Lessons from a Previous Yacht Build.

Learning From the XPM78-01 Mobius

The first XPM78, Mobius, was built by Wayne and Christine to an Artnautica design. Both are highly experienced sailors and good friends whose choices reflected their own priorities. That is one of the real advantages of building a boat: you get exactly what suits you.

Our boat, Vanguard (XPM78-02), evolves this design. Many features carry forward, but we made several key changes based on our own experience, needs, and preferences. Here are the major lessons and what we chose to adjust.

General Interior Layout: Three Cabins With Natural Light

We needed three cabins—master, family, and guest—with each serving a specific purpose.

Master Cabin

• Located near the center of buoyancy

• This is the most comfortable place aboard in a seaway

• Ideal for sleeping on long passages

Family Cabin

• Close to the main access points

• Easy movement, easy watchkeeping transitions

Guest Cabin

• Has its own access for privacy

• If we carry crew, they are not intruding on family space

Because my wife is claustrophobic and prefers daylight, all cabins include skylights and small through-hull ports for natural light and ventilation.

On a 78-foot hull, this layout is easy to achieve, but it required two structural changes:

1. Raising the saloon by 300 mm to gain headroom

2. Reconfiguring the fuel tanks below to match the new levels

Expanding and Refining the Saloon

We also extended the saloon forward by 1000 mm to create:

• More space around the helm

• Room for an additional companionway

• An improved day-to-day living area

Both the FPB and Arksen designs have excellent saloon arrangements, so we drew inspiration from them rather than reinventing what already works.

We added double helm chairs, ensuring my wife can sit comfortably (and give me instructions, as she puts it!).

With the saloon raised, we worried the superstructure looked top-heavy. To soften this visually, we added a 300 mm bulwark running from the foredeck to amidships. This:

• Raises the visual sheer line slightly

• Helps shed water with built-in freeing ports

• Keeps the foredeck drier in rough conditions

Stability Systems and Boat Handling

Mobius uses a flopper-stopper rig and derricks for tender handling, with plumbing installed for powered stabilizers (but not fitted).

We decided to install stabilizers from the outset, avoiding later complexity and top-hamper.

We chose DMS Magnus Effect Rotors because:

• They promise superior zero-speed performance

• They fold away when maneuvering near ice or docks

• They allow stable operations at anchor without fins

Critical Systems: Redundancy and Reliability

For an explorer yacht, anything mission-critical must:

• Be duplicated or

• Have a very high MTBF (Mean Time Between Failures)

This is standard commercial-marine thinking—and one of our main lessons.

We chose:

Twin Main Engines

• Identical engines

• Derated for continuous running

• Together produce twice the required installed horsepower

• Supported by:

  • Two gearboxes

  • Two drivelines

  • Two rudders

This keeps us operational even if a major component fails offshore.

Hybrid Drive: Efficiency and Capability

We are fitting a hybrid drive system, which offers several advantages:

• Rapid battery charging using surplus propulsive power

• Ability to drive both shafts from one engine

• Silent maneuvering on electric drive

• Dynamic positioning made simple

• Independence of rudders and thrusters works very well with electric propulsion

Hybrid drives are not for everyone—they require careful thinking about goals and redundancy—but for us, the benefits were clear.

Electrical System: Battery-Centric Architecture

Wayne’s major decision on Mobius also suits our needs: everything is centered around the battery bank.

All charging sources feed the batteries:

• Shore power

• Mechanical charging

• Solar PV

All utilities then draw from the battery bank.

We specified large banks (2 × 60 kWh). In the age of EV technology, this is no longer unusual, and the extra mass acts as ballast.

We selected type-approved marine systems, each with:

• Dedicated cooling

• Heating

• Charging

• Safety systems

Thanks to the hybrid charging capability and the battery size, we do not need additional generators—two fewer systems to maintain.

Final Thoughts

There are many smaller changes throughout the design, but the points above represent the major revisions informed by our needs and lessons learned. The last step is to recalculate our stability curves with the final specification—though we expect to fall well within safe limits.

As always: each to their own. What matters is designing a vessel that fits your life, your voyages, and your priorities.