I'm planing to use my MP to make boat videos. I've watched few video of hand landing and gived a try. It's preaty easy and I think that is the best way to bring it abord safely !
What is your experience ?
Note: I did not turn the collision sensor off but if you don't hesitate to grab it, it wont have time to go back up.
If the boat is moving/drifting or rocking then don't bother catching it. It is dangerous. If its calm, make sure the boat is anchored.
Another option is to land it on terrain and go pick it up.
But if last resort then buy a really big net and fly into it. The props will shut the moment it tangles or get obstructed.
A few pointers - look at the back of the mavic when landing. This helps orientation and minimises confusion. Make sure you advise all on board that you are landing a drone. Use the palm landing technique. Palm out 30cm under belly of mavic and left stick down until it shuts motors off on your palm. The grab hand catches freaks out the Mavic and causes it ascend from you.
And finally, practice hand launches and palm landings on terrain before heading out to sea.