Why the deck answers before the machine does
A floor in a plant tolerates water because the room was designed to shed it. A deck tolerates or refuses water depending on what is glued, caulked, cored and drilled into it. On one vessel the non-skid covering is moulded into the laminate; on the next it is teak laid over a substrate with bedding compound between the planks; on a third it is a painted coachroof with a textured additive. The same wand, the same operator and the same mode will behave differently on all three, and the difference shows up in the joints rather than on the open face.
That is why a mode chosen by habit is the most common cause of a bad deck job. Steam that leaves the surface loaded with water is useful where the deposit is thick and the surface is solid. Steam that arrives nearly dry is useful where the surface cannot be allowed to hold water, or where the water has nowhere to go. Neither choice is correct in the abstract; the deck supplies the criteria.
Walk the deck as a list of places, not as one surface
Write the deck down as separate line items before touching a control panel. A useful list names the foredeck, the side decks, the coachroof, the cockpit sole, the cockpit side walls, the transom face, the swim platform, the waterline band, and the vertical surfaces you can reach from the dock. Each line gets its own material note: gelcoat finish, painted, bare brightwork, teak, moulded non-skid, cored area, bonded fitting, through-deck fitting.
Two columns matter more than the rest. The first is how old the finish is and whether anyone has touched it up locally, because a repaired patch responds differently from the film around it. The second is whether the line item has an edge you can lift, because any edge is a place where forced water can get behind something. Anything you cannot name goes on the list as a question rather than as a surface.
Deck hardware first: what must not be wetted
Before the mode question, put a do-not-wet block at the top of the sheet. On a yacht deck it normally covers the seam where the deck meets the hull, the bedding line under stanchion bases, lifeline sockets, cleats, chainplates, deck fills, hatches and their gaskets, the base of any mast step, instrument pedestals, speaker grilles, and every deck drain and its strainer. Owner approval on that block belongs on paper before a wand is lifted, with a hand-clean fallback written beside each excluded line.
The reason is specific. Steam under pressure at a bedding line does not announce itself; it travels along the bed, into a core, or behind a flange, and the result appears weeks later as a soft patch or a weeping joint. A deck is not a machine exterior where the failure is visible on the next walk-around.
Name the deposit before you name the mode
Deck deposits come in recognisable families: a dry salt film, green growth in the pores of a moulded non-skid, a greasy film from engine work or from handling, bird marks, rubber transfer from fenders, and rust staining from a fitting. Each family behaves differently under heat and differently under water, and one line of your list may carry two families at once.
Write the deposit against the place. That pairing is what lets you judge a mode later, because the same mode tested against the wrong deposit looks like a failure of the machine when it is only a mismatch. Where the deposit is loose grit and salt on an open face, adding water to the job is a cost, not a help. Where the deposit is growth held in a textured surface, water is part of the work and the question becomes how to get it off the deck again.
Dry steam and wet steam on a deck: what each choice commits you to
Treat the two settings as two different commitments. A drier setting commits you to working closer, moving slower, and trusting heat plus dwell rather than volume; it is the choice where the surface must not hold water, where the seam is the risk, and where the deck is being read while it is being cleaned. A wetter setting commits you to a water-management plan; it is the choice where the deposit is bonded and needs to be lifted, and where you can accept that the deck will be wet for a while afterwards.
Do not settle the question in prose. Put one patch of each setting on one line item of your list, in a place that can be cut out and replaced if it goes wrong, and record beside each patch which setting was used, how long the wand stayed, and what the surface looked like once it was dry and cool. A mode comparison written before the patches is an opinion; written after them it is a specification.
If a supplier offers a hot-water stage as part of the range, treat it as a third commitment rather than a stronger version of the other two, and ask in writing what it is for on a deck and what it leaves behind. The catalogue wording names the modes; it does not say what a mode does to a marine surface, and that gap is yours to close on a test patch.
Water that has nowhere to go: deck drains as a working decision
On a boat the drainage question is not housekeeping, it is part of the mode choice. Find each deck drain, note whether the strainer is clear, and follow where the water exits: overboard at the hull side, or into a cockpit well, or into a locker you did not know was there. Afloat, the run-off leaves the vessel by gravity. Ashore on a cradle, the deck drains to the yard surface, and the yard surface may not be allowed to take what comes off a hull.
Then check the reverse: how long the deck stays wet once the work stops. A cockpit sole in sun and wind clears quickly; a cored coachroof in a shaded berth does not, and anything trapped under a cover or a sail bag stays wet far longer than the visible surface. Decide, before the job, whether you are willing to leave standing water on that line item at the end of the day. If not, the mode choice narrows on its own and the wetter setting drops out of the plan for that place.
Reach, supply and the working window at the berth
A mode discussion is meaningless if the equipment cannot stand where the work is. Settle where the unit sits, whether that is the dock surface, a pontoon, a quayside hard standing or inside a shed, and check what it has to cross to get there: a finger pontoon, a step, a gate, a hose run over a rubbing strake. Note the freeboard between the dock and the deck, because it decides the angle you can hold the wand at and how far the deck edge sits from you.
Then write down what the berth gives you: whether a shore supply point is permitted and who permits it, how far the deck is from it, and how many hours a day the vessel is available. If the work has to stop and restart, the mode that suits a short uninterrupted stretch may not suit a job broken into pieces, because a partially wetted deck left overnight is a different problem from a wetted deck finished in one pass. Put the interruption in the plan and let it rule the mode.
Working around the rig: people, lines and fixed fittings
A deck is a shared working surface while the job is running. Standing rigging, shrouds, stays, the mast step, the boom, stanchions, pushpits and the lines that run between them all sit at the height your arms will pass through, and several of them are fixed points you cannot move. Ask who else is on board, who is working above you, and who is handing tools across the deck, and write the answer into the sequence rather than solving it by shouting.
Treat a fitting that flexes under a hand as a stop condition for that line item, not as something to work around. A stanchion base that moves, a lifeline socket that turns, a deck fill that is loose in its collar: those are the places where the mode with the most water is the most expensive mistake. When a fitting flexes, stop on that line, record it, and go back to the owner with a question rather than a workaround.
Decide what done looks like before the first pass
Write the release condition per line item, in observable terms: no standing water left on the surface, no lifted edge at a seam or a plank, no flexed fitting, no dulled patch beside the one you cleaned, no staining driven into a joint, and no water collected under a cover. Have someone who did not hold the wand confirm each line once the deck is dry and cool, and let a failure on one line stop the sign-off for the whole list rather than becoming a note.
Record the outcome in the same detail for a place you stopped as for a place you finished. The record becomes the specification for the next visit, and on a yacht that record is often the only thing that tells a later crew which part of the deck has already been tested and which has not. A single page per material family, with a date on it, is more use than a set of instructions for the whole vessel.
Questions worth sending to the supplier
Send the mode question to the supplier as a list of fields to fill in for the exact unit being quoted, and mark clearly that the deck in question is marine so the answer is not read as a general endorsement. Useful rows to ask for: which settings the quoted unit offers, whether the mode can be changed mid-job, how the unit is fed with water and where that supply can sit relative to the deck, how far the working lines reach from where the unit stands, what the unit weighs and how it is moved onto a pontoon, and which protective functions interrupt the job.
Ask those as rows rather than as numbers, and refuse a figure that belongs to a different model in the range. The industrial steam cleaner category page is where the modes and the mobile range are described, and customized steam cleaning equipment is where you would put the deck description for a written answer. If the answer comes back as a general promise instead of a filled row, that is the information you needed.
