rswannabe |
03-21-2006 07:20 PM |
Quote:
Originally posted by dd74
Tugs are very cool. I like them because they're ugly, small, very powerful, and every ship, no matter how sleek and opulent, eventually needs one to get in and out of harbor.
I've always wondered how a tug is set up: do they usually have just one big honkering engine that enables them to move a big liner, or is it all about a small push and leaving the rest to momentum?
Great photos, BTW.
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The simple answer is lots of power. If a tug is pushing or pulling a load they have to constantly overcome the resistance of wind and water. If it is a harbor tug maneuvering a ship into berth, they are constantly making adjustments. Granted, the better the pilot, the fewer the adjustments they will make and they will use less throttle. Still when you are trying to maneuver a 600+ foot ship weighting 100's of thousands of tonns, you need a lot of thrust to make any significant change to their vector.
The older tugs (up to the '60's and 70's often only had one large engine (600 - 2,000 hp the normal range) turning one large propeller with one big rudder. Then you started to see the twin screw (two propellers with two rudders) became much more common with bigger engines. Then the kort nozzle (basically placing the propeller inside a circular shroud to get more power/efficiency) were added. Now the most powerful ocean going tugs are usually twin screw with tens of10,000hp or more.
The newest developments in tugs are the introduction of "tractor" tugs. These are tugs with with cycloidal drives (look like an egg beater sticking out the bottom of the hull) or Z drives (properllers mounted on vertical shafts that can rotate 360 degrees) which allow the tug to generate full thrust in any direction, including sideways. This is very useful for a harbor tug which needs to be very powerful and maneuverable when maneuvering large ships into port. These tractor tugs are very cool and a hec of a lot of fun to drive.
Bill - I love the old harbor tugs. They have way nicer lines than any of the new stuff. Thanks for posting the pics. My favorite tugs are the old Miki class built by the Navy just before WWII. Ever seen one of those. Their lines are simultainiously graceful and powerful.
Brooke
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