A corridor that smells and a system that passed

A guest head is open to its carcase, the pan gone, and the hose taken out of it that morning is coiled on the sole with its clamps still on. The bore looks dark but open, and nothing beneath it was ever wet. A fitter closes a hand round it until the rubber warms, holds a rag against it, and passes the rag over. That is the whole test, and the hose has just failed it.

Most systems aboard are argued against an instrument first: a dial gauge on a shaft line, a thickness reading on a coating. This one is judged by a sense. Nobody asks what the discharge pressure is; they ask whether the guest corridor smells on the second warm evening at anchor. That is why a yacht sanitary system refit is the work most likely to pass its own tests and fail the owner.

The rag says where to look. Almost everything reported as a toilet problem belongs to the run, not the fixture — a fall, a bore, a tank, its vent and a valve, in that order, with joinery over most of it. A refit either corrects that run or closes it in until the next time the panels come off.

A new fixture on an old run

The specification arrives with the fixtures on it, because they are what an owner can see and choose. The run is not on it. So new pumps get bolted to hose that has been aboard since she was built, and the fault survives the refit with a warranty round it. What it does settle is the standard: systems are renewed to current regulation, and which one depends on where she will operate, the owner's answer and the captain's, not the yard's.

The old run has become two things. The bore narrows, because what comes out of solution here is hard and holds to rubber, and a half-closed bore makes a new pump sound as though it is fighting something. And the fall is often no longer a fall: a hanger moved or a sole lifted years later leaves the run holding a standing column. Neither shows with a torch; both answer to a short length cut out while the compartment is open. Whether she draws on vacuum or on gravity changes the evidence rather than the argument — the tank end of it is settled in a tank as a measured vessel.

The hose is sound and it still smells

Permeation is the fault with no event in it. Sanitary hose is a wall of rubber, and the wall is not a barrier for ever: what the run carries works into the material from the inside and comes out the other side as a smell. Nothing leaks, no clamp is loose, and the run holds whatever pressure is put on it: a pressure test asks about the joints, and the hose is answering another question.

That is why the rag works. Warmth brings it out, so a hand held round the hose does on a bench what a warm week at anchor does aboard. The cure is a length of run renewed rather than a gasket or a clamp — a decision about the compartment rather than the hose, because the hose costs little and the panel costs the refit.

Odour is a reading, not a nuisance

A smell is the only continuous instrument the system has, and the first thing to read off it is whether it is local or general. Local means a leak — liquid or air — and it sharpens as a panel comes off. General means the material of the run itself: the corridor smells, no panel smells worse than another, and every joint is sound. An owner told the system has been pressure-tested and holds is being told something true about the joints and nothing about the wall of the hose.

The vent decides how much of either reaches anybody. A tank breathes both ways, and a vent that is restricted, or run with a low point holding water, turns a working system into a pressurised one that finds the weakest closure in the path, a long way from the tank. A vent that breathes freely but terminates where the wind returns it to a deck people use has no pressure problem, and is still the fault the owner reports.

The grey water nobody suspects

Grey water is the part nobody specifies and nobody suspects. Shower trays and basin drains run long, shallow and warm, carry hair, soap and skin, and are the stretch most often laid flat to save head height. What settles there does what organic matter does in a warm, still pipe.

Then there is the sump. Where a tray cannot drain by gravity it drains into a box with a float switch, and the float is where hair and lint collect. A fouled float either holds the pump on or never calls it, and a sump that never quite empties is a warm reservoir behind a panel somebody screwed shut at fit-out.

When a guest cabin smells, the black water system gets the blame, because that is the system with the word on it. Often it is a trap dried out in a cabin nobody has slept in since she arrived, and a water seal works only while there is water in it.

A head is a room with a system behind it

A head is the one compartment aboard where a finished room and a working system share a wall. The joiner owns the face of it, the fitter owns what is behind, and the two trades meet at a single panel. That panel is usually decided late, by whoever is closing the room, and a screwed and filled one looks better on the day than a removable one.

The owner lives with that decision. A run reached by lifting a panel gets looked at; a run behind a bonded mirror surround does not, and the next person who needs it will cut. That is the same argument as the joinery that closes over it, made in the smallest room aboard.

The panel somebody takes off in the dark

Every joint you cannot reach is a future haul-out, and the sanitary path is the run the interior is built to hide. Serviceable is a design decision. It comes down to three objects: the pump that will need lifting, and whether it comes out without cutting what closes over it; the valve somebody has to find in the dark and prove shut, which is a question about the handle as much as the line; and the length of run that will be renewed one day, which wants breakable joints rather than a fused line, the same argument as where a run is cut into spools.

Then it has to be proved, and clean water only proves the joints. A system filled from a hose and run for an afternoon will pass. What fails it is time, warmth, solids and a tank that has been full. What costs only attention is leaving the run warm and loaded rather than flushed clean, putting a rag on every length that cannot be seen, working every valve from where a person will actually stand, and writing down, for the next engineer, which lengths are original, which joints can be broken and remade, and which are shut for good.

Written at the yard in Tuzla. Which arrangements her heads and grey water runs have to satisfy is her owner's, her captain's and her flag's answer rather than ours.