Marine diesel engines for Lagoon catamarans
Lagoon is the largest production cruising catamaran builder in the world, and a substantial part of the Australian cruising cat fleet, including a good deal of ex-charter tonnage.
The usual arrangement
Lagoons are delivered with twin engines on saildrives, most commonly Yanmar, with Volvo Penta on parts of the range and in certain periods. Engine sizes step up with model size across the range.
Verify from the plates — there are two, one per hull, and they should match.
Ex-charter boats are the local issue
A large share of the Lagoons sold in Australia have been through a charter fleet somewhere in the world. That is not automatically bad — charter boats are serviced to a schedule because downtime costs money — but it produces a specific condition profile:
- High hours, often accumulated in warm tropical water
- Heavy low-speed manoeuvring, which is hard on gearboxes and control cables
- A lot of engine-charging hours, which is low-load running
- Legs that have worked hard in warm marina water
- Documented servicing that stops at handover, with a gap afterwards
The question on any ex-charter Lagoon is not the hour meter. It is the records, the leg condition, the diaphragm dates and what happened between the fleet selling it and you looking at it.
What comes up on these boats
Two diaphragms, and their age. The single most important thing to establish.
Leg anodes in the tropics. Ex-charter boats from the Caribbean, the Med or Southeast Asia have spent their lives in warm water. Anode and leg condition should be assessed, not assumed.
Engine bay heat. Lagoons place engines in the aft sections of each hull. Access is generally good; ventilation on a hot Australian day is worth checking, particularly on a boat that motors in still air.
The generator, where fitted. A separate engine with its own raw water circuit, impeller, anodes and service schedule, and it is routinely forgotten until it stops.
Charging strategy. Owners who run engines for power rather than propulsion accumulate low-load hours, which glazes bores. If that is your pattern, run them up under real load regularly.
Repowering a Lagoon
Twin saildrive installation, so both engines and both legs are in scope, and the drive family constrains the engine choice unless you take on hull work.
Ask for the quote itemised per hull, and establish whether legs, diaphragms, propellers, panels and looms are included.
Frequently asked questions
What engines do Lagoon catamarans have? Twin saildrive auxiliaries, most commonly Yanmar with Volvo Penta on parts of the range. Check both plates — there is one engine per hull.
Is an ex-charter Lagoon a bad buy? Not automatically. Charter fleets service to a schedule. What matters is the records, the leg and diaphragm condition, and what happened after the fleet sold it.
How do I assess a Lagoon’s saildrives? Diaphragm replacement dates, leg oil condition, anode wastage, and whether the legs have been antifouled with an aluminium-safe system.
Why do the engines have high hours but low sea miles? Charter and liveaboard use accumulates hours charging and manoeuvring at low load, which is not the same duty as propulsion.
Should I service the generator at the same time? Yes. It is a separate engine with its own raw water circuit, impeller and anodes, and it is the most commonly neglected item on these boats.