Biofouling risks on Gulf-delayed vessels

Maritime operators are grappling with a highly volatile, stop-start environment in the Persian Gulf in which fragile ceasefires are frequently overshadowed by renewed blockade activities and prolonged disruptions. As a result, an unusually large number of vessels has remained at anchor there for extended periods with consequences for biofouling and hull condition, explains Capt. Harshvardhan Kumar, Director – Marine Technical Services at Charles Taylor.

Capt. Harshvardhan Kumar, Director – Marine Technical Services at Charles Taylor

AIS data gathered by Marine Traffic puts the number of stranded vessels in the Persian Gulf at 958 as of mid-June 2026, with 602 stranded for 100 days or more.

Whether these vessels return to service in the coming weeks or remain at anchor for several more months, prolonged inactivity or operating levels may have adversely affected vessel hull condition, creating operational, environmental and biosecurity concerns.

What happens to an idle hull

Marine growth begins forming almost immediately once a vessel is in seawater. Within minutes, a conditioning film of organic molecules, proteins and microorganisms develops on the hull. A slime layer of bacteria, algae and diatoms follows within days. Left undisturbed for weeks or months – as many vessels anchored in the Gulf have been – the layer progresses to a macro-community and hard growth of barnacles, mussels, tubeworms, sea squirts and seaweed. If not removed periodically, these organisms multiply rapidly, increasing hull roughness and hydrodynamic drag.

The operational consequences of biofouling include reduced vessel speed and performance, higher main engine loading, increased fuel consumption and a corresponding rise in emissions. According to Jotun’s 2025 report based on a survey among 1,000 shipowners and operators, more than half (50.4%) of shipowners canvassed reported experiencing increased fuel consumption and reduced operational efficiency as a result of biofouling.

Favourable biofouling environment

Several factors present in the Persian Gulf make it particularly conducive to marine growth:

Warm water temperatures. Sea temperatures remain high for much of the year, accelerating the growth of algae, barnacles and other fouling organisms.

Nutrient-rich coastal waters. Busy ports, industrial activities and coastal runoff can increase nutrient availability, supporting biological growth.

Extended anchorage periods. Vessels waiting for cargo, instructions, security clearances or berth availability have remained stationary for prolonged periods, giving fouling organisms sufficient time to establish themselves.

Reduced vessel movement. Many antifouling coatings are designed to perform optimally when a vessel is underway. Prolonged inactivity reduces their effectiveness.

High salinity. Although the Gulf’s high salinity can inhibit some species, many fouling organisms are well adapted to these conditions and continue to thrive.

Biosecurity and invasive species

Beyond operational impacts, biofouling presents a significant biosecurity risk. Fouled hulls can transport invasive marine species across international boundaries, introducing non-native organisms into sensitive ecosystems.

This is a major concern for countries with strict biosecurity regulations. In the Asia Pacific region, Australia enforces comprehensive measures under its Biosecurity Act 2015. Vessels arriving in Australian territory must comply with one of three options: removing biofouling within 30 days prior to arrival; maintaining and implementing an effective Biofouling Management Plan and Record Book or using an alternative biofouling management pre-approved by the Department of Agriculture, Fisheries and Forestry.

New Zealand’s Craft Risk Management Standard similarly requires vessels to be assessed against risk-based ‘clean hull’ thresholds, and to file a Biosecurity Pre-Arrival Report – non-compliance can trigger a Notice of Direction, mandatory cleaning or refusal of entry.

Elsewhere, in California, the California Code of Regulations – via the State Lands Commission’s Marine Invasive Species Program – requires vessels of 300gt or larger to maintain a Biofouling Management Plan and Record Book, and file an Annual Vessel Reporting Form, with vessels idle for more than 45 days flagged for closer scrutiny.

Brazil introduced a framework under NORMAM-401 which has been in force since June 2025. Described as a hybrid between the New Zealand, Californian and Australian models, it enforces a strict threshold of IMO Level 1 where only microfouling, or slime, is permitted.

Impact on vessel performance

For vessels detained or delayed for several months, hull fouling should be considered as a potential contributor to any post-delay drop in service speed, rise in fuel consumption or engine loading, or general deterioration in voyage efficiency. Underwater inspections – by diver surveys or remotely-operated vehicle (ROV) – should be conducted to determine the extent of fouling and identify whether any remedial action is required.

Security considerations

There is another risk from extended time at anchor: the possibility of a vessel being inadvertently used for illicit activities, including the attachment of contraband or other unauthorised items to the underwater hull.

Regular underwater inspections and robust security procedures should therefore form part of the risk management process before the vessel resumes normal trading operations.

The bottom line

The prolonged delays experienced by vessels in the Persian Gulf may have consequences that extend well beyond schedule disruption. Extended idle periods in a biofouling-prone environment can create increased fuel consumption, maintenance requirements and regulatory compliance risks, while also raising significant biosecurity and security concerns.

Ship managers, owners, operators and charterers with vessels that have remained idle for extended periods should undertake hull inspections before returning the ships to service, and ensure compliance with destination-country biosecurity requirements well before arrival. Taking these steps can minimise operational disruptions, protect marine ecosystems and safeguard commercial performance.

Read more like this in the latest issue of DryDock magazine

Capt. Kumar has over 46 years of experience in the maritime industry and began his career as a deck cadet, serving on merchant vessels in various ascending capacities and obtaining his command in 1997. He spent 28 years at sea, 11 of them as a Master on bulk carriers with major global shipping lines where he faced numerous challenging situations. He then hung up his ‘sea boots’ in 2008 and moved to Australia to work as a marine surveyor. Since then, he has undertaken a wide range of marine surveys, including damage assessments, risk surveys, project cargo discharge surveys, investigations into major maritime losses and surveys on behalf of various P&I Clubs.

He is also a Master Mariner, Associate Member of the Association of Average Adjusters, Associate Fellow of the Nautical Institute, Senior Associate of the Australia New Zealand Institute of Insurance and Finance and Affiliate of the Australian Institute of Chartered Loss Adjusters.