why do drydock overruns occur and how to prevent them?

Drydock overruns occur when the planned scope is incomplete or changes faster than procurement, planning, and yard execution can absorb, and they are prevented by locking scope early, validating condition, and controlling change through disciplined maintenance scheduling and cost estimation.

How drydock overruns occur and how to prevent them

• Scope gaps from limited pre-docking inspection, where underwater condition, scantlings, corrosion extent, or coating failures are only confirmed once the vessel is opened up, driving additional steelwork and rework.
• Change-order dynamics during execution, where new findings trigger procurement lead times and additional labor hours that are not reflected in the baseline schedule or budget, increasing repair delays and cascading into other work packages.
• Planning and logistics mismatches, including late arrival of materials, missing spares, or insufficient access planning for blasting, coating, and alignment work, which can stall critical-path tasks.
• Yard and resource constraints, such as drydock availability, workforce leveling, or subcontractor capacity, which can extend duration even when technical work is progressing.
• Pre-docking inspection and scope lock practices that reduce uncertainty before the vessel enters the drydock, for example through structured pre-docking checks and documentation discipline (pre-docking before dry-docking).

Operational Impact

1. Budget visibility and cost control: Unplanned work increases direct costs and can also inflate indirect OPEX through extended off-hire time, crew cost during layup, and additional supervision, so fleet managers need tighter cost estimation baselines and change-order governance to prevent uncontrolled spend.
2. Downtime risk and schedule integrity: Technical managers face repair delays when critical-path items slip, which can force re-sequencing of maintenance scheduling, delay class-related tasks, and increase the probability of further defects being discovered after access is restored.
3. Asset reliability and audit readiness: Incomplete documentation of what was found, what was changed, and why can weaken corrective action tracking and complicate future maintenance planning, especially when multiple drydock cycles are compared for trend analysis.

Important to know: Treat the drydock plan as a living baseline with a formal change-control workflow. Before docking, require condition evidence for each work package (inspection findings, thickness measurements, coating condition, and defect mapping), then link every approved change to an updated schedule impact and a revised cost estimation template so maintenance scheduling decisions stay financially and operationally defensible.