{HEAD ~ The hydrogen fuel tank} also functions as {TAIL ~ the vessels} ballast having adjustable draft depending upon its fullness 
functions as
{ HEAD ~ The hydrogen fuel tank } also functions as { TAIL ~ the vessels } ballast having adjustable draft depending upon its fullness
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH