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The Navigating in tidal rivers,
the access to major locks, and mooring problems for ULCoCs
Compiled by Capt. Marc Proost, M.Naut.Sc. MNI, Individual Member CESMA.
The Navigating in tidal rivers,
the access to major locks and mooring problems for ULCoCs.
- During the last decades a continuous increase of the main dimensions of certain ship types can be observed.
- On the other hand, the dimensions of access channels, rivers, canals and ports frequented by these vessels often do not increase at the same rate.
- As a result, the behaviour of ships arriving at or departing from harbours will increasingly be influenced by waterways restrictions. The asymmetric flow around a ship induced by the vicinity of banks causes pressure differences between port and starboard sides.
- As a result, a lateral force will act on the ship, mostly directed towards the closest bank, as well as a yawing moment pushing her bow towards the centre of the waterway.
- This phenomenon, known as bank effect, depends on many parameters, such as bank shape, water depth, ship-bank distance, ship properties, ship speed and propeller action. A reliable prediction of bank effects is important to determine the limiting conditions in which a ship can safely navigate a waterway. However the knowledge of the bank effects induced by the typical bank geometries is very limited.
Operation principle. (simulators)
- The navigator (pilot, captain, trainee) has to perform an imposed manoeuvre. From the bridge the ship's behaviour can be monitored on the bridge instruments and through the bridge windows. By changing rudder and telegraph settings, and by giving orders to tug masters, the navigator controls the observed ship behaviour. By setting telegraph and rudder tiller, electrical signals are transmitted to the simulation computer where the balance of all forces on the ship is calculated. This results in a continuous update of ship's acceleration, speed and position. Signals are sent to the bridge in order to display this information on the instruments. The radar, ECDIS and outside view are also continuously updated in real time.
All this is meant to give the navigator the impression of being in charge of a real ship, to make him/her act as natural as possible while executing the manoeuvre.
- The human aspect of navigation is so important that the human being is the only element which is not schematised. It is necessary to take account of the navigator's experience, but also of the human reactions on ship and environment, which are not always logical or predictable.
- hydrodynamic forces: powers on hull, rudder ..etc..
- shallow water effects: bottom level in function of location, water level in function of tides
- propulsion: propeller, engine dynamics, bow propeller, stern propeller, defects
- restricted water effects: bank effects
- wave drift: wave height and direction in function of the position
- effects of non-uniform current: current speed and direction in function of position
- contact forces: reaction and friction powers of fenders, pole and quays
- hydrodynamic powers: current effects
- interaction with meeting and overtaking target ships.
Non-vessel bound forces.
Consequently as a vessel enters the approaches to a lock coming from a tidal river, sufficient tugboat power should be available in order to deal with the changing forces due to the slowing down of the vessel and the reduction in steering capacity of the vessel.
- Which position will the vessel be searching, when she becomes non manoeuvrable ?
- Which is the safe minimum speed whereas the vessel can still keep her course ?
- How much space in the fairway does the vessel need to achieve a certain ground course?
- In which way can the wind be used in favour of the manoeuvre ?
- Can the manoeuvre under the prevailing wind safely been carried out (meaning, with sufficient power in reserve)?
- With a constant current the influence on the whole submerged surface is the same and the vessel will move in the direction of the current with a fixed heading and speed. In a narrow fairway with differing bottom profile and bends, the forces due to turbulences are the reason that the vessel diverts from the main current direction.
- The final resultant (moment of forces) is formed by the dry surface resultant force and the forces on the (wet) submerged part and/ or the current. They are determinating in order to use additional forces to keep the vessel on her required position (e.g. bow/ stern thrusters, tugboats, mooring lines, anchors).
To increase the knowledge Flanders Hydraulics Research has commissioned the Maritime Division of Ghent University to execute a research program involving bank effects. Both institutions are involved in research of ship manoeuvring in shallow and restricted waters, squat, ship-ship interaction, bank effects, etc.
The Flemish Pilots train regularly on the ship manoeuvring simulator of Flanders Hydraulics Research. For training purposes it is very important to model all significant forces. Due to the lack of knowledge on bank effects induced by sloped and semi-submerged banks an extensive research program was initiated.
An overview of major input parameters is given:
- Speed Propeller Rate, Drift Angle, Rudder Angle, Lateral Distance and Under Keel Clearance (UKC).
Mooring problems with ULCoCs.( 300m +).
- Access to locks and tidal docks:
- PCC is more influenced by wind force and has less inertia.
- A part of the Length and draught other matters are important for tug use :
- The proportion between dry and wet surface --- drifting which means --- The greater the proportion Dry/ Wet, the faster she will drift e.g. Ballast , full deck cargo….
- Keel clearance : Small keel clearance --- ´´blocking effect´´ Tugs encounter severe problems to shift the vessel in “shallow” water.
- The “angle of attack” (wind or current influence on the vessel). If this is a big angle, tugs have problems swinging the vessel around.
- Position of the “sailing point” versus the centre of gravity of the submerged part will influence the ship which will turn to the weather side, faster in case of more containers on the aft part.
- Bow thrusters are often not in proportion with the deadweight of the vessel, smaller vessels have relatively stronger bow thrusters.
- Becker rudder/ Schilling rudder would be an asset to provide more “lift” instead of power ahead by using its engines.
- Visibility astern is not always that well ---distances are difficult to estimate.
- It is often expected that the vessel has to moor perpendicularly to or from the berth. With crosswind and /or little keel clearance this is
- Often there are not sufficient tugboats available, and if there are tugs they are often underpowered.
But as everyone knows, safety and quality has its price.
- In general Container terminals are not sheltered from the wind.
- Mooring facilities do not satisfy by crosswind. Often works continue with strong wind and there are not sufficient facilities to solve the problem of cross forces due to heavy wind impact.
- Mooring lines are mainly in an unfavourable angle (+ 30°) and vary in length, which means that they vary in tension (and stretch). Long breast lines are merely impossible to put.
- If one mooring line breaks, other follow, as the tension becomes to big. ´Tension winches´ can not be used due to unequal mooring line tension.
- It is not the Master who decides how the vessel is safely moored, but the Port Authorities.
- A berth tolerance would be appreciated due to the correct placement of the mooring ropes. Mooring distances between ULCoCs is to small and should be much enlarged, so that the angle of the lines could decrease.
- Ships’ crews are often very substandard and do not anticipate, nor understand what is going on due to a lack of training, proper certification and nautical knowledge as a whole. Good communication herein is a crucial factor.
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