The concavity has {HEAD ~ a longitudinal axis} of symmetry coincident with {TAIL ~ a longitudinal axis} of symmetry of the watercraft 
coincident with
The concavity has { HEAD ~ a longitudinal axis } of symmetry coincident with { TAIL ~ a longitudinal axis } of symmetry of the watercraft
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH