Start with a surface map, not a machine
Before any equipment is moved, walk the boat and write one line per area: substrate, coating condition, what sits next to it and how water can get behind it. A practical set of areas covers topsides and cove stripe, the non-skid panels on deck, the transom and swim platform, running gear and the boot stripe, the hull below the waterline, plus the superstructure windows, radomes and antennae. Each row should record whether the coating is sound, chalked, repaired or previously blistered, because a coating that is already lifting will not survive any hot method, steam included. This map becomes the trial plan, and later the acceptance record; a surveyor asked why a patch failed will want to see which areas were declared in scope, which were excluded and which were proven before work continued.
Record the yard condition with the same care. On afloat work, the boundary that matters is overboard discharge: rinse water, loosened growth and any residue must be captured or treated where the yard, the flag state and the local rules require it, and the vessel's own classes — fuel tanks, ballast tanks, holding tanks and sea chests — are not cleaning targets at any setting. On a hard stander or in a shrink, drainage, splash radius and ventilation are the controls instead. Ask the yard in writing which method is permitted, which absorbents and capture they expect, and what they consider an acceptable discharge route. Their answer decides whether the trial is a dockside job, a cradle job, or a job that stays out of the water until the surface can be contained.
Write the exclusions before writing the procedure
A safe steam trial on a vessel is defined more by what it never touches than by what it cleans. Standing exclusions should cover every seal and penetration: stern gear and shaft seals, rudder and thruster bearings, seacocks and skin fittings, anode mounts, deck hardware fastenings, cored deck edges, windows, portlights, vents, exhaust outlets, mast bases and any cove trim that has been re-bedded recently. They should also cover soft and sacrificial coatings, antifouling that is designed to ablate, vinyl tops, canvas, spray hoods, telemotor and steering cable runs, and any area where core material could be exposed at a fastener hole. Anything on that list that cannot be physically shielded is out of scope for the trial and is cleaned by a cold, low-pressure method instead.
Then add the operational exclusions. Do not direct the jet into a fastening, a lap seam, a through-hull or a keel joint, because the risk there is not the surface, it is the waterway behind it. Do not treat the vessel's structure as an industrial floor: cored panels and balsa decks cannot take the same treatment as a solid laminate. Do not work above an open deck fitting, and never let rinse water travel into a core plug, a mast step or a deck drain. If a fouled area sits within reach of any of these, the correct answer in a trial is masking and shielding, or deferral — not a reduction in distance held in the operator's hand.
Build a small sample panel you are willing to lose
A yacht trial should be run in stages, each one reversible. A common order is an inconspicuous transom corner, then a vertical topsides panel away from fittings, then a horizontal surface, then — only if the previous stages are clean and the yard agrees — the fouled area that motivated the job. Each stage is a test of three different behaviours, because vertical adhesion, horizontal pooling and growth that has been underwater for a season all respond differently. Keep every test patch small, keep a clear boundary line with tape so the treated area can be inspected under raking light, and photograph the same patch before, immediately after, and after the surface has dried. Drying is part of the test: blistering, whitening and edge lifting often appear later, and a patch inspected only while wet has not been inspected at all.
The order of the trial should be chosen so that failure is cheap. Do not begin with the boot stripe, the waterline or the most visible side of the vessel; begin where a problem would cost a polishing compound, not a repaint. Between stages, stop and inspect. If any patch shows gloss change, texture change, colour change, softening, edge lifting or a halo, that whole area class moves to the excluded list and the trial does not progress to a larger area, however good the rest of the boat looked.
Choose between an on-board unit and a shore-side unit
Marine trials split on power and water. A boat in a marina with shore power and a safe water supply can be served by a Fixed Steam Cleaning Machine PowerDe HW02, which stays at its own supply point while the crew walks the vessel around it, so the machine never has to come aboard. Afloat work with no reliable supply, or a vessel that has to be moved, points instead to a mobile steam cleaning machine that travels with the crew between berths, hard stands and sheds; the published application wording for this kind of travelling unit is written for garages and forecourts, not for boats, so on marine work its suitability has to be re-proven rather than assumed: how the unit is lifted on and off a pontoon, how it is kept level, where its exhaust and steam vent, and how far its hose reaches along a hull without dragging through standing water.
For a fleet operator — a charter base, a marina service team, a rescue or patrol squadron — the choice is a purchasing decision rather than a single job, and it should be put to suppliers as a documented requirement. The customized steam cleaning equipment route exists for exactly that kind of case, where the hull length, the berth layout and the power situation at each yard do not fit a published configuration. Send the surface map and the exclusion list to each supplier with the same wording, and keep the questions about the vessel's own condition inside the survey, not inside the machine claim.
Control the variables that decide whether a surface survives
On coated marine surfaces, results are driven by a small number of controls, and a trial should vary one at a time. The first is distance: the gap between the nozzle and the coating is the difference between warming a surface and forcing water under it, so it should be fixed at the start of each patch and written down, not felt by hand. The second is dwell: how long the jet stays on one spot. A stationary pass on a horizontal panel does something a moving vertical pass does not. The third is the wetness of the surface — whether the area is steamed dry, pre-rinsed, or steamed while still wet — because the coating's water state changes how heat and pressure behave at the film. The fourth is what happens afterwards: how the water is recovered, whether the patch is allowed to drain into the water or into a capture tray, and how long the area stays wet around a fastening.
Read the equipment documentation for the rows these controls depend on — supply, tank capacity, runtime, hose reach, and the protection functions the machine is described as having — and then confirm them at the berth, because published descriptions vary between listings and pages, and a figure that is not printed in the document you hold is a gap to close, not a number to assume. Protection features should be treated as a description, not a count: ask the supplier to state in writing what the machine stops, under what condition it stops, and what it does not protect against. The controls that protect a yacht are still the operator's distance, dwell and shielding.
| Control | What to write in the trial record |
|---|---|
| Nozzle distance | The gap held for each patch and the pass pattern used |
| Dwell and pass count | How many passes, in what direction, with what rest between them |
| Surface state | Dry, pre-rinsed or still wet, and how that was decided |
| Shielding | Which fittings, seams and trim were covered and how |
| Water capture | Where rinse water and removed growth went, and who confirmed it |
| Dry-down | Time to dry, and where water was seen standing afterwards |
| Re-inspection | Second look once dry, under raking light, with photographs |
Inspect at the points where boats actually fail
Damage on a vessel rarely shows up in the middle of a clean panel; it shows up at transitions. A trial should therefore end with a deliberate inspection of the places where water is expensive: the boot stripe and any repair boundary in the antifouling, fastening beds around deck hardware, the join between the hull and the rub rail, window and portlight frames, the shaft log and strut, the anode pockets, keel and skeg bolt lines, the transom's core edge, and every deck drain. Run the inspection after the area has dried and with light raking across the surface, so lifting, whitening and blister edges are visible rather than hidden by gloss. Where a coating has been rebuilt in patches, compare treated and untreated repair boundaries side by side; a fresh repair that changes appearance has told you the method does not belong on repairs.
Treat the interior as a separate risk entirely. Steam's heat and moisture travel; on a vessel they can reach bulkhead insulation behind a liner, timber veneer, cushion core and electronics behind a panel. For that reason the trial should keep doors, portlights and vents managed, and should not run inside a cabin while any opening leads to a locker, a bilge or an engine compartment. Deck electrical, compass installations and instrument housings are excluded unless the manufacturer has stated otherwise in writing for the method being used.
Protect the people doing the trial
Marine conditions make ordinary steam hazards worse. On a pontoon or a toe rail, the operator is standing on a wet, sloped or moving surface with a hose under tension; the correct response is to fix the position before fixing the machine, using the vessel's own rails, a stable platform and a second crew member who can shut the supply down. Hot surfaces, steam venting and hose ends need the usual covering protection and gloves, and the crew needs a rehearsed shut-down that does not depend on walking back along a wet deck. Ventilation matters on any enclosed or partially enclosed area, including a shrink, a berthed cabin saloon after a hatch job, and a engine bay whose fuel or vapour situation has not been confirmed safe. Fuel, bilge and battery spaces stay excluded from a steam trial until the yard and the vessel's own procedures say otherwise.
Write the stop conditions into the trial so a crew member can act without permission. Any sign of coating softening, any water seen entering a fitting, any lifting at a repair boundary, any change in a seal, any loss of footing, any machine fault or unexplained behaviour, any wind that carries steam or spray toward an opening: each of these halts the work, and the halt is recorded with the observation. A trial that cannot be stopped by the person holding the nozzle has not been made safe; it has only been described.
Decide what counts as a pass, and what forces a stop
Agree the acceptance criteria before the trial, in words the buyer and the yard both sign. A pass normally means the growth or deposit released without the substrate changing appearance, no change at the patch boundary, no lifting at any repair edge, no water traced behind a seal or fastening, the area drying within the window the yard considers normal for that coating, and no change at the next scheduled inspection. Anything else is a stop: whitening, blistering, a soft or tacky film, colour change in the antifouling, a changed gloss line, water found standing at a fastening bed, growth driven into a seam rather than off it, or an area that needs a second treatment to look clean. Where a patch needs a repeat pass to look clean, that is a finding about the method, not a routine to standardise.
Keep the decision itself separate from the equipment decision. A trial that passes on one panel does not license the whole hull, and a trial that fails does not condemn the method; it narrows the method to the surface classes that passed. Write the resulting scope in the same language the exclusion list uses — areas in, areas out, areas that need shielding — so the next crew applies the boundary without re-litigating the reasoning.
Ask for written confirmation on the gaps in the record
Equipment pages for steam cleaning describe the machine and its published rows; they do not describe your vessel, your coating system or your yard's discharge rules, and they should not be read as if they do. Before committing to a fleet programme, send each supplier the same list: which machine or configuration is actually quoted for this vessel class, what the published rows mean in the buyer's own berth conditions, which protection functions exist and what they do not cover, what the supplier requires for water capture on afloat work, and what the supplier's written position is on coated hulls, antifouling, cored decks and seals. Ask for the answer in the same document order for every bidder so the comparison is fair. When the requirement is genuinely outside what is published — a hull length, a berth with no supply, a service round that has to travel between marinas — a supplier discussion about PowerDe cleaning equipment is where that requirement is put on the table, with the trial record attached and the vessel's own limitations stated first.
Keep the record that the trial produces
A safely run trial produces a document, and that document is what makes the next job safe. It should carry the surface map with its exclusions, the yard's written permission and discharge route, the patch order with the distance, dwell, pass count and surface state for each, the shielding list, the photographs taken wet and dry, the acceptance result against the agreed criteria, every stop and what it revealed, and the operator's name against each stage. Keep the machine paperwork with it, including the rows that were checked and the answers the supplier gave in writing. If the trial ends with a decision to buy, the record becomes the acceptance basis; if it ends with a decision to change method, the record is the reason. Either way the crew who repeat the work next season inherit a boundary instead of a rumour — and that, on a vessel whose coatings are expensive and whose waterways are unforgiving, is what "safely" actually means.
