Alternative fuels and energy efficiency: two sides of the same coin

In its Energy-efficiency measures and technologies report, DNV estimates that a 10% reduction in speed for a displacement vessel could yield a reduction in fuel consumption by 27%. But such a speed change must also be balanced with commercial considerations, and while an operator might have the option, it will have to be evaluated with all stakeholders in mind. “However, to assess the total fuel saving on a voyage basis, one should consider the possible need for a larger fleet to carry out the transport work, yielding a total fuel saving typically between 10% and 20%,” says DNV.

And, as Mr Koehne rightly points out, wind-assisted propulsion systems (WAPS) are gaining a strong following, with some of the best use cases in large bulk carriers and small- and medium-sized tankers, with projections of 5-40% in efficiency gains.

“High-performance coatings have the largest impact on energy efficiency”

“Wind is the only energy source which delivers truly well-to-wake zero-emission propulsion power. It is entirely cost-free and thus future-proof,” says DNV.

High-performance coatings that can effectively minimise biofouling growth between drydockings have “by the far the largest impact on the energy efficiency of a vessel,” says DNV. The class society estimates capex of between US$50,000 to US$600,000, but efficiency gains of 2-8%.

And speaking of a ship’s bottom, air-lubrication systems (ALSs) that create a carpet of microbubbles on the bottom of a hull have seen a strong uptake in the LNG carrier and cruise ship segments. The capex for such systems can be expensive — between US$500,000 and US$3.5M — and existing vessels will be required to go into drydocking for a retrofit.

But DNV estimates an efficiency gain of potentially 8%.

“Some technologies work better than others for certain segments,” says Mr Koehne. “We are fuel and technology agnostic, and we set rules and notations to ensure that they are used safely.”

Mr Koehne emphasises that it is vital for ship operators to undertake energy efficiency measures now to prepare for the tougher road ahead, involving higher-cost carbon-neutral fuels with lower energy densities. These more expensive alternative fuels will need to be adopted to lower the cost of compliance with FuelEU Maritime, the EU Emissions Trading Scheme, and IMO’s GHG Fuel Intensity and carbon pricing mechanism.

And all the alternative fuels will require substantially more storage space onboard than conventional marine fuels: methanol (2.5 times), LNG (1.9 times), ammonia (4.5 times), liquid hydrogen (eight times) and compressed hydrogen (13 times).

Ship operators should plan their decarbonisation strategy in parallel paths, says Mr Koehne: “What alternative fuel are you going to adopt? What are you doing now to lessen the amount of fuel you will need to burn?”