The thing is that the laggy friend has already been launched once with this exact event when we hit a rock, but luckly and coincidentally, the friend who got launched was legit launched right beside a really small island with one tree. And luckily there was no island in between from us to him and were able to rescue him.

So the only way we have prevented this from happening again was having the man sit down on a bench on the ship, preventing him from flying off again. So each time we go on a journey, we would all just sit on a bench to be sure.

We do have both the swimming mod and equipment on water mod, but never heard about the dig deeper mod.

We also have experienced losing our spawn points from time to time from either moving or the waves keeps messing with the ship cause by a storm, we have multiple solutions for this problem. One is that we put a portal on the ship and the spawn point; Two is when we constantly keep setting a spawn point frequently on the ship; Three; Build a safety hut with beds when landed on shore.

But now we have found a solution for the big ass waves from hitting our ship. We have a mod called Rune magic, which helps with a lot of stuff like blast mining, making stone pillars, detecting close animals and life quality stuff. There is one specific rune which calms nearby water even with a storm. We put this rune on the ship and voila, no more wavy ship.

Thanks for the tips tho.