How to decide if your boat really needs a generator ?

One of the most common questions I am asked is, “Do I need a generator on my boat”. As with everything, the answer is not always straightforward. The first question is:

“What do you need the power for, and can this be accomplished with solar power and battery storage?”

For most people that do NOT need air conditioning, stabilizers, electric cooking, or water makers, then the answer is with properly sized solar systems, alternators, and batteries, then a generator is not normally necessary, provided you are prepared to run your engine to charge the batteries every other day if it is overcast. Generally we recommend sizing a solar/battery system to provide between one and two days at anchor without running the engine when it is sunny out, so only when these conditions are not met, is it necessary to either run a generator if fitted, or to run the main engine.

Very often, the engine is run to provide hot water also, so this is not usually any disadvantage, but of course water heaters will also be charged where a generator is running.

Where stabilizers, air conditioning, or electric cooking are required, these usually require a generator owing to the large power requirements. While these loads can in theory be managed from batteries through an inverter, the amperages involved can be very large (170A for a single induction cooktop), and hence this is usually not desirable or practical, although recently there are 48V engine driven alternators and smart controllers, that make running these types of loads possible without a generator provided sufficient battery storage is available.

Water makers are a 50/50 decision - smaller water makers are available for 12V or 24V, and will usually be operated when the engine is running, so can run from an alternator off the engine. Larger water makers usually require 120 - 240V and so require a generator.

On the Classic Trawlers, we generally recommend a generator where the customer wants stabilizers, air conditioning, electric cooking, or larger water makers. For all other customers we recommend a well sized solar/battery system. See our other blogs for recommended sizing of solar systems.