Air Ride, Low Drag Sea Trains and PV Electric Sail Boats

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Water craft have little drag at slow speed.  A couple years ago a 1000 plus ton asphalt barge drifted down into my sail boat tied along side it.  No one was around the first time so I got on a rope and pulled it about 40 feet back to the end of the slip and tied it up again.  Once it started to move I, slowly pulling hard, walked with it back to the end of the slip.

Once a boat or ship starts to move fast they encounter mostly water resistance that makes a hump not normally visible of water elasticly with little turbulence pushed upward and outward around the boat.  This is hull crosse section area, displaced water.  Beyond the invisible hump at very slow speeds waves of different forms cremate a bow shock wave that often has a lot of turbulence and creates the lost energy of the wake and spray that is exciting to watch but makes boat less efficient at really high speeds than railway trains of the same tonnage.  Most 10,000 ton freight trains can go 60 to 80 MPH with 6,000 to 8,000 HP.  They occasionally have more for hull climbing.  If freight trains were streamlined and had lifting wheel bearing seals a 10,000 ton freight could achieve 100 MPH or more with 8,000 HP.  As a ship this amount of power might only get you about 25 MPH at best.

As speed increases water skin friction and air friction resist going faster.  Longer slender sharp pointed boats and ships usually go faster than blunter fatter ones.  If we made a 10,000 ton boat as skinny as a freight train to flex over larger waves it might go 35 MPH with 8,000 HP but no one has ever tried it and calculations for this are imperfect to know.  High  water skin or surface friction replaces wake drag after about a 15:1 to 20:1 width to length ratio.  Hull shape helps only a little to improve things.  Hydrofoils and planning hulls have a limited advantage in reducing hull frontal area drag like an airplane wing improved with aspect ratio.  Much above 30:1 lift to drag ratio is the limit for a hydrofoil efficency.  As speeds increase the in air frontal area drag becomes a problem.  Large ships often look like jet fighters where water might contact thevhull and like square corner buildings where air drag is concerned.

All of this may have been short sighted.  By putting a boat or heavy ship up on an inverted pocket of air the 15 times or more water friction is reduced.  hover craft bleed air out under their flexible skirts that move up and down over wave tops.  They often take half of their energy used to pump lubricating air under their hulls.  Surface effect shipsplace catamaran side hulls and flaps that press against the water to seal the compressed air in and lose less power to compressing more to lift the boat out of the water.

If these seals and compressed air were the only support these boats would mostly just roll over since ther is no displacement hull to resist rolling over.  All known common SES or surface effect or air bearing systems need pitchcand roll stability to keep them upright.