Hi Stanly,
what mounting position and angles worked best?
Find getting the horizon level is hard. Although downhill seas can add to sense of speed

Tried a back of boom top mount. Had waist up sailor in view. So your mounts are better. May try a under boom mount next time. Reluctant to have it too exposed (sticking out from the boom) in waves.
Will be slightly different to your mounts as I have a Countour HD 135 degree wide lens camera with water proof housing and a bike reflector holder at the moment.
What editing software do you have and does it include video stabilizer enhancement? I had a lot of jarring when sailing in rough seas south of Wello markers on a 5.0 and wave board as wind kicked in before dark. Which format and resolution do you save it in before uploading to YouTube?
Roj