I've entered the boats that run across the ocean of tears by swimming under them and being pulled into the lower level.
So far, I've only done it by accident -- jumping off the boat early when it gets to Butcherblock and swimming to the shore, the boat over took me and I was inside. I've never managed to do it on purpose, but I have heard of people doing that.
I've read you can get on the lower levels of the Butcherblock-Timmorous shuttle boats that way. I was unable to do it though.
This is actually a bug, that is utilized on the zek servers ( um....I...um...I never did it, yea, thats the ticket! )
If a boat is in motion, you can "warp" through the hull. If it is stationary you cannot. Its as if the boat swallowed you.
(Mind you most of this was Pre pop, and players HAD to use boats more often to get around ) Now remember, you cannot cast spell while ON a boat. So what we would do is get SOW and Levitate before the boat came and hide out in the water ahead of the boat. Wait for some unsuspecting enemy to board the boat, then jump on with him and stay hidden until you zone. Once in the next zone, you would target the poor fool and run off the side of the boat. At which point you could run just a bit ahead, stop and cast spells. Root works very well, keeps em from jumping off the boat. Then you have your way with them, running alongside the boat, casting away till they die. Heres the best part, remember this is PVP.... When the boat zones again, their body is dropped to the ocean floor
Makes for a nice long corpse run, muhahahaha.
Khama Khameillion lvl 52 Illusionist / 250 Grandmaster Jeweler of Sullon Zek
Khaamma lvl 60 Phantasmist / 181 Jeweler of Al'Kabor