I like to share my solution for mounting my GoPro. Before i attached it to the boom, but this is not optimal: eg the view is always tilted. Any camera attachments on deck, transom, rudder results in a very limted view (without surroundings).
So i bought a 'suction handle' with a hollow handle.
Next i cut off 1 half, and then all you need is to find a stick with the right diameter . That results in:
And now the camera gives a super view: