If you are on a cruise ship - don't do this!
Lately I have come across a series of news items of people being banned from cruise lines - for life! What did they do? They risked their lives. Here is the most recent - https://news.sky.com/story/woman-banned-from-cruise-after-dangerously-posing-on-ship-for-selfie-11838548
Now, cruise lines go to great pains to make it difficult to fall off of their ships. You really have to go out of your way to fall off. But still, some people, in search of the perfect selfie, will put themselves in danger.
There are no shortage of great photo opportunities on a cruise - there is no need to risk life and limb to get a special photo. On most ships you can’t get away from professional photographers hoping they will get such a good picture of you that you will buy a copy. Don’t risk getting kicked off of the ship (or worse) just for the sake of your Instagram feed.