{HEAD ~ A propulsion system} for a watercraft includes {TAIL ~ a concavity} formed in a hull of the watercraft 
includes
{ HEAD ~ A propulsion system } for a watercraft includes { TAIL ~ a concavity } formed in a hull of the watercraft
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH