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