How do you clean a cargo hold between cargoes?
It is three jobs, not one. Each needs different kit, and the rules on wash water usually decide the schedule.
Sweep out what can be recovered, wash down the rest, then mechanically treat the steel wherever coating or scale has failed. An air-assisted water gun on the fire main throws a solid jet about 30 m, enough to reach upper hopper plating from the tank top. Descaling is the slow part, at about 5 m² an hour. On most voyages the real limit is what MARPOL Annex V lets you do with the water.
Three jobs, three kinds of kit
"Grain clean for the next fixture" and "ready for coating" are different projects. Decide which one you have before you choose tools.
- Dry
Sweep and remove
Anything recoverable comes out by shovel, brush and bobcat. It sets how much of everything else you have to do, and it is the only stage that keeps residue out of the water in the first place.
- Fast, covers area
Wash down
Water takes off the film of residue, the dust in the frames and any loose paint or flaking rust. Thousands of square metres, so it has to be quick: an air-assisted gun off the fire main.
- Slow, covers little
Treat the steel
Nothing sprayed at fire-main pressure takes failed coating or heavy scale off steel. Where the plating will be primed and painted, a cutter head or a needle scaler has to do it.
Wash-down: the three realistic options
Only one of them runs on services the vessel already has.
Air-assisted water gun
Air injected into a fire-main water stream turns a soft spray into a tight, solid jet with range.
- Needs
- Fire main + service air
- Reach
- 30 m (Hydraflex)
- Removes coating
- No
- Ordered by
- IMPA code
No pump, no power, no fuel. The Trelawny Hydraflex and the Strømme Maxi-Gun both work this way.
Portable high-pressure water blasting
A pump unit generates several hundred bar and an operator works with a lance.
- Needs
- Pump, power or fuel
- Rate
- ~13 m²/h at 500 bar*
- Removes coating
- Yes
- Crew
- Trained operator
A machine to crane aboard, and flash rust on the cleaned steel to deal with before coating.
Hoses and brushes
What happens on plenty of ships.
- Needs
- Fire main
- Reach
- Head height
- Removes coating
- No
- Cost
- Lowest
Cheap and slow, and it does not reach anything above head height.
* Trelawny's own figure for 500-bar water blasting.
The two common guns, on published figures
The Maxi-Gun reaches further, but wants roughly twice the water pressure and ballast tanks to hold it down. Which is better depends on what your pumps deliver at the hold.
| Factor | Trelawny Hydraflex | Strømme Maxi-Gun |
|---|---|---|
| IMPA code | 590742 | 590745 |
| Jet reach | 30 m (100 ft) | About 80 m at 11 kgf/cm²; about 60 m at 7 kgf/cm² |
| Water pressure | 5.9 bar (85 psi) recommended | Minimum 4 kgf/cm² (≈3.9 bar); 11 kgf/cm² (≈10.8 bar) for maximum reach |
| Air pressure | 6.9 bar (100 psi) | 6-8 kgf/cm² (≈5.9-7.8 bar) |
| Water consumption | 454 l/min | Not published |
| Air consumption | 33 l/s (70 cfm) | Not published |
| How it stands up | Tripod, 8.6 kg | Three water-ballast tanks |
| Kit weight | 14.1 kg total | Not published |
What 30 m of reach needs from the ship, and from the crew
The reach figure is quoted at the recommended water pressure. The gun is not the variable. The fire main is.
- Water
- 454 l/minA real draw. A main sized for two jets will generally carry it.
- Water pressure
- 5.9 barAt the gun, recommended. Working range 6.2 to 7.6 bar.
- Air consumed
- 33 l/s70 cfm at 6.9 bar (100 psi).
- Compressor
- 47.2 l/s100 cfm free air, Trelawny's recommendation, to hold pressure steady.
Measure pressure at the hold, not at the pump. Hose runs and height eat the difference, and below the working range the jet softens and the reach drops off.
More air does not mean more jet. Trelawny's manual says excess air breaks the jet up. Open the air valve until the jet goes hard and tight, then stop.
"One-man operation" needs two people. One operator does the cleaning, but Trelawny's manual has a second person slowly open the water valve at the main or pump, and the same in reverse at shutdown. The gun kicks back with 10 to 18 kg of recoil, which is also why the tripod is not an accessory. Crew it as two.
Descaling: plan on 5 m² per hour
Where the wash leaves scale or failed coating attached, a flexible-drive descaler such as the Trelawny Trident Neptune takes it back to sound steel. Its 3 m shaft drives cutter heads or wire brushes into frames, brackets and vertical plating a walk-behind machine cannot reach.
Trelawny's datasheet gives an average of 5 m² per hour. A walk-behind deck scaler on open deck is rated at up to 30 m² per hour, so this is a spot-repair rate. Identify the areas that need it and scope those, not the whole hold.
- Declared vibration
- 8.7 m/s²
- To action value
- 40 minof trigger time
- To limit value
- 2 h 39 minof trigger time
Under Directive 2002/44/EC. On a job measured in square metres per hour, trigger time is most of the shift: two operators rotating get more done in a day than one working through. Vibration guide and calculator.
Where can the wash water go?
Under MARPOL Annex V, as revised in force since 1 January 2013, cargo residues in hold wash water count as garbage. Answer three questions to see where your wash water can go.
Discharge en route, 12 nm or more from land
Outside special areas, with non-HME residues, wash water may be discharged only while the ship is en route, as far from land as practicable and never less than 12 nautical miles from the nearest land or ice shelf.
Anything you recover dry before the hose comes out is water you do not have to account for later. Summarised from ITOPF/UK P&I, Skuld, West of England P&I and TT Club guidance. An outline, not legal advice: the cargo declaration and your operator's procedures govern.
Which tool for which part of the job
- Residue across a whole holdFilm, dust in the frames, loose flakesAn air-assisted gun off the fire main. Check the pressure at the hold before you buy anything. See the Hydraflex →
- Failed coating and scaleFrames, brackets, vertical platingA flexible-drive descaler or needle scalers. Scope it at about 5 m² per hour and rotate operators. Needle scalers →
- The hold is going to be coatedSurface preparation, not a washPlan the mechanical work and the wash water separately. Flash rust from water blasting moves the dates again. Water blasting or scaling →
Hold cleaning between cargoes: common questions
What pressure does a hold cleaning gun need, and how far does it spray?
The Trelawny Hydraflex is rated at 30 m (100 ft) at its recommended 5.9 bar (85 psi) of water at the gun, within a working range of 6.2 to 7.6 bar, plus 6.9 bar of air. The Strømme Maxi-Gun needs at least about 3.9 bar and reaches about 80 m at about 10.8 bar. Both figures assume the pressure is actually there, so measure it at the hold rather than at the fire pump.
Can one person operate a hold cleaning gun?
One operator does the cleaning, but Trelawny's manual requires a second person at the water valve during start-up and shutdown. With 10 to 18 kg of recoil, the gun must be held securely and mounted on its tripod before the water is turned on.
Can you discharge cargo hold washing water at sea?
Only in limited circumstances. Under MARPOL Annex V, discharge outside special areas is permitted only while en route, at least 12 nautical miles from the nearest land, and only where the residues are not classified as harmful to the marine environment. Inside special areas, which include the Baltic and the North Sea, the conditions are far narrower, and HME residues always go to a port reception facility.
How much area can you descale in a day?
Trelawny gives the Trident Neptune an average productivity of 5 m² per hour. Flexible-drive descaling is spot work: treat the areas that need it rather than planning a whole hold around it.
How long can a crew use a descaler before hitting the vibration limit?
For a tool with a declared emission of 8.7 m/s², such as the Trelawny Trident Neptune, the EU daily exposure action value of 2.5 m/s² A(8) is reached after about 40 minutes of trigger time and the 5 m/s² limit value after about 2 hours 39 minutes. Declared values come from standardised tests, so carry out your own assessment.
Keep planning
Hydraflex and Trident Neptune
The hold cleaning range, with part numbers, IMPA codes and what the ship has to supply.
View the range → MethodSteel to bare metal without blasting
Power-tool preparation to SSPC-SP 11, and when water jetting still wins.
Read the guide → VibrationHAVS and the Vibro-Lo range
How trigger time limits a descaling day, with a workforce calculator.
Read the guide →Tell us what your vessel can support
We specify the kit against your fire main and air supply and quote it in EUR, delivered. Already know the code? Send an RFQ on ShipServ TradeNet, TN 317548.
- Vessel type
- Number of holds
- Water pressure at the hold
- Air supply
- Cargo
- Delivery port
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