The frost behind the shelf standard

A provision store door stands open against its catch in a stripped galley in Tuzla, and the hand lamp is inside the box. The lining looks sound. Low on the back face, where a shelf standard is screwed to it, there is a bead of frost on two screw heads.

That frost is where the fault is, and the compressor is the last place to look for it. A yacht refrigeration refit reaches a specification as an appliance with a capacity to be matched, and the machine is the smaller half. The larger half is a piece of building — an insulated envelope with a vapour barrier, a drain, a door and a gasket line.

It is also one of the few systems a yard period cannot simply switch off. A cold store either keeps running or it is emptied, defrosted, left open and recorded, and which of those belongs in the specification, not to whoever switches the board off.

The complaint is almost never the plant

The unit has a nameplate and a set of gauges on it; the envelope has neither. A refrigeration plant short of temperature has not usually lost capacity: it is answering a heat load larger than the one it was selected against, and its own gauges do not report that. The same error on the air side leaves the cabin that is cold and still damp; here it is a screw through the vapour barrier.

Heat enters by three routes: through the insulation, around it, and through the openings. The first is a material question and the rarest; the other two are workmanship, and a refit makes them. So the envelope is proved while the linings are off, and the plant judged against a corrected load.

A fixing is the usual breach

The insulation does the work; the vapour barrier on the warm side keeps it able to, which is why the barrier is worth proving. A puncture lets warm, wet air into the thickness, where it condenses and stays, and nothing in a cold box dries it out again. The drain is the only opening meant to let something out, and a box below freezing keeps it busy: a hole to be detailed, not bored through an insulated cold box.

The usual breach is a fixing. A shelf standard, a rail or a lamp wants a screw, and one driven from inside goes through lining and barrier alike, ending as a cold spike with a wet halo. The fitting was always wanted; the detail was not drawn, so somebody invented it at a bench without sight of the barrier. A lining in a cold box is the plainest case of what a panel has to carry before anybody looks at its face.

The other way round the insulation is the frame, carrying heat from the cold face to warm structure as fast as the plant takes it out. The symptom shows outside the box: a wet line on a bulkhead, a stain in a locker, none of it cheap to find once the panels are back on. Which is why the camera that finds gaps in a lagged duct run has a use on a cold box.

The door, the gasket line, and the joinery that moved

A cold box door is a moving insulated panel that has to land flat on a continuous gasket, and the line it lands on is a plane. If any part of the frame has moved, the gasket touches in places and bears nowhere: a seal bearing on three sides and clear on the fourth leaks without the latch having changed at all. The plane is what gets measured, not the closure.

A refit moves that plane. A sole built up for a new covering lifts the threshold; a lining remade slightly proud carries the hinge face forward. Each is a change of a few millimetres in a line with no tolerance left, and the last anybody re-measures — worth a sheet of paper drawn round the seal once the joinery is finished.

What happens to the boxes during a yard period

A yacht cold store joins the short list of systems that cannot simply be isolated and left, and nobody writes the decision down for it. A box kept live keeps a wet, cold face and an open drain in a compartment full of dust and hot work. A box shut up is a warm, damp void nobody opens for weeks — and the lining that comes out is not the lining that went in.

The specification carries it as three lines, not one.

• a named supply, and whose it is once hers is off
• an emptied box, propped open and dry, with the date on it
• a reading, and the person who takes it

Neither is free, and the decision is cheapest while the specification is still open. A yard period leaves the boxes aboard either way, in Turkey as anywhere, and on the first morning it falls to whoever is switching the board off.

The duty changed when the interior changed

A refit that opens a galley, moves a bulkhead or adds a provision store changes the volume to be held, so the plant that suited the old arrangement is wrong in the new. A unit whose volume has changed is selected again; a swap is not a selection, and the selection is somebody's signature against a figure.

A box moved to a wall with an engine room behind it loses more through the same envelope. A wine system is asked to hold a narrower band than a provision store — what that band is belongs to her owner and to the maker, and swing spoils what it holds sooner than warmth does. And a box that holds alongside on a cool morning is answering a smaller load than she carries at anchor in high summer, so the duty is written against the worse case.

Which shop the box belongs to

Refrigeration is not one of the eleven doors. It is a discipline inside AC Repairs, the climate shop on the Tuzla waterfront, with the chillers, handlers, controls and the lagging of duct runs. Galley refrigeration, the cold store and a wine system leave that shop commissioned, with their spares written down against them; the galley equipment they serve is outfitting's. What a yacht refrigeration refit asks of it is a reading of the box before a figure for the plant.

The box is opened by the trade that built the lining and judged by the trade that holds it cold, two different shutters. A packing detail at a breached fixing is the refrigeration side's drawing, taken off the opening, not invented at a bench. Where both answer to one yard that is an ordinary sequence; split between two companies it becomes correspondence, which is not drawn off an opening.

What to send with the enquiry

Photograph each door shut on a strip of paper, with the strip left in the picture: where it pulls out freely the gasket is not bearing. Photograph the inside of every lining with the shelf standards still fixed to it, close enough to read the screw heads. Then say what sits on the other side of each back face — a passage, a locker, an engine space — because that decides how hard the envelope works. They are rarely in a refrigeration enquiry, and they settle more than the plant details.

Written at the yard in Tuzla. Every figure in a refrigeration scope comes from the maker and from the specialist who signs the duty against her own arrangement. What is written here is only where to look before any of those figures is argued over.