I don't post much but I just did some filming over water and from a boat this weekend and can provide some experienced feedback.
First tip is film from land if at all possible it is much easier.
The first vessel was all steel and could break ice - I didn't even try to launch from it but if I did I would have hand launched. Keep the compass in mind on metal boats.
The second boat was a fiberglass charter fishing boat with a large stern and outboard motors - so no metal. Launched right from the stern deck no problem. Good tip posted above me to fly away from the boat asap. The drone will stay still but if the boat is moving/rocking it could hit the drone. If you are on a sailboat watch the rigging,
While filming over water I stayed at about at 10-20 feet due to the action I was filming. I think below 10' is where the downward vision sensors start getting messed up. Keep the wind speed and direction in mind. I had to come back into a steady 15 mph wind. Also - if you are low like I was have a spotter (I had the boat captain) looking out for other boats - especially taller sailboats.
I was able to have the boat captain hand catch the
MA on the first try. Since all the sensors were on I just brought her aft and slid in sideways and he grabber it and flipped it. If that didn't work we had a large fish net on standby - I'd rather that damage than it drops in the water.
I tried to send her out again on another battery but got an IMU calibration warning. For S&Gs I tried to calibrate it on board the boat but that does not work - it hung up. Probably wouldn't have flown it if it did, but maybe. I think the motion of the boat just messed it up. Once on land the calibration ran fine.
So - launching is not too hard. Getting it back on a boat can be tricky, and risky, but is doable.
Next time the only things I would do differently is turn off the down sensor (they don't work well over water anyway) just to see how it does and change the RTH so it doesn't go back to the launch point.