Anti-pæleorm

Control of shipworm

3 Summary and conclusions

This report describes the execution of the project "anti-shipworm". The project was carried out with support from the Danish Environmental Protection Agency from January 2001 to December 2002.

The goal of the project was to gather information about the conditions that influence wooden boats when phasing out biocide antifouling, relating to marine pests like shipworm and crayfish.

The project shows the different kinds of problems phasing out biocide antifouling experienced by owners of wooden boats.

Until now the wooden boats have been protected against shipworm by the traditional biocide antifouling agents. During the project the consequences of waterproofing the wood with natural oils were examined. Afterward treatment, the wood was sealed with ordinary primer for wood.

The following natural oils were used on different types of wood: Australian tea tree-oil, Chinese tung oil as well as Danish linseed oil.

The tests includes untreated wood and wood treated with biocide antifouling. The aim was to show the extremities – untreated and well treated wood.

By the selection of types of wood, we have chosen the commonly used type of woods for the boat industry, like oak, larch and mahogany – and focus is on these types of wood.

Floats with wooden pieces of 20 x 7,5 x 2,5 cm were immersed in the harbours of Frederikshavn, Hirtshals, Skærbæk, Helsingør, Rønne and Roskilde for about one year.

At the test station in Roskilde attacks were not found during the test period. Surprisingly, an attack of shipworm was seen at the test station in Rønne, Bornholm.

Further, at the test station in Skærbæk, tests were made to see whether special parts of the shipside are especially exposed, but this seems not to be the case. The sheets measured approx. 80 x 60 cm.

The occurrence of attacks is in accordance with the temperature conditions and saltwater concentrations on each station measured during the test period. Further, these test results correspond to former tests made back in the 1940’s.

The effect of the oil treatment and the sealing is that the attacks of shipworm is reduced to approx. 1/7 of what was demonstrated during the test of the untreated wood.

The oils do have an effect, and as at the same time they contribute to maintaining the quality of the wood, it seems to be a good idea to apply oil before primer and paint.

In order to examine the tests different kinds of non-destructive analysis methods as well as digital X-ray were carried on each piece of wood.