Change course and gear (4)
I believe the answer is:
tack
I believe this is a double definition.
'change course' is the first definition.
(I've seen this before)
'gear' is the second definition.
(tack is a kind of gear)
'and' acts as a link.
(Other definitions for tack that I've seen before include "Nail - direction (eg of boat)" , "Small nail with broad head" , "pin" , "Short, flat-headed nail" , "Food; nail" .)