In ESL grammar books, go is usually taught to be used with gerund of recreation-related verbs such as go camping/swimming/surfing etc.
He is going swimming. Where is he going? Swimming.
He is going [to swim]. Why is he going? To swim.
He [is going to] swim. What is he planning? He is planning to go swimming.
went sailing off the rock ≠ went where?I hit her and we both went sailing off the rock into the river.
went sailing off the rock = sailed off the rock
This 'sailing' is not the same as 'swimming' in 'go swimming'. 'go' in 'go sailing off something' does something else. I can't explain what. Others will help.
EDIT: in 'go swimming' go retains its meaning: to propagate
in 'go sailing off the rock', go does not mean to propagate in a certain direction.
Student or Learner