What a refit does to her weight, and to her stability

Almost no refit quotation has a weight column in it, and almost every refit is a weight transaction. Stone where there was veneer, heavier cable trays overhead, a crane sized for a bigger chase boat.

Yacht refit weight and stability is the one account nobody opens at the start, which is why so few are reconciled at the end.

Weight is a discipline rather than a calculation.

Every refit is a weight transaction

The spending is rarely dramatic. A battery bank where a locker was. Acoustic insulation fitted to answer a complaint about something else. Added tankage, larger glass, a chilled-water plant moved up a deck. Each is defensible in isolation, and isolation is the problem. Together it is weight growth.

The credit side is as real and as unrecorded. Linings and furniture that never went back, a redundant tank cut out, insulation that left heavier than it arrived. Deducted weight is half the account, and the order the work runs in leaves that half to trades who have gone before the additions arrive.

The register is opened with the first panel out

The deliverable is not a report at the end but a weight and centres register, opened at the first item stripped out and closed on the day she floats. Each line carries the same fields.

• What it is — a named item, not a compartment or a trade: a pump and its seating, a run of cable tray, a stone counter.
• Mass — and whether it was weighed or calculated. Either is acceptable; confusing the two is not.
• Position — longitudinal, transverse and vertical, against the datum her own drawings use.
• Sign — removals entered as rigorously as additions, on the day they leave the vessel.
• Status — estimated, ordered or installed, because a register that cannot tell a plan from a fact is a wish list.

Kept that way, the number is known while it can still be changed. A stone specification questioned during strip-down is a conversation; the same stone found once she floats leaves ballast or removal. Which is why a refit specification three yards can price asks each yard for a mass and a position, and what a panel itself has to weigh is a joinery question.

Where the weight sits moves the centre of gravity

Total mass is the least interesting number in the register; position does the work.

A few hundred kilos at the head of a deck crane is little against her displacement and a heeling problem the crane maker never saw, because it sits on a lever arm. Height works less visibly: the booklet was approved against a centre of gravity at a given displacement, not a tonnage, so weight added high can take her outside it while the total barely moves.

A slack tank carries a free surface effect, and the loss does not depend on how much is in the tank — an inch across a wide tank top costs what a half-full one does. It depends on the width of that surface and the density of what lies on it, so tankage subdivided in a refit is recalculated across the loading conditions.

An owner sees none of this as arithmetic. He sees a standing list, a roll gone slower and softer, less freeboard aft, less reserve before a low opening nears the water. Metacentric height and righting arm are what the booklet is written against; a list and a lazy roll are what they look like from the deck.

Three exercises owners hear as one name

Three exercises get one name in a yard meeting, and answer three different questions.

A weight estimate is a prediction, updated as items are specified. It says where the refit is heading while there is time to steer, and carries no authority.

A deadweight survey measures what she has become. Read her draughts in still water, tanks and stores in a known state, and you have her displacement and longitudinal centre of gravity. What it cannot see is height.

An inclining experiment can. Known masses are moved athwartships, the heel is measured, and the vertical centre of gravity is established for the lightship condition. It has conditions attached — upright, free to heel, moorings slack, tanks pressed or empty, the water quiet — which is why it is booked against the weather, not the programme.

The estimate steers, the survey confirms displacement, the inclining settles height.

The stability booklet is a deliverable with a lead time

Owners speak of the stability booklet as though it survives the yard period. Past a certain change it does not stop existing; it stops being true, and nothing on it says so.

Which change is large enough is not the yard's decision. The booklet was approved against a lightship weight and a set of centres; once the refit moves either beyond it, the owner's naval architect, the attending surveyor and the flag decide whether a deadweight survey closes it or an inclining is required. The register says how far she has moved before anybody measures. What class asks of the yard is a separate calendar.

A reissued stability booklet is bought: naval architecture hours, an inclining or a deadweight survey the yard supports, revised loading conditions, a submission and an outside review. A yacht waiting alongside for one accrues berth and staging as if a trade were aboard, so it belongs on the exclusions page, named, with the exercise it depends on stated: excluded without saying who produces it, it is a cost that lands after she floats.

The margin, and the refit after this one

The margin she launched with was never only weight. It is centres, generator capacity, crane and davit rating, and the volume new equipment must fit into. Yacht refitting spends across all of them at once.

Spending the margin is not the failure; spending it without recording it is. The yard standing in this compartment in ten years works from whatever documents leave this shed. If those say one thing and the yacht says another, it re-measures what was already known here, or declines the work.

Yacht refit weight and stability is a record-keeping discipline before it is a naval architecture one. Naval architecture and interior design are in-house here, minutes from the berth, so a weight question is a walk rather than a letter. Stage One ends with a written condition report, an approved scope and a price that does not move; a scope agreed without a mass and a position has priced only half of each line.

A weight and centres register is how a yacht stays refittable.

Written at the yard in Tuzla. Which calculations a given vessel needs, and whether they close, is for the owner's naval architect and the attending surveyor to say.