Drydock plan: schedule and budget

The vessel has been on blocks for four days. Grit-blasting the hull has exposed a patch of corrosion nobody had seen, the yard has just tabled an additional quotation for two seized sea valves, and the work list — thirty-five items when she left the berth — now runs to fifty-one. By the time she floats off, the final invoice exceeds the initial budget by 30 to 40 %, an order of magnitude most fleet managers will recognise without difficulty. None of this is inevitable: it is the signature of a drydock plan written too late, or never written at all.

Drydocking is almost always the largest maintenance item of the year. Between the off-hire time, the dock rental, the hull work and the mechanical jobs bundled into the same window, a single yard period can weigh as much as twelve months of routine maintenance. It is also the item that drifts the most, because it concentrates everything maintenance hates: discoveries below the waterline, long procurement lead times, a contractor in a position of strength once the ship is on blocks, and a redelivery date that does not negotiate.

What separates a drydocking endured from one under control is a document prepared twelve months in advance: a plan that fixes the schedule, the work list, the trade-offs and the budget — then serves as the reference during the yard period for deciding fast, and afterwards for measuring the variance. Here is the method, milestone by milestone.

What is a drydock plan?

The drydock plan is the steering document that organises the yard period as a project: the date and yard selected, the work list priced and prioritised, the budget with its contingency, the long-lead purchases, and the decision rules for whatever is discovered once the ship is out of the water. It is distinct from the yard's own schedule, which sequences the jobs day by day, and from the execution checklist, which verifies each item: the plan decides what to do, when and for how much; the other two describe how.

Plan, checklist, software: three tools, three moments

Three articles on this blog complement each other here, and it is worth placing them side by side. The drydock plan — this article — covers the upstream work: the multi-year schedule, the trade-offs, the budget. The annual haul-out checklist covers execution: item by item, what to inspect, photograph and sign off once the vessel is on blocks. And our article on drydock planning software deals with the tooling: what a maritime CMMS must be able to do to carry all of it. A mature operator uses all three: the plan to decide, the checklist to execute, the software to keep the record.

How often must a ship be drydocked?

For classed vessels, the general rule is two inspections of the ship's bottom in dry condition within each five-year class period, with no more than 36 months between them; one of the two normally coincides with the class renewal survey. Some classification societies accept, subject to the vessel's age and type, an in-water survey in lieu of the intermediate docking. Passenger ships and certain flags impose tighter rhythms — and operators of US inland and coastal towing vessels will find their own drydock and internal structural examination intervals in 46 CFR Subchapter M. In every case, the authority is your classification society and your flag administration.

The regulatory frame has one direct consequence: the docking schedule is built at fleet level and over several years, not vessel by vessel as the deadlines come up. Three constraints stack on top of each other:

• Class and flag deadlines: bottom surveys, renewals, tailshaft surveys. They bound the possible window; running them from the certificates module of the CMMS avoids discovering a due date three months too late. Our article on the classification survey calendar details this mechanism.
• Operational seasonality: a ferry docks outside the summer season, a fishing vessel between two campaigns, an offshore wind CTV during the winter weather window when transfers stop anyway. Immobilising the ship at the wrong moment costs more than the docking itself.
• Yard capacity: good docks are booked six to twelve months ahead, longer for larger units. An operator with six vessels that lets each ship book alone ends up with two of them on blocks the same month — and four crews stripped thin to cover the watchkeeping.

The deliverable of this step is a multi-year fleet docking calendar: for each vessel, the docking window for the next three years, set against the class deadlines and the operating seasons. It is revised once a year, and it is the backbone of the maintenance budget forecast, since drydocking is its largest line.

Twelve months ahead: a work list that builds itself

The first cause of budget drift is not the yard: it is the improvised work list. Written three weeks before docking, from memory and around a meeting table, it misses half the subjects — which resurface once the ship is on blocks, at unplanned-work rates and in a schedule already under tension.

A good list builds itself, throughout the cycle. Every anomaly observed but not urgent joins the list at the moment it is seen: a stern gland weeping a little more than usual, a sea valve stiff to operate, a patch of blistered coating spotted during a dive inspection, a stern tube clearance approaching the tolerance, anodes 60 % wasted by mid-cycle. In a CMMS this gesture takes thirty seconds: the engineer raises a deferred work order from his phone, photo attached, tagged "next docking". Because the app works offline, the observation is recorded at sea and synchronises at the port call.

Twelve months later, the technical manager filters the work orders tagged "docking" and the list exists: dated, photographed, located equipment by equipment, without having mobilised anyone. That is exactly what the maintenance module is for: turning the ship's observation into usable data ashore. The difference with the from-memory list is not cosmetic: on a typical docking, 20 to 30 % of the lines come from observations made more than six months before the yard period — precisely the ones a preparation meeting would have forgotten.

Six months ahead: sorting the work into three groups

A raw list of fifty lines is not a plan. Not all work carries the same weight, and the budget will not absorb all of it. The arbitration is done by sorting every line into one of three groups:

The regulatory group is framed early with the classification society: which surveys can be credited at this docking, which opening-up is required, which thicknesses must be gauged. The reliability group is where the CMMS history supplies the decisive argument. This bilge pump cost €6,800 in corrective work and two emergency call-outs over the cycle: replacing it in dock for €4,500 defends itself in one line. That heat exchanger has cost nothing for three years: it will run one more cycle. Without history, these decisions are taken on intuition — and intuition, under budget pressure, tends to defer exactly the job that would have prevented September's breakdown.

The output of the arbitration is a priced, prioritised list in which every deferred line records who decided the deferral and why. The detail matters: when the deferred valve fails mid-cycle, the point is not to find a culprit but to retrieve the reasoning — and improve it next cycle. Our article on the vessel maintenance budget develops this documented arbitration and how to present it to management.

Why does a drydock budget drift by 30 %?

Because what gets budgeted is the known work list, while a drydocking structurally carries three layers of cost: the fixed costs of the dock, the planned work, and the discoveries — and that third layer, statistically certain, is rarely provisioned. The drift is not an accident: it is the gap between a two-layer budget and a three-layer reality.

A serious drydock budget is structured like this:

Three rules make this budget hold. First, the contingency is a line item, not an admission of weakness: a budget for a ten-year-old vessel without a 10 to 15 % provision is a communication exercise, not a steering tool. Second, every work line carries a sourced estimate: last cycle's quotation updated, a list price, or the yard's figure — never a round number set from memory. Third, the budget is defended with history: two cycles of actual costs recorded in the CMMS give a docking cost per vessel per year, and turn the annual budget negotiation into a simple update. It is the same principle as for the rest of the technical OPEX, set out in our method for reducing vessel maintenance costs: you only cut what you measure.

Three months ahead: tendering the yards and launching the purchases

The specification package

The arbitrated list becomes a tender package sent to two or three yards: a description of each job, the vessel's drawings and particulars, the target window, access conditions on board, and a clear split between yard supply and owner supply. The more precise the package, the more comparable the quotations — and the less room the yard has to requalify as a variation order what was left ambiguous. Compare the quotations line by line rather than on the bottom total: a yard that undercuts on the docking lump sum but charges twice the hourly rate on additional work will cost more in the end, because the discoveries will be paid at that rate.

Purchasing drives the schedule

At three months out, the critical path is no longer the yard: it is procurement. Anodes in the right references and quantities — the anode replacement plan is calculated from the cycle's wastage readings, not from a rough safety margin —, sea valves, coatings and antifouling compatible with the existing system, stern gland packing, bearings, shaft seals: some of these lead times exceed eight weeks, more for maker's parts. The scenario of a ship on blocks waiting for a part ordered too late is paid at full price: every additional dock day is invoiced whether the yard works or not.

This is where a purchasing workflow linked to stock makes the difference: purchase requests are generated from the docking work orders, supplier lead times are known, and the existing stock is checked before ordering — it is remarkably common to find, in the store, valves bought for the previous docking and never fitted. Every part received is matched to its work order: at docking, the technical manager knows precisely what is on board, what is in transit and what is missing.

During the yard period: discoveries, variation orders and acceptance

The plan does not stop at the dock gate; this is where it earns the most. Three disciplines hold the budget during the stoppage:

• The daily meeting: fifteen minutes every morning between the ship, the superintendent and the yard, on yesterday's progress and today's discoveries. A deviation flagged the same day can be negotiated; discovered on the invoice six weeks later, it can only be endured.
• The variation order rule: no discovery is handled verbally. Every additional job gets a written quotation, checked against the contract hourly rate, approved by the person named in the plan — and attached to a work order in the CMMS, with a photo of the finding. This traceability changes the balance of power when the final invoice is discussed: you answer recollections with dated records.
• Acceptance item by item: every completed job deserves a dated record, before-and-after photographs, and a signed acceptance — the annual haul-out checklist details the inspection points, from gland packing torque to anode electrical continuity. Accepting as you go, rather than in a block the day before undocking, gives you the right to have a job redone without moving the float-off date.

This documentation pays twice. Immediately, on the invoice. Years later, when the hull's upkeep has to be proven to an insurance surveyor after damage, to a Port State Control officer, or to the vessel's buyer — a complete, photographed docking file bears directly on resale value.

After undocking: turning the docking into data

The docking that ends prepares the next one, on four conditions:

• Close the work orders with their actual costs: parts, hours, the yard invoice broken down item by item. This is what makes the next estimate reliable.
• Reset the counters on replaced or overhauled equipment, so that the preventive schedule restarts from a true baseline.
• Carry the deferred work forward explicitly: every line not done is re-entered on the next docking list, with its justification. A silent deferral is a lost deferral.
• Compare actuals to budget, line by line: where were the variances, which discoveries could have been anticipated, was the contingency well calibrated? This two-hour review is worth more than any good resolution.

After two cycles, the operator has a docking cost per vessel per year, a measured drift rate, and a work list for the next docking already two-thirds built. Drydocking stops being the dreaded event of the year and becomes an instrumented process — a handful of maintenance KPIs such as the deferred backlog and the budget variance are enough to steer it. That is the spirit of the complete maritime CMMS guide: making each operation a data point for the next.

The drydock plan timeline in one table

Key takeaways

A drydock plan is neither a checklist nor a yard schedule: it is the steering document that turns the year's largest maintenance item into a managed project. Its raw material is time: a work list fed by observations for twelve months, trade-offs decided six months out on the cost history, purchases launched at three months, and a budget that owns its contingency instead of pretending there will be no discoveries. During the stoppage, the discipline of written variation orders and photographed acceptance protects the budget; afterwards, the line-by-line comparison prepares the next cycle.

None of this requires sophisticated tooling — but all of it assumes that the ship's observations, the work orders, the purchases and the costs live in one place, reachable at sea as well as ashore. That is precisely what a maritime CMMS does: the observation recorded offline becomes a deferred work order, the docking list is filtered in one click, purchase requests flow from the work orders and the acceptance file builds itself as the stoppage progresses. Smart Sailors is designed in Marseille by seafarers and deployed on more than 700 vessels, from fishing to offshore wind. Tell us about your next docking, or take a look at our plans — the trial is free for 30 days, long enough to build your first work list.