Make an offer for a boat (6)
I believe the answer is:
tender
I believe this is a double definition.
'make an offer' is the first definition.
(I've seen this before)
'boat' is the second definition.
(tender is a kind of boat)
'for a' is the link.
(Other definitions for tender that I've seen before include "Offer, gentle, boat" , "Gentle, not tough" , "Delicate sort of bid" , "Fuel truck" , "Gentle, affectionate" .)