For as long as weve been building boats and putting them in the water, weve been battling those pesky little ocean critters that want to attach themselves to our boats for a free ride. The ubiquitous, determined barnacle not to mention tubeworms, oysters, algae, and an array of other invertebrates has long been the bane of many a fleet and flotilla. Pitch, copper sheaths, oils and gums, pesticides, silicone, arsenic over the centuries all have been tried, and none have completely solved the problem.
And no wonder the barnacle, for instance, is very good at what it does. This critter secretes a rapid underwater-curing cement that is among the most powerful natural glues known with a tensile strength of 5,000 lbs per square inch and an adhesive strength that has been measured at 22 60 lbs per square inch. And thats just barnacles. Blue mussels know how to make 21 different kinds of adhesives.
Attaching themselves to ship hulls, billions of crusty foulers cost the U.S. Navy over $50 million a year just in fuel costs due to drag. Its estimated that a newly painted destroyer would lose 2 knots of speed every six months if not scraped and cleaned and this doubles in tropical waters.
Its an age-old battle, says Dr. Steve McElvany, ONRs Program Manager for Environmental Quality, who also studies the mechanics of adhesion. ONR is looking hard at the development of non-toxic, foul-release polymeric marine coatings.
The problem is the toxicity of so many of the coatings that are used worldwide. The old copper-based coatings are now known to be lethal to some marine organisms, says Dr. Linda Chrisey, who as manager of Environmental and Marine Biotechnology at ONR, tries to understand which organisms settle on what surfaces, and why. An environmentally concerned U.S. Navy never implemented the widespread use of the much more toxic tin-based paints on its ships, and has been using copper-based paints since the mid-1980s, but thats not true
Contact: Gail S. Cleere
Office of Naval Research