The GM/YM family is Yanmar's small auxiliary range for sailing yachts and small displacement craft. In our catalogue it runs from the 9 MHP single-cylinder 1GM10 through the two-cylinder 2YM15 (14 MHP) to the three-cylinder 3YM20 (21 MHP) and 3YM30AE (29 MHP) — all naturally aspirated, indirect-injection diesels built around simplicity, compact size and easy servicing in tight engine bays.
The GM line is one of the most recognisable names in sail auxiliaries, and the 1GM10 continues that tradition: a light, raw-water-cooled single that remains a default choice for small yachts where weight and simplicity matter most. The YM series superseded Yanmar's older two- and three-cylinder GM engines with freshwater heat-exchanger cooling, smoother and quieter running, modern emissions compliance and straightforward access to routine service points — a meaningful upgrade for boats that live on saltwater moorings.
The GM/YM Series range
Choosing within the family mostly comes down to displacement and how hard the boat has to punch into a seaway. The 1GM10 suits small, light yachts where a simple, light single is enough; the 2YM15 adds a second cylinder for noticeably smoother running in small cruisers and trailer sailers; the 3YM20 is the all-rounder for mid-size yachts; and the 3YM30AE gives heavier or higher-windage boats the reserve to hold speed into wind and tide. Note the YM engines are freshwater-cooled while the 1GM10 is raw-water-cooled — worth weighing for a boat kept on a saltwater mooring. Hull type, waterline length and propeller all shift the answer, so we size each engine to the actual boat rather than a rule of thumb.
Drive options
Shaft drive (KM gearbox)
Paired with Kanzaki KM-series mechanical gearboxes (KM2P-1) — the natural fit when repowering a yacht with an existing shaft and stern gear.
SD25 saildrive
Yanmar's current saildrive is engineered to match the 1GM10, 2YM15, 3YM20 and 3YM30AE. Many older boats carry the earlier SD20 — we check bed and hull-aperture compatibility as part of any repower quote.
V-drive (1GM10V)
The 1GM10 has also been offered as the 1GM10V, fitted with Yanmar's KM3V V-drive gear for aft-engine layouts; ask us to confirm current availability for your installation.
Boats this family suits
Pricing, repower advice or a spec for your boat
Tell us your vessel and how you use it — we'll recommend the right model and drive, with dealer pricing.
Why buy your GM/YM Series from Mariner
Proven small-yacht pedigree
Decades of GM-series service earned this family its reputation for starting when asked and running for thousands of hours. The YM engines add freshwater heat-exchanger cooling, quieter running and easy service access to that same simple, mechanical formula.
Authorised dealer, factory-trained
As an authorised Yanmar dealer we supply new engines with full factory warranty, service them with factory-trained technicians and fit genuine Yanmar parts — all from our Spotswood workshop.
Repower done properly
We handle the whole changeover: engine beds and mounts, shaft or saildrive alignment, exhaust and fuel systems, then commissioning with a sea trial on Port Phillip Bay before handover.
Yanmar GM/YM Series — your questions answered
Which GM/YM model does my yacht need?
As rough guidance, lighter small yachts run happily on the 1GM10 or 2YM15, while mid-size and heavier cruisers step up to the 3YM20 or 3YM30AE. But displacement, waterline length, windage and propeller matter more than length alone, so we confirm sizing against your actual boat — over-propping a small diesel is a more common problem than under-powering.
Can a YM engine replace my old Yanmar GM?
Usually, yes — the 2YM15, 3YM20 and 3YM30AE are the factory successors to Yanmar's older two- and three-cylinder GM engines, and they're the usual repower path for those boats. That said, mounts, beds, exhaust and control runs often need work, so we inspect the boat before quoting rather than promising a bolt-in swap.
Saildrive or shaft drive for a repower?
If the boat already has a shaft, staying with a KM gearbox is normally the simpler, cheaper path. If it has an existing saildrive, the current SD25 pairs with every engine in this family, though boats with the earlier SD20 need a compatibility check on the bed and hull aperture. Switching between the two systems is possible but involves structural work, so it needs a genuine case.
Who services these engines in Melbourne?
We do — Mariner Engineering is an authorised Yanmar dealer in Spotswood with factory-trained technicians, genuine Yanmar parts and warranty support, servicing boats across Port Phillip Bay. Call (03) 9399 5888 to book.
Ask about the GM/YM Series range
Tell us your vessel, how you use it, and whether this is a new build or a repower — our team will recommend the right Yanmar GM/YM Series model and drive, with pricing, usually within 1 business day.