Barnacles: The Hidden Drag on Fuel, Speed & Cooling Water

Summary: Even thin slime and light barnacle growth can quietly raise fuel burn, slow you down, and choke sea water circuits. Smart biofouling control protects CII, schedules, and your bottom line.

Quick Facts:
• A 0.5 mm slime layer on ~50% hull can raise fuel/CO₂ ~20–25%. [1]
• Light barnacle/tubeworm fouling can push the penalty up to ~55% on a typical container ship. [1]
• Sea chests/strainers & internal sea water systems can clog with barnacles/mussels → hot jacket water & cooler under-performance. [2]
• Propeller polishing typically delivers ~3–4% main-engine fuel reduction (1–3% annualised). [4]

Barnacles roughen the hull, increasing frictional resistance. Result: more fuel to hold schedule or speed loss at constant power either way, higher costs and CO₂; impacts from thin slime to light calcareous growth are larger than once assumed. [1]

Sea chests, gratings, strainers and cooler tubes are biofouling magnets. Growth here restricts flow, raises temperatures and can trigger derates/trips across fleets. [2]

• Protect niche areas: Apply the right AFS and extra attention to sea chests, bow-thruster tunnels, bilge keels, sensors, ICCP, etc. Explicitly flagged in the 2023 IMO Biofouling Guidelines. [3]

• Keep the propeller smooth: Routine polish restores efficiency fast; typical savings ~3–4%. [4]

• Clean smart and compliant: Many ports expect capture/filtration of removed fouling during in water cleaning (IWC); plan permits and documentation. [6]

• Watch the signals: Trend speed–power and sea-strainer ΔP/temps; warm-water idle and long anchorages accelerate fouling and can create charter-party performance exposure. [5]

Can we clean in water?

Hull cleaning is not allowed at Bosphorus/anchorages in Türkiye; it must be done in shipyards/dry dock with controlled waste handling. We arrange urgent dry-dock slots at competitive pricing in Istanbul (Tuzla shipyards), Yalova, Izmit Bay, Ordu, and Çanakkale. [7]

Emergency exceptions (permit-based): If there’s a direct navigational safety risk e.g., sea chest grate blockage or a propeller fault the Harbour Master may allow daylight, fair weather diving/ROV intervention at anchorage; any waste must go to an approved reception facility, and the Harbour Master must be notified after completion. Hull cleaning is not included in this exception. [7]

What we can do in those permitted emergencies:
• Sea chest cleaning & grate clearing [7]
• Propeller inspection, polishing/cleaning, rope /net-removal (case by case, with permit) [7]
• Niche-area cleaning and debris capture/filtration per IMO guidance [6],[3],[7]

Routine & non-emergency work:
For hull cleaning, we book yard/dry-dock and handle method statements, risk assessments, waste logistics, and before/after HD reports. For planning between dockings, we follow IMO in water cleaning guidance with capture and the 2023 Biofouling Guidelines for niche areas. [6],[3],[7]

How often should we polish the propeller?
Depends on trade and water temps; we use condition-based triggers (roughness/ISO class, speed power trend). Expect measurable savings on a rough/fouled prop. [4]

[1] IMO – Impact of Ships’ Biofouling on GHG Emissions (prelim. report): slime 0.5 mm → ~20–25%; light calcareous → up to ~55%.
[2] Davidson et al., 2021, Frontiers in Marine Science: internal sea-water systems biofouling & clogging impacts.
[3] IMO – MEPC.378(80), 2023 Biofouling Guidelines: niche-area focus and risk-based management.
[4] IMO GreenVoyage2050 – Propeller Polishing: ~3–4% ME fuel reduction (1–3% annual).
[5] Britannia P&I (Apr 17, 2025): warm-water idle/anchorage → heightened fouling & performance/charter exposure.
[6] IMO MEPC.1/Circ.918 (Apr 29, 2025): guidance on in-water cleaning and waste capture/filtration.

[7] Republic of Turkiye – Ministry of Transport and Infrastructure, Directorate General of Maritime Affairs. Implementation Instruction 2022/03 (Dec 6, 2022)