Swell ultimately cutting boat ride off (5,4)

I believe the answer is:

tidal bore

I'm a little stuck... Click here to teach me more about this clue!

'swell ultimately cutting boat ride off' is the definition.
I can't tell whether this definition defines the answer.

'swell ultimately cutting boat ride off' is the wordplay.
'ultimately' says to take the final letters.
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'off' indicates an anagram.
The final letter of 'swell' is 'l'.
'boat'+'ride'='boatride'
'boatride' is an anagram of 'tidabore'.
'l' inserted inside 'tidabore' is 'TIDAL BORE'.

Can you help me to learn more?

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.