This is the first of the Tech Talk style of articles I promised in THIS previous posting. Many of you have been asking for a more in depth and technical look at the What, Why and How of all the various major systems required for an XPM boat such as Möbius. And not to worry, I will continue to do the weekly progress updates and then as my time permits, I will also post these Tech Talks for a bit of a change of pace and a different look at these boats.

Note that there is a tag in the blog for Tech Talks so you can filter on this whenever you want to have just these articles show up on your screen.  These Tech Talk articles will also be a bit different in that I will update them if things change or there are other additions or edits to improve them so much like your author here, these will be a continuous work in progress.

As with all my writing on the Möbius.World blog please keep in mind that the context for all my writing and all our decisions is always and only, what is “just right, just for us” as we are living on our all aluminium XPM78 eXtreme eXploration Passage Maker. As in our past boats, this will be Christine and my full time home as we double-hand** our way around the world’s most remote locations at all latitudes from polar to equatorial with equally eXtreme degrees of Safety, Comfort, Efficiency and Low Maintenance.

** We were both formerly single handed sailors until we met, fell in love and married in our 60’s and are now about to set off “double handing” our way around the world on our new XPM78 Möbius.

If you would like to learn more about our use case THIS previous post has the full explanation.

And before I go any further please keep the following in mind about all these Tech Talk articles:

  • These are NOT recommendations on what YOU or any other boat owners should do or what equipment you should buy.
  • I am NOT suggesting that our choices are “the best” I merely hope to explain OUR (Christine and my) logic and why we believe that these are the Goldilocks “just right, just for us” choices in the design, installation and equipment aboard XPM78-01 Möbius.
  • I am NOT an expert nor do I have any qualifications or certifications in any of these topics and while we have enlisted the help of true experts, engineers, designers and naval architects throughout the design and build process please only use the information provided in these Tech Talks as additional information to assist you in developing YOUR OWN opinions, ideas and designs.

· These Tech Talk articles are intended to generate lots of questions, suggestions, and ideas. I hope to learn as much as you do by writing these Tech Talks and more so by responding to your comments and provoking more good discussions.

· In doing so we can all contribute to the wealth of information and knowledge already out there for all of us to access and learn from. Indeed this is the primary purpose and value of these articles, so don’t be shy and please add your contributions to the “Join the Discussion” box below. I only ask that you keep the above notes in mind and of course keep the discussion respectful, polite and on topic as you always have.

SCEM boxAs mentioned in our use case overview and in many previous posts, we have four fundamental principles or priorities which we have used throughout the entire design and build process to guide our decisions. These are Safety, Comfort, Efficiency & Maintenance. We strive to keep the first three as high as possible and the last one, Maintenance, as low as possible. I will therefore add a “SCEM Review” section for each system’s Tech Talk and summarise how each system contributes to each of these fundamental priorities and principles.

All right, with all that out of the way, lets dive into the details of the What, Why and How of the XPM Electrical System.


XPM Electrical System

The Electrical System on our new boat can best be described as a DC Battery Based electrical system meaning that ALL of the electrical power consumers on the boat, both AC and DC, get their power from the large 24 volt “house” battery bank. This is in contrast with many other boats that could be characterized as “AC Based” boats because their systems are optimized for AC inputs from onboard generators and shore power. Both models work well and the question is not which system is “best” but which system is best for a given boat, owner and use case.

Given that by design and use case there is no generator onboard Möbius and shore power is rarely available as we live on anchor almost all the time, a DC Battery Based boat is the just right, just for us solution.

Our large 24 volt 1350Ah battery bank is charged from either the +5kW bank of 14 solar panels and/or via the two large alternators, 250A @ 24V each, 12kW total, driven off the main engine when on passage.

This is very much a “world boat” so all four of the most common voltages are available onboard at all times. 24V DC and 220V 50Hz AC are the primary voltages we use and 12V DC and 120V 60Hz AC outlets are located throughout the boat as well for devices and guests which require these voltages

There will be shore power connectors at the front and rear for those infrequent occasions when the boat is hauled out for maintenance or to leave for extended times for trips back to be with our three Grandkids and other family and friends. These shore power connections come aboard through a Victron Isolation Transformer primarily to ensure we have no connection from the boat to shore side grounding wires and gives us the significant advantage of being able to plug into any shoreside power from 100-240 Volts @ 50 – 60Hz.


  • House Battery Bank: 18 FireFly Carbon Foam L15+ 450Ah @ 4V batteries connected in three 24V banks 6S3P (6 Serial 3 Parallel) = 1350Ah @ 24V = 32kWh
  • 220 Volt Inverter/Chargers:  3 Victron MultiPlus 24V 5000W 120A
  • 120V Inverters:  2 Victron MultiPlus 24V 3000W 70A
  • DC-DC converters Victron Orion 24V to 12V 70A
  • Engine Alternators:  2 Electrodyne 24V @ 250A = 6kW each = 12kW total output.
    • Both with remote rectifiers and remote “smart regulators”
  • Battery Monitor: Victron BMV 712s for monitoring each of the 3 battery banks and the overall DC electrical system. 
    • Augmented with Maretron monitoring
  • Solar Panels: 14 each 96 cell 360W = 5.04kW peak total
  • MPPT Controllers:  14 Victron SmartSolar 100/30 MPPT controllers
    • one per solar panel
  • Engine Start Battery:  2 FireFly G31 110Ah Carbon Foam batteries in series 110Ah @ 24V

I hope you have found this first of my Tech Talk articles to be of some value and I would be most appreciative of any and all comments and suggestions on ways I can improve them. With this Electrical System Overview done I will next dive into each of this system’s components and I think it is appropriate to start with the true center of or Electrical System; the House Bank batteries and then progress through each of our Charging Sources which are solar and engine alternators.

Please add your comments, questions and ideas in the “Join the Discussion” box below each post.


– Wayne