Even with a map program YOU need to program the course changes via waypoints at each alteration. The system will not 'take you around' charted obstacles.
This text copied from the manual:
A route is a sequence of waypoints that lead you to your destination. A route must have at least two waypoints and can have as many as 50. The GPS 72H can store up to 50 routes. Create or modify a route using the Routes page, and add waypoints to a route. You can also create routes using MapSource mapping.
To create a route:
1. Press MENU twice > select Routes.
3. Press MENU to add a waypoint from the map or from your saved waypoints.
4. Select OK to add it to the route.
5. Repeat steps 2 through 4 to add additional waypoints to the route.
6. Press MENU > select Start Navigation.
This model does not appear to support charts so you're entering waypoints by lat/long most likely (taken from a paper chart, for example). It does say you can add routes from mapsource - that would require buying the program and creating routes on your PC and then downloading them to your unit.
We once preplanned a route from Tacoma to Vancouver BC on a 76MAP and had at least 20 waypoints for the Snohomish Canal (aka the La Conner ditch) alone.