The costs of hull fouling

One of the biggest performance killers that all charterers and owners face is hull fouling. From the first day the vessel touches the water, fouling starts to build up and increases the hull resistance - resulting in reduced performance.

Even minor biofilms affect the hydrodynamics of a ship's hull by increasing drag and, therefore, the required propulsion power. Fouling conditions can grow worse if the vessel has long idle periods or low activity such as frequent stays in port. The rate of growth increases with rising seawater temperature.

Keeping ships’ hulls free from just a thin layer of slime can reduce a ship’s GHG emissions by up to 25 percent, according to the preliminary findings of an IMO study.

But what are the real costs of fouling for a specific vessel and voyage? The costs of fouling is an impossible task to derive from vessel (noon) reports, due to many variables, like wind, waves, currents etc. You will need to correct for these weather effects.

This is exactly what we do with our Digital Twin.

By comparing performance before and after a hull cleaning, while normalising for these weather effects, the impact and costs effects of fouling can be calculated.

Assessing the impact of fouling

One of our clients - a charterer- approached us with the following request:

"We have MV ** on charter, which departed from Brasil to sail to China via Singapore. Vessel's hull is heavily fouled, however Owners did not allow cleaning prior to departure. Possibly Owners may allow us to clean in Singapore [...] So, we would like We4Sea to analyse the performance for this vessel in order to obtain better information about vessel's performance till Singapore and after when she is cleaned."

We4Sea uses a Benchmark Digital Twin and historic operational data to assess the performance of the vessel prior to cleaning. By normalising the actual observed speed for weather effects, we derived the weather-corrected Performance Speed on the first leg to Singapore.

The benefit of using this approach versus the traditional approach of using "Good Weather" periods only, is that this method can be used on any voyage, any time period and any sailing day. Each 15 minutes, we calculate the weather-effect on speed and derive the Performance Speed.

In below plot (red dot), it can be seen that the vessel underperformed significantly, sailing at just 10.3 kn at 20.7 MT/day, versus a Charter Party speed of 12 kn at 20.1 MT/day.


After cleaning in Singapore, we repeated the assessment. The vessel improved her performance significantly, with a Performance Speed increase of 1.3kn for about the same consumption rate (orange dot).

Assessing the costs of fouling

Using current market rates, we can transfer the fouling and following cleaning to impact on costs.

Before the cleaning, costs were US$ 103 per mile. After cleaning, costs dropped to US$93, a decrease of US$ 10 per mile. Based on about 9000 miles sailing from Brasil to Singapore, the fouling related costs for this leg amounted to 90,000 USD.

It must be noted that also after cleaning, the vessel is still above the Charter Party warranted speed and consumption, and only just below the warranted speed and consumption when including a margin for "abouts". The Digital Twin can be used to keep a close eye on developments over the next legs.

The benefits of using a Digital Twin for performance assessments

The benefit of using a Digital Twin to analyse performance of speed-instructed vessels offer great opportunities:

  • Any weather: compared to the traditional approach of using "Good Weather" periods, this method can be used on any voyage and any sailing day.
  • Charter Party: The results can be directly compared to the Charter Party, both with and without abouts.
  • Benchmarking: performance of vessels can be directely compared to other vessels in the same sizeclass.
  • Fast: Results are available in 1 working day.
  • Value for money: The cost impact of inefficiencies become immediately clear.

Are you in doubt on the performance of one of your vessels? Just reach out, we're happy to support!