Power Systems
Power systems on cruising boats have gotten complicated with all the lithium battery debates, inverter sizing questions, and charging source options flying around. As someone who has rebuilt the entire electrical system on a 42-foot trawler from scratch, I learned everything there is to know about designing a power system that actually works for extended cruising. Today, I will share it all with you.
When I first started cruising seriously, I had a vague idea that I needed “enough batteries” and “some way to charge them.” That lasted about two weeks before I was running the generator five hours a day and still watching my voltage sag every evening. The problem wasn’t any single component — it was that nothing was sized or integrated properly. A boat’s power system is exactly that: a system. Every piece has to work with every other piece, or the whole thing underperforms.
Designing a Power System That Actually Works
Probably should have led with this section, honestly. Prepare your vessel by mapping your actual power consumption for a week before you change anything — you need real data, not guesses. Develop your understanding of how battery banks, charging sources, inverters, and loads all interact, because optimizing one piece in isolation often creates a bottleneck elsewhere. Plan conservatively on battery capacity, because you should never discharge lead-acid below 50% or lithium below 20% if you want them to last. That’s what makes power system design endearing to us cruisers — when you get it right, you have quiet, reliable power that supports the way you actually live aboard, and the freedom to stay on the hook as long as you want without worrying about running out of juice.
