Sustainable Cruising

Before cruising full time many people start with weekends or weeks on the water.  If you keep your boat at a local mooring or dock without full time power then it’s pretty standard to pack ice and coolers as part of that process.  The most frustrating part for us was that spontaneous overnight/short trips still required time, effort, and planning.  Not very spontaneous!  We felt that the point of cruising was to feel free and untethered …and we were missing out.

What type of Refrigerator?

Given that we wanted a cold fridge full time and did not have shore power available we knew we needed something that took a minimum of power.  That meant an efficient heat pumping mechanism, good insulation, and likely a small cooled volume.

Although thermoelectric (solid-state/peltier) coolers are common and affordable, they are not very efficient at cooling and don’t have the ability to create as much temperature differential as desired (in warmer temperatures, if air cooled, they can’t get cold enough).  Another option, absorption refrigeration, has been around for a long time, but really suffers from the same two drawbacks, and is more expensive.  The one upside to absorption is that some have electric and propane power options.

This leaves us with the standard compressor option as is found in common home refrigerators and freezers, but one designed to run on 12V DC.  So how much power, how to power it, and can I afford it?

How to Power it?

Still under the assumption we don’t have shore power available, what are the options?  Most  power vessels, sailboat diesels, and even sailboat outboards have charging capability …but that doesn’t really help when you’re away from your boat.  This leaves us with solar and wind …and where we need to get creative.  There are cloudy days, and windless days, so both options are reliant on weather (and in the case of solar, time of day).  At some point I’ll hopefully get to a discussion of wind generators, but we opted for solar in our installation.  The main reasons for this were noise, cost, safety, and the knowledge that mechanical devices typically require more maintenance and have more limited lifetimes.  Please see or article on solar installation for details on this part of the project.

How much Power?

So what are the numbers?  As cruisers thinking about budgeting our electrical resources we need to be concerned with two things: power and duty cycle (what percentage of time is power being consumed).  Typically both items are fairly straightforward …but a refrigerator’s duty cycle varies based on the ambient temperature.  The hotter it is, the more it runs to keep the inside cool.  Fortunately, when it’s hotter out there is typically more sun, so you’re generating more power at the same times that it needs the most power!  This is another reason solar may be a better option than wind as a main source of power generation (assuming refrigeration is one of your largest energy consumers).

So I’ll be honest, I am presently biased to a specific model refrigerator/freezer.  It’s the model we decided on because of efficiency, physical size, and cost.  The duty cycle changes based on temperature, but often runs ~20% of the time in the evenings when it may be around 70 degrees.  When it is running, it only consumes ~40W. Dometic rates it at 3.1A, though I’ve seen it at low as 2.5A (30W) when running! Although this a fairly significant power requirement in a world of low power LED lighting and cell-phone chartplotters, it is providing you with cold beverages and cheese….

What’s the Cost?

Dometic makes a full line of various size portable 12V refrigerators.  Many use the same compressor, so running power should be the same.  As you go larger, however, the duty cycle increases, and of course so does cost.  Given the limited space we have to work with, and the geometry of the lid hinge/shape, we opted for the CF-18 (18L volume).  The price fluctuates some, but typically this fridge runs about $320 with free shipping if ordered from amazon.com.

Get the Dometic CF-18 @ amazon.com

Specifications (confirm at dometic.com for any updates):

Need something larger?