Super Yacht Engines: We Come to the Subject of Engines

When it comes to superyacht engines, we quickly find ourselves in a quandary. Not all yacht engines are created equal. Put simply, there are big engines, reliable engines, heavy engines, high-performance engines, engines requiring more or less maintenance, engines laden with accessories, emissions-regulated engines, and engines that are not. The list goes on, but at some point, a decision must be made.

Redundancy First: Why We Chose Two Super Yacht Engines

The easiest part of the decision was this: we wanted two engines for redundancy.

Vanguard will have:

• Two engines

• Two independent service fuel tanks

• Separate filtration systems

This ensures that if we ever encounter fuel contamination, we can still make progress on one engine, provided we never co-mingle bunkers.

Our hull is hydrodynamically efficient, requiring approximately 120 kW for a theoretical 12 knots. That’s extremely modest for a motor yacht of this size, more akin to a fast sailing yacht.

Propellers, Shaft Speeds & Eliminating High-Speed Diesel Engines

Efficient propellers are slow-turning propellers. Large merchant ships often run at less than 100 RPM. We can’t go that low, but our 700–750 mm propeller diameter limit requires:

• A gearbox reduction around 2.5:1

• A maximum engine speed of roughly 2300–2500 RPM

This immediately eliminates a whole class of high-speed diesel engines.

Regulations Matter: US EPA Tier 3 Compliance

Because Vanguard will likely operate in US waters, we needed engines meeting EPA Tier 3 emissions standards in this power range. That rules out beautiful classics like the Gardner engines used on Mobius.

We also required global parts and service support, leading us to a shortlist:

• CAT (Perkins)

• John Deere

• Yanmar

Excellent engines such as Scania or Cummins were eliminated due to minimum power output.

The Final Choice: John Deere 4045 AFM85 (M1 Rated)

After considerable study, including advice from Steve and Linda Dashew’s FPB series on SetSail.com, we settled on:

John Deere 4045 AFM85

• M1 rated

• 120 kW @ 2300 RPM

• Tier 3 compliant

• Common-rail, turbocharged, aftercooled

• Continuous-duty capable

• Built on a block used in configurations exceeding 700 bhp

This gives us a strong, reliable, conservatively loaded engine. The supporting systems (turbo, aftercooler, common-rail injection) add complexity, but the benefits outweigh the drawbacks.

And we have two redundancies that continue to be our guiding principle.

What About Yacht Generators?

That answer will likely surprise you and deserves its own post.

👉 Read next: How We Picked Yacht Generators (or Not)

Additional Reading

• Yacht Propeller Choices: Autoprop vs. CPP?

• Greening Your Explorer Yacht