Cruise ships are enormous structures! Keeping control of them even with wind, waves and ocean currents is challenging. Thankfully the steering systems on modern ships are more than up to the task. So how do we steer cruise ships hundreds of meters long?
Types Of Steering Systems
To turn a big ship, you need to use a lot of force. This force comes from the propellers and the forward motion of the ship, and there are a few ways we can change this forward motion to sideways motion that actually turns the ship.
The simplest type of steering is the rudder. This hasn’t changed a lot since first invented – simply a big flap in the water that can be moved from side to side. It is usually limited to only 35 degrees in each direction.
The rudder directs some of the water that the propellers push to one side, but also creates lift similar to an aeroplane wing. These forces push and pull the rudder to one side, a force that is transferred through the entire ships hull. Even an angle of 5 or 10 degrees gives plenty of force to turn the ship!
These rudders are almost as simple, but the rudder is split with a movable ‘flap’ on the back. A common brand of this rudder type is the ‘Becker’ rudder.
The benefit of the extra flap is having additional ‘lift’ even with small rudder angles. These rudders can also direct water at almost 90 degrees when using maximum rudder angles!
This is totally different! Rather than having the propeller and rudder separate like you’ve seen above, they’re combined in one unit. A common brand is ‘Azipod’ made by ABB, fitted to many modern cruise ships.
Instead of diverting some of the flow from the propeller, this type of steering turns the ENTIRE propeller. The full force can be sent in any direction by turning the pod 360 degrees. This allows the ship to not only
Steering Control Systems
Now we’ve seen what happens underwater to turn the ship, how do we control it?
Just like aeroplanes, ships have autopilot systems. We use this mainly when we’re in the open ocean, to sail the long straight lines. There are different ways we can set it up –
- Heading Control – this tells the ship which way to point. We set this direction as a gyro compass heading eg. 280 degrees. The autopilot will line up the ship and keep this heading. However, it doesn’t account for wind or current so we need to adjust it regularly.
- Course Control – this combines information from the compass with a speed sensor such as GPS or a
dopplerlog. By using this information, we can set the autopilot to sail a course and it will account for wind and current, adjusting the rudders to make sure the ship keeps moving in the right direction.
- Track Control – this takes the same heading and speed
information,and adds our position from GPS. By knowing where we are, and where we planned to be from our electronic navigation charts, the autopilot can keep us sailing exactly along our planned route.
It’s a clever system, but like anything else onboard it’s only as good as those operating it. We need to make sure we use the correct settings to make sure the autopilot works safely and efficiently.
Like our other control systems, our autopilot has backups in case there is a breakdown at sea. Even if the autopilot is steering the ship, we still need to closely monitor it in case something doesn’t go to plan!
In case our autopilot fails, or we just want more direct control, we can steer the ship manually. Again, there are different ways to do this but most commonly is the hand wheel.
The helmsman is the person operating this hand wheel. They will take orders from the Captain, the Pilot or the Deck Officer (depending who is in control at the time) and carry them out. The entire bridge team is constantly monitoring the order, the actual rudder angle and is the ship is proceeding as expected.
So now you know how we steer a cruise ship, why not take a look at what powers a ship, or even what happens if we break down at sea.
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