While the global shipping industry looks to clean up its act, more should be done

Shipping is coming under increasing environmental pressure; not only from regulation but also from charterers and owners of cargoes, many of whom want to demonstrate their own environmental credentials by using ‘cleaner’ transport.

Shipping already offers a low carbon solution, with legislation driving reduced outputs of harmful exhaust emissions. And there is legislation governing the discharge of oily waters, sewage and ballast waters, along with rules governing the carriage of heavy fuel oils in ecologically sensitive areas, such as the Arctic/Antarctic.

However, much more can be achieved given that two significant areas of marine pollution have gone undetected by the regulatory radar. Take two examples: the discharge of operational lubricating oil from ship propeller shafts and the transfer of non-indigenous marine organism via the ship’s hull.

Let us first consider the impact of operational oil pollution on the ocean environment. Propeller shafts need bearings for support, and bearings need lubrication. As sealing materials improved, ships began to use stern tubes filled with mineral oil – a highly effective lubricant, and one which enabled the use of metal bearings, offering a far longer life than the original seawater-lubricated bearings made from lignum vitae.

However, over time the seals which prevent the oil leaking out into the sea become worn or damaged, and the lubricant escapes to pollute the oceans. A typical stern tube contains around 2000 litres of oil. Studies suggest that the global fleet can, in total, leak as much as 15 million litres per year of lubricant into port waters. Assuming that similar discharge rates occur when the ships are on the move, then it is not unreasonable to estimate that some 60 million litres of oil leaks into the oceans every year. 

The effects of this leakage can be mitigated to some extent by using environmentally acceptable lubricants (EALs), as mandated for many vessels under the US Environmental Protection Agency’s Vessel General Permit rules. Similarly, the IMO Polar Code prohibits any discharge into the sea “of oil or oily materials.” But not even EALs solve the problem.

These are typically synthetic oils that create the same hazards to wild life as their mineral oil cousins. What’s more there is concern that these so called biodegradable lubricants fail to biodegrade in extreme cold temperatures. EALs are also several times more expensive than mineral oils, and are not always compatible with conventional seal materials. Seals can still be damaged, and shipowners are not only required to report any discharge, but can be held responsible for clean-up and disposal.

For these reasons, and with an increasing trend for expedition type cruising in the polar regions, many shipowners are looking, once again, to seawater-lubricated systems. In the US, the EPA recommends that all newbuild vessels should endeavour to use seawater-based systems for stern tube lubrication “to limit the discharge of oil to the aquatic environment.”

Advances in bearing design and use of new polymer bearing materials, have made seawater-based stern tubes viable under modern conditions, and give these systems similar performance and life-expectancy to oil-based systems.

Craig Carter, of Canadian stern tube bearing system specialist Thordon Bearings, points out if seawater itself is used as the lubricating medium and returned to the sea, there is no need for storage of mineral or synthetic lubricating oils or indeed disposal of contaminated oil.

To help raise concern about the impact of operational oil seeping into ocean environments, Thordon Bearings was invited in December 2016 to present a paper to representatives of international organisations, government agencies, industry and academia attending the World Ocean Council’s fourth Sustainable Ocean Summit.

In addressing more than two hundred SOS16 delegates, Carter explained that the fleet of 48,000 ocean-going vessels that continue to operate oil-lubricated shaft bearings are estimated to be leaking the equivalent of five Exxon Valdez oil spills into the ocean year-on year.

Acknowledging the raft of environmental challenges shipowners are already faced with, he said that the shipping industry must decide whether ocean sustainability can really be achieved with the continued use of a system that discharges between 130 million and 244 million litres of operational oil into the ocean environment every year.

Falling short of calling for an outright ban on these systems, Carter said: “Shipowners have a decision to make – continue to use oil systems that have the potential to pollute and may not meet pollution regulations or return to seawater lubrication. Since we started installing seawater lubricated bearing systems in the early 1990s, we have prevented over 65 million litres of oil being discharged into our oceans and seas. A seawater lubricated propeller shaft bearing system is the only system that guarantees compliance with all pollution regulations and has zero impact on environment.  Isn’t it time we prevented propeller shaft discharges of oil from all commercial ships?”

The annual event brought together ocean industry leaders from shipping, oil and gas, fisheries, aquaculture, ports, mining, insurance, finance, renewable offshore energy, tourism, shipbuilding, marine technology and other industries.

Authoritative presentations were given on 15-year projections for 14 ocean business sectors, many of which were delivered by the heads of global industry associations, including UNESCO, the World Bank, IMO, WWF and the European Commission.

The results of the Ocean 2030 session will now feed into WOC and ocean business community efforts to address ocean sustainable development and the Sustainable Development Goals of the UN, especially for SDG 14 on the Ocean.

Carter concluded: “Today, a seawater lubricated propeller shaft bearing system offers considerable advantages, not only in bearing wear life predictability and reliability, but they are also cheaper to maintain, easier to install, have absolutely zero risk of pollution and are future compliant.”

The other area of marine environmental concern that has gone largely unnoticed by the shipping community is the spread of invasive aquatic species by way of the ship’s hull.

While the large-scale transfer of invasive organisms – a phenomenon that has resulted in outbreaks of cholera in some areas – is now being addressed with the implementation of the International Maritime Organisation’s Ballast Water Management Convention, there is no legislation governing hull biofouling.

The fact that hulls need to be kept clean from biological fouling is well known. Fouling itself has environmental consequences of course: increased resistance through the water leads to more fuel being burned, and hence more exhaust emissions. But there are other considerations.

Traditional antifouling coatings work by leaching a small amount of biocide throughout the life of the coating. The biocide is designed to kill organisms that would otherwise attach themselves to the ship. That means, of course, that toxic matter is slowly released into the water. In mid-ocean, this is usually of little consequence, but in ports and harbours, or around anchorages, the problem can become severe.

Another consideration is transporting alien species. The role of ballast water in this respect is well known, but organisms are carried on the ship exterior too. A study, published in2017 (Gewing, M-T, Marine Pollution Bulletin (2017), http://d.doi.org/10.1016/j.marpolbul.2017.05.041) by Mey-Tal Gewing and Noa Shenkar of Tel Aviv University, looked at the magnitude of marine vessel infestation by non-indigenous ascidians (NIAs) in the Mediterranean.

The study looked at 45 drydocked vessels of various types and sizes. Around half of these showed evidence of non-indigenous invertebrates. Military vessels proved most prolific, while certain areas of ships, such as sea chests and propellers, exhibited the highest occurrence of NIAs. It noted that this is far from a new phenomenon – marine invertebrates have been ‘hitch hiking’ as hull fouling since sea travel began, but even so the monitoring carried out for the study showed a first occurrence in the area of one particular alien species, so it is a growing phenomenon. NIAs have a major impact on indigenous fauna, aquaculture and marine infrastructure, and contribute to degradation of the ecosystem and loss of biodiversity.

Conventional antifouling, of the self-polishing type, work by erosion of the paint surface by water currents, and as the paint is eroded, toxins are released, including highly toxic organotins that are known to cause imposex in Dog Whelks and other species.

The study suggests that different types of surface coatings should be considered, particularly for sea chests and propellers but also for areas where there is reduced water flow, and thus limited toxin release.

One such alternative is Ecospeed, from Subsea Industries. This is a two-component hard resin-based coating which is sprayed onto hull surfaces, and gradually hardens, even when in contact with water. Once the surface is fully hardened, it is polished to remove any surface irregularities, resulting in a smooth, non-stick finish, to which it is difficult for NIAs to adhere.

Subsea Industries’ founder and chairman Boud Van Rompay, said: “The NIA threat is increasing because the antifouling systems in use since the TBT ban have been less effective in eliminating hull fouling. There is currently no miracle cure that will, on its own, prevent the spread of NIAs. The only known way of removing the threat is to clean the fouling organisms off mechanically, which is only possible with a hard-type coating. This ensures the underlying protective coating is not damaged. The industry has to consider taking a different approach to hull protection.”

This is a view supported by the research findings. The Monitoring the Magnitude of Marine Vessel Infestation by Non-Indigenous Ascidians in the Mediterranean paper states that “self-polishing hull coatings are ineffective” in controlling biofouling in “hidden and protected” areas.

The research also finds: “The method of rapid high-pressure fresh-water wash fails to provide adequate treatment for removal of invertebrates inhabiting internal hidden areas; especially ascidians, that can survive the dry-docked time outside the water. Of greater concern is that it allows vessels to continue their regular operations and at maximal speed for longer periods; conducting a thorough maintenance procedure every 3–4 years rather than every 1–2 years.”

The need for a more efficient, more environmentally-friendly antifouling has never been greater; particularly since the use of tributyl tin (TBT) in ships’ antifouling has been banned. TBT was a highly effective antifouling, but had adverse effects on numerous non-target species and was, justifiably, described as one of the most toxic substances introduced to the marine environment. The result was other, non-tin based biocides were introduced, mostly based on coper or zinc. Another solution was non-toxic foul release coatings (FRCs), but despite the name these have proved to have toxic effects, resulting from employing organotin compounds, similar to TBT, as catalysts.

Alternative low-adhesion non-stick coatings, would seem to avoid these potential difficulties and should be well worth considering by environmentally-conscious shipowners. Saving fuel, and thence emissions, and minimising risk of NIA introduction can sit comfortably alongside oil-free stern tubes as positive contribution to marine environmental issues.

Van Rompay said: “There has to be mandatory legislation in place to prevent biofouling on ships’ hulls. Hopefully the TUA research will generate greater awareness of the problem and result in appropriate action.”