أمر يعكس إتجاه/ السير /أو الحركة أمر بالتراجع
Explanation:
أمر التراجع / أمر يعكس إتجاه/ السير /أو الحركةر يعكس إتجاه/ السير /أو الحركة
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Note added at 4 hrs (2007-09-27 12:17:42 GMT)
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AZIPODS-Memo for the pilots’ use
By Rodolphe Striga
The pods are tractors ; this means that the
control levers on the bridge have to be
orientated in the direction where the pulling
is required and not in the direction to where
the ship should go.
T he following information are partly coming from technical data bases available on builders’ experi
websites (mostly ABB and Alsthom) and partly from the very experienced master Pietro Esposito who accepted in June 2002 to spend some moments giving me the practical results of its own ence on the azipod handling on the passenger vessels European Stars and European Vision. His explanations are coming from his theoretical training during the vessels’ delivery and from his personal tests while performing handlings in the very beginning times of this technique.
Captain Esposito’s data
These levers are composed of a classical handle to put ahead or astern with a small window in the middle in which it’s possible to read the rpm required by the lever position. This handle can be orientated aver 360°; in contrary with the water jets joysticks, the azipods levers have a sense (ahead or astern) materialized by an arrow showing the preferred position of the pod.
Many limitations exist:
• In the direction of the arrow, the maximum rpm is 180; 150 in the opposite direction. This means that in the case of a crash-stop, it is better to rotate the handle 180° and put the maximum order of rpm than to put directly astern (with a maximum 150 rpm).
• When the pod speed is over 50 rpm, an order in the opposite sense is considered by the computer to be a mistake and the power unit does not change the pod speed and direction of pulling. If there is no change in the order in a short delay decided by the designers and adjustable, the rpm will be set to zero without any alarm. This means that when the vessel has to move astern, the handler have to reduce pod’s speed in advance to be under 50 rpm before giving an order astern.
• There is a long delay between the order and the reaction of the electronic and mechanic plant; this means that a succession of short and fast orders will not have any chance to be effective.
• In fairway driving, the two levers are twinned so that the two pods can be controlled in
parallel with a single handle. (the name is like for water jets, “common lever”). While the
vessel is out of the harbour, the helmsman acts as on a classical vessel fitted with two
rudders and the power is given on the lever themselves.
• The shipyards advise while the vessel is in berthing phase, close to the berth, to put the pod on the berth side in a longitudinal position in order to move ahead or astern, and the other one perpendicular to the berth, acting like a stern thruster. In this case the electronic plant gives a preference to the longitudinal one and reduces automatically the power available for the perpendicular one. Indeed, the ship electrical power outlet is not sufficient to supply both the pods and the bow-thrusters operating all together at 100%. So, the handler has to remind that the entire pod’s power should not be available while the thrusters are used at maximum power.
• While the vessel is proceeding, without any order on the rpm control (lever on zero), the screw is kept rotating by the wake ; so when the lever is set on the zero position, it doesn’t reduces the ship’s speed because there is no resistant torque. So, when the handler wants to slow down the vessel, he has to give a small negative rpm order.
• The pods’ efficiency is quite bigger than the bow thrusters’ one ; the handler has to keep in mind the difference of powers to adjust the position of the bow before the position of the stern.
• At the moment, regarding to the reliability of this system, azipods require a lot of
maintenance (especially for water tightness, dampers, or cooling systems)
Technical data
The pod principle is set in an electrical engine fitted in a hub that can be orientated over 360°. This engine is coupled to a shaft as short as possible on which is connected a reversible propeller. The electrical variation of rotation speed allows a very thin control of the shaft speed, very smooth, with a big torque since the reduced speeds very close to the zero rotation. The azipod maximum power is close to 25 MW. On a theoretical point of view, the azipod should offer a bigger dynamism in the control of the command and also reduced turning circles. These characteristics drive the builders to point out the reduced times for handling but also the consumption reductions and the high swinging abilities.
Hub details
Air cooling module
This unit contains intercoolers and fans in order to maintain an acceptable temperature in the hub.
Transmission and Steering Module
Composed of an hydraulic unit , transmission shafts and wheels , and a big bearing (source of main troubles)
Azipod module
It is composed of an electric engine and a shaft on which is mounted a fix propeller ; water
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Note added at 4 hrs (2007-09-27 12:19:25 GMT)
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من الآخر أمر بتحويل دفة عجلة القيادة لللإتجاه المعاكس مع الإحتفاظ بزوايا الدوران
http://www.empa-pilots.org/pdf/AzipodsEJ06.pdf
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peer agreement (net): +1
