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