> I may also rig a temperature sensor to the boat hull, or via a tether.

If you want this to scale to potentially commercial end users, I would 
consider an NMEA based off the shelf sensor?  Although the prices are 
quickly > £100, ie non trivial, NMEA 0183 sensors are plentiful and 
NMEA2K is getting rapidly available (add an Actisys bridge to get data 
into the computer)

> What concerns me about openstreetmap, is I had envisioned a system where
> the database is downloaded to the operator's embedded system depending
> on the anticipated area of local/regional travel, thus not having to
> depend on constant/reliable internet access.

Can you not download openstreetmap?

Your bigger issue is that it's not really a nautical mapping system?

In the USA you can have all the raster nautical and aviation maps for 
free (cool).  The argument goes that the tax payer already paid for 
them, so the data is made completely freely available


> My reason for using this list, is to flush out any gentoo-ish
> common ground or any hardware suggestions; not an expose
> on openstreetmap....

I think you should consider some other options also:

- Small embedded server which collects the information, with a handheld 
system then connecting via http or similar.  I like the PC Engines Alix 
boards.
- OpenCPN customised for your needs

The top one is similar to something I'm working on.  We 
(http://www.mailasail.com) are building a small embedded router for 
connecting all the communications bits on a boat together and we can 
easily take in NMEA and repeat it via GPSD.  I plan to either write, or 
pay someone to write, a fancy javascript based instrument console 
something along the lines of the ipad "NMEARemote" app.  The goal would 
be to use all the responsive magic that's easy to get these days to make 
it scale from a phone to tablet screen.

I think with a decent browser on your tablet you can fairly easily build 
decent web apps these days, especially if you don't need to target IE.  
To my eye this dramatically simplifies the problem because you can use 
off the shelf components and focus on the software

As an aside if anyone here is interested in extra work I have a fairly 
big backlog of web based work.  Probably need backbone+jquery skills 
with a Rails/Mojolicious backend to talk to

Good luck

Ed W