Smithbrother, I boat in LI Sound, Fisher's Island Sound and Block island Sound. There are many obstructions which are not marked, however every one that I've seen is visible regardless of the tide. Any obstruction that is submerged or temporarily submerged due to tides, is marked with a navigational aid. The aid might not be directly in front of the obstruction. You might find 2 markers, that when lined up, will keep you in navigable water provided you're on the correct side and give the navigational aids a wide berth.
That being said, Garmin, Raymarine and Furuno are the most popular and have, in my opinion, the widest variety of models. Garmin used to be the leader in GPS/chartplotting, while Raymarine (Raytheon) and Furuno were traditionally very popular for Radar. Garmin has been making inraods in Radar in teh last few years. Personally, I like either Garmine or Raymarine for GPS/Chartplotters. There are some other brands out there as well, such as Lowrance, Simrad, Standard Horizon.
If you take a look in the Buy/Sell section, I think you might even find someone who is selling a used Garmin GPS/Chartplotter (color) with the charts already loaded. You might even be able to make an offer. I know for a fact that it hasn't been sold. I also know that it would be perfect for what you're looking to do.
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