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.
Many studies have identified the effect 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 a cleaning?
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.
The main 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. This means that, with a 30MT daily consumption and a 9% reduction, the savings can be close to 1000 USD per day. With hull cleaning costs of 15 to 20 thousand USD, the payback time is less than a month.
But after a hull-cleaning, the fouling process will be starting all over. 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. With our Digital Twin, We4Sea can help to find the optimal timing.
The Digital Twin will calculate the expected consumption of the vessel, taking into account the draft, speed, and weather conditions. By benchmarking with noon-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.