A cruise ship typically spends from $80,000 to $200,000 per day on fuel, Belgian-based Subsea Industries said in a note to highlight its coating – Ecospeed.
An analysis in the Second IMO GHG study explained fuel’s usage: “43% of the fuel energy is converted into shaft power, while the remaining energy is lost in the exhaust or as heat losses.
“Due to further losses in the propeller and transmission, only 28% of the energy from the fuel that is fed to the main engine generates propulsion thrust in this example. … The majority of these remaining 28% are spent overcoming hull friction….”
Hull friction is the enemy of fuel efficiency, Subsea said. A very high percentage of the energy generated by a ship’s engines is expended in overcoming the resistance to the ship’s hull, as it moves through the water.
Assuming that the hull has been efficiently designed and built, there are two main factors that contribute to the fuel efficiency, or inefficiency:
- The roughness or smoothness of the hull itself which, assuming the ship has been well built, comes down to the paint, its application and its maintenance over time.
- The degree of biofouling accumulated on the hull.
Ensuring that the hull coating is smooth and remains so, and keeping it clean of biofouling, – even a small degree of accumulated slime – can save as much as 20% of the ship’s fuel consumption or more.
In the case of heavy fouling, the fuel penalty can be 80% or higher, Subsea said.
The company explained that there were three main types of underwater hull coatings in use today:
antifouling coatings (AF), which leach poisonous substances into the water continuously to kill vegetable and animal fouling before it can attach;
foul release coatings (FRC), which have a slick surface which biofouling cannot easily attach to and which is designed to release any fouling that does accumulate when the ship moves, particularly at speed;
and hard, inert surface treated composites (STC), which provide a hard, smooth surface which does not degrade over time and which can be cleaned in the water to remove accumulated fouling without harm to the coating or the environment.
The biocidal antifouling coatings are by far the most common.
Within the third type of coating comes Subsea Industries’ Ecospeed, which is a hull coating system designed to fully protect the hull for the life of the ship without need to repaint, while achieving maximum fuel efficiency throughout the ship’s lifecycle, the company claimed.
As it is entirely non-toxic, it avoids any contamination or pollution of the marine environment.
Ecospeed is a system consisting of a hard, inert glass platelet reinforced vinyl ester resin combined with in-water cleaning as needed to keep it free of biofouling.
The main characteristics, which distinguish it from conventional antifouling and foul release coating systems, include:
- Designed to last the life of the ship without any need to repaint. Minor touch-ups to repair mechanical damage are very easy to carry out, and leave the repaired coating as smooth as the original.
- Does not emit any contaminants into the water, such as copper, zinc or other heavy metals, biocides such as pesticides or herbicides, PFAS or microplastics. It has been tested and proven to have no harmful effect on the marine environment.
- Can be cleaned as often as needed in the water without any damage to the coating or loss of thickness and without any harm to the environment. Any degree of fouling can be safely removed. The coating is restored to its original smoothness.
- Cleaning the coating underwater using the correct tools also has a buffing effect, which will make the hull smoother over time. Trying to clean a conventional antifouling or foul release coating damages the coating, particularly if macrofouling has to be removed. Barnacles and other fouling organisms can penetrate the softer AF and FR coatings, whereas with Ecospeed they cannot.
Claimed to be a notable fuel saving success by using Ecospeed was a major cruise line, which applied the coating to four ships in its fleet.
First, two existing vessels were recoated during routine drydocking. The ships sailed mostly in the Caribbean where fouling is fairly rapid.
They were cleaned every six to 10 weeks on average in order to maintain maximum fuel efficiency.
The company’s President said publicly that these Ecospeed coated ships were saving 10% fuel costs, compared with their previous AF coating.
Based on this success, the cruise line applied Ecospeed to two newbuildings, claiming an even greater success.
Because Ecospeed is durable and designed to last, when the ships drydocked there was no need to repaint – at most just some minor touch-ups of mechanical damage.
The cost of cleaning the ships eight to 10 times per year was dwarfed by the fuel savings. plus the additional savings of drydock fees, offhire time, materials and labour required in maintaining the AF coating that the company had previously used.
Subsea Industries also said that when deciding to switch to Ecospeed or apply it at the newbuilding stage, it is vital to take the cleaning requirement into consideration.
As the coating does not leach any poison, it will accumulate biofouling. This will occur at different rates depending on the ship’s sailing pattern and operating environment.
For example, ships operating in the tropics will require cleaning much more often than those sailing in ice conditions.
Each ship’s situation is discussed with Subsea Industries to decide on out how the cleaning requirements will be met.
