Barnacle-free hulls would be a dream come trueJune 7th, 2009 by cdunagan
Barnacles and other organisms that attach themselves to ships’ hulls are the focus of an enormous amount of attention, as experts try to find nontoxic methods of keeping hulls clean.
Historically, bottom paints have included compounds that deter organisms with their toxic effects. To be successful, such antifouling paints must slough off at a sufficient rate. That places these toxic compounds into the water, where they can build up in enclosed bays.
When and where such compounds actually reach toxic levels in the environment is a complex problem, involving the toxicity of the compound, the amount that gets released within an enclosed inlet and the level of mixing that occurs in the waters.
Puget Sound Naval Shipyard in Bremerton is struggling with the issue of copper, a primary component in antifouling paints now that tributyltin has been banned. TBT builds up in marine life and is quite toxic to clams and oysters.
The Navy recently reached an agreement with the Department of Ecology to reduce the amount of copper in its stormwater discharges. Most of the copper comes from releases during sandblasting and painting activities. The Navy has tightened up its processes. (See Kitsap Sun, May 29.)
The Navy is considering treating such stormwater before release, and negotiations are under way for a new federal discharge permit. I’ll be writing more about this issue in the coming weeks.
Behind the scenes, the Navy is spending an enormous amount of money to develop new materials and processes to prevent growth on the hulls of ships. The reasons are obvious. Fouling of ships hulls can reduce vessel speed by up to 10 percent, requiring a 40 percent increase in fuel consumption to counter the extra drag. That’s amounts to roughly $1 billion a year the Navy has to spend, according to the Navy’s own figures. (See story on the Web page of the Office of Naval Research.)
It’s hard to tell whether there are any absolute breakthroughs, but some interesting findings are coming out of studies into why barnacles attach to some marine animals, such as gray whales, but not to sharks. Anthony Brennan at the University of Florida is looking at the unique surface pattern found on sharkskin and trying to mimic that for a ship’s hull. The best explanation of the concept can be seen in a video produced by the Office of Naval Research (bottom of page).
That report also mentions work by Shaoyi Jiang at the University of Washington, who is working on anti-fouling coatings that incorporate mixed-charge compounds, which alternate between positive and negative charges and seem to keep organisms from binding.
For recreational boaters, the University of California Sea Grant Extension Program has been studying alternatives in San Diego Harbor and Newport Bay with the idea that the ideas could be applied elsewhere. One study looked at silicone- and epoxy-based coatings.
For more details, check out “Demonstrating a Solution to Copper Boat Bottom Paint Pollution!” (PDF 28 kb).
When you think about it, the need for a low-cost product that will keep hulls clean is obvious, but I’m frankly amazed at how many ideas are floating around, as can be demonstrated by plugging the words “antifouling” and “hull” into a search engine.