How can small tugboats pull and tow massive ships and barges?
When people realize that tugboat speed is pretty low when compared to other vessels, they often can’t figure out exactly how they can push such large ships. When people see a tugboat pushing a ship many times its size with relative ease, they’re often astonished. So, how are tugboats powerful enough to tow ships? We’re glad you asked!
Why Are Tugboats Used to Move Large Ships?
Using tugboats to move large ships that need to be salvaged or barges that can’t move on their own is a lot more efficient than using a huge vessel for the job. But, the biggest reason they’re used is that these large ships often need to be moved through narrow areas or for docking and mooring purposes. This is more easily done when the towing vessel is smaller and able to navigate these tight spaces.
How Are Tugboats Powerful Enough to Tow Ships?
Tugboats have a wide range of horsepower behind them, but it typically falls between 680hp and 3,400hp. For comparison, a large ship that operates with a heavy workload might have an engine that goes up to 2,700hp. The primary reason tugboats can move much larger vessels and barges through the water, however, is all about the physics involved such as buoyancy and a low level of resistance.
Methods Used by Tugboats to Move Large Ships
Although the word tug is in its name, a tugboat can actually pull or push, depending on the situation and the vessel being moved. There are three types of methods that may be used:
- Direct Towing — A towing line is attached to a vessel using a motorized winch. Once a connection has been made, the tugboat will pull the vessel behind it.
- Indirect Towing — The tugboat pushes the vessel along its hull, which cause it to rotate and change its course. If this isn’t enough to allow the ship to propel itself forward, then direct towing will be used to finish the job.
- Pushing — In certain cases, it may be more appropriate to push a vessel for the entire distance. When this occurs, the tugboat will typically be equipped with reinforced hulls and bumpers designed to fit against a section of the vessel’s stern.
Three Types of Propulsion Systems Found in Tugboats
Since buoyancy assists in making it possible for a much smaller tugboat to push a huge vessel or barge, they don’t need a lot of power to overcome that first surge of inertia. That being said, tugboats are equipped with one of three powerful types of propulsion systems:
- Simple Screw Propulsion — Typically found in older tugboats, this propulsion system consists of a propeller fan and movable rudder. Although effective, it’s difficult for these tugboats to easily change course, so they’re not used nearly as much these days.
- Azimuthal Drive Propulsion — Propeller fans are fixed to a motorized pod known as the azimuth. This allows the tugboat to switch direction very quickly without using a rudder, making them quite agile.
- Voith Schneider Propulsion — This emerging technology had show a lot of promise. It involves a cyclo-rotor and rotating blades, with thrust and direction being achieved by changing the rotor speed and blade angle, respectively.
Tugboats Are Divided into Inland Tugs and Oceangoing Tugs
Tugboats are divided into two basic classifications- inland tugs and oceangoing tugs.
- Inland Tugs — These tugboats are for operations that take place in relatively shallow waters and are divided between harbor tugs and river tugs. Harbor tugs get vessels in and out of harbors, ports, and channels. River tugs, as you might have guessed, move barges through rivers and in and around seas.
- Oceangoing Tugs — Oceangoing tugs are built to work in a deep ocean or sea and are divided into conventional tugs and barge tugs. Conventional tugs can push or pull all types of vessels, which makes them perfect for salvage operations and — with a few modifications ice-breaking jobs. Barge tugs, as the name suggests, are specifically designed to connect with a barge and push them along.
Contact Dann Ocean Towing to Schedule Tugboat Towing Services
Dann Ocean Towing has a fleet of 17 tugboats varying in tugboat speed, size, and capability. If you have any questions about our fleet or are in need of service, give us a call at (813) 251-5100 today to schedule a free consultation.