Tech knowledge needed for hand launch and catching

That's got to be fun to watch.
The GPS is trying to keep the bird stationary. Difficult to do in a boat.

Do the same launch and catch while on land. Start the motors then walk a couple feet. See what your bird thinks of that. You will experience the same battle when catching.

After catching, if you release, it should go back to where you caught it. It's fun to do. I've done it.

 

With regards to your last question...

There's a barometer altimeter that indicates if the quad is rising, falling, or stationary (landed/caught). The FC allows the shutdown to occur when there's no change in the barometric readings.

 

I've seen folks ask "Why do we have CSC?". I guess landing on a boat or other moving vehicle is a good reason to have CSC for shutdown.

 

When it's descending, it's watching the barometric altimeter for changes that tell it it's still descending. When the altimeter has stopped changing for a couple of seconds (despite the fact that it's continuing to reduce motor speed and keep the system level) it realizes it can't descend any further and will allow you to stop the motors.
As stated above, if you in GPS mode and you are moving, it will think it's being blown by wind and will try to compensate and fly back to where it was.
You may have better luck switching to ATTI mode after you get a hand on the landing gear.

As for hand launching... ??? I've never tried. I would try launching from a flat surface and kick the throttle up fast.
I've seen videos where an assistant hand launches. The pilot throttles up and the assistant lets go when they feel it pulling upward.
As above though, you may want to launch in atti mode to prevent it from trying to hold position.

 

Just a few years back I used MEMS gyros on CP-helis (yaw axis only). When powering up it was importrant to not disturb the heli during warm up and gyro initialization.

Possible magnetic disturbances from the boat aside, the Naza employs similar sensors so could it be problematic to try and start a P2 in a moving environment?
(pitching and rolling as boats do)

 

Here's another one, HypervisionAustralia has a bunch of well done videos which are very informative.

 

I know the feeling... If I had one of those, you would be on your own right now.

How about a picture of your boat, so I have some idea what I'm working with here.

I'm thinking a small deck/platform attached to a pole which can be inserted into a pole holder. Make sure the Phantom can't lift it out of the holder. They are strong when they are **** determined.
Hang a rope, or bungee cord from the belly of the phantom. Figure out a quick release method to secure the bird to the platform.