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Tugboat Ocean Towing
One ton of bollard pull on a tug can pull how big of a barge?
I'm having a hard time understanding bollard pull ratings on tugboats. One tug I looked at had a rating of about 27 tons of bollard pull. The ship itself weights over 250 tons. So how big of a load could it actually pull. A large tug can pull ships that weight thousands of tons. So, how much does one bollard ton actually pull in terms of weight of boat/barge. Can a 27 ton bollard pull handle a 500 ton barge? I'm sure this all boils down to Archimedes principle somehow....
The Bollard Pull of a tugboat is a rating of how hard it can pull against a fixed bollard on a dock. This is not directly related to the deadweight tonnage of the vessel under tow in actual conditions.
As the previous posters have correctly stated, even a small amount of force will move a large vessel. The larger the Bollard Pull the faster you will be able to reach towing speed and also slow the vessel safely. The Bollard Pull is determined by the horsepower of the engines, the shape of the propeller, and the type of propulsion system. There are trade-offs with the propeller shape, a propeller with a higher top speed will not be as powerful for close in handling.
The difficulty comes when you are trying to determine if a specific tug will safely and efficiently handle a specific tow. Here are some factors to be considered:
--Will the tow be on flat inland bays and rivers or on the open ocean?
--What currents will be encountered?
--What will the winds be like?
--Does the vessel being towed have a large "sail area" like a ship or is it flat like a barge? Even barges loaded with containers are significantly affected by the wind
--Are you considering just the towing or the actual maneuvering encountered in docking? Will you have assistance for this?
In order to make an informed decision about your future tug I would talk to several boat brokers and to as many tug captains as you can to get their opinions on Bollard Pull, horsepower of the tug, type of propulsion, and typical deadweight tonnage handled.
Do a Google search for "bollard pull" and read as many articles as you can.
http://www.google.com/search?q=bollard+pull&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7GGIG
I have listed several below to get you started. Even though Wikipedia is not always a good source in this case it has a reasonable summary of Bollard Pull.
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Goliath Crane Tug Boat
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