Hi, I currently working (with a team of other people) on making an autonomous boat (a small size boat, not the kind of boat designed to carry people). For our boat, we want it to be able to navigate to certain GPS coordinates.

We are using a Raspberry Pi 3 with a Navio2 to control the boat. The Navio2 is basically an addon Raspberry Pi hat that has GPS, 2 IMUs, and PWM outputs for motors. It's mostly used for drones, but there are a few people out there who have actually used the Navio2 for boats. Any suggestions on the best way(s) to steer our boat? Is it worthwhile to use PID control for the boat? Among our team, we were discussing whether we really needed PID or if it would just be good enough with P-only control (proportional without integral and derivative). Any thoughts?

In addition, do you guys think the Navio2 even the best solution for controlling a robotic boat? If not, what other alternatives would you suggest for controlling boat movement/steering and acquiring GPS coordinates?

Raspberry Pi setup is complicated, you can use more simplified arduino based ARDUPILOT - APM board via Ardu rover (Ardu boat) firmware to make your boat autonomous.
You can check out the links here: Rover Home — Rover documentation

I use APM board for my autonomous plane and truck.

Video:

Happy to see that you are working on autonomous boat. Keep it work

ican3d good work man appreciated

The ArduRover autopilot software has a boat configuration. I would drop you a link but this forum won't let me yet!