I navigate by a combination of paper charts and chartplotting on a computer, depending on where I am and what charts I have. Along coasts and in harbors, electronic charts are really nice to have--letting you know at a glance where you are--not requiring you to determine and then plot your position. Offshore, paper charts are far nicer to work with than electronic charts, because you can see the big picture easily and things like isolated islands and reefs are shown on small-scale (overview) charts (on electronic charts, these may not be shown at all zoom settings, so they can be missed).
Previously, I've used laptop computers (connected to the ship's GPS) to run chartplotting software (mostly the excellent, open-source OpenCPN software), and slept the computer whenever I wasn't looking at it (to save power). That worked fairly well, but involved a delay between waking up the computer and having the position update, and laptops still use a fair amount of power, and all the ones that I had ran on 19-22VDC, which I could only get by converting the ships power (24VDC) to 110VAC, and then using the laptop's power adapter to convert to 19-22VDC (each conversion wastes power, so this was inefficient).
Since LED displays have become inexpensive and pretty power-efficient, I wanted to try using a low-powered computer to run the plotter software, and turn the display on and off whenever I wanted to look at it. This would give me a big display (much easier to navigate with a big display) without using a lot of power, and allowing the navigation computer to be left on (rather than slept), so the track (periodic log of positions) would be complete (not having gaps when the computer was sleeping).
After looking at a youtube video of OpenCPN running on a Raspberry Pi computer (very low power, very popular single-board computer), I thought I needed something that was faster. I bought a Utilite computer with a 16GB SSD that has an ARM processor, an HDMI output and should only use 9 watts of power at 12VDC. I bought a 20" LED display which runs on 14.4VDC (it came with an external power adapter that converts 110VAC to 14.4VDC). I am running both the display and the Utilite computer from a 24 to 12 volt DC converter (so there is only one voltage conversion--less inefficient than converting voltages twice), which actually puts out 13.8VDC.
I built a wooden frame to hold the display and the computer. The frame is bolted down to the chart table with one bolt so it can be turned to allow watching movies when seated at the table. Clear acrylic on the front keeps spray away (it has to be quite rough to get spray down below, but that does sometimes happen), and can be lifted up to access the display controls on the front of the display.
The Utilite computer and keyboard are attached to the back of the display (the keyboard is rarely needed--OpenCPN does what I need using a mouse for almost everything). In front of the display in the picture is the paper logbook (there are way too many ways for computers, power and wiring to fail in salty, humid, bouncy environments to not want to have a paper record of a fairly recent position).
The Utilite has an ARM processor, so software has to be compiled on it (or for it)--binary distributions are not available for much other than the operating system (Ubuntu Linux 12.04) itself. I've been running OpenCPN Beta Version 3.3.1731 (the latest beta version at the time I put the system together).
How well does the system work? This has been my primary navigation computer for nine months, during which we've traveled over 8,000 miles. Performance is slow--annoyingly slow at first, but people get used to it (I sail with different crew at different times, so several people have used it), and it is usable.
The Utilite has no internal fan and runs very hot (the case gets hot to touch, which the manufacturer says is ok). At first, I had problems with hangs that required power-cycling the Utilite to get it running again. I worked around that with daily reboots for a while, then wired in a small 24VDC fan (running on 12VDC power, so slower speed & less power consumption) blowing air across the case. With the external fan, the computer has run reliably for several weeks with no hangs, reboots or powercycles, and I have not seen the case temperature go above 38 degrees C.
There are some problems with zooming into some levels of charts, but they are easily worked around by restarting OpenCPN (I assumed this was a problem with the beta version and haven't tried to do anything about it yet--when cruising I rarely have an internet connection, don't want to mess with what works well enough).
On the whole, the system works pretty well, has low power consumption (the original goal), and has a much nicer display than a laptop. I'm content with it. I am planning to update the OpenCPN version (there is no update for the operating system yet).
Compared to a really good navigation system like Navigatrix (http://www.navigatrix.net -- a ready-to-use version of linux that can run from a USB stick on most laptops which includes a great variety of useful tools for navigators), my system is pretty basic (because I only compiled what I needed to get OpenCPN operational). Due to the amount of learning that would be required to compile the software, I would not recommend doing what I did to anyone not already very familiar with linux and make.
Why am I so concerned about power consumption? For electrical power, Issuma has alternators on the engine, solar panels, a wind generator and a portable gasoline generator. While that is a lot of ways to generate electricity, the solar panels only work when the sun is on them and no part of them is shaded, the wind generator only puts out significant power in moderate to strong winds, the engine does not get run simply to charge the batteries (the light load that the alternators alone represent is bad for the engine--all the fuel doesn't burn at very light loads so it washes oil off the cylinder walls), and the gasoline generator is noisy, so I don't run it often.
As a result, I'm very conscious of conserving electricity--all lights are LED, there is no refrigeration (or air conditioning), cooking is by gas (propane/butane), heating is by diesel and wood, and computer use is limited.
Edit August 2017: The Utilite computer has been replaced with a (newer) Raspberry Pi 3, which performs better, http://www.sailblogs.com/member/rhudson/430312
Edit 2021: The Raspberry Pi3 has been replaced with a Pi 4, which is faster. The monitor has also been replaced (I suspect a circuit board developed a crack, but I don't really know--the monitor developed an intermittent problem and replacing it resolved the problem).