Moving Big Things in Small Spaces

Posted by PITHOCRATES - September 11th, 2013

Technology 101

Ships once used Tugs to Maneuver around in Small Spaces but Today they use Tunnel Thrusters

As technology progressed the more things we needed to make other things.  Small factories grew into large manufacturing plants.  Which consumed vast quantities of material to produce vast quantities of goods.  Requiring ever larger means of transportation.  And we have built some behemoths of transportation.

Water transport has been the preferred method for heavy transport.  Which is why most early cities were on rivers.  As time passed our cities got bigger.  Our industry got bigger.  And our ships got bigger.  Huge bulk freighters bring iron ore, coal, limestone, etc., from northern ports across the Great Lakes to docks on small rivers and harbors further south.  On the open lakes these ships can put the pedal to the metal.  Roaring across these lakes at breakneck speeds of 15 mph.  If you’ve ever seen a Great Lakes freighter at full throttle you probably noticed something.  They push a lot of water out of their way.  Something they can’t do in those small rivers and harbors.  As their wake would push the river over its banks.  So they slow down to a non-wake speed of something slower than a person walking.

Lakes are huge bodies of deep water.  But these Great Lakes freighters, or lakers, often enter narrow and shallow rivers.  Some rivers even too shallow.  So they dredge a channel in them.  So these lakers don’t bottom out.  Some lakers have to travel upriver to offload.  Then turn around.  Which isn’t easy in a shallow river when your ship is 700-1,000 feet long.  They once used tugs to push these ships around.  But today they use tunnel thrusters.  An impeller inside a tunnel through the ship at the bow and stern perpendicular to the beam and below the water line.  Which can turn a ship without the forward motion a rudder requires.  Allowing it to move as if a tug is pushing it.  Only without a tug.

Interesting thing about Trains is that they don’t have a Steering Wheel

With the introduction of the railroad cities moved away from rivers and coastlines.  But the railroads only became a part of the heavy transport system.  Cities grew up along the railroads.  Where farmers in a region brought their harvests to grain elevators.  Trains took their harvests from these elevators to ports on rivers and coastlines.  Where they could offload to ships or barges.  And it would take a large ship or a barge.  Because one long train can carry a lot of harvest.

Interesting thing about trains is that they don’t have a steering wheel.  For there is only two directions they can go.  Forward.  And backward.  If you’ve traveled passenger rail to the end of the line you may have experienced a train turning around.  The train will reduce speed to a crawl as they switch over to a perpendicular-running track.  For trains do not travel well on curves.  Because the wheels are connected to a solid axel.  So in a turn the outer wheel needs to travel faster to keep up with the inner wheel.  But can’t.  Causing the wheels to slip instead.  Causing wear and tear on the train wheels.  And track.  Which is why curved track does not last as long as straight track.  The train travels a while on this perpendicular track at a crawl until the rear end passes another switch.  It then stops.  And goes backward.  Switching back to the track it was originally on.  Only now backing up instead of traveling forward.  The train then backs into the passenger terminal.  Ready to leave from this end of the line going forward.  To the other end of the line.

Freight trains are a lot longer than passenger trains.  Some can be a mile long.  Or longer.  And rarely turn around like a freight train.  Rail cars are added to each other creating a consist in a rail yard.  A switcher (small locomotive) moves back and forth picking up cars and attaching them to the consist.  In the reverse order which they will be disconnected and left in rail yards along the way.  Once they build the consist they bring in the go-power.  Typically a lashup of 2-3 locomotives (or more if they’re the older DC models).  The lead locomotive will typically face forward.  Putting the engineer at the very front of the train.  In the old days they had roundhouses to switch the direction of these locomotives.  Today they turn them around when they need to like the passenger train turning around.  Which is much easier as they only have to turn around one locomotive in the lashup.

Planes may Fly close to 500 mph in the Air but on the Ground they move about as Fast as Someone can Walk

Airplanes are big.  In flight they’re as graceful as a bird in flight.  But it’s a different story on the ground.  Planes are big and heavy.  They have a huge wingspan.  And the pilots sit so far forward that they can’t see how close their wingtips are to other things.  Such as other airplanes.  When they leave a gate they usually have a tug push them back and get them facing forward.  At which time they start their engines.  As it would be dangerous to start them while at the gate where there are a lot of people and equipment servicing the plane.  They don’t want to suck anything—a person or a piece of equipment—into the jet engines.  And they don’t want to blow anything away moving behind the engines as the jet blast from a jet can blow a bus away.  And has.  In flight they use their ailerons to turn.  The flaps on the tips of each wing that roll a plane left or right.  Causing the plane to turn.  The rudder is used for trimming a plane.  Or, in the case of an engine failure, to correct for asymmetric thrust that wants to twist the airplane like a weathercock.  On the ground they use a little steering wheel (i.e., a tiller) outboard of the pilot (to the left of the left seat and to the right of the right seat) to turn the nose gear wheel.

Pilots can’t see a lot out of the cockpit window while on the ground.  Which is why they rely on ground crews to give them direction.  And to walk alongside the wings during the pushback.  To make sure the wings don’t hit anything.  And that no one hits the plane.  Once the tug disconnects and the plane is under its own power the flight crew takes directions from ground controllers.  Whose job is to safely move planes around the airport while they’re on the ground.  Planes may fly close to 500 mph in the air but on the ground they move about as fast as someone can walk.  For planes are very heavy.  If they get moving too fast they’re not going to be able to stop on a dime.  Which would be a problem if they’re in a line of planes moving along a taxiway to the runway.

When we use big things to move people or freight they work great where they are operating in their element.  A ship speeding across an open lake.  A train barreling along straight track.  Or a plane jetting across the open skies.  But when we rein these big things in they are out of their element.  Ships in narrow, shallow rivers.  Trains on sharply curved track.  And planes on the ground.  Where more accidents happen than when they are in their element.  Ships that run into bridges.  Trains that derail.  And planes that hit things with their wings.  Because it’s not easy moving big things in small places.


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