Inboard Boat Maintenance & Annual Service

Recommended inboard boat maintenance is mostly a calendar problem — oil and filters, impeller, anodes and bellows all come due on different intervals, and we track them so you don't.

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⭐ X.X from N reviews · Done at your slip or lift · Published rates

The schedule

Gas inboards and sterndrives. Whichever comes first — hours or calendar.

Intervals vary by engine and drive manufacturer. We work to your boat's published schedule — tell us what you have and we'll confirm.

⚠ Winterisation on an inboard is not optional

This is the single biggest difference between owning an inboard and owning an outboard, and it is where the expensive mistakes happen.

An outboard largely drains itself when you tilt it down. An inboard does not. Water sits in the block, the manifolds, the risers, the heat exchanger and the hoses. If it freezes, it expands — and it cracks whichever of those it's sitting in.

A cracked block is an engine. A cracked manifold is an expensive afternoon. Neither is covered by anything.

Proper winterisation means: draining every water passage — block, manifolds, risers, hoses, raw-water pump — or filling with the correct antifreeze; fogging or stabilising as appropriate; changing the oil before storage so acidic used oil isn't sitting in the engine for five months; and dealing with the battery.

"I'll do it next weekend" is how blocks crack in this climate. The first hard freeze doesn't announce itself. Book it in autumn.

This isn't hypothetical. Our technician has replaced multiple engines over his career for exactly this — water left in over winter, frozen, expanded, and split the block. Transmission coolers go the same way. Every one of those was a boat that was fine in October and finished by March, and every one of them was preventable in an afternoon.

An engine is the single most expensive thing on your boat. Winterisation is one of the cheapest jobs we do.

What annual service includes

One visit, at your slip or lift.

Engine — oil and filter, fuel filter and water separator, plugs, cap, rotor and leads where fitted, belts and hoses, and everything checked while running.

Cooling — impeller condition assessed (replacement is a separate job), thermostat, hoses, coolant condition on closed-cooling engines, and the raw-water side inspected end to end.

Exhaust — manifolds and risers assessed. On raw-water-cooled engines these are a wear item on a schedule rather than a fail-and-fix part, and why that matters is explained here.

Drive — outdrive gear oil, bellows inspected, gimbal bearing greased, anodes checked and replaced at half-worn, alignment verified.

Everything else — transmission or V-drive fluid, steering and trim, batteries and charging, bilge pumps, and a look for anything developing.

You get written notes on condition and anything found, with a price, before it happens.

The items owners skip — and what it costs

Anodes. Cheap, and they stop protecting once half-consumed. Corrosion in an aluminium outdrive doesn't reverse.

Bellows. Nothing feels different until water is in the gimbal housing. This is the one that sinks boats.

Exhaust manifolds. Rust from the inside where nobody looks. When a riser lets go it puts water into a cylinder.

Alignment. Silently destroys couplers, gimbal bearings and transmission thrust bearings over a season or two.

The impeller. Scheduled, not condition-based — a vane that's taken a set still pumps at idle and stops under load.

None of these announce themselves. That's the entire argument for a schedule rather than waiting.

We track the calendar

Different intervals, different clocks, and an hour meter most owners never look at. We keep a record for your boat — what was done, at what hours, on what date — and tell you what's due before the season rather than after something fails.

Ask about ongoing service when you book.

What it costs

Annual inboard service is quoted per boat, because access varies more between inboards than any other job we do — an engine bay you can stand in and one you reach through a hatch are different jobs with the same parts list.

Rates and how we quote. Anything found is priced before it happens.

Frequently asked questions

What is the recommended maintenance for an inboard boat?
Annual service covering oil and filters, ignition, cooling, drive and anodes, plus winterisation in autumn and commissioning in spring. The interval table above covers the detail.

How often should an inboard boat engine oil change be done?
Every 50–100 hours or annually, whichever is first — and always before winter storage, so used oil isn't sitting in the engine all winter.

My boat barely gets used. Do I still need annual maintenance?
Yes. Most of what fails on a lightly used inboard fails from sitting — bellows perish, impellers take a set, anodes still corrode, and fuel goes off. Low hours is not low risk.

What happens if I skip winterisation?
In this climate, potentially a cracked block, manifold or heat exchanger. It's the one maintenance item where a single missed year can cost more than the boat's annual running costs combined.

Do you do this at my slip or does the boat need hauling?
At your slip or lift. Nothing in annual service requires a haul-out.

Is inboard maintenance more expensive than outboard?
Yes, mostly because of access rather than parts. More on why.

Do you service inboard outboard (I/O) sterndrives too?
Yes — the schedule above covers both straight inboards and sterndrives, with the drive items applying to I/Os.

What about diesel inboards?
Different schedule and different diagnostics. Marine diesel maintenance is here.

Book annual inboard service

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