Emerging Technologies

Frictional resistance hinders a ship from moving through the water. It can be reduced by injecting air bubbles between the stationary and moving water (turbulent boundary layer). This will assist in reducing fuel consumption and CO₂ emissions.

In a similar way to modern cars all electric and hybrid ships use Lithium Ion(Li-ion) batteries for energy storage. This contributes to reductions in emissions. The cost of batteries and installation is high and until battery technology is further developed may be seen more on small, short sea vessels.

This is a technology which has been mostly seen in shore power plants and is at very early development stages for ships. Up to 90% of the CO₂ emissions from fossil fuels can be captured. However suitable storage tanks are needed to transport the very dense carbon dioxide to the specially selected underground geological rocks which are used for long term storage.

These are energy saving devices (ESD) aimed at improving a ship’s propulsive efficiency. There are many different designs which can be positioned ahead of the propeller on the ship’s hull or behind it on the rudder or propeller hub.

The Mewis duct, for example is positioned in front of the propeller along with an integrated fin system. Forward thrust is created as the duct straightens and accelerates hull wake into the propeller.

Some makers claim energy efficiency gains up to 8% but this depends on the type and service speed of the vessel.

A fuel cell provides an electrical output in a similar manner to a battery. However, it does not run down or need charging and has a higher power density and lower weight than batteries.

Hydrogen is fed to the (–) anode, and oxygen is fed to the (+) cathode.

The platinum catalyst activates the hydrogen atoms/molecules to separate into protons (H+) and electrons (e–), which take different paths to the (+) cathode.

The electrons go through an external circuit, creating a flow of electricity which can be used to power smaller vessels such as ferries and river vessels. They can also be used for auxiliary loads on larger vessels or providing shore power to docked vessels.

The high costs of hydrogen as a fuel and the bespoke vessel and storage tank requirements mean that this lower carbon option may need to be incentivised before it’s used more. Fuel cells have been used for small ferries as part of a hybrid system with batteries.

As the name suggests optimisation means finding the best solution with many variables. It can be applied to all vessel types and ages. However, there is a larger potential for saving where the expected operating profile differs from the standard design. A container ship, for example may have been designed for a service speed of 22 knots at a fixed draft. If continued slow steaming is required at less than 16 knots, then hull form and propeller optimisation may be required to gain the best efficiencies which in turn will reduce emissions.

A comprehensive series of model tests and computational fluid dynamic (CFD) assessments are needed to optimise a hull form. In some cases, the costs for this may be in excess of 100,000 USD so by arranging this for a group of Sister vessels it may spread the cost.

Hybrid is a merge of an electrical and mechanical source of rotating energy. There are many different types of hybrid systems in use for ships. But the common denominator is usually lithium ion (Li-ion) batteries. Batteries may be fitted for energy storage to work alongside internal combustion engines or in rare cases hydrogen fuel cells where the batteries are secondary to the main engines and generators.

Power demands placed on ships vary dependent on their mode of operation. The type and trade of the vessel also plays a big part in this. If cargo is carried there may be high load at sea and when coming in and out of port for bow thruster and starting air compressor operation. For typical mechanical propulsion systems with one or two main engines directly connected to the propeller batteries may provide little in the way of fuel savings. However, power take off (PTO) and power take in (PTI) may be useful here.

PTO systems have been around for some time and a shaft generator is a classic example. The propulsion engine’s power is transferred into the electrical network via gearboxes and generators. The stored electrical power can be used in lieu of starting another generator which reduces emissions.

PTI works as part of the propulsion system and more like the operation of a hybrid car seen in the 2020’s. Fully electric mode can be used for limited periods in lower power ranges as an emission free option. Hybrid mode can also be used to add propulsive engine performance where extra power is required.

Hybrid technology is seen more in smaller vessels and ferries at present but as battery technology improves, we may see this being developed for other types of larger ships.

In the same way that an electric car needs re-charging to continue so does a full electric propulsion ship. This can restrict trading patterns for obvious reasons and means that ferry operations such as Fjord crossings with few variables and repeated nature are feasible if there is a suitable infrastructure on shore for charging between crossings. Class rules dictate that there are two independent battery systems so that there is a back-up if one fails.

Batteries can be charged by an AC/DC converter which can be located either on the vessel or ashore.

The below diagram shows a typical layout of battery propulsion for an all-electric ship.

Waste heat recovery systems convert thermal energy from exhaust gases into electrical energy. An exhaust gas boiler may be assisted by an oil-fired boiler to drive a power turbine and /or steam turbine which in turn rotates an alternator.

It’s important to note that waste heat units can be retrofitted, but the cost of fitting, weight of additional machinery, pipework, controls and maintenance costs all need to be factored in.

A container ship, for example which was built with a service speed of 22 knots and now slow-steaming at around 17 knots may not benefit as much from waste heat recovery because of all of the heat from the exhaust gases may be needed for fuel heating or other equipment in colder climates.

There is a potential for a reduction in main engine fuel consumption up to 8% which contributes to emissions reductions overall.

A ship with a lower friction hull coating reduces drag which results in lower fuel consumption and reduced CO₂ emissions. This has always been the aim for hull coatings but recent products such as Nippon paint’s A-LF-Sea (advanced low friction) have brought this onto the next level. The concept was inspired by tuna fish and means that the hull coating uses a hydrophilic compound called hydrogel. The science behind this means that the hull coating traps a layer of sea water into the surface membrane. This reduces friction by increasing the hull’s boundary layer.

Shore power is sometimes referred to as cold ironing. Below you will see a brief description of what’s involved and where it may be used.

When a ship is in port it no longer needs propulsive power. However, many different types of vessels still need energy in port for pumps, control systems, cargo handling systems, heating, cooling, ventilation and IT systems as well as domestic use. Generators are commonly used to provide the required power in port. However, use of shore power may prevent localised noise and air emissions created by generators. Dependant on the energy source shore power may also reduce CO₂ emissions overall.

Smaller vessels with power requirements below 100 KW can make use of normal grid voltage and frequency and a small investment may only be required. For larger vessels up to as much as 15 MW with high power requirements it gets far more complicated with a higher expense.

The required modifications to serve higher power vessels on land and ashore include but are not limited to upgrading grid capacity, frequency converters and complex, high-power connectors. This reduces the amount of ports and ships which can make use of shore power.

It should also be considered that this will only reduce fuel consumption whilst the vessel is in port so recharging of batteries may be possible in addition to supplying power but for larger vessels with internal combustion engines fuel consumptions in port will only represent a very small proportion of fuel used overall. This may translate to a smaller reduction in Co2 emissions when you consider the trading pattern of the vessel.

It may be feasible to provide small amounts of AC or DC power to certain types of ships including car carriers, bulkers, passenger ferries and smaller domestic vessels by using marine grade solar panels. However, this may not suit container vessels because of the space required.

This technology is in its infancy and there are certain development projects also considering the fitting of marine grade solar panels onto the sails to combine solar and wind power.

Sail power on its own will not be the magic solution in achieving a zero-carbon means of propulsion. But if harnessed, wind-assisted propulsion can reduce a vessel’s fuel consumption, resulting in lower GHG emissions. The difficulty of course is harnessing the power of the wind, which seafarers have been tackling for millennia.

Modern wind propulsion comes in a variety of forms and some are already being used on cargo ships at sea.

There are many different types in this North article giving more info on this.