Shiphandling Explained: Let the ship do the work

01 Feb 2018 The Navigator

Captain Nigel Allen FNI is a Master, Pilot and instructor with years of shiphandling experience around the world. He shares a few thoughts on the basic principles behind what is a deceptively complex art to master.

Some of the best shiphandlers I have seen and worked with are the ones who appear to do the least. They let the ship do the work for them and only intervene when the ship departs from their ‘planned track’. In other words, if the ship has some way and you do nothing, it will continue to travel under its own inertia, sometimes quite some distance, before eventually coming to a stop. So, by controlling the speed and having enough inertia the ship can get to the berth without too much interference. Having a plan is crucial to success. Anticipating how the ship will behave will help you to carry out that plan. It is important to remember that, when berthing a ship, the faster you go, the longer the manoeuvre will take.

When a manoeuvre goes wrong, it is common for shiphandlers to look back at their last order to figure out the reason for the problem. However, almost always, things had been going wrong for some time beforehand, manifesting itself in the vessel hitting the jetty. Invariably, too much speed or a poor approach will be to blame. Going slowly and methodically tends to ensure better results. A calm, measured approach will instill confidence in the bridge team and get you in the correct position more quickly and with far less drama.

Knowledge is power
STCW makes the presumption that you will learn from others. However, this means that you are limited to the extent of their knowledge. Many shiphandlers who appear to know what they are doing cannot explain the procedure to others often due to their own lack of formal shiphandling training. I have seen many Masters berthing their own ships and, whilst they got there safely, it was apparent that they didn’t fully understand the principles of shiphandling and so were making hard work of it.

Principles of shiphandling
So, what makes a ship turn? Sounds like it should be an easy question: the rudder! However, it is not that simple. What actually causes the hull to turn is the water pressure around the hull and the difference between the pressure to port and starboard. By using the rudder, we can control this pressure differential and steer the ship. We can see that effect in practice by looking at a directionally unstable ship. A ship is considered directionally unstable if, when 20° per minute RoT is achieved with starboard rudder, and the rudder is put amidships, the RoT continues to increase. That’s not just the rudder! Something else is going on.

The rudder is a very efficient device that acts like a servo system, controlling a large and heavy ship at relatively slow speeds. We often take the rudder for granted, but it is remarkable that such a small flap can control such a large object at slow speeds. Fortunately, a ship only needs a small force to develop rotational inertia in water. However, in very shallow water this effect can be severely restricted.

Forces management
Some control forces can be manipulated, such as the rudder, engines, thrusters, anchors and tugs, while other control forces and unseen forces, such as wind, current, cannot be controlled. Still others – squat and interaction – can be managed if their effects are properly understood. The effect of wind on a ship can be calculated if we know the lateral area and check that the control forces we have under our control are adequate for the circumstances. As wind speed doubles, its force quadruples, so a strong gust of wind can easily overwhelm your control forces. Unstable wind conditions associated with low pressure can easily double the geostrophic wind speed. Generally, a maximum practical wind speed for tugs is around 33 knots (17m/s). Beyond this limit it won’t take much to lose control of the ship.

Shiphandling or water handling?
As a ship displaces water, which is not compressible, we need to think about how the water will shift as the ship passes through it, bearing in mind that water will be squirted out by the propeller, thrusters and tug wash. Instead of thinking about how I can move the ship, I prefer to think about how I can shift the water to make the ship go where I want it to. This aspect of the task could be called ‘waterhandling’ and is an important part of the considerations when planning and executing a manoeuvre. For aspiring junior officers, watching the Pilot is a great first step in gaining confidence in your ability to call the correct orders. Go one step further and in your head pretend that you are issuing the orders and see if what you are thinking reflects what the Pilot is actually doing - I remember doing this and it gave me confidence to follow a career in shiphandling. From talking to many Pilots and shiphandlers around the world, it generally takes around ten years for them to feel fully confident to travel anywhere in their district with any ship. Even then, it is healthy to have an open mind to learning more. With twenty years experience, I’m still learning about shiphandling!