Good .. that solves some potential problems.
That you have to launch from the ship instead of nearby, suggest that it will be afloat somewhere, so it will still be drifting a little.
In that case, do not use RTH to land the drone as the recorded home point will not be the same part of the ship you launched from.
It could be anywhere including in the water.
Everytime I travel more than 30 miles the
Mavic 2 compass needs to be calibrated.
Good old DJI doing their best to confuse drone flyers.
They programmed some models to force you to do that, even though there is no physical reason for it.
If yours asks for recalibrating when 30 miles away, do it, but well away from the ship.
Am a little afraid to hand catch but did hand launch ok with auto take off.
I figure that landing on the deck the compass shouldn’t matter as much as take off.
Hand catching is easy, more so with a spotter so you still have two hands for the controller.
But it's something you need to practise before doing on the job.
There are lots of youtube tutorials available to show how to do it safely.
If you tried landing on the steel deck, the drone would start wandering as you get close to the steel.
That could cause problems if there are obstacles or people close by.
You could get an idea of how this works by slowly lowering the drone towards a steel roof.
As it gets closer, you'll see it start to wander and look like a drunk walking home.
It's easy to go up and out of the magnetic influence of the roof so you can try it a few times safely.
