Intro. Only training and « hands-on » experience take the mystery out of shiphandling. Intro. Manoeuvring characteristics of ships: « Course keeping ability » and « Dynamic stability »
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Intro Only training and « hands-on » experience take the mystery out of shiphandling
Intro Manoeuvring characteristics of ships: • « Course keeping ability » and « Dynamic stability » • Dynamically stable ship after small disturbance move along a new straight course without using rudder • Dynamically unstable ship performs turning circle with rudder amidships • Dynamically unstable ships are more difficult to handle • « Turning ability » • Measure of ability to turn the ship with hard-over rudder • Obtained by performing a « turning circle » manœuvre • « Initial turning ability » is defined by the amount of heading deviation per unit of distance travelled
Intro/ Dynamic stability • Dynamically stable - Fine line ships (cargoships, containerships, passengerships) tend to be directionally stable • directionally stable ship will move on a straight course if rudder is kept amidships • When during a turn, rudder is put amidships: rate of turn reduce to zero and vessel continues on straight course • Directionally unstable • ship deviates with the smallest disturbing cause • If rudder put amidships during turn: reduction of rate of turn but vessel keeps turning on a track with larger diameter
Intro / Qualities of a good shiphandler • Patience • Anticipation: be « proactive » • instead of « reactive » • Quietness • Experience • Steadfastness • Concentration • Knowledge / Know-how • The « Art » of shiphandling
You will see: Fast captains, You will see: Old captains, Very seldom will You see: Old and fast Captains
Chapter One Various factors influencing the manoeuvring of the ship
Ch1. Effect of Fixed Factors on shiphandling Fixed factors of the ship • Design and dimensions of the ship • Propulsion unit • Propellers • Rudders
Ch1. Effect of Variable Factors on shiphandling Variable factors inherent to the ship - Draft • Trim • Displacement • Fouling • Variable factors outside ship • Wind, Sea, Swell • Current • Interaction: Depth of water / Shallow waters • Interaction: Proximity of other ships
Ch1. Factors influencing the shiphandling Size of the ship • Ships are designed to make speed , not to stop • Engine power does not increase in proportion to ship’s size • Large ships: • Difficult to judge speed from the bridge • When swinging in port: large swinging room required • Estimation of distances to berth difficult • Bridge is isolated from forecastle or poop • Large ship causes more damage when colliding with berth
Ch1. Factors influencing the shiphandling What is a large ship? • In 1952 biggest tanker in the world was 45000DWT • Lenght is a more relevant criterion than tonnage: • Below 100m : small ship • Longer than 200m: large ship • Between: medium size Size of ship versus available space gives degree of difficulty: • For small ports 5000DWT ship is big • A 5000 DWT ship does not present same problems of dimensions, mass, inertia and momentum as a 50.000DWT.
Ch1. Design of ship / Bridge amidships • Bridge amidships: • Advantages • Shiphandler near the pivoting point when swinging • Best position in a small ship • Close to forecastle and poop / visual communication • Good indication of rate of swing • Disadvantages • On large vessels: each end far from the bridge
Ch1. Design of the ship / Bridge forward • Bridge forward • Advantages • Shiphandler has excellent view of berth on arrival • Close to anchor when anchoring / easy communication with anchor party • Close to entrance of locks + good visual communication with the shore • Disadvantages • Difficult to assess the ship’s heading without looking aft • From the wings: objects on one bow may appear on the other
Ch1. Design of the ship / Bridge after • Bridge after • Advantages • Easy to judge rate of swing / start and end of swing • All ship is seen when looking ahead / ship’s heading visualized • If bridge is near stern: astern clearance easy to assess • Disadvantages • Shiphandler far from forecastle : visual communication impossible when mooring, anchoring, approaching lock or berth • Difficult to select precise spot for anchoring • Vessel passing ahead from bridge may still collide with foredeck • With restricted visibility
Ch1. Design of the ship • Ratio Lenght/Breadth (L/B) • Big L/B : bad turning / good course keeping (dynamically stable ship) / good speed • Ratio Lenght/Draft (L/D) • Big L/D: bad dynamical stability (example: bulkcarrier or tanker in ballast) • Ratio Block coefficient (Cb = V/LBT) • Big Cb: bad dynamical stability, easy turning
Ch1. Effect of ship parameters on manoeuvring perf. Good turning Bad Bad course keeping ability Good
Ch1. Effect of the bulb on performance Reduce the water resistance: Increase of speed: one knot / depending on draft/trim Consumption reduced Better course keeping ability Worse turning ability
Ch1. Vorm achtersteven / Forme de la poupe Design of the stern influences the flow of the water striking the propeller and the rudder
Ch1. Design of the Hull New hulls are designed to improve the quantity of water passing through the propeller/rudder area.
Ch1. Propulsion of the Ship / Diesel motor • Manoeuvrability is function of type of propulsion • Most common: diesel engine + fixed pitch propeller Ship is called m/s (for motorship) or m/v (for motor vessel) • advantages • Can be instantly stopped • Can be quickly reverted • During a stop manœuvre: engines can be stopped at the moment that the ship is stopped / propulsion ceases immediately. • Can be quickly accelerated for emergency or kick ahead Disadvantages • Compressed air : quantity limited / N°of cons.starts. • Big engines cannot run slowly / deadslow = 9 or 10knots • Difficult to start astern when speed ahead to high
Ch1. Propulsion of the Ship / Steam turbine • Second most common: Steam turbine. Ship is called s/s for steamship. • Disadvantages: • Stern power only 40 to 50% of ahead power (smaller turbine used for astern) • Problems to stop the vessel ; mostly in emergency • Turbines can keep turning slowly ahead when supposed stopped.
Ch1. Propellers • Fixed right handed propeller • Variable pitch propellers • Twin propellers • Outturning • Inturning • Kort Nozzle • Azimuth stern drive (ASD) • Voith Schneider
Ch1. Effect of Variable Factors on shiphandling Variable factors inherent to the ship - Draft • Trim • Displacement • Fouling
Ch1. Effect of Draft / Fully loaded ULCC Difficult to stop and to bring in a turn
Ch1. Effect of draft / Ship in ballast Ship heavily affected by wind
Ch1. Effect of Trim • Trim by the head: • will turn into the wind • difficult to steer • rudder and propeller come out of the water when ship is pitching Trim by the stern: vessel tends to fall off with side wind
Ch1. Effect of Fixed Factors on shiphandling • Variable factors outside ship • Wind, Sea, Swell • Current • Interaction: Depth of water / Shallow waters • Interaction: Proximity of other ships
Ch1. Effect of the wind Loefgierig schip Lijgierig schip
Ch1. Effect of waves on the ship The stability of the ship is affected by stern waves
Ch1. Interaction between ship and shore Closeness of obstacles like shore, berth, etc… will modify the pressure fields around the ship and provoke changes of heading, uncontrollable swings, due to suction and repulsion forces.
Ch1. Interaction between ships Close quarters
Ch1. Interaction between ships Overtaking ships
Ch1. Interaction between ship and assisting tugboat The tug is affected by the closeness of the ship Dangerous position when close to the bow