Navy Lab continues to fight an age-old enemy
A sailor scratches the barnacles of a rigid-hull inflatable boat aboard the Nimitz-class aircraft carrier USS John C. Stennis (CVN-74).
Navy Photo by Apprentice Seaman Christopher Frost
The Naval Research Laboratory is not giving up the battle against one of the navy’s toughest and oldest enemies: barnacles.
For sailors, barnacles are an ancient scourge. Even today, they cost the Navy billions of dollars and continue to pose a difficult problem for scientists.
Barnacles, mussels and algae are the main sources of biofouling and seek out a place to settle. They will try to stick to anything, including the bottom of a ship.
The Navy wants barnacles to feel unwelcome, said Kathryn Wahl, a chemist and materials scientist at the Naval Research Laboratory and a coatings and biofouling program officer at the Office of Naval Research.
Barnacles are particularly problematic because they slow down a ship and increase fuel consumption. Even the most recent vessel or the most recently cleaned hull will be subject to biofouling as soon as it enters the water. Unless protected by an anti-fouling coating, in just two weeks their presence is enough to cause a trail and they start to become difficult to remove.
In just six months, a guided missile destroyer’s speed will be reduced by two knots unless the bottom is cleared, and this effect increases in warmer waters. It takes time and resources to eliminate them and take ships offline and away from their operational functions. This is why the Navy wants to gain the upper hand against these submarine parasites.
Better to keep them off the ship first.
“Their success is in large part due to its ability to adhere to various substrates by secreting a thin adhesive layer that is deposited as the organism grows and expands its base,” Wahl said of barnacles.
Barnacles, like mussels and tubeworms, secrete extremely strong glues that harden under water. Molds can make more than 20 kinds of protein in glue; and scientists have found and started to identify more than 50 proteins in the adhesive interface of the barnacle.
Researchers in the lab examine the chemistry of glue, how it is made, and how it is applied to a surface.
They are also studying how the shape and design of the shell, which serves as armor for the barnacle, contributes to the difficulty of removing them from surfaces.
“We are working to better understand how barnacles adhere to surfaces, and through that, inform new ways to produce alternatives to toxic paints and surface treatments. Some of our research materials show promise in this area, ”said Wahl.
The Navy has identified some interesting aspects of the barnacle interface that can help develop new strategies to combat fouling, she said. Researchers are trying to develop anti-fouling coatings that more easily release barnacles and prevent their growth on surfaces without using toxins.
“Understanding the interaction of the barnacle and its interface with active chemistries in surface treatments is one way to explore these opportunities,” she said.
According to Paul Armistead, head of the coatings and biofouling program at the Office of Naval Research, anti-fouling coatings come in two main varieties: ablative or self-polishing. These prevent fouling by the release of a toxin.
The rules of the International Maritime Organization regarding anti-fouling paints have become stricter. Tributyltin, or TBT, was the biocide of choice and was effective in preventing the growth of algae, barnacles and other marine organisms. But TBT also killed other marine organisms and was subsequently banned internationally. Today, paints have become more respectful of the marine environment.
Self-polishing coatings generally require a constant flow of water over the hull, like a merchant ship which sails most of the time and moves at a fairly constant speed.
With Navy ships, which may be in port for several days or underway at high speed, ablative coatings can help eliminate marine life that has made it their home.
The anti-fouling coatings are based on silicone resins. “They are not self-polishing and do not contain biocide. They don’t prevent fouling, but have a very slippery surface, which makes them difficult to adhere to, ”Armistead said.
Their abilities improve. “With the old anti-fouling coatings, the barnacles lifted off at 20 knots. With the most recent, the barnacles leave at 10 knots, ”he said.
The subjects: Navy News, Marine Safety, Shipbuilding