Extending the drydocking interval to 10 years

Drydocking a ship is a complex, expensive, time-consuming and stressful activity, regarded by most ship owners, operators, officers and crew as a necessary evil. Time spent in drydock is time spent out of service. It is becoming increasingly difficult to find drydock time available when and where one would like it. 

Drydocking often takes a vessel well away from its normal operating route. Many different activities need to be scheduled for accomplishment during a drydocking and these activities may interfere with each other. The weather can be an important factor, particularly since drydocking usually involves painting.

That drydocking is necessary is not in question. In order to keep ships operating safely and efficiently for 25 years or more they have to be taken out of the water periodically for inspection and any needed repair. What is in question is how often this needs to occur. Technology is advancing and conditions which were prevalent twenty or thirty years ago are not necessarily present today.

Currently the usual interval between mandatory drydocking for most ships is five years, depending on type and age of ship. This has been extended to seven and a half for certain ships. A ten-year drydocking interval is a dream for most ship owners, operators, officers and crew – one which, if it could be attained, would reduce operating expenses and lower the cost of marine transport.

The challenge to extending the drydock interval


The main challenges to a ten or even twelve year interval between dockings are hull protection and fouling control. By “hull” here is meant the entire external underwater part of a ship including the wetted hull, the rudders, propulsors, stabilizers, thrusters, sea chests, bilge keels, cathodic protection system and all the other external, submerged features and appurtenances of a vessel.

The continual attack by salt or fresh water, cavitation, oxidation, abrasive particles (gravel, lava, sand), ice and occasional solid contact renders these parts of a ship particularly prone to damage, erosion, corrosion and general reduction or weakening of the steel, aluminum or other material from which they are made. Salt water is potentially more damaging than fresh.

The accumulation of biofouling in the form of plant and animal life which naturally adheres to any submerged object, manmade or not, causes the hull to become rougher and can also damage the protective coating. This in turn adds friction or drag to the hull and propellers. The result is that more fuel must be burned to achieve the ship’s cruising speed. The rougher the hull and propellers become, the higher the fuel penalty incurred. This not only shows up in higher costs to the operator but also in increased environmental impact through additional noxious gas and particulate matter emissions resulting from the higher fuel consumption. With conventional coatings, the longer the vessel remains out of drydock, the rougher the hull will become.

In addition to this fuel penalty, biofouling on the ship’s hull has recently come to be regarded increasingly as a vector for the translocation of invasive, non-indigenous marine species from one environmental zone to another. Precautionary guidelines and regulations are being proposed and enacted to combat this threat. In general terms, the more fouled the hull, the greater the risk of spreading NIS.

Answering the challenge


The protection of the hull over a ten or even twelve year period can be accomplished with Ecospeed. This coating system of hull protection and fouling control can easily last for ten or twelve years without any need for drydocking. It can keep the ship’s hull well protected and virtually free of biofouling for that length of time, avoiding the fuel penalty and preventing the translocation of NIS.

Ecospeed is non-toxic and environmentally benign. It is also cost-effective and will, when standardly applied and maintained, result in considerable savings for both owner and operator over the service life of a ship when compared to conventional coating systems.

We have published a White Paper that focuses on hull protection and fouling control to lengthen the interval between mandatory drydockings. If you are interested in receiving a digital or printed copy of this White Paper, contact us at 
info@subind.net or +32 3 213 53 18.