In-Water Hull Cleaning: 12 Proven Ways Shipowners Cut Fuel and Costs

Simple Summary

Teams clean the hull in the water using tools or ROVs that vacuum and filter the waste so nothing drifts into the port. Removing slime and light growth reduces drag, which lowers fuel burn and the emissions bill tied to that fuel. Closed-loop methods make approvals more likely than open scrubbing.

Bang for the Buck

Typical closed-loop cleans run about 12,000–35,000 USD depending on hull size, fouling level, and port rules. If your speed-power penalty is around 3–6 percent and you have 30–60 steaming days before the next clean, the math often works.

Example: at 28 t/day and 650 USD/t, reclaiming 4 percent saves roughly 728 USD per sailing day. A 18,000 USD clean breaks even in about 25 sailing days. Use the quick calculator to test with your numbers and voyage window.

Quick saver — is a clean worth it?

Edit your numbers. Result shows net over the effect window.

If your next voyages are warm water or include idle days, shorten the window and re-check. Add ETS cost if you want a stricter test.

When it pays

• Warm-route exposure where slime returns quickly and ports require capture.
• Higher fuel or ETS costs that make even small penalties worth removing.
• A few weeks before yard to log a clean speed-power baseline for coating choices.

Planner’s notes

• Ask for capture evidence, filtration spec, and waste-disposal paperwork.
• Match tool aggressiveness to coating maker guidance to avoid damage.
• Log before and after noon data at fixed drafts to verify savings.

Permit checklist (quick)

Simple Summary

Proactive grooming wipes off early slime before it turns into drag. Think light, regular passes using soft or brushless tools that respect the coating. Because you never let fouling build up, you avoid heavy cleans, keep speed–power close to baseline, and reduce both fuel and emissions exposure.

Bang for the Buck

Typical grooming runs lower than full cleans because you’re removing slime, not established growth. As a ballpark, plan a few thousand to low tens of thousands USD per session depending on hull size, access, and capture requirements.

In warm routes, a light pass every few weeks can prevent a 2–4 percent penalty from forming. At 28 t/day and 650 USD/t, even preventing 2 percent is about 364 USD per sailing day—enough to justify frequent, gentle sessions if access is easy and port rules are met.

Grooming program: do the numbers

Estimate annual savings from preventing slime vs doing nothing until a heavy clean.

If warm-water exposure and idle days increase, raise “Penalty prevented” or “Sessions” and retest. Keep tools gentle to protect the coating.

When it pays

• Trades with warm water and stop-start schedules where slime forms quickly.
• After drydock to protect a fresh coating and hold speed–power baselines longer.
• Fleets aiming to minimize heavy closed-loop cleans and associated delays.

Planner’s notes

• Confirm port permission. Some ports treat grooming as cleaning and expect capture/containment.
• Use low-abrasion heads and follow coating guidance to avoid warranty issues.
• Log short, frequent sessions; attach photos and noon data to show stability over time.

Program checklist (quick)

Simple Summary

A remotely operated vehicle adheres to the hull and removes slime or light growth while a surface unit vacuums and filters the waste. It lowers personnel risk, helps meet ports’ capture expectations, and restores speed–power without waiting for a yard stay.

Bang for the Buck

Pricing varies by hull size, fouling level, and port rules, but expect low tens of thousands USD for a full closed-loop pass on a large merchant hull, less for partial areas. If you recover 3–5 percent fuel penalty for the next 30–60 sailing days, the net usually beats cost, especially if the port allows work alongside cargo operations.

If growth is heavy or coating is fragile, plan multiple lighter passes or a different method. ROVs shine on large flat areas; niches and appendages may still need targeted tools.

Quick saver — ROV clean vs fuel

Estimate net over the effect window for a diverless, closed-loop clean.

If port rules limit cleaning time or areas, test with fewer effect days. Record noon data before and after to confirm the penalty drop.

When it pays

• Ports or terminals that prefer diverless work and require capture/filtration.
• Tight port calls where coordinated cleaning can fit around cargo operations.
• Fleets seeking uniform quality and repeatable results across multiple ports.

Planner’s notes

• Ask for filtration details, capture efficiency, and waste handling documents.
• Confirm tool aggressiveness and pressure settings are coating-safe.
• Plan separate treatment for niche areas and appendages if the ROV head is too large.

Permit checklist (quick)

Simple Summary

Divers guide cleaning heads that are connected to a vacuum line, so removed slime and growth are captured and filtered topside. This method reaches niches, weld seams, sea chests, and complex curves that larger machines miss. With proper settings it restores a clean surface without damaging the coating.

Bang for the Buck

Costs range from several thousand USD for targeted areas to low tens of thousands for a full pass, depending on hull size, fouling level, and filtration spec. If you recover 2–5 percent fuel penalty for even a month of sailing, it usually pays for itself. It is also often the only practical way to clean niches under capture rules.

Example: at 26 t/day and 600 USD/t, reclaiming 3 percent saves about 468 USD per sailing day. A 15,000 USD job breaks even in roughly 32 sailing days, sooner if warm routes or ETS costs are high.

Quick saver — diver clean with capture

Estimate net over your effect window using simple inputs.

If visibility, current, or terminal restrictions limit progress, reduce effect days and retest. Log before and after noon data to confirm the penalty drop.

When it pays

• Ports that allow divers under capture rules and need niche areas handled well.
• Mixed fouling where selective, gentle passes beat a single aggressive clean.
• Short port stays where divers can work parallel to cargo ops under permit.

Planner’s notes

• Request capture and filtration specs plus waste-disposal documentation.
• Coordinate with terminal and pilotage for diver safety and VTS notifications.
• Match head pressure and abrasiveness to coating guidance. Use softer tools on fresh coatings.

Permit checklist (quick)

Simple Summary

In-water propeller polishing removes slime and micro-roughness from the blades so they slice water cleanly again. A smoother prop needs less power for the same speed, which lowers fuel burn and emissions. Keep passes gentle and finish fine; the goal is smooth, not metal removal.

Bang for the Buck

Typical in-water prop polishes cost a few thousand USD per visit, scaling with diameter, location, and access. Even a modest 1–2 percent shaft-power reduction can pay back in days on a laden service speed. Many fleets schedule a polish every 1–3 months on warm routes, or after fouling exposure.

If blades are heavily pitted or nicked, polishing cannot fix geometry; plan repairs at next yard. Avoid aggressive grinding that removes material or affects class tolerances.

Quick saver — prop polish vs fuel

Estimate daily saving, breakeven, and net over the effect window.

If routes are cold or activity is low, shorten the effect window or lower the gain. Recheck after hull condition changes.

When it pays

• Warm routes and idle periods where micro-slime forms on blades quickly.
• After exposure to silty water or heavy berth time that dulls the finish.
• When speed–power curves show rising shaft power at constant speed.

Planner’s notes

• Specify fine finishing passes and avoid aggressive abrasives that remove metal.
• Photograph blade surfaces and record surface appearance to track roughness over time.
• Coordinate with terminal and pilotage for diver safety; check local permit conditions.

Permit checklist (quick)

Simple Summary

Biofouling hides in intakes, gratings, tunnels, and coolers. Niche-area cleaning uses compact heads or carts with suction so debris is captured and filtered topside. Clearing these bottlenecks restores cooling flow, protects thruster efficiency, and stops re-seeding of the flat hull.

Bang for the Buck

Targeted niche work often costs a few thousand to low tens of thousands USD, far less than a full-hull pass. Gains show up two ways: slight fuel savings from less recirculation and smoother tunnels, and avoided off-hire from cooling alarms or thruster underperformance.

If sea chests are partially blocked, one short session can remove a hidden reliability risk. Add this to port calls after warm, fouling-prone legs.

Quick saver — targeted niches

Estimate net from small efficiency gains and optional downtime avoidance.

If you expect warm idle periods, shorten effect days and rerun. Add a realistic avoided off-hire value only when there’s a credible risk.

When it pays

• Rising seawater temps or debris leading to high cooling‐water ΔP or alarms.
• Thruster tunnels showing vibration, noise, or lost thrust at standard loads.
• After long port stays in fouling-prone waters to stop rapid re-seeding.

Planner’s notes

• Use capture nozzles and fine filtration; log waste handling and disposal.
• Follow coating and cooler maker limits; prefer soft tools and low pressure.
• Combine with a prop polish and a light groom of forward flats for best effect.

Permit checklist (quick)

Simple Summary

Ultrasonic systems bond transducers to the dry side of the hull or inside niche areas. The vibration pattern helps keep early biofilm from sticking, especially in sea chests, box coolers, and quiet zones. It is a prevention tool; it won’t remove established growth and it doesn’t replace coatings or cleaning.

Bang for the Buck

Costs vary with coverage. Small systems are a few thousand USD; multi-zone, ship-scale installs can run into the mid–high five figures. Power draw is low (often tens to a few hundred watts total), so running cost is minor. ROI depends on how much slime you prevent on routes where fouling forms quickly.

Treat it as a helper: it can reduce how often you groom or clean and protect niche areas where manual access is hard. Expect best results in warm, idle-prone trades and in sea chest/box cooler circuits.

Quick saver — ultrasonic prevention (yearly)

Estimate annual fuel saving from avoided slime vs annualized system cost.

Keep “Penalty prevented” conservative. If you also reduce grooming or capture-cleans, add those avoided costs to the benefit off-line.

When it pays

• Warm routes and idle periods where biofilm forms quickly.
• Niche areas that are hard to reach routinely: sea chests, box coolers, bow-thruster tunnels.
• As an add-on to coatings plus a light grooming program to stretch intervals.

Planner’s notes

• Map coverage. Large hulls need multiple transducers and careful placement for structural paths.
• Verify mounting surfaces are dry, clean, and accessible; route cables with EMC in mind.
• Log baseline fouling in niches and monitor ΔP/cooling performance to confirm effect.
• Treat as prevention; schedule periodic grooming/cleaning regardless.

Implementation checklist (quick)

Simple Summary

This means crew make brief, controlled passes on reachable areas (boot-top, forward flats) while adrift or at very low speed using poles or magnetic pads. The goal is to wipe early slime so drag doesn’t build. It is not a heavy clean. Safety and local environmental rules come first — many places restrict in-water cleaning without capture.

Bang for the Buck

Costs are mainly crew time, a small tool kit, and any schedule slip to drift. If you prevent even a 1–2 percent penalty for the next few voyages, fuel savings can outweigh those costs — but only when done safely and legally outside restricted waters.

Treat this as a stop-gap between proper capture cleans or grooming. Do not attempt overside work with way on without the Master’s authorization and SMS permits.

Quick saver — short drift-and-groom vs fuel

Estimate net after crew time, tool cost, and schedule slip.

If rules or conditions force a shorter effect window, reduce “Effect days” and retest. Never trade safety for a few tons of fuel.

When it pays

• Warm-water routes where slime forms quickly between port calls.
• You can safely drift with propellers stopped and a rescue watch posted.
• You are outside restricted areas and local rules allow non-capture slime grooming.

Planner’s notes

• Master signs off. Follow SMS: permit-to-work overside, lifelines, spotters, MOB gear, VHF watch, rescue boat ready.
• Limit to reachable zones; use gentle pads that are coating-safe. No aggressive scrubbing.
• Check biosecurity/port state guidance. Many ports ban in-water cleaning without capture — even outside the harbor limits.

Safety and compliance (quick)

Simple Summary

Soft-tool methods use gentle, coating-safe pads or brushless heads at low pressure to lift slime without scratching the paint. They protect expensive SPC or foul-release coatings, keep roughness low, and delay the need for aggressive cleaning or early repaint.

Bang for the Buck

Costs are typically lower than heavy cleans because you’re removing light slime, not hard growth. Expect several thousand to low tens of thousands USD per session by hull size and access. The return comes from avoided drag (fuel) and, just as important, from preserving the coating so you don’t pay for early re-coats or lose warranty coverage.

Use this as the default setting for fresh coatings and warm routes. If fouling is already established, plan staged, gentle passes or switch to a capture clean.

Quick saver — soft pass vs fuel + avoided damage

Estimate net over the effect window, including optional “avoided damage” value for coating preservation.

Keep “Penalty prevented” modest. The bigger win is delaying aggressive cleans and protecting the coating — capture that value in “Avoided damage.”

When it pays

• Fresh coatings after drydock, or any hull under warranty terms.
• Warm, idle-prone routes where slime forms quickly but hard growth hasn’t set.
• As a first response before scheduling a full capture clean.

Planner’s notes

• Follow coating guidance on pad type, pressure, and maximum passes; record tool settings.
• Avoid silty bottoms and abrasive media; rinse pads often to keep them soft.
• Document before/after photos and noon data; escalate gently if slime returns quickly.

Compliance & care (quick)

Simple Summary

Treat in-water cleaning like a regulated operation. Get port approval, prove capture and filtration, follow the coating limits, and hand waste to a licensed receiver. This protects you from fines and stoppages, and it keeps your speed–power gains on schedule.

Bang for the Buck

Compliance has a cost, but the avoided risk is bigger. One denied service can burn a day of hire. A single fine can exceed the whole job. A clean paper trail keeps terminals cooperative and lets you repeat the method across ports without renegotiating each call.

The win is predictable operations. You lock in the fuel saving and avoid last minute surprises.

Quick saver — compliance value estimator

Estimate net by comparing expected avoided costs vs paperwork and disposal costs.

Keep assumptions conservative. Use recent port letters and terminal rules to set the probabilities and delay hours realistically.

When it pays

• Ports that require capture and filtration and verify documents at berth.
• Tight schedules where a stop or redo would push laytime or miss a window.
• New coatings under warranty that need method statements on file.

Planner’s notes

• Ask vendors for a method statement, capture spec, filtration rating, and waste plan upfront.
• Coordinate with terminal, pilotage, and VTS. Confirm safe zones and work windows.
• Log before and after photos and noon data to show effect and protect against disputes.

Permit and documentation checklist

Waste handling matrix

Simple Summary

Biofouling accelerates in warm water and during idle time. Use route temperature bands and forecasted warm-idle days to set “clean or groom” triggers. If the expected fuel saving pays back the job within the coming warm-idle window, book it before the penalty grows.

Bang for the Buck

A simple schedule rule (e.g., “groom every 45 warm days” or “after >5 warm-idle days”) locks in fuel savings and avoids heavy, coating-damaging cleans later. Tie your trigger to sea-surface temperature (SST ≥ 20 °C), planned layby/anchorage, and capture-permit availability at the next port.

Trigger planner — warm-water & idle days

Set your typical fuel burn and costs. The tool suggests a payback-based trigger and a route-risk interval.

Use “Payback (warm days)” as your minimum trigger. If forecast warm-idle ≥ payback within the next leg, schedule a groom where capture permits are available.

When it pays

• Trades with long stretches in SST ≥ 20 °C or frequent anchorage/layby in warm ports.
• Terminals that allow capture cleaning alongside, so no extra port call is needed.
• Right after a prop polish to lock in speed–power gains with a clean forward flat.

Planner’s notes

• Set route-specific rules (e.g., “>5 warm-idle days” or “every 45 warm sailing days”). Review quarterly.
• Align with port capture rules and waste-receiver slots. Pre-approve the vendor method statement.
• Track noon data: if shaft power at constant speed drifts up, pull the trigger sooner.

SST band quick guide (rule of thumb)

Simple Summary

Treat fouling as a ship-system issue. Clean or groom the forward flats and run a prop polish, then clear sea chests, tunnels, and coolers so they don’t re-seed the hull. Log before/after shaft power at constant speed and keep the permits and waste records tight. When you do all four pieces together, the savings stick.

Bang for the Buck

The best returns come from stacking small gains: a clean forward flat, a polished prop, and de-fouled niches often beat a one-off heavy hull clean. Add a light grooming cadence in warm water and you extend intervals, protect the coating, and avoid emergency downtime from clogged intakes.

Records close the loop: with a simple speed–power baseline, each task’s benefit is visible, making the next approval easy.

Execution playbook (order & cadence)

1. Propeller first: polish to a smooth finish; verify vibration and RPM at fixed speed.
2. Forward flat + boot-top: soft-tool or capture clean to restore the laminar lead-in.
3. Niche areas: sea chests, box coolers, tunnels with capture and filtration; confirm ΔP/cooling.
4. Light grooming rule: every 30–60 warm sailing days or after >5 warm-idle days.
5. Compliance packet: permit, method statement, capture spec, waste manifest filed.

KPI set to prove savings

Record calm-water points before and after each task. Note SST and draft so comparisons are fair.

ROI stack — typical gains (illustrative)

Documentation packet (keep on file)