This winter, we finally bit the bullet and replaced the 60-year-old dock at Osborn Cove.
The old dock had been built around the start of World War II using creosote-impregnated telephone poles and locally sawn heartwood oak planking. About half of the planks on the decking were original, the untreated red oak remaining amazingly durable after almost 22,000 days of sun, ice and rain. But the pilings, pounded into the bottom with an iron weight, were shot through at the waterline with the estuarine shipworm borer.
This damaging organism, Bankia gouldi, is not a worm at all, but a mollusk like clams and oysters. It has evolved until its shell has become a mere scraper that grinds a pencil-size cavity through wood along the grain, through which it trails its vermiform body, lining the bored tunnel with smooth calcium.
At first, the only sign of their presence are pinhole-size entrance ports through which they extend siphons for breathing. Their more southern and higher salinity cousin, Teredo navalis, is the ship or Teredo worm, which has been feared worldwide by wooden ship mariners in warm seas since antiquity.
At the cove, it was the carving of tide-driven ice floes that eventually opened the outer burrows and exposed the damage from these silent critters. Several pilings were almost completely honeycombed and about to collapse.
When our contractor pulled up the 30-foot pilings, though, the sections below the mud were still perfect and oozed with traces of their original creosote — they would have been perfectly usable were they not now illegal. Their driven ends, hand-sharpened with an axe decades ago, revealed every cut and delicate wood shaving.
Pilings that have been in seawater for many years host a remarkable living community incorporating scores, even hundreds of species. While they are a fascinating empire of creatures, one of their important roles in the ecosystem is to destroy wooden structures, lest the seas at some future time fill with debris. It’s only because of the toxic content of treated wood that their work is slowed over the decades and these structures persist.
Creosote, a toxic coal-tar product, is a “distilled” mix of about 700 chemical compounds, many of which have now been determined to be teratogenic or carcinogenic. Creasote is a byproduct from coal during the production of coke for steel refining and the “gasification” process that used to produce gas for lighting and heat in cities.
Creosote was marketed as a preservative by entrepreneurs such as Peter Reilly, who purchased his first distillery in 1896 and developed the Reilly Still, which produced more and better creosote oils than his competitors. Immersing wood in a tank of this stuff under extremely high pressure impregnated the entire timber — and usually resulted in the heavy toxic contamination of treatment sites. A number of these sites are in the Chesapeake, from St. Mary's County in Maryland to Virginia’s Elizabeth River watershed.
Ship timbers were not pressure-treated with creosote and suffered a different fate.
Across the creek from my cove is an unnamed backwater we call “Wreck Cove” because it holds the remains of Henrietta Bach, a schooner from the late 19th century. She was run into the shallows and abandoned during the Roaring ’20s. Neighborhood children at that time called her the “pirate ship,” alluding to her purported final role as a rum runner.
She appears in the background of photos taken from a neighbor’s yard up until the late 1930s, with some paint still on her and one mast still standing.
In the 1970s, we scuba-dove on her long-submerged remains. There were only suggestions that this had once been a ship, and it was only during winter’s clear cold water that her opened skeletal form could be seen from the surface.
The reason, of course, was the work of fouling organisms boring and chewing into wood cellulose. Once-solid timbers of pine and oak became a fragile honeycomb and fell apart.
In the late 1980s, National Geographic’s Emory Kristoff, one of the world’s best underwater photographers and explorers, brought a remote underwater survey vehicle to St. Leonard Creek and mapped her bones. The survey of the Henrietta, was a cornerstone of Maryland’s present underwater archaeology program.
Each year, Henrietta becomes less and less identifiable and the worms are running out of places to burrow. Soon, she will be only traces on the bottom.
Fifty miles away in the Chesapeake, and not far from Annapolis, lies another and very different wreck from the turn of the 20th century. She is the Herbert D. Maxwell, 186 feet-long. She was built in 1905, and in 1910 was struck by the steamer, Gloucester, and sent quickly to the bottom — in deep water, not in the shallows.
Hopes for raising her were entertained in 1912, but her mastheads, which were a hazard to navigation, were broken off and she was subsequently forgotten.
In 1996, scientists from EdgeTech, in Milford, MA, discovered the Maxwell wreck and later shared an image they’d taken using a sidescan sonar, essentially an underwater sonogram of this ship’s hull lying deep in the lightless Chesapeake Bay. She was in remarkable condition after being submerged for eight and a half decades. How had she survived?
Since colonization and later agricultural and industrial development, increasing loads of nitrogen and phosphorus-laden sediments have entered the Bay from its tributaries. These loads have led to an increase in algae blooms that rob the water of its oxygen as they decompose and sink to the Bay’s bottom.
Since early in the last century, a vast, deep reservoir of oxygen-deprived water has occurred in the Chesapeake beginning in May and sometimes lasting into November on an annual basis — a phenomenon that does not appear to have been a regular condition of the pre-colonial Bay.
These waters bathe the Maxwell wreck for months, and while fouling organisms may get a foothold in the spring, and perhaps briefly in autumn, they’re soon smothered and die for lack of oxygen.
This has served to protect the ancient ship’s timbers, which are intact, and eerily preserved in the Bay’s depths.
The Bay’s earliest ships did not fare so well. The pinnace Dove, which brought settlers to Maryland in 1634, became embroiled in a court case the subsequent year, during which she was abandoned by her captain in a Virginia creek during the hot summer. By the time the matter was settled, she had become worm shot.
She was nonetheless laden with valuable cargo and sent to sea. The gamble was ill made on a ship with worm shot timbers and the Dove and her crew were never heard from.
Maryland shipwright Jim Richardson built a replica of the Dove in the 1970s. It was installed as an attraction at St. Mary’s City — the site where the original ship had discharged her people and equipment — which was undergoing archaeological reconstruction.
The budget was tight a few years later and a decision was made to forgo the annual process of hauling her out and repainting the bottom with antifouling paint. Within a year or so she’d suffered the same fate as her namesake: Many of her heavy planks were thoroughly honeycombed by shipworms, and they were faced with carpentry bills of more than $100,000, many times the cost of painting her. That mistake has never been repeated.
The danger of shipworm and of wood-boring crustaceans, generically called “gribble,” have plagued mariners since antiquity. The Phoenicians, seafarers who occupied the Western Mediterranean around 1250 B.C., used copper strips to inhibit fouling. British naval vessels in the 18th and 19th centuries copper-sheathed their entire bottoms for protection, a very expensive proposition.
Athenians around 500 B.C. and centuries later, the Venetians, used to roll their galleys out of the water between uses, both to dry out a waterlogged ship, and to remove the threat of worm and fouling.
Well-made Greek galleys therefore lasted 20 years, and in one case, more than 25, while the better Venetian ships lasted an average 13 years. Poorly built ships survived hardly half that time.
From the 15th century on, large trading vessels and naval ships became too large to be easily hauled. Bottoms were painted with tar or pitch, a byproduct of the charcoaling process.
Ship planks were also smeared with hot tallow, stiff and waxy when chilled by seawater, which also reduced friction. Vessels still had to periodically be taken into a dry dock, though, to be scraped of their prodigious load of accumulated barnacles and other growth, where they were also checked for the worm.
Ships away from such facilities were taken into a quiet backwater, and “careened.” In this process, the ship’s contents, much ballast and most of her rig were backbreakingly removed to float her as high as possible. Tackles to anchors or other solid supports ashore were then used to haul her down — roll her on her side — to expose half of her bottom for cleaning.
This might include burning — slightly charring the cleaned planks to dry and kill embedded worms, a process frequently aided by the hot tropical sun. She was then tarred and/or tallowed and refit for sea.
Often this involved replacing a plank or two that were affected by worms. For some reason, worms tend not to cross the boundary between adjacent timbers. For this reason, the keels of ships, which are most likely to have their protective coatings scraped off in grounding, were covered by a separate, sacrificial timber called the worm shoe.
Another alternative to careening was to run ships upriver into fresh water where all marine growth and borers would die in a few days. William Vernon, a late 17th century colonial naturalist records that the ship on which he sailed was run up Maryland’s Tred Avon River in summer to “avoid the worm.”
Ships with clean bottoms sail faster, deliver more timely cargoes and outmaneuver adversaries in combat. As power-driven vessels were introduced and speed and operation costs rose, the concept of drag became better understood and it was quickly perceived that wetted surface (the actual area of bottom in contact with the water layer) was directly related to the power needed to drive a ship. A thick layer of barnacles or other critters, each a little pyramid of roughness, adds a lot to the surface area of a clean bottom, dramatically slowing a ship’s progress.
The fouling by marine growth took on different dimensions with the proliferation of steel-hulled ships and later in the 1950s, aluminum or fiberglass resin hulls. While the threat of marine borers was removed, though, there still the matter of drag.
By the 19th century, an alternative to expensive copper sheathing — which worked very well — was developed. An antifouling paint with a suspended copper oxide (cuprous oxide) containing a fine, micromilled suspension inhibited the formation of the initial bioactive slime layer that attracts and paves the way for more substantial or damaging marine growth.
These soft paints, which could be lightly scrubbed and thus stay clean a relatively long time, would eventually wear off. Therein lies the rub: Copper bottom paints work only as long as the fresh copper oxide, exposed at the surface, inhibits the growth of fouling organisms. Once the paint is all or nearly gone, fouling and boring organisms can have a field day that begins as the surface becomes less toxic.
First, a transparent slime of bacteria appears followed by a succession of other organisms colonizing and roughening the hull on a microscopic scale.
Among the first of these bacteria in Chesapeake waters is a relatively pollution-tolerant diatom called Schizonema grevelleii, the cells of which grow like railroad cars in a mucous tube. As fouling progresses, barnacle cypris larvae smell the colonized surface and decide it’s safe to attach to and grow into their characteristic volcano shapes. Later in the season, minute animals called bryozoans form spreading, crust-like colonies. The roughness of this colonial growth, even at a few millimeters height, can quickly take 10–15 percent off a vessel’s speed, adding thousands of dollars a week in fuel costs for commercial shipping.
For a time, preparations were tried that would make the paint surface simply too slippery to allow growth. These included a bronze (copper alloy) paint that one polished to a smooth glow before launching; coatings layered atop the copper paint that would hydrate in water to make a slippery gel surface; and Teflon additives. In the end, none provided the enduring solution mariners had sought for thousands of years.
Modern chemistry has developed some astoundingly toxic materials to inhibit biological growth. One is a class of chemicals: tributyltin fluoride, tributyltin oxide or TBTs.
For a while, industry used quite a bit of these chemicals. And, because of their persistent toxic releases, they seemed the ideal base for marine antifouling bottom paints. I used them myself. Manufacturers claimed that the paint would last at least two, and maybe even three years between coats.
In the mid-1970s, when copper paints sold for $25 a gallon, TBT paints cost $100.
For the commercial fleet, paints were compounded to give five or more years of continuous service. Copper paints also caused electrolytic corrosion on unprotected aluminum hulls, popular for light military craft and many workboats serving offshore oil rigs. Nonmetallic Tributyltin paints did not cause corrosion.
Clean bottoms, high speed, profitability, maneuverability in combat: Fouling seemed to be a thing of the past — until French biologists noted a distortion in oyster shells and traced it to TBT, along with a variety of other unanticipated and unstudied ecological effects.
In U.S. studies, notably at the Virginia Institute of Marine Sciences, researchers found toxic levels of TBT around and downstream of marinas with large numbers of TBT-painted boats. The fight to stop yet another contaminant from accumulating and having persistent effects in the Chesapeake Bay began.
The EPA and partner agencies eventually engineered a ban on the sale or use TBT paints in this country, except for aluminum boats and the retractable aluminum alloy outdrives used on many motorboats. Even for these, a pesticide applicator’s license is required, and the paint formulas are in a binder coating that, like some of our medicines, gives a timed release of the active ingredient, enough to supposedly control fouling without fouling environment.
For the world merchant fleet, though, no such ban has been achieved, and vessels on the high seas still use TBT paints. Thousands of shipyards, especially those in tropical seas bordering third world countries, scrape and sandblast residuals and generously apply these paints.
Antifouling paints for the U.S. market today again tout high concentrations of copper. But remember, it too is a widely dispersed toxic in the Bay and other waters.
Nowadays, that initial slime layer is inhibited using additives, some as simple as the antibiotic tetracycline, which are added to many top-of-the-line paints. One can easily spend $150–$170 a gallon, even at discount suppliers.
The protection of pilings, bulkheads and other wooden shoreline structures in the era after the creosote ban shifted to wood protected with the CCA (copper-chromium-arsenate) pressure-impregnated product we see in today’s treated wood with its 20-year to lifetime guarantees for ground contact.
The marine stuff has a higher concentration of CCA than what is generally available for homeowner use. I’ve seen wood treated with this product survive 17–25 years of immersion.
Just recently, the EPA announced that this product will also be removed from the market by the end of 2003.
One study is looking at copper napthenate, a preservation compound first discovered in Russia in the 1880s. Forest products treated with this compound did well after 12 years of exposure.
After that, where does marine construction turn? Possibly to recycled plastic piling cast around reinforcing rods, or hollow spun fiberglass tubes (like some highway light poles) impregnated with polyester, epoxy or vinyl chloride resins.
The Chesapeake Bay Foundation last winter erected a pier at their Bay Ridge, MD, headquarters using several advanced materials, but at an astoundingly high price.
We might also profit from Otto Dubrau — dead many decades — who occupied the original house across Osborn Cove from us. He built a frame of steel-reinforcing rods around which he cast concrete pilings, just a few inches wider at the bottom than at the top.
They were, for at least six decades, impervious to fouling organism damage and safe from being pulled up by tightly gripping winter ice. At low tide, the ice would form, but break away from the taper as the tide rose. They would freeze again at high tide, but as water level fell, the wedge action of the taper would break it apart.
They never failed, while driven wood pilings all around were jacked up, tide after tide, sometimes 12 feet.
Sometimes the old ways, simply conceived and executed, just might be best.