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Biofouling and greenhouse gas (GHG) emissions from ships

Biofouling on ships' hulls increases hull surface roughness, which in turn increases frictional resistance and ultimately increases fuel consumption and total GHG emissions. The penalty in fuel consumption can vary significantly due to a wide range of technical and operational parameters, but it may be in the order of 2% to 12% for a ship with a modestly fouled hull (refer to chart from Townsin et al, 1986).

Reduction of GHG emissions from ships through biofouling management

Chapter 4 of MARPOL Annex VI, which came into force on 1 January 2013, calls for substantial improvements in ship energy efficiency including both the design of new ships (Energy Efficiency Design Index – EEDI) and the operation of all ships (Ship Energy Efficiency Management Plan – SEEMP). This represents the first ever mandatory global CO2 reduction regime for an international industry sector. CO2 emissions from international shipping in 2012 amounted to 796 million tonnes, corresponding to 2.2% of global CO2 emissions. To reduce CO2 emissions from international shipping, a number of studies have identified measures that could significantly increase the energy efficiency of ships. Amongst these measures, the increased hull roughness associated with biofouling is taken as one major aspect that needs to be controlled or managed, as otherwise it will increase the ship’s frictional resistance and, ultimately, fuel consumption and total GHG emissions. Specific reductions that can be achieved in CO2 emissions from international shipping through the management of ships’ biofouling is dependent on ship type, size, speed and operational profile, making it problematic to generalize. However, estimated energy reduction potentials for a range of biofouling management approaches include from 3 to 8% for propeller polishing, from 1 to 10% for hull cleaning, and from 1 to 5% for the application of efficient hull coatings . As these measures are not necessarily mutually exclusive, the sum of estimated reductions if all approaches were implemented could range from 5% to over 23%. With annual CO2 emissions from international shipping such as outlined above, a decrease of 10% across the entire global fleet could correspond to a reduction of around 80 to 90 million tonnes CO2 emitted on an annual basis. This corresponds to the total annual CO2 emissions of a country such as Greece, Nigeria or the Philippines.

It is generally expected that an average 10% of the High Energy Efficiency gains will be due to the three main measures related to biofouling management:

 

  • advanced hull coating to reduce fouling

  • propeller polishing to reduce propeller roughness and

  • hull cleaning to reduce hull roughness

 

This percentage  is based both on the estimated reductions of 5 to 23% presented by an ICCT White Paper and also the estimates documented in a IMO-commissioned LR and DNV Study.  According to this report, out of the total Ship Energy Efficiency Management Plan (SEEMP) related measures, the hull conditions could account for 8.66% to 13.06% of total CO2 reductions, depending on various ship types and sizes.

Adoption of new technologies and practical biofouling management measures

Measures related to the management of ships’ biofouling such as improved hull coating system and hull cleaning are among the most important tools for the reduction of shipping GHG emissions. Some of these are practical measures that may be relatively easily implemented to new and existing ships, and they do not rely on aspirational, emerging or future technologies. A very important aspect of such measures is their 'win-win' nature, as they lead to reductions in fuel consumption, thereby achieving consequential reductions in both GHG emissions and operational costs at the same time. Combined with their increased practicability compared to other 'tools', this can make these measures more readily acceptable to the shipping industry giving them a realistic potential for more immediate tangible results. However, due to lack of capacity and awareness, the development and uptake of such tools and measures is low in developing countries. Additionally, another barrier for effective uptake of these measures is the perceived impact of such measures on accelerated IAS transfer to local ports. The uncertainty associated with the environmental impact of such practices is real and justified under current circumstances when there is little knowledge or policies on how to deal with relevant issues. It is this latter barrier that the GloFouling Partnerships project will seek to address.

 

The GloFouling Partnerships project is expected to act as a catalyst for the environmentally safe uptake of energy efficiency measures related to biofouling management and will therefore contribute to activities that are underway by the maritime industry in fighting climate change.

 

The economic and cost-effectiveness aspects of hull and propeller biofouling management with regard to GHG emissions reductions are addressed by a number of researchers. Propeller polishing and hull cleaning are amongst measures with significant negative marginal abatement cost levels (for propeller polishing about US $225 per tonne CO2 negative cost, i.e. denoting actual economic saving; and for hull cleaning about US $170 per tonne CO2 negative cost).