Presently, waterways and everything ship related can be placed on the Vulcanus lava. I wouldn't be surprised if this also works on Fulgora's Oil Ocean, but I haven't been there to try.

From my personal experience in my playthrough, this is actually really fun! I'd hate to see this get completely removed, but a ship with a tungsten hull and more lava-y VFX would be very enjoyable on Vulcanus.

And the other thing that seems more like a bug. If you place a ship on anything but completely straight rails, it just...doesn't spawn with an engine. I think that's what is causing it? Or that seems to be the most consistent culprit. I haven't done much testing on that but it's absolutely infuriating. In any case, thanks for making this awesome mod!

Okay. I just found out that specifically signal buoys cannot be placed on lava. Rather unfortunate.

The engine thing is a bug. It's supposed to undo the ship building is there is no space for the engine. I'll take a look.

Placing waterways on lava is also a bug atm. Haven't considered going further there yet!

Thanks for responding! I will say that with the default generation presets, Vulcanus doesn't really have enough lava to warrant a ship ever. In my playthrough, though, I messed with the world generation, and there's lava everywhere. Lava boat, ahoy!

Found the cause of both issues, will probably release an update this weekend with that and other fixes.