Bottom line up front: GPS works on ArduSub and BlueROV2, but it needs to be mounted on a mast and out of the water to work properly.
After getting a proper tablet earlier in the week, I set about doing various ROV tests. One of these was to finally get the system wet.
The results are below.
Screenshot 8 shows the ROV out of the water with a good GPS lock.
Screenshot 9 shows the ROV in the water, disarmed and on the surface. You can see how it looses lock and the GPS wanders according to inputs from the IMU.
So what next? Well, we are either going to need to make a mast and mount an antenna externally or reconfigure an antenna inside the hull. There isn’t a lot of room to do the latter, so I am open to ideas.