Is a ballast water treatment system necessary?

Malcolm Latarche
Malcolm Latarche

30 January 2018


There is a widely held view that all ships will eventually be obliged to fit treatment systems but this is not actually the case. There are a number of reasons why; two are exemptions permitted by the IMO and US regulations and the third is a technical solution which has been sought after for some time but which remains elusive.

To understand why a system may be unnecessary it is first important to understand why ships carry ballast. When a ship is sailing in empty or part laden condition, its ballast system allows the propeller to be submerged ensuring more efficient use of the ship’s engine. Even when ships are in a loaded condition, small amounts of ballast can be used to ensure optimum trim improving fuel efficiency by as much as 5% if the conclusions of developers of trim optimisation software are accurate.

Ballast is also used for other operational reasons on occasions and in special circumstances. Examples include maintaining optimum distances between loading and discharging apparatus such as conveyor belts, altering the attitude of a ship to carry out repairs to the hull while still afloat and carrying out similar actions to raise breaches of the hull above the waterline after a collision or other cause of damage.

A typical ballast system consists of tanks located in the double bottom or void spaces in a double hull or as wing tanks in bulk carriers. In some ships, ballast tanks may be located athwartship between cargo holds. Pumps are used to move the water from the intakes to the chosen ballast tanks although it is possible in many ships to take ballast into the double bottom tanks by gravitating without using the pumps. The tanks are fitted with a means of releasing air as they are filled usually through pipes with a nonreturn valve to prevent water ingress into the tanks from above.
Depending on ship size and type, the number of pumps may vary, large vessels usually have two. The pumps can generally handle all tanks but commonly one serves the tanks on the starboard side and the other the port side tanks, except in times of need or breakdown.

The no ballast ship concept

There have been several proposals for building ships that do not make use of water ballast but the idea has gained little traction. Before the IMO Convention was adopted in 2004, the Japan Ship Technology Research Association had experimented with designs for large tankers that did not require ballast when empty.

The basic principle involved a ship with a wider beam and a vee-shaped hull. There were some successful model tests and the project concluded that such a ship would be perfectly feasible and could prove attractive when the ballast water convention eventually came into force. Later Japanese classification society ClassNK did grant AIP (Approval in Principle) to an adaptation to a MIBS (Minimal Ballast Water Ship) VLCC design developed by Namura Shipbuilding in cooperation with the Shipbuilding Research Centre of Japan.

Namura’s MIBS VLCC design, addressed the challenges via the use of a new hull form, which greatly reduces the amount of ballast water necessary for safe operations. The design reduced the weight of ballast water required in normal ballast conditions by around 65%, paving the way for the use of smaller ballast water treatment systems and reducing fuel consumption.

In December 2017, Lloyd’s Register announced that LNG containment specialist GTT and Dalian Shipbuilding Industry had received approval in principle (AiP) from LR) for their 30,000m³ B-FREE LNG carrier design. At the time, LR said savings in build cost are expected through the avoidance of fitting a treatment system and not having to comply with the Performance Standard for Protective Coatings (PSPC) for ballast tanks, ballast piping, pumps and values.

LR replied to a question from ShipInsight explaining that this ship design also had a vee-shaped hull and while it has no seawater ballast tanks, the ship does have the option for some fresh water permanent ballast. Trim control is provided by various tanks located fore and aft. The distribution of consumables such as bunkers can be changed between to alter trim, and there are also specific fresh water trimming tanks that can be used to alter trim both fore and aft and athwartships during operations and docking.

Yet another proposal would see the return of solid ballast particularly in container ships with the ballast being in containers that would be placed at the bottom of stacks under cargo containers. Such concepts have generally been disregarded by ship operators as impractical and not addressing the issue of ballast being also used for trim adjustments for operational and safety reasons.

On ships built without a treatment system, space requirements for components of the ballast system are minimal. By contrast, treatment systems can make quite large demands on the space available in the machinery area. This may be less of an issue for newbuildings than for existing ships as space can be reserved for a treatment system even if one is not installed at the building stage. It could be argued that all vessels that may have been affected by the deadlines for newbuildings contained in the convention should have been constructed with this in mind although a small number probably have not.