A DC to DC regulator
is the best option. We went with a model from Carnetix
. They make a Mac Mini adaptor. Their regulator
is supposed to be quite efficient compared to the smaller converter "bricks". I believe the Carnetix units have also been used with Macbooks.
also makes ready-to-use Macbook adapters.
I use Mac OS to earn my living and prefer it to anything else. However, I decided it wasn't the smartest choice for a boat computer. There's simply a way bigger selection of marine-related software
on the Windows side of things. The Windows-based navigation software
in particular is more mature, generally higher performance, and offers more (useful) features.
I would have much preferred to stick with Mac OS, but I only would have been doing so for the sake of convenience and familiarity. If you're serious about your boat computer, I believe you're much better off with a Windows 7 boot-camp partition.
If for some reason you can't (or really don't want to) run Windows on a spare partition, MacENC / MacWX are the best combo by far. MacENC in particular is the furthest ahead out of any of the Mac options.