When this happens to me, I find it slightly annoying. And it happens rarely to me. I find it only
slightly annoying because you can swim over the largest oceans for as long as you like without ever drowning. The only downside of swimming is that it just takes longer than walking.
If Minetest wouldn’t allow you to swim for an infinite time, that would be different, because then, spawning in the middle of an ocean would mean a quick death. In this case, I would find spawning in the middle of an ocean very annoying.
If it annoys you too much, you could add static_spawnpoint to minetest.conf.
Your phone or window isn't wide enough to display the code box. If it's a phone, try rotating it to landscape mode.
Replace “X”, “Y” and “Z” by the coordinates.
I sadly don’t know how to do this on a per-world basis. :-(
Alternatively, you could try to build a platform at the spawning position. ;-)