In the main it's the going rate (5)
I believe the answer is:
knots
'rate' is the definition.
(knots is a kind of rate)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for knots that I've seen before include "Looped fastenings" , "Nautical mph" , "They secure" , "Tangles" , "the going rate, in the main" .)