How much bunker costs do you spend on hull fouling?

Every ship is facing the same problem: fouling of the underwater part of the ship with algae, seashells, and other marine life. The ocean is full of living organisms, especially well growing in the tropical zone. Several places, such as the South American coast and the Indian Ocean are most susceptible to hull fouling. Two types of hull fouling can be distinguished. Macro hull fouling (by plants and animals) and micro hull fouling (by algae and bacteria).

Many studies have identified the effect of hull fouling on fuel consumption. As fouling leads to higher hull resistance, many owners and charterers periodically clean the hull of their vessels. But what is the impact of hull fouling on the vessel? And what are the effects of a cleaning when the vessel has problems with hull fouling?

Up to 17% fuel savings from periodic hull cleaning to remove fouling

Hull fouling has a negative effect on the performance of the vessel. A 2018 paper investigated the impact of periodic hull cleaning on oil tankers' energy efficiency for a fleet of eight identical Aframax-size crude oil tankers.

Fuel consumption is being affected by hull fouling. Hull fouling can be diminished by periodically cleaning.

The results show that periodic hull cleaning leads to a significant reduction in the daily fuel consumption; dry-docking leads to an even greater reduction in fuel consumption, approximately 17% versus 9% for hull cleanings.

Hull fouling has an indirect impact on fuel consumption and voyage costs. By preventing hull fouling, costs can be significantly reduced. For example, with a 30MT daily consumption and a 9% reduction, the savings can be over 2000 USD per day. With hull cleaning costs of 15,000 to 20,000 USD, the payback time is less than a month.

But after a hull-cleaning, the fouling process will be starting all over. Hull fouling is a never ending process. In a scenario based on a hull cleaning trial, we found the overconsumption was reduced by 10% after cleaning the hull and propeller, deteriorating within eight months to about 5% fuel saving.

These findings show we should be looking at optimization of cleaning intervals. This to diminish the impact of hull fouling on the performance of the vessel. With our Digital Twin, We4Sea can help to find the optimal timing.

How a Digital Twin can help with detecting hull fouling and optimising hull cleaning intervals

The Digital Twin will calculate the expected consumption (Achievable Performance as we call it) of the vessel, taking into account the draft, speed, and weather conditions. This is the performance the vessel would have if she was in good condition. By benchmarking with the Actual Performance (based on the vessel-reported consumption), and trending the difference between the two over time, will give you a clear insight into the trend in performance loss. In the below plot, we show a recent example from a bulk carrier.

The blue bars show the reported main engine consumption, the green the expected consumption as calculated by the Digital Twin.  In April, the two are comparable. After an 11 day anchorage period in Brazil, you can see a large difference between the two. The vessel was sailing at a slower speed and reported consumption was also lower compared to April. But the reported consumption was about 5.5 MT per day higher than expected by the Digital Twin, an additional 2,200 USD bunker cost per day.  

The reported consumption should have been far lower, due to lower speed, different draft, and favorable weather!

This was clearly related to hull fouling, and the charterer ordered a cleaning at the next port.  The reported payback time was about 10 days.

Are you interested in how a Digital Twin can help you in assessing the impact of hull fouling and optimize cleaning intervals?  

Read our other blog on hull fouling or download our Whitepaper about vessel performance or contact us for a personal consultation.