I have a 330 C Lowrance unit on my 84 V-20. Combination GPS and Sonar. Bought combo with external unit, and mounted sat receiver on my rail with a clamp like used for antenna.
Best graphics at the time I bought it, and looked at Garmin for comparison. Has a variety of settings for day and night.
Lowrance has a site for demos of their systems so you can also test drive before you buy.
Install was simple to do, when I read the instructions. I pulled two sets of marine wire from the battery directly to each unit to power. This supposedly eliminates noise on the system, and protects your unit from drawing battery power by installing throw switch circuit breakers inside the cuddy for positive disconnect. This season had to change from the inline fuse parts included with system to waterproof yellow plastic fuses, and souldered them to be sure of good contact.
Bought the RAM ball mount instead of permanent install in the dash, this way, I can change the angle of unit to view sonar for depth and fishes while anywhere in the boat.
I disconnect my unit when not in use.....unfortunate that it would dissappear if I didn't do it.
Unit came with surface of the water information, meaning bouys, day markers, etc.,. however no depth contours. If you want depths, you have to use Navonics $199 extra (sp) or buy the Lowrance product $99 when it becomes available. BUT I fish Indian River and Delaware Bay and Ocean City MD, Susquehanna Flats, and these areas, except for Delaware Bay are not charted anyway!!!
I really considered the new hand held model H20 I think is the name....for the expense.... thought it was also a great tool and excellent graphics
Only my opinion....