Free Seaways Article: MPX - beyond the basics

What the pilot needs to know about your ship – rudder and propeller control and ship manoeuvring characteristics.

Ed Verbeek, FNI

As a pilot, you get used to having to learn the quirks of the ships that you are handling very rapidly – but sometimes they are not easy to pick up. On one outbound pilot trip I could not figure out which way the controllable pitch propeller turned – not after the Master/Pilot Exchange (MPX), and not during my attempts to clarify the situation during the hour’s trip from berth to lock. In the end I just entered the lock very slowly, gave a short Slow Astern to see which way the ship was turning, and acted accordingly. But it should not have to be this way!

As a ship’s officer, it is important not just to be familiar with the relevant characteristics of the ship you’re on, such as the rudder and propeller control and ship manoeuvring characteristics, but also to think about how you can clearly communicate these characteristics in a concise way. This is necessary not just for the MPX – which may be a more or less frequent occurrence, depending on the trade – but also when captain or bridge officers go on leave. Here, too, the characteristics need to be clearly communicated at the handover.

Compare and contrast

There is an important difference in perception between captain and pilot. Generally speaking, captains compare their present ship to the last ship they sailed on. Pilots compare the present ship to what they’ve come to believe is ‘normal’ for this class of vessel. To give an extreme example, suppose the captain previously sailed on a capesize bulker and is now on a containership. Compared to the bulker, the container ship stops exceptionally quickly, and that is what the captain might say in the MPX. The pilot might then come to the conclusion that the ship stops exceptionally quickly compared to the average container ship, which might be completely incorrect.

It would be very helpful if the captain could give quantifiable results, rather than general impressions. The results from the crash stop test and the 10-10 Zig Zag could give a real insight here. It would be very helpful if captains/bridge teams were able to show these tests, and point to any aspects that are way outside the normal, if (and only if!) there are any. Pilots would need to be so familiar with the general outcome of these tests that they would be able to understand the main aspects at first sight. Which values are normal? What do abnormal values signify? The aim here is not to prompt long discussions and explanations, but to find a quick and quantifiable way of identifying anomaly. The MPX should be short and to the point, especially during arrivals when the ship is still being navigated.

 

Your pilot should be familiar with manoeuvring characteristics before this point!

What to highlight

So what are the most important features to know? And how do you communicate them concisely? Here are some points to consider highlighting that will help the pilot know how best to advise. Start with power generation – what type of engine have you got, diesel, diesel-electric, battery electric or wind-assisted? Then look at how they affect manoeuvring characteristics.

STOPPING

The FPP

In the case of a diesel engine: is it a directly reversible/fixed pitch propeller (FPP); a geared/FPP; a controllable pitch propeller (CPP); an azimuthal thruster?

If it is a directly reversible engine: how much time does it take to start? I have had cases where it has been more than 20 seconds – definitely information I needed to know!

How many starts are available? Once I was on a ship with an apprentice: the ship had six consecutive starts. The apprentice was not used to this kind of set-up and in his enthusiasm used several stopstarts to stay nicely lined up in the approach to the lock. After four starts I reminded him that he only had two more – something he had completely forgotten while concentrating on getting a good approach. Where are the critical revs?

Is there a load program within the manoeuvring range?

So what might good MPX communication look like, taking all these things into account?:

We have a start-stop engine and a righthanded FPP. It takes about ten seconds to start, we have approximately eight starts.

The critical revs are eg ‘in between Slow and Half’ or ‘above Manoeuvring Full’.

The load program kicks in above half, but can be overridden in emergencies.

The conversation should also cover any unusual arrangements that influence shiphandling – for example if there is a fixed nozzle around the propeller, or a rotating (Kort) nozzle, and if this nozzle is equipped with a fin or additional rudder, etc.

Avoid CPP confusion

As mentioned above, the controllable pitch propeller (CPP) can often be a source of misunderstandings. When the captain says the ship has a ‘right handed’ CPP, does that mean that the direction of rotation of the propeller is right handed, so that ship will turn to port on astern? Or does it mean that the propeller acts like a right handed FPP, and the ship will turn to starboard? To avoid this situation, I will always ask: ‘When we give astern, which way does the ship generally turn?’ If I ask: ‘Does the bow turn to starboard?’, there are captains who correct me and say: ‘The stern turns to port’… (they are completely correct!)

There are load systems for CPP as well. Sometimes the astern pitch is quite limited. It is necessary to communicate this too.

On some CPP ships, steering is lost if the pitch is reduced too quickly. If this is a known phenomenon, it needs to be mentioned in the MPX. Another example of good MPX communication: 

‘We have a CPP. When giving astern, the ship tends to come to (starboard/port), generally (‘quite controlled’ or ‘fast’).
Our load program takes 25 seconds from manoeuvring Full Ahead to Full Astern.

Maximum pitch astern is about 70% of ahead.

If you reduce pitch very quickly, she loses steering quite easily and it might be hard to get her under control again.

Pitch 0 will give a slight thrust forward, around 0.5 kt.

It is important that the ship’s crew know the failure modes of the CPP. Most modern CPPs maintain the set pitch when failures occur. Older CPPs fail into either Full Ahead or Full Astern. In some cases, the way the CPP behaves will depend on the type of failure experienced – for example, whether it is an electric failure or a hydraulic failure. There are ships with CPP that also have reversible engines. In this case, the CPP fails in Full Ahead, and the ship can be manoeuvred from the engine room using old fashioned telegraphs. I can only encourage you to know your system!

Occasionally, you come across a ship with a diesel engine and an azimuthal thruster. Although an azimuthal thruster in some respects gives a similar feel to a pod, there are some differences that need to be taken into account, so communicate clearly that it’s an azimuthal thruster.

In general, on ships with azimuthal thrusters or pods the manoeuvring takes place hands on: the communication (‘thinking aloud’) is aimed at keeping the team members informed of the intended outcomes, rather than the settings to achieve them, as the settings are continually adjusted according to need.

Electric: FPP; Pod; Azimuthal Thruster

If electric propulsion is driving conventional propellers, be aware of the time that is needed to reverse the electric motor – as mentioned earlier with the combination diesel – azimuthal thruster/pod. 

Unusual systems 

Systems like waterjets, Voith-Schneider, Vectwin have their own specialities when operating including reversing: be prepared to explain the system in a very short, concise but still understandable way. 

STEERING

Let’s start with installations which have a separate rudder. You need to know something about the type: is it (semi) spade? Balanced? And even more important: is it of a high lift type? 

With fish-tail rudders and other single blade rudders, high lift rudders are easily identifiable by the rudder indicator, which will go until something of the order of 60°. Becker and other rudders consisting of two blades are more tricky: generally the indicator will only show the angle of the main blade. If you don’t know what you are dealing with, in the first instance it looks like you have a ‘normal’ rudder. If the pilot is not explicitly told that this is a high lift rudder, they might be in for a shock at the response of the ship!

On ships with two propellers, the rudder installation is even more important. Twin propeller, single rudder ships are notoriously difficult to turn. There are ships on which the rudders are placed at the inward side of the propeller shafts so that the shaft can be pulled without detaching the rudder. Because of this position the flow of the propellers partially bypasses the rudders. This is especially a problem when the engines are split (one ahead and one astern). I call this system ‘single rudder in disguise’ as the ship handles a bit like a twin prop-single rudder ship. If a ship is equipped with this, it needs special attention at
the MPX.

The Kort nozzle is another point worth highlighting: it is separate from the propeller/propulsion but it has a great influence on the astern and steering  characteristics. A Vectwin system has this as well.

Bow/Stern thrusters

According to a document circulated to Dutch pilots, bow thrusters that fail to perform when required are the top mechanical factor contributing to damage. So when I hear during the MPX that a ship has a [bow] thruster, this always gets my special attention. Of course I’d like to hear how strong the thruster is. My next question will be if all that power is available to use. Before I made a point of asking this, now and then when entering the lock, the captain would say: ‘You cannot use step three, we’ll have a black-out.’

With larger units, you need to know the response time. How long does it take before the thrusters start to deliver? I’d also like to have an idea at what speed the thruster starts to become noticeable. As a rule 
of thumb, the more tunnels, the higher the speed at which the thruster starts to have a noticeable effect. Anti-suction tunnels increase this speed even further.

Whatever the details of the thruster system, tunnelled or non-tunnelled, the particulars need to be communicated. 

Creating a pilot card

Communication during the MPX communication is greatly assisted by using an appropriate pilot card. We’ve seen that a lot of information needs to be covered – far more than can ever be remembered. The pilot card needs to be available for the pilot until they leave the vessel. The pilot card is not a piece of paper to ensure there is a paper trail. It should be a practical, handy aide memoire, available at need throughout the pilotage.

I have given a few examples of good MPX practice for individual system components above. Let’s look at a model MPX for a more complicated ship. Please remember that throughout this MPX (and afterwards) the pilot card should be in front of the pilot, so that they can read along:

So Pilot, we have a diesel electric propulsion here, it takes a bit of time to change the direction of the propellers.

Twin FPP out-turning propellers, so when you split the engines, the propeller effect will help.
Ahead 18,000 HP each propeller, astern power is about 75%. You’ll find we have enough power to stop or accelerate as you would expect of a cruise ship.

We have twin rudders, but unfortunately they are off-set inside the propeller shafts. I’ll make a small drawing to show you how this will affect steering. She might react less to the rudder than you would expect.

Two bow thrusters, 2,000 HP each, with an anti-suction tunnel. You would normally start to notice an effect from 5 kts.

Only one stern thruster of 2,000 HP, combined with the off set rudders that means that transverse power at the stern is limited.

Depending on the situation, we generally start to think of a tug when winds exceed 10 m/s, and need a tug with winds above 13 m/s.

To summarise:
● Know all relevant characteristics of your ship. 
● Know how to communicate them.

The nice thing is that you can practice every time you take a pilot!