The most common and most likely answer to this crossword clue is the 8 letter word NAUTILUS
I've seen this crossword clue in The Times
N
A
U
T
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L
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S
More clues leading to the result NAUTILUS
- Nasty insult about gold vessel
- . Mostly employ Union to replace insurgents, initially, after an uprising in submarine
- Sea creature — as usual, it changed after new start
- Sea creature behaving badly, one hears, left America
- Mollusc appears as gold among shimmering sunlit surroundings
- Shellfish’s underwater vessel
- One man cuts film out — losing all extreme characters — and finally appreciates Finding Nemo’s craft
- Submarine, reportedly in good shape, reaches America
- Guardian follows one into unlit derelict submarine
- Designed usual tin vessel used by Nemo
Buddy explains!

The straight part
We know that "vessel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vessel = nautilus.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NAUTILUS mean?
NAUTILUS noun- A marine mollusc, of the family Nautilidae native to the Pacific Ocean and Indian Ocean, which has tentacles and a spiral shell with a series of air-filled chambers, of which Nautilus is the type genus.
- A kind of diving bell that sinks or rises by means of compressed air.