This allows {HEAD ~ a gas pressurizing blower} to either maintain cushion gas pressure for minimum draft or evacuate {TAIL ~ the gas cushion} from minimum above water profile 
to evacuate
This allows { HEAD ~ a gas pressurizing blower } to either maintain cushion gas pressure for minimum draft or evacuate { TAIL ~ the gas cushion } from minimum above water profile
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH