The 276c looks like a nice hand held unit. http://www.garmin.com/products/gpsmap276c/

As far as fixed or portable, I guess it depends on if your planning on using it just on the water or wanting the flexibility of using it on land too.

I have the gpsmap 196, same body as the 276c and 176c. Its an aviation unit but also has a land and water modes. I really like the user friendly menus that garmin has. Its also very easy to update the garmin products online with a simple download and cable that came with the unit.

If I win the lottery, my next gps will be the gpsmap 296, but for now, Ill be happy with my 196.