The inventive structure includes {HEAD ~ a tunnel} that defines {TAIL ~ a concavity} formed in a hull of the watercraft 
The inventive structure includes { HEAD ~ a tunnel } that defines { TAIL ~ a concavity } formed in a hull of the watercraft
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH