Student or Learner
1. The boat is going under fast.
How can a boat travel under the surface of water?
Does the "under" above mean below the surface of water?
A boat that is going under (unless it's a submarine) is sinking.
It's sinking fast.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.