Circular ripple around boat propeller making a loud noise (7)
I believe the answer is:
roaring
'making a loud noise' is the definition.
'circular ripple around boat propeller' is the wordplay.
'circular ripple' becomes 'ring' (I can't justify this - if you can you should believe this answer much more).
'around' is an insertion indicator.
'boat propeller' becomes 'oar' (I've seen this before).
'ring' going around 'oar' is 'ROARING'.
Can you help me to learn more?
(Other definitions for roaring that I've seen before include "The Lion's part, nothing but this (MND)" , "& 1 Across Strong winds in S. Hemisphere" , "Do a - trade, - forties" , "Sounding as a lion" , "Making cry (like a lion)" .)