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A clean hull starts with a weekly routine that crews will actually follow. Catching slime early protects speed, cuts fuel burn, and reduces the need for aggressive cleaning later. The trick is to make the inspection repeatable, fast, and useful on shore. Start with cadence and evidence.
1 Set the cadence 15–25 min per week
Why cadence beats “whenever”
Fixed weekly checks create comparable evidence and let shore teams spot trends early. That means you clean sooner, with lighter methods, and avoid performance disputes.
| Item | How to do it |
|---|---|
| Pick the day | One weekday, same watch. Add to bridge calendar and noon-report template. |
| Assign roles | Shooter captures images, spotter calls angles, logger files names and notes. |
| Keep it short | Target 20 minutes. Same path and framing each week. |
| Close the loop | Upload with the rule Vessel_Port_YYYY-MM-DD_Angle.jpg. Shoreside shares a 3-slide summary monthly. |
Angles: P-bow boot-top, S-stern boot-top, mid-body port, mid-body starboard, rudder/prop.
Mini ROI: does the weekly check pay?
Compare weekly crew time cost with fuel saved by catching slime early.
Heuristic: if net is positive, your weekly routine is self-funding. If marginal, tighten cadence only in warm, high-nutrient waters.
2 Shoot the five angles evidence that travels
These five shots capture where growth shows up first and where it costs you most. Keeping the same angles and framing each week lets shore teams spot trends, set cleaning triggers, and defend performance with repeatable evidence.
Angles and what to catch
| Angle | Why it matters | What to capture |
|---|---|---|
| Port bow boot-top | Leading edge shows first slime and scuff. | 1–2 m strip; color note: green film vs brown strands. |
| Starboard stern boot-top | Eddies trap nutrients near stern. | Same framing every week for comparison. |
| Mid-body port & starboard | Stable baseline for trending. | Use a fixed reference (chock/handrail). |
| Rudder & stock | Small area, big drag if fouled. | Trailing edge close-up; look for filaments. |
| Prop hub & blades | Prop condition dominates efficiency. | Blade face and leading edge; two opposite blades if visibility allows. |
Consistency beats resolution. If water is turbid, take more stills and a short video.
Make it actionable on shore
- One folder per week with photos and a noon-report export. Keep a running 4-week trend.
- Tag by severity: LS light slime, MS moderate slime, WS weed strands.
- Auto-brief: three images, one line of notes, one trigger status for management.
- Protect coatings: heavy strands call for capture cleaning; avoid aggressive pads on fresh SPC/silyl.
3 Check the niches first small area, big drag
Sea chests, gratings, bilge keels, thruster tunnels, log sensor, and ICCP anodes make up a small fraction of hull area, yet they can contribute a large share of added drag. Inspect them first and act fast, because clearing these spots often delivers the quickest fuel win.
Niche checklist and actions
| Niche zone | What to look for | Action |
|---|---|---|
| Sea chests & gratings | Filament growth, clogged mesh, shell | Brush or cavitation with capture. Verify valves shut and intake safety. |
| Thruster tunnels | Rings of slime, weeds at lips | Low-aggression pads. Protect blades and seals. |
| Bilge keels | Edge strands along the keel | Edge-focused sweep. Avoid cutting into coating edges. |
| Log sensor housing | Film on face, false readings | Gentle wipe. Recalibrate if speed bias suspected. |
| ICCP anodes and cabling | Slime bridging, shell close to anodes | Do not abrade anodes. Clear gently and log condition photos. |
Record tool, pad aggressiveness, and diver remarks to protect coating warranties.
Niche impact estimator
Estimate fuel penalty and dollars per day if specific niches are fouled.
Heuristic only. Actual penalties vary by vessel, speed, and coating condition.
4 Do the glove test quick severity check
If you can feel slime, you are already paying for it. The glove test turns a touch and color read into an action signal. Light green film points to a routine clean; brown or weed strands call for faster attention and a more protective method.
How to run it and read it
- Wipe the boot-top with a clean glove at two fixed points. Note feel: slick film, slimy, or strand pull.
- Note color: light green film usually means early growth; dark green or brown and any visible strands signal higher urgency.
- Photograph the exact spot after the wipe for a weekly like-for-like comparison.
Pair the glove test with a steady-RPM trial to confirm the fuel impact.
Urgency helper
Pick what you feel and see. Get a next action and the cost of waiting.
Heuristic only. Confirm with steady-condition trials where possible.
5 Log the numbers evidence in the noon report
At steady RPM and draft, small drifts in speed and fuel tell you when slime is costing money. Log speed over ground, wind and sea state, and daily tons. Rising specific fuel oil consumption at constant conditions is your fouling alarm.
Make the numbers comparable
| Signal | How to record |
|---|---|
| RPM & draft | Hold RPM constant for the trial. Note fore and aft drafts. |
| Speed over ground | Average over 30–60 minutes. Note current and tide if material. |
| Wind / sea state | Record Beaufort and swell. Avoid trials above Bf 5 if possible. |
| Daily fuel (t/day) | Use flowmeter or consistent ROB method. Same tank sequence each trial. |
Keep one “clean baseline” from post-drydock or post-clean to compare against.
Fuel drift checker
See percent rise in daily tons and the extra dollars per day at today’s bunker price.
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6 Set simple triggers action thresholds
Triggers turn observations into action. Use a simple two-step rule so crews know when to polish the prop and when to book a light hull clean. Keep it tied to steady-condition data to avoid false alarms.
Suggested thresholds
| Signal | Trigger | Action |
|---|---|---|
| Weed strands on prop | Any visible strands | Propeller polish at next safe port |
| Fuel rise at steady RPM | +3–4% for 3 days | Prop polish; reassess hull after |
| Hull strands at boot-top | Any strands on two weeks | Light in-water clean with capture |
| Fuel rise persists | ≥5–6% at steady state | Schedule in-water clean and prop polish |
Match method to coating. Avoid aggressive pads on fresh SPC or silyl systems.
Trigger helper
Enter what you are seeing and the recent fuel drift. Get a simple next action.
7 Protect the paint method + warranty fit
Cleaning method must fit coating chemistry and age. The wrong pad or cavitation level can void warranties and add roughness that costs fuel every day. Match tool aggressiveness to coating type and days since application.
Compatibility quick-guide
| Coating | Clean early-stage slime | Cautions |
|---|---|---|
| Self-polishing copolymer (SPC) | Soft pad, low RPM; low-energy cavitation with capture | Avoid aggressive brushes, especially < 90 days from application |
| Silyl / hydrolyzing | Very soft pad; gentle sweep | No stiff bristles; confirm vendor pad spec |
| Foul-release silicone | Soft microfiber; water-jet or cavitation at lowest setting | Never abrade; keep nozzle distance consistent |
| Hard epoxy / tie-coat | Soft to medium pad; controlled RPM | Mind edges and welds; avoid cutting into corners |
Log tool type, pad aggressiveness, RPM, and vendor in your inspection file.
Method picker
Pick coating type and age to get a conservative cleaning method.
Vendor and warranty terms prevail. When in doubt, choose the gentler option.
8 Close the loop prove the gain
After any prop polish or hull clean, repeat the same photos and a steady-RPM trial. Confirm the improvement in fuel and speed. Share a one-pager with before-and-after shots and the math so charterers and managers see the value.
Proof pack
- Before-and-after photos at the five angles, same framing and light where possible.
- Steady-RPM trial results: daily tons and speed over ground at similar sea state.
- Vendor report with tool, pad, RPM, and capture details for the record.
Save as a dated PDF and file with chartering and technical.
Gain and payback
Enter before/after fuel, bunker price, days to evaluate, and the cleaning cost.
Reconfirm against a steady-condition trial to avoid weather bias.
Clean hulls save real money when routines are simple, repeatable, and tied to action. Run the weekly cadence, shoot the same angles, check the niches, and use steady-condition numbers to trigger prop polish or a gentle clean. Protect the coating, prove the gain after every job, and your fuel curve stays flat while disputes stay quiet.
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