Hand catching on land is MUCH easier than on a boat that is drifting along. You will find its hard to just come straight down, because any small breeze can push your boat or if there is tide currents or swells you will be moving. So you will have to continue to pace the Mavic to keep up with the boat.
Im actually thinking of selling my Mavic and going to a
P4 for this reason. Getting footage while recreating on my boat was the main reason I bought a drone. After taking it out on the water one time on the lake, I think the
P4 may be a better option because of the landing skids on the
P4 make catching the drone much less accident prone to conflict with its props and fingers.