Your boat electrics system needs help!

There are a variety of boat electrics and alternator maintenance philosophies used in commercial and offshore-based rigs and ships.

The traditional and most accepted is the Planned Maintenance System (PMS). This is based on maintenance tasks based on time intervals, either set periods or operational hours, and is still a useful basis for maintaining equipment. In most cases the only planned maintenance undertaken is engine oil changes based on running hours.

The previous FMEA exercise allows the implementation of what is called Risk Based Maintenance and Inspection. We have evaluated all the areas most critical to boat operation, so the maintenance strategy should be centered on this. For example we know that the main failure causes in boat electrical systems are poor connections so routinely checking and tightening them reduces the failure rate. As a start point perform the recommended maintenance on all critical equipment and systems.

About Boat Electrics Motor Starters

Starter motors have relatively low failure rates, as actual operating hours are also relatively low in comparison to motor vehicle applications. Boat-electrics failures are usually dependent on operational frequency with seized bearings, or stuck brush-gear being the major failure causes. Regular operation reduces failures, so running the engine regularly has positive advantages.

In addition this will generate heat, which assists in displacing moisture within the windings. Starter motors should be cleaned or overhauled on a regular basis, ideally not exceeding two years. I usually take it off, take it to my favorite automotive electrician, and back in the same day. If your boat has not had the starter out in years then a service is a good precaution before you head off.

About Boat Electrics and Alternator Reliability

Alternators on boats actually have quite a low failure rate, as actual operating hours are also relatively low. The main failures are generally caused by diode rectifier failures, or overheating, this occurs in particular with fast charge regulators and oversized battery banks. Alternators should be cleaned and overhauled on a regular basis, ideally not exceeding two years. Consider a higher output rated alternator to reduce overloading and heating. Again it is cheaper to take it to an automotive electrician and have it overhauled before you set out.

Boat Electrics and Battery Reliability

In vessel electrical systems the batteries generally have the highest failure rate of all components. This is not a failure in the true sense but is due to either incomplete and inadequate charging with resultant plate sulfation, lost capacity and failure, or flattening of the battery with subsequent damage. In most cases this is due to poor systems design or human factors.

The second highest boat electrical system failure cause is inadequate inspection and topping up of electrolytes, with resultant plate damage. Consider different batteries such as AGM types with lower failure rates, improved charging characteristics and elimination of the human and maintenance factor. A consequence of the tragic Sydney – Hobart yacht race is a coroners recommendation for installing only sealed batteries. All these are good reasons to upgrade and improve overall electrical systems reliability.

Boat Electrics and Wiring Termination Reliability

The greatest cause of failure with boat electrics is that of the electrical wiring connection or wiring termination failure. All wiring connections on boat and yacht alternators, engine starters, engine blocks, and batteries should be check tightened every six months, it is an easy task and results in fewer intermittent and complete failures. It is as not as onerous as it seems, and will pay dividends. Remember to switch all power off before you start the exercise.

Boat Electrics and Spare Parts

It is amazingly rare to see a boat with a spare starter motor, or alternator and these should be a prerequisite on an extended ocean voyage. Whilst some boats may carry spare bearings, diode plates and brush-gear the task does require skills and tools and it is quicker to change out the entire alternator. Invest in a spare starter motor and alternator, it is a small price to pay in the overall scheme of things

Boat Electrics and How to Improve Your System

After carrying out an FMEA of the alternator and battery charging system and made a systems assessment, and implementing some modifications, just how much further ahead are we. The most salient point is that there is now a significant reduction in single point failures. With two separate charging circuits there is full charging system redundancy and there are now significantly reduced connections in both the positive and negative circuits, the negative having a backup with the starter motor negative.


In a typical system using a changeover switch arrangement there is a reduction of up to 75% in possible failure points. In addition, the person has been designed out of the system as the possibility for accidental switching off the changeover switch is removed. There is a significant improvement in charging efficiency, with a gain of up to or exceeding 0.5 VDC due to lower circuit resistance in both the positive and negative circuit. This reduces alternator loads, and can shorten charging time, reduce charge current and extend alternator life by imposing less stress.


The starting system is more efficient with the negative at the starter reducing voltage drops, lowering current, reducing run time, and improving starting times, which also reduces stress on the motor. Coupled with carrying a spare starter motor/solenoid, there is a reasonable chance of being operational within an hour. Separation of the start and battery charging systems eliminates the many problems of voltage surges and transients.


There are now two redundant power systems, each one being capable of powering the vessel, and any single failure of one system will not affect the other. The alternator negatives provide some redundancy to the main starter negative. As critical equipment has been evaluated and appropriate maintenance strategies implemented, the average time between failures is also extended.

The question remains, “How great is your battery charging system risk? And how are you going to reduce it?” More about Boat Electrics.