I have a boat and I like to travel. I was interested in the garmin 650 at $199.00 but with my limited research it seems this would be useless on the water. I don't need depth charts etc, just to find my way back to the dock after a few.
When you say Garmin 650, I assume you are referring to the Garmin Nuvi 650 model. That is a car model for roads.
If what you are looking for is to set + locate waypoints, obtain the current latlon, navigate the waters, record a track, and set your course for a waypoint, etc., then there are lots of GPS that will do that for you, many for under $100, like the Garmin eTrex. In fact, I just found a used Garmin-45 unit for less than $5 on eBay. Many sailors sailed across the ocean using a old Garmin-45, made in the 90's.