You will need to pick up data-out, data-in and ground from the Raymarine
E-80 and connect respectively to pin 2, pin 3 and pin 5 on the 9-pin
serial
plug. Raymarine used to use there own protocol, called Seatalk, not
NMEA,
and a converter was necessary, but I don't know if that still applies. I
suspect that Coastal Explorer requires NMEA sentences.

Right, Coastal Explorer uses NMEA. The question is what're the options on
getting NMEA in/out of a Raymarine setup and what's better about each? I
can, of course, just go with an NMEA serial right out the back. Actually, I
can't in this boat's setup as that port's already taken. So I have to get
it from somewhere else. Either throught a Seatalk, hs, hs2 or high-speed
port. And then out of there as either serial or usb.

So whose bridge works best (and whose should I avoid)?