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1979 Montauk.

I replaced my old unit with a Simrad Cruise 7. 7 means 7 inch screen. There are other sizes also.
It has charts, depth finder, fish finder, water temp and navigation plotting. It also has voltage reading, so you can check the power supply of the boat .
You can split screen left and right OR top and bottom.
The navigation plotting shows every dock and slip in a marina. The chart part show a length of river.

It also Can be seen in the sunlight, something my old one did not have. Easy to install and about $700. at West Marine.