 116 questionnaires were answered. The silicone had been damaged by the cleaning according to 43 % of the respondents, whereas only 11 % had observed damages in the epoxy. Throughout the whole project many participants regularly commented on how unacceptable it would be to clean the boat, as had been done in this project. The questionnaire answered at the end of the season (25 out of 29 participants answered) showed that 92% would not accept to have to clean their boat in the future, as they had done during the 1998 season. Based on the results obtained, Hempel concludes that the release properties of the experimental paint 86330 should be further developed. It should however be mentioned that there were no commercial biocide-free silicone-based bottom paints on the Danish pleasure craft market in the 1998 season.

The concept of mechanical cleaning

Tests involving hauling boats ashore for cleaning, have not been performed previously in Denmark. Thus the project represents the first experiences.

The chosen harbours had different equipment to haul the boats ashore and a large number of the available methods were utilised. The inspection time of a boat varied from 30 minutes to one hour depending on the harbour. The length of the time depended on whether the boat owner could clean the boat while other boats were taken ashore. The time used for sailing to the crane, lifting, cleaning and launching was estimated to vary from 1 hour and a half to 2 hours on average per boat.

On the basis of the experience obtained from the project, the Danish Sailing Association concludes that if boats should be taken ashore in the future, washing stations must be established where installations and machines are available all the time. Likewise, stands should be automatic and independent of boat size. It should be possible to collect the washing-water and rinse it automatically. Such a washing station should be able to handle a minimum of four boats if the hauling/launching process should be kept going without unnecessary stops.

The Danish Sailing Association further concludes that if boats were to be brought ashore for cleaning, insuperable difficulties and very large investments would be attached. In many places it would simply not be feasible and the sailing sport would be diminished as a leisure activity.

Practical tests with biocide-containing test paints

Two biocide-containing experimental bottom paints, Hempel's Bottom Paint 87910 (Cu + Zinc Pyrithione) and Hempel's Bottom Paint 8191C (Cu + Sea-Nine), were tested during the project. These paints are expected to have a reduced environmental impact compared to the commercial paints at presently available on the Danish pleasure craft market.

The antifouling performance observed for the two biocide-containing experimental paints corresponded to the participants' expectations of efficient bottom paints.