Many call-outs at sea are not caused by a mechanical failure but by an electrical one: a flat battery that will not start the engine, a corroded terminal or an alternator that stopped charging without anyone noticing. The good news is that almost all of these faults can be prevented.
Know your batteries
Most leisure boats have at least two circuits:
- Starter battery: delivers a very high current for a few seconds to start the engine.
- House battery: powers lights, fridge, electronics and pumps for hours.
Ideally they are separated by a battery switch or a charge splitter, so the fridge can never leave you unable to start.
The most common causes of failure
- Deep discharge: running a battery below 50 % damages it progressively.
- Corroded terminals and connections: the salty air oxidises terminals and increases resistance.
- Faulty alternator or regulator: the engine runs, but the batteries are not charging.
- Loose connections caused by vibration, which lead to intermittent faults that are hard to trace.
- Old batteries: even if they seem to work, they lose capacity over the years.
A quick check before you go out
- Check the resting voltage: a charged 12 V battery reads around 12.6–12.8 V.
- With the engine running, voltage should rise to about 13.8–14.4 V; if it does not, the alternator is not charging.
- Make sure the terminals are clean and tight.
- Test the bilge pump and the navigation lights.
Navigation electronics
Chartplotter, echo sounder, radar, VHF and autopilot all depend on a stable supply. Voltage drops cause reboots and false readings. A tidy installation, with correctly sized cables and protection, avoids many problems.
If the voltage does not rise when you start the engine, do not head out: it is the clearest sign of a charging fault.
Marine electrics and electronics in Mallorca
Ocean Pro Nautic diagnoses and repairs electrical installations, replaces batteries and chargers, and installs and sets up navigation electronics. Tell us what is wrong with your boat or see our services.
