Report Title: Deliverable 4.6: Summarise current ...

Report Title: Deliverable 4.6:

Summarise current operational practice and limitations

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AZIPILOT Project Steering Committee.

AZIPILOTIntuitive operation

and pilot training

when using marine

azimuthing

control devices

Current operational practice and limitations Final

Mel Irving, Stephanie Short (TYNE) Page 2

Contents

1. Publishable Executive Summary 3

2. Types and configurations of vessels fitted with Azimuthing

propellers (ACD’s). 4

2.1. Single ACD: 4

2.2.Single ACD in conjunction with fixed propeller: 4

2.3.Twin ACD’s: 5

2.4.Triple ACD’s: 6

2.5.Four or more ACD’s: 6

3. Standard Manoeuvres. 8

3.1.Reducing Speed of the vessel. 8

3.2.Moving sideways. 9

4. Emergency manoeuvres. 11

4.1.Crash stop. 11

4.2.Emergency turn. 13

5. ASD tug fitted with twin Aquamasters and Azipilot control. 14

6. CONCLUSION 18

7. APPENDIX 1. 19



1. Publishable Executive Summary

WP 4 Operational Practice is aimed at collating, reviewing and auditing available material

that is relative to the operation of azimuthing control devices when manoeuvring ships in

Pilotage waters.

Task 4.6 summarises operational best practice while highlighting the limitation for pilots and

ships officers when operating ships equipped with azimuthing control devices. The use of

azimuthing control devices provides the ship handler with an infinite number of solutions

which itself introduces potential problems that may be detrimental to both the success of the

intended manoeuvre to the preservation and protection of the azimuthing device itself and to

the Port infrastructure. This report identifies the most suitable ship handling procedures to

validate operational best practice and identifies the limitations of each manoeuvre.

The task culminates in this report and constitutes one deliverable at M27 of the project.



2. Types and configurations of vessels fitted with Azimuthing

propellers (ACD’s).

2.1. Single ACD: Can be found on a variety of vessels from small tugs to cargo ships and large tankers.

2.2.Single ACD in conjunction with fixed propeller:

Gives a highly manoeuvrable but economical configuration. Propellers are contra

rotating.



2.3.Twin ACD’s:

The most common configuration of Azimuthing propellers, found everywhere from

tugs and harbour craft through to large Cruise Ships and Tankers. The units may be

fitted at the bow or stern, or even, as in the case of many Ferries one at either end of

the vessel.

Aft ACD on the Isle of Bute, note contra rotating propellers, similar unit forward.



2.4.Triple ACD’s: A popular configuration for the latest generation of tugs, (Rotor Tugs).

2.5.Four or more ACD’s: Usually found on barge type vessels, often linked to Dynamic Positioning systems.

The above listed configurations are further diversified by the type of propeller and

power units. The propellers may be fixed or controllable pitch, reversible or non-

reversible. They may also be open or shrouded. The power units may be within the

pods or external, as in the case of mechanical Z-drives. The type of control system

used is also variable, although generally it will consist of either a single joystick, with

computers controlling the azimuthing of the units, or a single Aquamaster type

controller for each of the units, giving full manual control. The single joystick

operation may also be linked to the vessel’s thrusters giving full control of the ship

with just one lever.

Given the diversity of vessel configurations, it would be impractical to give a set of

rules on how to handle an Azipod vessel, which would apply to each and every one.

In all cases the peculiarities of the individual installation needs to be considered.

Factors that have to be considered would include the following:

1. Position of the ACD’s.

2. Interaction between units.

3. Interaction with vessel’s hull.

4. Manufacturer restrictions on rpm’s used.

5. Restrictions on the use of reverse pitch.

6. Availability of thrusters.

7. Control system restrictions, e.g. Sea or Harbour mode.



It is important to consult manufacturer’s recommendations (Appendix1), any guidelines

issued by the ship owner/operator and also the manoeuvring data obtained from the vessel’s

sea trials. The environmental conditions will also have a bearing on how the manoeuvring is

performed. There are documented problems with Azipod bearings when fitted to large Cruise

Liners. Such problems lead to recommendations as to how best to operate the units with

longevity in mind. Thought also has to be given to the gyroscopic inertia generated if units

are quickly rotated at full power.

ACD units can either push the vessel through the water or pull the vessel through the water

but which ever unit is chosen consideration needs to be given to the benefits of always using

positive thrust as opposed to the problems of using negative thrust. It is recognised that there

is loss of power if reversing the thrust, this can be as much as 60%. It is better to rotate the

pod than put the unit into reverse as such an action now has the thin trailing edge of the blade

becoming the leading edge, a job it is not designed to do so not only do you increase the risk

of damage to the blade but the shape of the blade is no longer the optimum one for the job it

is designed to do and there will probably also be noise and vibration caused by cavitating

propellers. In addition moving from positive rpm to negative rpm you pass through zero and

loose the oil film that helps lubricate the bearings. It ought to be acknowledged though that

the ship handler may find him/herself in a manoeuvre that may warrant operating negative

rpm in a time critical situation

During Project interviews with ships Masters, used to operating ACD units, it became

apparent that it is necessary to be aware of certain situations that can lead to a loss of the oil

film on the bearings or cause vibration that can increase bearing stress during manoeuvring

both of which may result in premature bearing failure. These include for example ensuring a

steady increase/decrease of ships speed thereby avoiding large differences between rpm and

ships speed., avoid cycling between zero and 25 rpm and where possible try and maintain a

minimum of 25rpm at all times, avoid directing wash from one unit directly onto another and

avoid water flow from one unit entering the propeller of the other unit and the adverse effects

when interaction between the ships hull and the ACD occurs.

Having taken all the above factors into consideration including the test results obtained

through Task 4.5 – Encapsualting Knowledge using Integration and Evaluation Exercises -

then best practice for the particular vessel can be formulated.



3. Standard Manoeuvres.

3.1. Reducing Speed of the vessel.

Can be achieved in various ways.

(i) Reduction in engine and propeller revolutions. Will give a gradual slow down.

(ii) Rotation of ACD’s outboard. Gives a faster reduction in speed. However can

cause vibration under the hull. Limit to the amount ACD’s can be rotated.

(iii)Rotation of units inboard. Units can be taken in to the Transverse arrest

position. This will give a very quick reduction in speed. The units can be

further rotated to give astern thrust as the vessel’s speed drops. The

propeller wash can cause problems to other vessels in close proximity.



(iv) Units turned into the Transverse Arrest position and power increased.

This gives a very high rate of slow down at higher speeds. As the speed

drops to around the 5 knot region, then retardation will be greater by

angling the units to give astern thrust.

(v) Units rotated to give astern thrust.

3.2. Moving sideways.

(i) Using one ACD at 90 degrees and the other inline. The sideways

movement is achieved in combination with the forward thruster. Easy

for beginners to understand but relies on the propeller being reversed

to alter the direction of thrust



(ii) Utilising both ACD’s together to give a resultant force in the required

direction. Can be used in combination with, or without, the bow

thrusters.

(iii) Vessels such as Ferries fitted with a single unit at either end. These

units will generally have contra rotating propellers to negate the

effects of transverse thrust.



4. Emergency manoeuvres.

4.1. Crash stop.

(i) Stop the vessel utilising hull drag by making a sharp turn. Azipod equipped

vessels are capable of stopping in a very short distance if the ACD’s are

used to give a combination of hard over turning and braking. This does

require some lateral clearance.

(ii) Transverse arrest. Units moved to give maximum outboard thrust, and then

moved to thrust astern as the speed drops.

(iii)Crash stop on twin Schottel equipped Ferry.



Power has to be reduced as the units are rotated away from the ahead position.

It is then increased to maximum once the units are in the astern thrust position.

However, care must be taken not to reduce power too much, as if too little power

is used, as the units come into the astern thrust position there is a risk that the

engines may stall.



4.2. Emergency turn.

The control system may require the mode of operation to be altered to allow both

units to be rotated towards the beam position. Large angles of heel may ensue.



5. ASD tug fitted with twin Aquamasters and Azipilot control.

The following diagrams show the positioning of control levers and ACDs on a

typical ASD tug:









6. CONCLUSION

It can be appreciated that due to the increased flexibility provided by ACD units and the

infinite number of responses and actions open to the ship handler it could be forgiven for

reaching the conclusion that little or no training would be required. This would be to

seriously underestimate the counter intuitive nature and complexity of this method of

manoeuvring and the potential consequences for the ship owner/operator should inappropriate

operational practices result in premature bearing failure or damage to the ship or to the Port

infrastructure.

Authorities responsible for the provision of Pilotage services and Ship owners/operators

should ensure that personnel operating ACD units receive a through and comprehensive

understanding of the theory behind the operation of such units and be trained in their efficient

and effective use to ensure the safety and security of life and property.



7. APPENDIX



































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