You're anchored in a bay you've been looking forward to for three weeks. The raw water pump starts making a noise you don't like. You go to the spares locker and spend forty minutes pulling out bags and boxes before concluding you either don't have an impeller, or it's somewhere you can't find it.
Every experienced cruiser has a version of this story. The answer isn't carrying more spares — it's knowing exactly what you have, where it lives and when you last used one. That's what a proper spare parts inventory does.
Why spare parts management matters more offshore
In a marina with good boatyards nearby, running out of a spare is an inconvenience. Offshore or in a remote anchorage, it's a passage-ending problem. Experienced cruisers treat their spares inventory seriously not because they expect everything to break, but because knowing what you have changes how you make decisions at sea.
Good spares management also stops you over-buying. Without a list, most boat owners buy duplicates of things they already have because they couldn't be sure, while going without items they actually needed.
What to include in your spare parts inventory
Engine and mechanical
- Raw water impellers (carry at least two)
- Engine oil filters and fuel filters
- Drive belts — alternator, raw water pump, any others fitted
- Impeller housing O-rings and gaskets
- Zincs — hull, shaft and trim tabs
- Injector seals (diesel engines)
- Thermostat
- Starter motor relay and solenoid
Electrical
- Fuses — full set of all ratings used on your boat
- Spare bulbs for navigation lights
- Wire terminals and heat shrink connectors
- Spare wire in common gauges
- Switches — spare rotary and toggle switches
Plumbing and bilge
- Bilge pump impeller and housing
- Hose clamps — various sizes
- Hose repair tape and underwater epoxy
- Seacock servicing kit
- Water pump diaphragm and valves
Rigging and deck (sailing vessels)
- Shackles — a range of sizes including twist-lock
- Blocks and turning blocks
- Clevis pins and split pins — common sizes
- Spare halyards and sheets (or at minimum the wire to replace them)
- Furling line
- Sail repair tape and a sailmaker's needle and thread
General consumables
- Engine oil (at least one full oil change quantity)
- Waterproof grease and anti-seize compound
- Acetone and contact cleaner
- Sikaflex or equivalent sealant
- Stainless steel screws and bolts — mixed bag
How to organise what you carry
Use containers, not drawers
Loose items in a locker don't stay organised. Plastic containers with lids — numbered or labelled by system — keep things findable under passage conditions when a locker has been inverted a few times. The key is that every item has a place, and the place is recorded somewhere you can search.
Record location, not just existence
The most common failure of spare parts lists is recording what you have but not where it lives. "Impeller — aft locker, blue box" is useful. "Impeller — yes" is not. When you need something at 0200 in a seaway, location matters as much as whether it's onboard.
Track quantities and set minimum levels
Some items you carry multiples of — impellers, filters, fuses. Tracking quantity lets you know when you're down to your last one, before you're in a situation where you need two.
Review before every passage
A spare parts review before a significant passage takes fifteen minutes. Check that the items most likely to be needed are at minimum stock levels, that nothing is missing from the last repair job and that anything used has been noted for replacement at the next port.
The right spares list depends heavily on your boat, its age, your engine, how far offshore you cruise and whether you do your own work. Use this as a starting point and adapt it to what you actually need — not a generic list of everything that could possibly fail.
The minimum viable approach
If you're starting from scratch, the most important thing is to have a list at all — even an imperfect one. Start with the items most likely to fail on your specific boat, record where they live and review it before passages. Add to it every time you do a repair or find a gap.
The goal isn't a perfect inventory managed to commercial-fleet standards. It's knowing that when you need something, you can find out in two minutes whether you have it and where it is.
Know what's onboard and where it is
Boatwise is a boat management app for independent boat owners. Track your spare parts inventory, set minimum stock levels and know exactly what you need to restock before the next passage.
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