Ten problems that show up on cruising boats.

Symptom

The house bank looks tired, but the tiredness showed up with the weather, not with a sudden failure.

Usual causes

• Solar did not put back what the fridge, instruments, and a leftover inverter took out.
• One connection or one battery is carrying the bank, so voltage sags under load.
• The monitor percent-full was never synced to a real full charge, so it is a story.

First measurement

Loads off for a while, read voltage on the battery posts, not at the panel. Then start the fridge and watch how far that voltage falls in the first minute.

Stop now

A cable, fuse, or terminal that is hot under charge or under a modest load. Shut the charger, solar, and alternator off. Do not keep pushing current through a hot joint.

Symptom

The dockside reading was a light test. The failure shows up when the alternator is asked to work.

Usual causes

• The belt slips once real current is flowing. Glaze and rubber dust are the tell.
• The cable or the ground between the alternator and the battery is eating voltage.
• The regulator is cutting back because the alternator is hot, and that gets blamed on a dead unit.

First measurement

At cruising rpm, with the bank accepting charge, measure voltage at the alternator output stud and again at the battery positive post. The difference is what the cable and the connections are losing.

Stop now

A burning smell, a belt throwing dust, or a terminal you cannot keep a hand on. Shut the engine down. Do not keep motoring to force a charge through a hot stud.

Symptom

The trip looks random until you write down which breaker, what was running, and whether it opened at once or after it had been warm.

Usual causes

• Two modest loads are on together: water heater, charger, and air conditioning is the usual pile.
• A loose lug heats up, and the heat trips the breaker even though the load did not change.
• A motor or compressor surge, or a breaker worn out from being reset.

First measurement

Before another reset, note the breaker, the loads, and whether it was immediate or delayed. If the breaker body or the lug was warm last time it held, that is part of the note.

Stop now

If the breaker, wire, cord, inlet, or a terminal is hot, discolored, or arcing, leave it off. Unplug shore power at the pedestal if that path is involved. Do not reset a hot breaker, and do not leave a hot cord plugged in.

Symptom

The crust is in one place, which means the water, the metals, or the current is in that place too.

Usual causes

• A leak path: deck fitting, chainplate, hose, or a hatch that only weeps on one tack.
• Dissimilar metals and salt making a small battery at the joint.
• Stray current from a bad ground or a shore-power problem eating the metal faster than weather would.

First measurement

Shore power unplugged and chargers off, find the drip above the crust. If you have a meter, read voltage between the suspect fitting or the bonding wire and battery negative. A standing voltage you cannot explain is a clue, not a verdict.

Stop now

A seacock, through-hull, or bonding strap that is badly eaten is not a cleaning job. If a terminal on that circuit is hot, discolored, or arcing, disconnect it and leave it off.

Symptom

Several boxes fail at the same moment, so the fault is usually shared power or the network, not three separate failures.

Usual causes

• One fuse, breaker, or backbone power tap feeds several devices, and that tap is loose.
• A connector is tired or wet. It holds at the dock and opens when the boat flexes.
• A missing terminator, a long spur, or a device that knocks the backbone down when it powers up.

First measurement

When they drop, look before you touch anything. Dark screens mean lost power. Screens still lit, with no heading, depth, or radar, mean lost data. Note what changed in the ten seconds before.

Stop now

A connector, fuse holder, or power tap that is hot, discolored, or arcing gets that circuit turned off. Underway, if the autopilot goes with the plotter, hand-steer first.

Symptom

The overnight setup spent more than the bank had, and the alarm was on the same bank as everything else.

Usual causes

• Fridge, instruments, a light left on, and an inverter in standby. The list looks small and is not.
• The alarm shares the house bank and dies with it.
• The engine was shut down before the bank was actually full, and the monitor was ahead of the truth.

First measurement

At dusk, with the real night loads already on, read house voltage at the battery and, if you have a shunt, the amp draw. In the morning, before you charge, read voltage again. The drop is the number.

Stop now

If you are not holding and the alarm is dead, get a watch on deck first. If a charger cable or terminal is hot, shut that source off. Do not charge overnight through a hot lug.

Symptom

Heat at a plug or inlet, often with the air conditioner, water heater, or charger running.

Usual causes

• A loose or worn contact, so current crowds through a small spot.
• Corroded pins. Corrosion is resistance, and resistance is heat.
• A plug that is half seated, or a cord asked to carry more than it should.

First measurement

Do not measure this with the cord left cooking. Unplug at the pedestal and let it cool. Then look for discoloration, pitting, a loose pin, or softened plastic, and write down which loads were on.

Stop now

If the cord, inlet, or a terminal is hot, discolored, or arcing, stop and disconnect at the pedestal. Do not leave shore power on a hot cord to finish charging or to keep the air conditioner running.

Symptom

Small steady loads work. A load with a hard start, or a picky charger, does not.

Usual causes

• Startup surge bigger than the inverter few-second rating. Nameplate watts are not the first-second watts.
• A modified sine wave that some chargers and motors will not accept.
• Battery voltage sagging at the inverter own lugs, while the panel still looks fine.

First measurement

Meter on the inverter battery terminals, not the nav panel. Read voltage while the load that fails is trying to start. A dive plus an alarm points at the battery, the cables, or the connections.

Stop now

A burning smell, a hot DC lug, or an inverter that keeps resetting into the same load. Turn the inverter off and that load off. Do not keep retrying it into a sagging bank.

Symptom

The trouble started with the weather, and it clusters on gear that got wet or shares a wet locker.

Usual causes

• Salt water in a connector or on a board. Wet, it conducts. Dry, it corrodes.
• A hatch or cable gland that only leaks on one tack.
• Power left on while the gear was wet, which plates metal and burns traces.

First measurement

Do not turn it on to see. Breaker off, look for the drip, white crust, and water standing in a plug. Note which tack or which wave started it.

Stop now

Water inside a device that still has power, or a hot-electronics smell, means that breaker stays off. Drying comes before power. If a cord or terminal there is hot, discolored, or arcing, disconnect that too.

Symptom

One failure takes the only radio or the only data link, because the spare was never on its own power.

Usual causes

• The radio or terminal shares a breaker, a battery, or an antenna with whatever just failed.
• The backup is buried, uncharged, or sitting on the same bank.
• Nobody has tried the handheld since the last haulout.

First measurement

With the house bank low and the inverter off, list what still works on its own battery: handheld VHF, a charged phone, the fixed VHF if it has a separate power path. At the dock, call the handheld to another radio on low power.

Stop now

If you cannot raise anyone and you have no second path, do not leave as if you can call for a tow. Prove the spare first. If a charger or terminal on that circuit is hot, discolored, or arcing, disconnect it and leave it off.