Ballast water is a traditional way to improve the stability, propulsion and manoeuvrability of a vessel. Nevertheless, it comes with some downsides which may be ecological as well as economical. So, what can be done to improve this? The answer may lies at removing ballast water systems altogether, adopting ballast free ships.
After the IMO’s Ballast Water Management Convention entered into force in 2017, ship operators are constantly looking for ways to enhance the efficiency of their ballast water systems.
Ballast water is currently vital for safe and efficient shipping operations, however taking up and discharging ballast water can lead to ecological and economic consequences.
These issues are arising mainly from the fact that ballast water contributes to the spread of invasive aquatic species (IAS). These are bacteria, microbes and small invertebrates which enter the ballast water during loading, and get discharged in new locations.
In case they survive, these species have the ability to establish a population in their new environment, competing with existing species. This has reduced fish stocks, and has caused coastal erosion.
Moreover, ballast water treatment can be proven costly. According to BWMC, ships must manage their ballast water in such a way so that IAS are removed or becoming harmless before ballast water is released into a new location.
Naturally, operators are trying to find new ways to implement efficient ballast water treatment systems, in order to prevent the increase of invasive aquatic species.
However, a new trend comes to provide a – previously – unexpected solution. Removing the ballast water systems altogether, using new ballast free ships.
How ballast-free ships work?
Traditionally, ballast water systems increase the weight of vessels in the light cargo condition, improving their stability, propulsion, manoeuvrability, and reducing stress on ship hulls during transit.
A change of thinking in this concept would focus on the use of ballast condition as a change of buoyancy, rather than an addition of weight in order to get the vessel to its safe ballast drafts. This led to the invention of the ballast free ship concept, where traditional ballast tanks are replaced by longitudinal, structural ballast trunks that extend beneath the cargo region of the ship below the ballast draft.
These trunks are flooded with seawater in order to reduce the buoyancy of the vessel while in ballast condition, thus getting the vessel down to its ballast drafts. What is more, due to the natural hydrodynamic pressure differential between the bow region and the stern region of a ship while it moves through the water, a slow flow is introduced in these open ballast trunks.
As a result, the ballast trunks are always filled with slowly moving “local seawater”, limiting the transport of non-indigenous aquatic species across the globe.
Pros & Cons of ballast free designs
As a recent study showed, a ballast free design could eliminate costly ballast water treatment equipment or ballast water treatment chemicals.
In addition, during the full load condition or any condition where ballast is not necessary, the outer ballast trunks would be segregated using valves at each of the cargo hold bulkheads. Its purpose is to provide the vessel enough damage survivability under current IMO requirements.
Moreover, a ballast free ship could have an extended service life, as it will not have to deal with the corrosion that sediment build-up is causing in ballast tanks. This is very important, as it could limit inspection and cleaning times.
Finally, such a ship could have better course-keeping capabilities, as the absence of heavy ballast tanks would decrease slamming impacts in heavy weather.
Nonetheless, ballast free ship designs are facing obstacles. This kind of design can reduce the costs of ballast water treatment, but they may lead to higher hull build costs and operational costs.
Furthermore, many ships have specific dimensional restrictions, which hold the adoption of a ballast free designs back. For example, if a tanker was to have ballast free tanks, it would need to have an increased beam in order to carry the same amount of cargo.
Nevertheless, we have to bear in mind one key thing. The shipping industry is largely conservative. This delays the uptake of the ballast free concept, as many operators are reluctant to launch a new vessel type, especially if they are not sure that it would be seaworthy.
In order to mitigate these problems, a number of solutions have been proposed. These solutions do not include a complete ballast free design, but they aim to minimise ballast discharge. Another solution could be cleaning water at ports.
Are there any ballast free projects?
Despite not being widely popular, ballast free projects do exist.
World’s first ballast free LNG bunkering vessel
Hyundai Mipo Dockyard (HMD) is scheduled to deliver the world’s first ballast free LNG bunkering vessel later this year. HMD considers a special hull form with dead-rise, while the ship will have a forward ‘engine room and deckhouse’ and a twin propulsion system with azimuth thrusters. This will help the vessel retain its damage stability and control the trim and heel without ballasting.
B-FREE LNG carrier
GTT, Lloyd’s Register and Dalian Shipbuilding Industry Corporation launched the second phase of their “30,000m³ B-FREE LNG carrier” Joint Development Project in April 2018.
The first phase of the project developed a design of ballast-free medium-sized LNG carrier, compliant with the Ballast Water Management Convention.
The second phase aims to develop the design further, and validate the initial results. This will be done by applying detailed analysis and verification, including model testing.
Variable Buoyancy Ship
The Ballast-Free Ship concept was invented and investigated at the University of Michigan, as a way to limit the risk of the further introduction of non-indigenous aquatic species into the Great Lakes and other coastal waters by ships arriving in ballast.
A scaled model of a Seaway-size bulk carrier was constructed, in order to optimize the location of the Ballast-Free trunk discharges. This has as a goal to reduce or even eliminate the propulsion power increase.
The design has three longitudinal trunks per side in a deepened hull, able to provide safe operating drafts. The pressure difference between bow and stern induces a flow of seawater that is exchanged about once an hour.
However, Professor Michael Parsons noted that without the usual bulkheads, there were problems regarding the damage stability of the design. For this reason, Mr. Parsons changed the design to include isolation valves to the two outward-most trunks on each side.
Wallenius Wilhelmsen Logistics has developed the idea of ‘E/S Orcelle’, a zero-emission car carrier. The idea includes fuel cells, wind, solar and wave power to propel the vessel, that will need no oil or ballast water. A car carrier like this will never be built completely, but the company hopes to see some of these elements in future vessels.
DNV GL Triality
DNV GL has also developed a ballast free ship. ‘Triality’ is a VLCC whose design is considered as a cost effective alternative to ballast water treatment systems. The ship also incorporates features to protect the environment.