Instrument area at base of boat (4)
I believe the answer is:
tuba
'instrument' is the definition.
(I know that tuba is a type of instrument)
'area at base of boat' is the wordplay.
I cannot quite see how this works, but
'area' could be 'a' (maths abbreviation) and 'a' is located in the answer.
'boat' could be 'tub' (tub could historically mean a small boat) and 'tub' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tuba that I've seen before include "music-maker" , "Brass instrument of low pitch" , "Big brass instrument" , "Noisy instrument" , "Deep brass instrument" .)