1. Garmin supports NMEA
interfaces and should be able to allow other software
to manually upload a route
say from a computer. Check for software
support based on the model of your unit and the software.
2. Since you mention free software you get what you get for ease of use. Look for output and input NMEA
support in the specifications of the software. Check out OpenCPN
in the forum here. It's a newer program that already is a better product than Seaclear. In looking at many products you couldn't pay me to use Seaclear. OpenCPN
is free too and plenty of support in it's own little forums
subsection here at CF. It's an open source program with a lot going on right now. Seaclear is dead.
3. Yes but you would connect up the GPS
to the laptop typically with a USB serial
4. Two depth
sounders will be a PITA. Since both will be located differently you don't want to mix the depth displays of both on the same bus as you'll never know which one is reporting. I would set them up and each have their own display not connected to anything. Depth is only useful at the wheel
unless you might have a repeater at the chart table below, but it's just extra..The only reason to have two is if one fails. I used to have two and I disconnected the display of one and left it in the locker when it might be needed later. I tested it every few months to make sure it still worked. eventually it died and the other one never did. Could have been the other way.
You need to verify which types of NMEA your devices support and what "sentences " they speak and can listen to. To connect multiple transmitters (called talkers) requires a multiplexer to serialize the multiple outputs into one steady flow of data. They are not cheap
. You can't have multiple devices all talking at the same time. But you could connect a PC to a GPS and the GPS to an autopilot
for a simple setup that is easy to work
with. Since you are just getting something going start with a GPS connected to computer. It opens lots of good things alone. From there you'll see how it works and make decisions. You are best to grow into using electronic navigation
. It's not magic and you need to learn how best to apply the features.