Marine Electrical Guides

Straight answers to the questions boat owners ask us most — how faults are diagnosed, how systems are specified, and what actually drives the cost of marine electrical work. Written from the work we do on the South Coast.

Problem

• Boat Battery Not Charging: How to Diagnose the Cause — A step-by-step diagnostic order for a boat battery that will not charge, shore power, alternator, split charging, wiring and battery condition.
• Signs Your Boat Needs Rewiring (and When It Doesn't) — How to tell whether boat wiring needs replacing or just repair, corrosion, non-marine cable, added circuits, breaker nuisance tripping and heat.
• Boat Shore Power Problems: Cables, Tripping and RCDs — Why marina shore power trips, what an RCD trip is telling you, polarity and earth issues, and how galvanic isolation fits into the picture.
• Boat Alternator Not Charging: Finding the Real Fault — Work out whether it is the belt, the alternator, the regulator, the sensing wire or the split charge device stopping your boat engine charging the bank.
• Galvanic Corrosion and Isolation on Boats, Explained — Why anodes disappear in weeks in a marina, how stray current differs from galvanic corrosion, and where isolators and isolation transformers fit in.
• Navigation Lights Not Working or Flickering: What to Check — Intermittent or dead nav lights are usually connections, not bulbs. Where faults hide on masthead and deck lights, and what LED swaps break.
• Bilge Pump Not Running, or Running Constantly: Causes — Float switch failures, corroded wiring, blocked strums and cycling pumps. What to check on a bilge pump circuit and why it must stay live at all times.
• Chartplotter or Instruments Losing Power: Why It Happens — Instruments that reboot, drop out or lose data under load are usually supply and voltage drop problems, not faulty electronics. How to find the cause.
• Damp, Corrosion and Green Wiring: Why It Happens on Boats — Green, crumbling wire and chalky terminals are a marine problem. Why it spreads inside insulation, what it costs you, and how to stop it.
• Boat Battery Drains Overnight: Finding the Parasitic Load — A boat battery that empties overnight almost always has a hidden standing load or a tired cell. How to separate the two and trace the draw properly.
• Shore Power Keeps Tripping: What the RCD Is Telling You — A pontoon RCD that trips is reporting current leaking to earth somewhere on board. What causes it, how to narrow it down, and why it must not be bypassed.
• Navigation Instruments Cutting Out Underway: Causes and Cures — Depth, wind and speed dropping out at sea but fine alongside points at power, network or connections. How to identify which one, in the right order.
• Burning Smell From Boat Electrics: What to Do Immediately — A hot plastic smell on board is a warning, not a nuisance. Isolate first, then find the cause. What overheats, why, and why this is not a DIY repair.
• Boat Fridge Not Cooling? Electrical Causes and Fixes — Why a boat fridge stops cooling: low voltage at the compressor, thin supply cable, poor ventilation, control faults. How to narrow it down before calling us in.
• Electric Boat Toilet Not Working: Electrical Checks — Why an electric marine toilet stops working: blown fuses, low voltage, failed switches, macerator jams and control faults. The electrical checks to make first.

Comparison

• LiFePO4 vs AGM Boat Batteries: Which Suits Your Boat? — How lithium and AGM marine batteries differ on usable capacity, charging, weight, installation requirements and whole-system cost.
• 12v or 24v on a Boat: How to Choose — Where 24v earns its place on a boat, the cable and voltage drop maths, equipment availability and how to run both voltages sensibly on one vessel.
• MPPT vs PWM Solar Charge Controllers for Boats — The real difference between MPPT and PWM solar charge controllers on a boat, output, cost, wiring and which suits small versus larger arrays.
• Drop-In Lithium Batteries vs Integrated Systems: What's the Difference? — Comparing drop-in LiFePO4 batteries with internal BMS against fully integrated lithium systems with external BMS, network monitoring and coordinated charging.
• Marine Generator vs Lithium Battery Bank: Which Solves Your Power Problem? — Comparing a generator against a larger lithium bank and solar for boat power, running costs, noise, maintenance, and which loads each is suited to.
• AIS Class A vs Class B: Which Transponder Suits Your Boat — The practical differences between AIS Class A and Class B transponders, and why most leisure boats fit Class B. Power, antennas and set-up explained.

System

• Victron Boat System Design: How the Parts Fit Together — How the parts of a Victron marine setup fit together, inverter/charger, MPPT, shunt, Cerbo and network, and the design decisions that drive the spec.
• Marine Solar Panels: Sizing, Mounting and Real-World Output — Marine solar panels for boats: flexible vs rigid panels, sizing an array to your consumption, mounting options and why shading dominates real output.
• Marine Battery Monitoring: Why a Shunt Beats a Voltmeter — How shunt-based battery monitors measure true state of charge, why voltage alone misleads, and what to look for when fitting one.
• NMEA 2000 on a Boat: Backbones, Drops and Common Mistakes — How an NMEA 2000 backbone should be built, terminators, drop lengths, power insertion, and the mistakes behind most instrument dropouts.
• How to Size a Boat Battery Bank Properly — Work out real daily amp hours, allow for usable capacity, charge rate and space, and size a boat battery bank that suits how you actually use the boat.
• Boat Inverters: What an Inverter Does on a Boat — Inverter sizing for boats, what a kettle really costs you in amp hours, surge loads, cabling and why the battery bank matters more than the inverter.
• Marine Electrical Systems Explained: DC, AC and How They Interact — How a boat's DC and AC electrical systems fit together, batteries, alternators, shore power, inverters and distribution, and where faults typically start.
• Marine Battery Management Systems: What a BMS Actually Does — What a lithium BMS does on a boat, cell balancing, protection cut-offs, communication with chargers, and how BMS faults are diagnosed.
• Marine LED Lighting Upgrades: What to Know Before You Switch — What changes when you upgrade boat lighting to LED, current draw, dimming, colour temperature, navigation light rules and wiring considerations.
• Marine Cable Sizing and Voltage Drop, Explained Properly — How to size DC cable for current and run length, why the 3% voltage drop rule matters, and what happens when boat cable is undersized.
• Marine DC Fuses and Breakers: Protecting Boat Circuits — How MRBF, ANL and Class T fuses and DC breakers protect boat circuits, where they need to be fitted, and how to size them correctly.
• Marine Inverter Sizing: Getting the VA Rating and Cabling Right — How to size a boat inverter correctly, continuous versus surge VA, DC cable sizing, fusing and why an oversized inverter causes more problems than it solves.
• Alternator Charging of Lithium Batteries: Risks and Correct Practice — Why standard alternators overheat charging lithium banks, what BMS load dump can damage, and how external regulation or DC-DC chargers fix it.
• Marine Radar Installation: Siting, Cabling and Setup — How to site a radar scanner, run the cable, integrate with a chartplotter and set up a marine radar properly, from mast height to overlay tuning.
• VHF and AIS Antenna Installation: Getting the RF Right — How to site VHF and AIS antennas, choose coax and connectors, check VSWR, and decide between a splitter and a dedicated AIS antenna on a boat.
• Marine Autopilot Installation: Drive Sizing and Setup — How autopilot drive units are sized, how rudder feedback works, and what a proper installation and sea trial involves on a sailing or motor boat.
• Boat Instrument Panel Upgrade: What to Plan Before You Start — How to plan a boat instrument panel upgrade, NMEA 2000 backbone, display choice, sensor compatibility, wiring and layout, before buying anything.
• Lithium Battery Upgrade: What Actually Changes on Your Boat — Swapping to LiFePO4 changes charging, protection, monitoring and how you use the boat. An honest account of what has to change with the batteries.
• Boat Heating: Electrical Requirements and Options — What boat heating asks of your electrical system: 12V start-up loads, shore power heaters, battery capacity and safe wiring for diesel and electric options.
• Bow Thruster Electrics: Cables, Batteries and Protection — Bow thrusters draw huge currents in short bursts. How to power one properly: dedicated battery or long cable run, cable sizing, fusing, isolation and charging.
• Marine Audio Installation: Getting Sound Right Afloat — How to install a boat stereo that survives salt and sounds good: marine-rated units, speakers, amplifiers, zones and wiring that won't drain the batteries.
• Marine Bonding Systems: When a Boat Needs One — What a marine bonding system is, when a boat benefits from one and when it can make corrosion worse. How to decide before anything is wired together.
• Boat CCTV and Camera Systems: Planning an Installation — Planning CCTV on a boat or yacht: camera types, positions, recording, remote viewing, power draw and wiring that holds up to salt and vibration.

Cost & Process

• Marine Electrical Fault Finding: How It Works, Step by Step — What happens during a marine electrical fault find, information gathering, systematic isolation, instrument testing, and what you get at the end.
• What Drives the Cost of Marine Electrical Work — The factors that decide what boat electrical work costs, access, cable runs, chemistry, certification, parts and how quotes are structured.
• Winter Layup: A Marine Electrical Checklist — What to do with batteries, shore power, solar and electronics before winter layup, and what to check again before the first spring launch.
• Shore Power Installation on a Boat: What Is Involved — Inlet, isolation, RCD protection, consumer unit, charger and cabling. What a proper boat shore power installation includes and what gets tested afterwards.
• Rewiring an Older Boat: What Is Involved and What to Expect — How a boat rewire is planned and staged, what drives the time and cost, what can be done in phases, and what documents you get at handover.
• Boat Rewiring Project Plan: Sequencing, Cost Drivers and Timescales — How a full boat rewire is sequenced from survey to commissioning, what drives the cost, realistic timescales and how to phase the work if budget is limited.
• Marine Electrical Installation: What Happens, Step by Step — What a marine electrical installation involves from first visit to handover: assessment, written quote, design, fitting, testing and the paperwork you keep.
• Electrical Damage and Insurance Claims: What Owners Should Know — What to do after electrical damage on a boat when an insurance claim is likely: make safe, record it all, get a written fault report and a clear repair quote.

Buying & Selling

• Pre-Purchase Marine Electrical Survey: What Gets Checked — What an electrical survey covers before you buy a boat, the findings that matter most, and how to use the report in negotiation.
• Boat Electrics When Buying a Used Yacht: What to Check — What to inspect on a used yacht's electrical system before buying, wiring age, battery condition, charging sources, bonding and past modifications.
• When to Replace Boat Batteries (and What With) — The signs a boat battery bank is finished, how to test before buying, and whether to replace like for like or move to LiFePO4. Practical advice.

Safety & Compliance

• Boat Electrical Safety Inspection: What Gets Checked — What a marine electrical inspection covers, from batteries and fusing to shore power and mast circuits, and what the report gives you.
• BSS and Boat Electrics: What Owners Generally Need to Know — A general overview of how the Boat Safety Scheme relates to electrical installations, common problem areas, and where to check the official requirements.
• Why Marine Wiring Differs From Domestic, and Why House Parts Fail — Tinned fine stranded cable, vibration, salt air, DC currents and support. Why domestic cable, connectors and fittings fail on boats, often within a season.
• Shore Power Safety on Boats: What Every Owner Should Check — Shore power risks on boats explained: RCD protection, galvanic isolation, cable and connector condition, and the checks that prevent shocks and fires.
• BMEA Standards and Codes of Practice for Marine Electrics — What the British Marine Electronics Association code of practice covers, how it links to ISO standards, and what it means for work done on your boat.
• Boat Electrical Safety Checks: What to Do Every Season — A practical seasonal routine for checking a boat's electrical system, battery, wiring, shore power and protection devices, before problems become fires.
• Marine Earthing and Bonding: What the Difference Actually Means — The difference between AC earthing and DC bonding on a boat, why they matter for shock protection and corrosion, and how they should be wired.
• Spring Recommissioning: Boat Electrics Checklist — A season-start checklist for boat electrics: batteries, charging, shore power lead, navigation lights, bilge pumps and instruments, in a sensible order.
• Lightning Protection on Boats: What Is Realistic — What lightning protection can and can't do for a boat: conductive paths to water, bonding, electronics damage and practical steps owners can take.

Question not covered here?

Tell us the boat, the berth and the symptoms — the initial assessment is free and every quote is itemised in writing.