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