Do You Need A Generator?


A few weeks ago, Chris and Eric, both engineers and sailors with deep experience and lots of technical smarts, got into an interesting discussion about diesel generators and when it makes sense to install one. I highly recommend reading that thread full of useful information. I did, and it got me thinking…

As a voyager who has had a generator for the past 20 years, it suddenly struck me that for most usage profiles, the decision, generator or not, is an amazingly simple one.

These days, with more efficient solar panels and much more efficient lighting in the form of LEDs, there are now just two criteria that will determine whether or not a generator is required for the average voyaging sailboat that spends long periods away from shore power:

While Cruising

Do you want to keep a significant amount of food frozen? If the answer is yes, you need a diesel generator. If the answer is no, you can probably manage without one, as long as you are careful and design your electrical system well. (Of course, if you want air conditioning a generator is mandatory.)

If you are not planning to make long passages, that’s probably really all you have to look at to make the diesel generator, or not, decision. And further, you might even be able to get away with a small gasoline (petrol) powered portable generator, as long as you have a safe vapour-tight place to store it and its fuel.

While at Sea

Once you head off on an ocean passage the biggest criteria that drives whether or not you need a diesel generator, assuming no freezer, is whether you use a vane gear or an autopilot.

If you will use a vane gear while sailing and have a well-designed system including solar, I don’t think you need a generator. Add in an autopilot and you need either a diesel generator or a water generator. Wind and solar (unless a massive and usually un-seamanlike array is installed) just won’t do it.

Also, I don’t believe that portable gas generators are seamanlike for offshore use. They are just too vulnerable to a splash of salt water, and messing about trying to fill them on a moving boat is dangerous.

Now the decision gets interesting. Since good water generators can cost nearly as much as a diesel generator and don’t work at anchor, we are probably back to a diesel generator being the best bet for many boats.

On the other hand, a diesel generator does not solve the problem of efficiently charging lead-acid batteries from about 75% to 100% full, when the amount of current (amps) drops off quickly. But that’s where solar comes in, as long as you can reduce your loads enough for 4-6 hours a day so that your array has enough capacity, after handling required loads (navigation gear for example), to regularly top up the batteries to 100%.


So there you have it:

  • You want to freeze stuff, you need a diesel generator.
  • You want to freeze stuff and use a powerful electronic autopilot, you definitely need a diesel generator.
  • You want to use a powerful autopilot for multi-day crossings, and don’t want to freeze stuff, you need a water generator.
  • Whatever you do, you probably want some solar, even if you have a generator, to take care of that awkward place in the charge curve of batteries where the generator, no matter how small, won’t be properly loaded, and to help out during long periods at anchor.
  • Even if you design your electrical system really well, don’t freeze stuff, use a vane gear, and have a seamanlike solar array, you will probably end up running the main engine occasionally for an hour or so to charge your batteries if you don’t have a generator. If so, make sure the alternator and regulator are specified and programmed to be efficient, and stop worrying about it. Yes, it’s not ideal, but as long as you do this for less than say 100 hours a year, and you give the engine a good run at high load regularly, it really won’t make that much difference to the engine’s life and does not justify buying, installing and maintaining a generator.

The Photograph

Our generator on Morgan’s Cloud, a Northern Lights 5kw, has been absolutely reliable for 20 years. The blue machine on the right is our large Glacier Bay refrigeration compressor (no longer made), capable of keeping over 100 lb. of food frozen, which makes a generator a requirement for us.

Further Reading

  • The rest of this Cruising Boat Electrical Systems Online Book will show you how to get the best charging out of a generator if you do decide to get one, ditto the alternator and regulator on your main engine. And Colin’s chapters will tell you everything you need to know about solar panels and water generators (wind too).

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 18 years, as co-editor/publisher of AAC.

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