8 Checks To Stop Our DC Electrical System From Burning Our Boat

Not Fused

Before we dig into how to upgrade our boat's DC electrical system, as promised in our last article on the subject, we need to check for the problems that we need to fix, starting with potential boat-burners.

Two thoughts on that:

  1. I'm pretty sure that fires started by 12- and 24-volt battery-supplied systems are a common cause of boat losses.
  2. I would also bet that more fires are started by 12- and 24-volt systems than by shore power 120- or 240-volt systems.

No, I don't have accurate statistics on this, and I'm guessing that, as is typical around recreational boating, no one does due to poor or non-existent reporting requirements. But using poor reporting as an excuse for inaction would be stupid...err...unwise. (If you know of useful stats on this, please leave a comment.)

What do I base this on?

The current (amps) in even a single small 12-volt lead-acid battery can turn any conductor with low resistance (think a length of wire) red hot, thereby starting a fire.

And the amount of dangerous amps lurking in the huge battery banks we see on modern cruising boats is positively mind blowing.

This battery bank on our McCurdy and Rhodes 56 is rated at 2190 cold crank amps, meaning it can produce that current for 30 seconds at at least 7.2 volts. That's plenty to heat up even a piece of AWG 2/0 cable, not to speak of the probable case rupture of the battery if it's called upon to produce that much current for long.

Wait, it gets worse. On many boats, even ones built comparatively recently, like our new-to-us J/109 (2004), the only over-current (short-circuit) protection is on a breaker/fuse panel, leaving the high-current conductors connecting batteries and alternators completely unprotected.

Contrast that to the shore power system that typically carries ten to twenty times less current (amps) and is pretty much always properly protected against a short-circuit-started fire by fuses and/or breakers.

(Shore power systems kill people, but that's another article.)


By the way, I will pull these tips, together with my earlier ones on AC high-voltage and DC safety, into a checklist we can use while inspecting any boat's electrical system, particularly one that is new-to-us or one we are thinking of buying.

But for now, let's dig into the details we need to understand to make a checklist useful:

  1. One Simple Law That Makes Electrical Systems Easy to Understand
  2. How Batteries Charge (Multiple Charging Sources Too)
  3. How Hard Can We Charge Our Lead Acid Batteries?
  4. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  5. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  6. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  7. The Danger of Voltage Drops From High Current (Amp) Loads
  8. How Lead Acid Batteries Get Wrecked and What To Do About It
  9. 11 Steps To Better Lead Acid Battery Life
  10. 10 Tips To Install An Alternator
  11. Stupid Alternator Regulators Get Smarter…Finally
  12. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  13. Smart Chargers Are Not That Smart
  14. Equalizing Batteries, The Reality
  15. Battery Monitors, Part 1—Which Type Is Right For You?
  16. Battery Monitors, Part 2—Recommended Unit
  17. Battery Monitors, Part 3—Calibration and Use
  18. Do You Need A Generator?
  19. Efficient Generator-Based Electrical Systems For Yachts
  20. Battery Bank Size and Generator Run Time, A Case Study
  21. Battery Options, Part 1—Lithium
  22. Battery Options, Part 2—Lead Acid
  23. Why Lithium Battery Load Dumps Matter
  24. 8 Tips To Prevent Lithium Battery Load Dumps
  25. Lithium Ion Batteries Explained
  26. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  27. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  28. Q&A—Are Battery Desulphators a Good Idea?
  29. Renewable Power
  30. Wind Generators
  31. Solar Power
  32. Hydro Power
  33. Watt & Sea Hydro Generator Review
  34. A Simple, Efficient and Inexpensive¹ 12 or 24 Volt DC Electrical System
  35. 8 Checks To Stop Our DC Electrical System From Burning Our Boat

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for 25 years, first in yachting magazines and, for the last 20 years, as co-editor/publisher of AAC.

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