Advantages of a cleanable hull coating (part 1)

Properly implemented, efficient hull cleaning on the right type of underwater ship hull coating is the answer to optimum fuel efficiency, long term hull protection and the elimination of the hull-borne invasive aquatic species problem.

Because of the types of hull coatings in general use on the world fleet, the subject of hull cleaning has become somewhat controversial. Most of these coatings are not suitable for in-water cleaning.

In this article we examine how the Ecospeed hull coating and cleaning system cuts through this controversy and delivers excellent ship hull performance with the advantages of significant fuel savings and benefit to the marine environment.

Historical perspective

Ship hull cleaning for performance is not a new subject.

The Greek author Plutarch (45–125 AD) discusses the benefits of clean ship hulls in his Symposiacs written around 100 AD. 

“…for the ship continuing dry, not yet made heavy by the moisture soaking into the wood, it is probable that it lightly glides, and as long as it is clean, easily cuts the waves; but when it is thoroughly soaked, when weeds, ooze, and filth stick upon its sides, the stroke of the ship is more obtuse and weak; and the water, coming upon this clammy matter, doth not so easily part from it; and this is the reason why they usually calk their ships.”

More recently, in 1770, Captain James Cook on his trip around the world notes in his journal that he was looking for a suitable location to careen (beach and lay on its side) the Endeavour with the sole purpose of cleaning the ship’s bottom.

Later, ship hulls were cleaned by divers using hand and mechanical tools with the ship still in the water. This avoided beaching and careening or the more modern equivalent, drydocking.

Highly toxic TBT in hull paints gave the illusion that ship hull cleaning was an unnecessary thing of the past. It was soon discovered that TBT’s damage to the marine environment was extensive, severe and unsustainable. Nevertheless, during the “TBT era” the subject and practice of underwater ship hull cleaning went into decline in terms of repute, technology, skill and general availability.

Vicious circle

However, the antifouling technology which replaced TBT-laden hull paint was relatively ineffective. All ship hulls develop a biofilm or slime layer at the very least, regardless of the bottom paint used, and this, combined with rough hull coatings which degrade over time, carries with it a fuel penalty of as much as 20% or more. These coatings could not be cleaned without damage to the paint and to the marine environment.

The hull coating industry has created a “damned if you do, damned if you don’t”situation for shipowners/operators which includes frequent drydocking and paint replacement, a built-in fuel penalty, and coatings which are ineffective in preventing fouling yet are not suitable for underwater cleaning (the only practical means of avoiding the fuel penalty incurred).

Today underwater ship hull cleaning thoroughly and efficiently done on an industrial basis and on a suitable hull coating is the answer to reducing fuel costs, cutting GHG emissions, preventing the spread of non-indigenous species while avoiding marine chemical pollution.

Ecospeed was invented to overcome these problems

There are two main liabilities of cleaning conventional AF and FR coatings:

1. Damage to the coating from the cleaning
2. Harm to the local environment.

The coatings in general use are not very tough and they are porous enough for barnacle glue to penetrate the coating scheme, all the way down to the steel. Because they are relatively soft, when one attempts to clean them, the coating is damaged by brushing even if only weed and slime are removed. This reduces the effective life of the coating and more fouling accumulates which then needs to be cleaned off – a dwindling spiral. Underwater high-pressure jets are not effective since they have to overcome the resistance of the water and have a strong repelling force against the hull.

At the same time, cleaning coatings that are laden with heavy metals, biocides, silicone oils, PFAS, and microplastics, results in a pulse discharge of these toxic substances into the water column and the sediment. There they remain until stirred up and resuspended.

Ecospeed, on the other hand, is a hard coating which can be cleaned regularly without losing any thickness and without any toxic substances being released into the water. It can also be high-pressure washed in drydock, but when cleaned underwater with the right tools, the result is a slight buffing effect which improves the hydrodynamic properties of the coating over time. This coating does not need to be replaced. Any mechanical damage can easily be repaired, leaving the surface as good as when the paint was first applied, just slightly smoother. So, ten years down the line, you still have a well-protected hull with the original coating intact and the bonus of better fuel efficiency than when new.

Case in point

One cruise line took the plunge and opted for the Ecospeed coating and cleaning system for four of their ships. They blasted off the traditional antifouling scheme on two ships, applied Ecospeed, cleaned regularly when the hull accumulated slime and light weed and measured the results.

The President of the cruise line was interviewed in Maritime Executive magazine and quoted as saying of the coating: “About five years ago, in an industry first, the [name of ship] had the same [Ecospeed] product applied to its hull and its fuel consumption was reduced by ten percent. The environmentally friendly coating achieves its fuel savings by reducing hull resistance in the water.”

The company went on to use the same system on two newbuild cruise ships with even better results.

There were other advantages of Ecospeed for the cruise line. The officers and crew nicknamed it the “wash and go coating” because when they drydocked, all they had to do was high pressure wash the hull, perhaps carry out minor paint touch-ups and the ship would be ready to sail. No more lengthy stays in drydock for repainting.

Conclusion

Ship hull cleaning has a long history with very mixed results. When the right type of coating is used, it is the answer to high fuel efficiency without any harm to the marine environment.

In a follow-up article we will cover the practical aspects of the coating system, when to clean, how to clean and other technical details.