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