If anyone feels like taking a little time to pass on some basics about chartplotter chart chips, I'd be grateful. I've never had a chartplotter before. In the past I used navigation software on a PC and bought charts on CDs or downloaded them. The boat we're buying has two chartplotters, both Raynav: an E80 in the cockpit and an RL72 below at the nav station. I've been trying to figure out what I would need to buy if I wanted additional charts for them. (The manuals would probably tell me but they're on the boat and the boat is 5 hours away.) Both chartplotters have a chip in them currently covering the boat's present location (New Bedford MA) but there are no additional chips on the boat.

It looks like the two chartplotters take two different kinds of cartridges that can't be used in both. Am I right about that? It seems odd that the previous owner would gone that route. (He was heavily into multiple redundancies and maybe wanted to have two different chart types for comparison?)

When I look up available chips in catalogs, they mention the coverage area but not how detailed the charts are. Are all chips vector plots or might some be raster scans? Can I always assume that every chip has the smallest scale detail that's available? There seems to be little correlation between cost and coverage area across different kinds of chips, which also seems odd. (Again, I apologize, you're educating the truly ignorant here.)

I'll also have a computer onboard with a full set of charts and navigation software. I can't see buying two sets of expensive chips for two chartplotters. Maybe I should give up on the RL72, the one below, when I'm outside the area covered by the one chip I have.

Any enlightment you can bring to my confusion will be most welcome. Thanks in advance.