I wonder if you have ores or bars on your ship, if that increase the spawns too. By value or weight in the ship. I carry enough stuff for work bench, portal, and now stone cutter in my long boat. That is how I found 2 them at the same time. One was already spawned while second spawned up. I was hauling around 100 iron ore on a long boat full sail. Was not going to fight them. It was strange seeing 2 of them chasing me.