Let’s Talk Power Budgeting

posted in: Boat gear, Maintenance | 1

As you’ve surely noticed, we’ve spent a lot more time lately hanging out on YouTube, sharing our sailing stories via video journal. For fear of boring you guys, we haven’t really talked much about the details of our boat, our set up and the modifications we’ve made to make Carthago our home at sea.  Given that this is the exact subject we spend most of our time discussing (because clearly we never really know anything about where we’re going until we get there), we were glad when one of our Patreon supporters sent in this question:

What is your power budget on the boat? How many amp hours do you have/use per day and how do you maximize your solar power?

So then…grab a beer and let’s chat power budgeting!

When we bought the boat:

  • 200W of flexible solar w/MPPT (high efficiency) charger
  • 4.5 kw diesel generator
  • 690ah AGM battery bank
  • 90ah alternator

Since then we’ve added:

Our power usage style:

The biggest power consumers are the Danfoss 35 fridge (~5ah) and the 6.7 gallon/hr Katadyn Powersurvivor 160E watermaker (~18ah) and Raymarine autopilot if we are under sail and not using the Hydrovane. The other major power consumers are the device chargers (iPad, laptops), lights (all LED), radio/speakers with amp.

If we want to use the microwave (which we never do – it works much better at storing eggs!), we’ll run the generator while we’re operating the appliance. If we have a cloudy day or two, we’ll run the generator so as to not dip under 60% of our battery bank. We very rarely use the water heater (solar shower bags are awesome!), but if we do, we’ll either run the engine or turn on the generator for about 15 minutes.

We consider ourselves to be very conscientious of our power usage. Maybe more than most. We take short showers  and wash dishes in salt water (rinse in fresh) so we don’t have to run the water maker as often. We don’t leave the fridge open too long, we don’t leave lights on and don’t even use our Raymarine GPS display, opting instead for the more efficient iPad. This said, there are things we aren’t willing to give up such as showers and our fridge. It’s basic to us, but for many boaters it it’s a luxury they skip.

If you’re heading out cruising, it’s really important to understand your consumption style when outfitting your boat. You might think you can live with salt water showers – and hey, maybe you can – but it’s best to be realistic and research based on a balance between your needs and your wants. There are a lot of people who run their generators on a daily basis. Some don’t even have one. It’s really up to you, your budget and your preferences. For us, we simply don’t like the noise getting in between us and our “zen” at sea.

What we produce:

Thus far, the solar panels contribute about 80-120ah on an average sunny day in the South Pacific. In Mexico, we were averaging about 100-140ah/day. Obviously, when the sun is not out, we’re not pulling in power. For those half/half days, we really wish we had hard panels that we could angle into the sun.They say the best kept secret of the South Pacific is the lousy weather!

The Silentwind 400W wind generator can vary greatly, but usually it’ll contribute around 70-150ah,  usually near the higher end when we’re under passage.

The alternator is 90ah, a cheap and very useful upgrade. However, we rarely use the engine…that’s the point of being on a sailboat, isn’t it? For a little context, we only used 53 gallons of fuel from La Cruz, Mexico to Tahiti!

Our thoughts:

We’ve always said that we hate turning on the engine and running the generator (yes, hate is a strong word). We look at them as back ups to our more “nature-powered” energy sources. Having reliable alternative energy sources that were none invasive with loud noise or bad smells was crucial for us.

But that being said, maybe we didn’t need to be as strict as we were. We’ve since made calculations and realized that we do have a bit more wiggle room than we thought. Hindsight is always 20/20, huh? Returning back to the boat, we’ll probably indulge in a few more hot showers and maybe even crank up the cold to freeze an ice cube or two! We’d prefer not to have a generator at all (you should really see our gangsta lean), but if we’ve got it, why could use it’s powers for good once in a while? ; )

Flexible or rigid solar panels?

Our flexible solar panels output significantly less than rigid panels. The reason we went with flexible is because of the convenience of just snapping them onto our bimini without having to pay extra for the stainless steel work that heavier rigid solar panels would require. Basically, it was a money thing and for once, we decided not to B.O.A.T.

What we would have done differently:

If we started from scratch, we would have used rigid solar panels instead of the flexible kind, two wind generators and would never have had a diesel generator. Under passage, the autopilot is what usually use up the most power…but it’s also when the wind generator works best! The generator adds 350lbs of weight to our lightweight Beneteau, it leans us heavily to starboard, since it’s located in the starboard locker and it requires messy maintenance and frustrating troubleshooting and repairs.

Want to know more? Have some advice? Leave a comment below!

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