Your Alternator Generator Starter needs your help!

About your Alternator Generator Starter. Your boat starting system must be looked at as not simply a collection of series connected components, but as an entire starting system. The typical boat electrical alternator generator starter system comprises the following important elements

1. The DC positive circuit, (and this includes the connections at the battery, the isolator or changeover switch, the solenoid connection, the solenoid contacts, the starter motor (which also includes several components such as brushes, brush gear, commutator, bearings, windings).

2. The DC negative circuit, (and this includes the connections at the battery, the engine block, the cable back to the battery, and the amp meter shunt if one is installed).

3. The engine control system (and this is from the panel and includes the key switch, the stop and start buttons, the wiring harness, all of the connectors, and the fuse protection etc.).

4. The preheating system (which includes the heating elements or glow plugs, and the connections, relays and connectors).

5. The engine starting battery.

Work it all out

The math of this detailed analysis is that there are also a total of around 14 separate connection points plus the solenoid coil, the starter motor, the battery, the key switch that can directly impact on the starting system and prevent the system functioning. That is a lot isn't it and this usually surprises people.

Each connection point represents a single point failure with subsequent total system failure, with no apparent redundancy. If you decide to continue turning over an engine that will not start, you may also burn the starter motor out as the windings overheat. There are other less common boat-electrics scenarios.


The key to minimizing failure or mitigating the effects of failure in any boat-electrical alternator generator starter system is the provision of redundancy. Redundancy in simple terms is having backup systems as part of the design, so that if one system fails the other will provide the charging or starting. In the average single engine boat, normal systems design and installation rarely incorporates any redundancy on charging, power or starting systems. When you break down, you break down!

In most commercial shipping, this is a basic premise in all systems design. There are several methods for improving redundancy and the following are the easiest and most economical to carry out. While not easy on some yachts there are some measures that can be implemented. This includes carrying appropriate spare parts, it is quite astounding how few people carry spare alternator or starter motor, a cheap investment I would have thought.


1. An engine powered DC generator. Compact units are available which are small diesel powered alternators

2. An AC generator with mains powered battery charger. The on board generator with a battery charger offers the best battery charging source, however its relatively expensive and has space and weight constraints limiting it to larger yachts

3. A combination of wind, solar and water powered charging systems. They are supplementary only as they depend on environmental factors, if the sun doesn't shine and the wind doesn't blow then no charging is possible

Read PART 3 of this 4 Part Series on the marine-battery charging system risk assessment and improve your power systems reliability.


Be sure to purchase a discount price copy of my books from Amazon, all you need to know about this and all other boat systems is there, your perfect and practical onboard reference manual. More about your Alternator Generator Starter