I've hesitated to add anything to this thread as the stated question is what is my back-up system for GPS. In fact the question does not apply to me. GPS is my back-up system for my eyes, ears and charts when running in cosatal navigation and GPS is the back- up system to my sextant when running in off shore out of sight of land legs.
In that way I keep my navigation skills honed and always front and center in my navigation tool chest. It is not that I am at all skeptical of the capability of GPS. It is a fantastic technology and highly reliable. But rather my choice is based upon my philosophy of sailing. I feel that sailing has become grossly over "technologisized" (if I can invent a term).
I strongly feel that one should learn to sail through direct observation and utilize ones brain rather than such a heavy dependence on technology. I don't need to keep my eyes on an electronic representation of my point in space. I need to keep my skills honed to know this through dead reckoning and keeping good llogs.There is also, in most cases - there are exceptions, no need to be so tuned into knowing exactly where you are at any given point.
I recall an ocean traverse I did a number of years ago prior to GPS, back when satnav was functioning. We could get a fix from satnav about once every four hours. We thought it was amazing as prior to that we ran exclusively by sextant and we may get a fix once a day, at best. At times it would be less often depending upon weather.
And that was way more than enough for an off-shore run. Now with GPS you know where you are every second. You can track you movements to such a high degree, and outside of difficult entrances, why do you need this? Learn to feel and see the sea. OK so if you are running some of the channels in the Georgian bay, for example, GPS is a godsend. But outside of the specific, and relatively few examples on the world scale, I really reject this dependence on GPS.
Run your coastal cruising with compass, chart, and dead reckoning, and then check your self with a back up GPS. That will teach you much more than the other way around.
Racing is a different story. If you want to be competitive racing you need to use GPS, and lots more....
dj