I am sure we all recall watching the pirate movies on the TV where the captain tells the First Mate to bring the ship about and he begins to turn the rudder wheel what seems like hundreds of revolutions in order for the ship to begin turning. This was because the wheel was connected to the ships rudder through a series of gears that allowed the rudder to move against the extreme pressure of the water in the ocean pushing against the rudder below the water. Today’s ships are over 20 times larger than those ships and the rudder is over 20 times as heavy and 20 times as difficult to move. To avoid having someone on the bridge of the ship having to turn a gear driven wheel over a thousand revolutions to move the ship one degree a new system of energy transfer has been employed in the design of large and medium sized ships. That energy transfer process is called – Hydraulics. (HSC online 1999).
Hydraulics is used in many applications where extreme force is needed over time while applying a much smaller effort. The principle of hydraulics allows for the application of minimal forces to achieve an output of multiplied work power. We see hydraulics in use with big construction machinery, in the logging industry and very extensively in the automation and control engineering field. Since ships are self contained communities that use a variety of machines and devices for propulsion, safety, cargo management and crew comfort they can’t call for more help while at sea. Therefore they must use technology to provide the necessary extra power assist when needed. In the shipping industry hydraulics is used in the steering gears, bow thrusters, various stabilizer and valve actuators and other processes in the engine room to reduce the manual workload of the humans on board.
To understand the benefit that hydraulics play in the operation of large ships we must first understand what and how the hydraulic process works. In simple terms hydraulics is the principle of applying force at one point and having that force multiplied and applied at another point where action needs to happen. This is normally accomplished by sealing a non-compressible liquid, typically an oil, in a none flexible container and then applying pressure to one end forcing the compressed fluid to actuate some device connected to the other end of the sealed flexible container. Since this oil can’t be compressed in the area it is contained it is force multiplied through the flexible container until the pressure on the other end is over a hundred times the amount of pressure applied. In most hydraulic systems in order to create the needed pressure the cylinders and pistons that compress the oil is connected through valves to a pump that that can supply the oil under high pressure. There are several primary systems on the ship that would not be able to work as effectively without the benefit of hydraulics. The first system is the ships stability system. If we think about a fish, how does it swim upright in water as the water is flowing all around it exerting pressure on it from different directions? The answer is fins on both sides of its body. These fins help to stabilize the fish and keep it from rolling side to side in the water. So to on today’s modern cruise ships they have fins or stabilizers that operate beneath the water to keep the ship upright without rolling as the waves of the water push against the sides of the ship. These stabilizer fins operate under hydraulic pressure to hold them in place and keep the ship stable.
The second system where hydraulics is important is in the steering of the ship. As mentioned previously the rudder of today’s modern ships weight in excess of several tons. To try and move this with just human mechanical effort would be almost impossible. So just like we use hydraulic power steering in our cars to make parking easier, ships use hydraulic steering assist to move the rudder and change the course of the ship without needing to turn a wheel a thousand times. These hydraulic systems are electronically controlled so that a single person with a joy stick on the bridge can move the ship 180 degrees in a matter of minutes. (Balu, S. 2011)
The third area where hydraulics is important on the ship is in the engine room. As the ships grew larger the nuts and bolts and valves in the engines got bigger also. Even though it is possible to make a wrench large enough to fit over the nut or bolt used to hold something together, it is next to impossible for a single human or even a couple of humans to exert enough force to properly torque the nuts so they will hold and not shake loose. This is where a hydraulic wrench comes to play, because it is able to exert tightening force hundreds of times that of a human to make sure the engine bolts and cylinder heads are locked into place. Also to lift and position some of these engine components there is not enough room to get enough people around a component to position it into place or lift it out of place, so hydraulic jacks and lifts are used to move materials, parts and equipment around. (Field, C. 2004).
A forth and most important place where hydraulics play an important role is in the ships close quarters maneuvering system. When the ship has to come into dock where it cannot use its powerful engines and propellers the ships must use what are called bow and stern thrusters to move around. These thrusters are propellers that are mounted transverse or sideways instead of longitudinal to the axis of the ship. These smaller propellers need to be positioned to allow the ship to makes the precise sideways movements necessary to be in position to deliver cargo while maneuvering in restricted waters. The only way to precisely position these propellers and hold them stable is with hydraulic pressure.
The final area where hydraulic systems are essential are in the control systems of the ship that open and close valves needed to pump oil in oil tankers or pump water for ballast. Opening these many valves sometimes requires precise openings so as to control the various pneumatic air pressures used to control other process functions; the hydraulic systems allow for that precise control. By using these hydraulic systems remotely many cargo ships that once required hundreds of crew members can now be operated on transatlantic voyages with less than 20 people. By using hydraulic deck cranes and hatch covers and winches ships crews are now able to load and unload cargo, raise and lower the anchor and secure the ship hatches in an emergency all from a control panel on the bridge. As the ship is moored to the dock instead of having crew to crank the winches to hold the ship in place they can use hydraulic winches which takes less time and only one person to operate. Everything is done and held in place by systems using hydraulic oil under extreme pressure. (Balu, S. 2011)
By using hydraulic systems today’s ships are able to grow bigger, operate faster and be much more efficient all with small crews and less risk.
- Naiad Dynamics – Motion Control, Stabilizers and Ride Control Systems (2014) Retrieved 10-25-14 http://www.naval-technology.com/contractors/motion_control/naiad-dynamics-ship/
- Maritime Park Association (2014), Principles of Hydraulics, Retrieved 10-25-14 Available:
- Field, C. (2004). “Pump Up The Volume – Manchester Hydraulic Heritage”. Culture 24. Retrieved 10-25-14Available: http://www.culture24.org.uk/places-to-go/north-west/manchester/art23500
- HSC online (1999). “Engineering Studies – Hydraulic Power”. Charles Stuart University Retrieved 10-25-14. http://hsc.csu.edu.au/engineering_studies/application/lift/3377/hydraulics.htm
- Balu, S. (2011), Hydraulic Applications on Board a Ship, Retrieved 10-25-14. Available: