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