Must add structure when you subtract
Loren is on the right track and the analogy is correct.
Whenever you make a hole in a structure, there must be additional framing and girders inserted to support what the removed wall section previously supported.
On the 63 meter Oceanco Lady Lola, we designed both a side opening door (top hinged) for the tenders to be launched by a double overhead beam crane on the starboard side as well as a huge hydraulic stern opening door (bottom hinged) on the transom to provide the tender embarkation point and swim platform.
In order to support the remaining structure around the two huge openings in the hull, we had to add three tons (3 MT) of steel in the hull, overheads and starboard aft corner consisting of headers, girders and framing.
Launching tenders from any crane from any location in rolling seas is a difficult and dangerous operation. The main ship is usually maneuvered to put the tenders being launched or recovered in the lee to mitigate these conditions, or simply move into a protected anchorage or harbor area. Tenders are not usually operated in the open seas.
Also, from a practical perspective, owners and guests don't normally play when the water is rough.