Start from criticality, not from the catalogue
Every ship carries too many of the wrong spares and too few of the right ones. That is not a criticism of any particular fleet; it is the natural result of inventories that grow by accumulation rather than by design, over decades, across changes of manager, crew and equipment.
The ISM Code requires identification of equipment whose sudden operational failure could result in a hazardous situation. That list is the correct starting point for spares strategy.
| Criticality tier | Definition | Stocking policy |
|---|---|---|
| A — Critical | Failure stops the ship or creates a hazardous situation | Hold on board; no stockouts tolerated |
| B — Important | Failure degrades operation or redundancy | Hold on board or in a regional hub |
| C — Routine | Failure is an inconvenience | Order against consumption |
| D — Consumable | Filters, seals, gaskets, fasteners | Min/max on consumption rate |
The classification must be done by engineers who know the ship, reviewed annually, and held against the same equipment register the PMS uses. If purchasing and maintenance classify differently, neither classification means anything.
Setting min/max levels
For each stocked item:
Minimum = (average consumption per month × lead time in months) + safety stock Safety stock rises with criticality and with lead time variability Maximum = minimum + economic order quantity
Lead time variability matters more than lead time. An item that reliably takes eight weeks is easier to plan than one that takes anywhere between two and twelve.
OEM versus equivalent: write the policy down
The decision should be made once, by policy, not per requisition under time pressure.
| Situation | Policy |
|---|---|
| Class-required or type-approved components | OEM or approved equivalent only |
| Critical equipment, warranty in force | OEM |
| Critical equipment, out of warranty | OEM or qualified equivalent with engineering approval |
| Non-critical rotating equipment | Qualified equivalent acceptable |
| Consumables meeting a published standard | Any compliant supplier |
| Safety and firefighting equipment | Approved products only |
The word doing the work is qualified. An equivalent that has been assessed by an engineer against the specification is a legitimate saving; one chosen because it was cheaper on a website is a future casualty.
Fleet-level thinking
Single-ship inventory optimisation is a local optimum. Across a fleet:
- Pool by sister class. Vessels with identical machinery can share a regional stock rather than each holding a full set.
- Regional hubs. Position slow-moving critical spares at a hub near the trading pattern rather than on every ship.
- Visibility across ships. A part sitting unused on vessel four should be visible to vessel nine.
- Consolidated purchasing. Fleet demand aggregated gets better prices and better lead times.
- Rotable management. Overhaul exchange programmes for turbochargers, injectors, governors and similar assemblies.
Onboard discipline
| Practice | Effect |
|---|---|
| Structured storerooms with location coding | Parts are found instead of reordered |
| Receipt checked against PO and equipment code | Wrong parts detected before the job |
| Preservation of stored spares | Corrosion in a store is pure waste |
| Shelf-life tracking for rubber, chemicals, batteries | Prevents fitting expired items |
| Annual physical stocktake reconciled to system | Keeps the data honest |
| Consumption recorded against the PMS job | Builds real consumption data |
That last one is the foundation of everything. Without consumption recorded against jobs, min/max levels are guesses forever.
Measuring it
| KPI | Target |
|---|---|
| Critical spare stockout rate | Zero |
| Urgent/AOG order rate | Falling; each one root-caused |
| Inventory value per vessel | Stable or falling with service level maintained |
| Stock turns on consumables | Rising |
| Obsolete stock value | Identified and written off, not hidden |
| Delivery on time in full from suppliers | Above 90% |
Inventory value falling while stockouts stay at zero is the signal that the strategy is working. Either measure alone can be gamed.
criticality framework aligned to ISM Code requirements on critical equipment. Weighting chart is an indicative model. Reviewed by the Zeaclub Editorial Team, 24 August 2026.
Frequently asked questions
How much spares inventory should a ship carry?
Enough that no critical spare is unavailable when required, and no more. The right number is derived from criticality, consumption and lead time, not from a fixed value.
Are aftermarket spares acceptable?
For many applications, where qualified against the specification and where class, type approval and warranty considerations permit. Write the policy by equipment criticality rather than deciding case by case.
How do we reduce urgent orders?
Link requisitions to PMS due dates so spares are staged before the job, and treat each urgent order as an event requiring a root cause.
Should spares be pooled across a fleet?
Where vessels share machinery, yes — regional hubs and shared visibility reduce total inventory while improving availability.