I designed and built this fully self driving boat with the following main components:

Microcontroller: arduino pro mini (knockoff)
GPS module: NEO-6M (with extended antenna add-on)
SD card reader: HiLetgo 3-01-0038-5PCS
ESC: RCelectricparts B071GRSFBD (although this part eventually failed, I recommend the brand for their awesome documentation/videos and well made datasheets/op manuals)
Transmitter: Flysky FS-i6X
Receiver: Flysky FS-iA6B
Motors: VGEBY1 F2838-350KV (works well but know how to solder if you order this)
Magnetometer: Adafruit LSM303AGR (also is an accelerometer but I didn't use that functionality)
Solar Charge Controller: Genasun GV-5-PB-12V
Solar panel: (cheap ebay garbage)
Battery: Batteries Plus AGM 12V 3.3AH .250 FASTON

Yes, I'm aware of Ardupilot. No, I didn't use it.

This boat follows a predetermined set of GPS coordinates which are stored in an onboard micro SD card. It steers autonomously with differential thrust. This system as is consumes around 40w maximum (without throttle limiting)

My plans for version 2 include:
-custom PCB
-optimized propellers
-sonar depth sensor
-data logging
-real time power consumption monitoring
-digital telemetry
-improved pontoon geometry and material selection
-upgraded microcontroller
-various efficiency improvements
-redundancies, reliability improvements, error sensing