Keeping crud off the bottom of a boat has been a problem for mariners … well, probably since before recorded history. From oil to tar; from tin and copper sheeting to tin- and copper-based paints; and even from chili powder to indelible markers … Boaters have tried everything to keep their boat bot toms smooth and clean. Environmental concerns, however, are forcing mariners to find new ways to protect their boats without poisoning their playground or workplace.

If you are a new owner, you might be wondering why you need bot tom paint. The Caribbean’s warm, salty water provides extreme fouling conditions. If you keep your boat in the water, many marine plants and animals will view the bot tom of your boat as a perfect home. Their attachment to your hull will, at best, slow your boat and, at worst, foul your intake valves and props. Your engines will have to work harder to move your boat, and that green stuff on the bot tom looks yucky.

In the 1960s, chemists developed anti-fouling paints that contained metallic compounds. One in particular, tributyltin, proved particularly effective … So effective that by the 1970s TBT could be found on the hulls of most seagoing vessels. Unfortunately, TBT proved to be toxic to more than just the slimy crud.

Scientists discovered by the mid 1970s that concentrations of TBT as low as half a nanogram (the plastic cap of a Bic pen weighs about one gram: www.wikipedia.org) caused a phenomena known as “imposex” in the female dogwhelk. What is imposex? It is a result of endocrine disruption so severe that females grow a penis and are unable to reproduce. By the early 1980s, French scientists linked declining growth rates of oysters in Arachon Bay to tributyltin. In 1982, France banned the use of anti-fouling paints containing TBT on vessels less than 25 meters in length. 1

According to sources in a report compiled by the International Maritime Organization, Focus on IMO—Anti-fouling systems, by the 1980s, high concentrations of TBT were reported in coastal areas around the world. That report went on to state that “In the open seas and oceanic waters, TBT contamination was seen as less of a problem, though later studies showed evidence of TBT accumulation in fish and mammals.” In case you missed it – that’s “fish” – what we potentially eat … And “mammals” – potentially us. “TBT has been described as the most toxic substance ever deliberately introduced into the marine environment and has been confirmed to be harmful to a range of aquatic organisms, including microalgae, mollusks and crustaceans, fish and some invertebrates.” 

Many countries, including Japan, United Kingdom, United States, New Zealand, Australia and Norway, followed France’s lead, strictly regulating the use of, and/or banning the production of, anti-fouling paints that contain TBT.

The International Convention on the Control of Harmful Anti-fouling Systems on Ships was adopted on October 5, 2001. The Convention’s purpose is to prohibit and/or restrict the use of harmful anti-fouling systems worldwide. The Convention contains an Annex that specifically prohibits the use of organotins compounds (TBT) in those systems. As of June, 2006, the Anti-Fouling Convention, which will only go into force 12 months after ratification by 25 States, had been ratified by only 16 countries. 3

It is up to the individual boat owner to be aware of the impact his or her activities have on the environment. If we are careful, commercial and pleasure boaters should be able to enjoy the beauty of the world’s oceans and its denizens without destroying them.

For further research, please see www.imo.org; www.imo.org/includes/blastDataOnly.asp/data_id{87af57bf33b759b13edf1201e0aac8ff568782d54202a219d5fee60abad8e986}3D7986/fouling2003.pdf; http://www.comnap.aq/publications/conmapatcm/2006_29atcm_ip082-h; http://extoxnet.orst.edu/pips/tributyl.htm; and www.sciencedirect.com – various articles.

Next month: Does the type of boating you do affect the type of bot tom paint you need?

1 The Science and Environment Bulletin, July/August 1998 http://www.ec.gc.ca/science/sandejulaug/article4_e.html

2 2006 – 29ATCM-IP082: The use of Anti-fouling Biocide Paints by National Antarctic Program Vessels (html)

3 http://www.imo.org: Anti-fouling systems

J. Summer Westman lives in St. Thomas, USVI, with her husband, Bill. When not out on their boat, Excellent Adventure, Summer writes boating articles and designs websites. Reach her at summervi@earthlink.net or www.livingbydesignvi.com.