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MANOEUVRING GZV/ GRADE II

3 COURSE BLOCKS

• 1 Grade I Repetition Propellers, Rudders, Manoeuvring data, Watch keeping.

Grade II hydrodynamics, Twin Propellers, Configuration, Manoeuvring

• 2 Grade I Repetition Some manoeuvres with current, wind, anchor. Storm and shallow manoeuvres, Taking pilot, Entering Harbour

Grade II Towing at sea. Dangers of tug use in port

• 3 Grade I/ II Subjects still to discuss. Repetition Grade II subjects Exam preparation

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Hydro dynamics

Hydro dynamics is caused by fluids in motion. Here the fluid is water.

Our vessel itself, rudder and propeler are body’s under influence of this fluid in motion

Where noticable: • The behaviour of the vessel in making a turn

• Interaction during overtaking and passing another vessel

• Bankeffect

• Shallow water effect (Squat)

• Unexpected effect when using bowthruster or forward tug whilst making speed ahead

• The special shape of a rudder and a propellerblade

• Duct or Nozzle around the propeller

A1

A2

The amount of liquid passing a random cross section of a tube (river-waterflow) per time unit is constant

When the tube gets narrower, the velocity of the liquid will increase

In formula: A1 x v1 = A2 x v2

Continuity Law

v1

V2

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• ½mV2 + P1 = constant

• Which means that:

When the speed increases, the pressure in the (here)liquid will reduce When the speed decreases, the pressure in the (here)liquid increases

Bernoulli’s Law

Propellers

See book for the items:

• The Pitch

• Propeller speed

• Slip

• Suction/Pressure plane

• Right/Left handed

• Fixed/Variable

Right handed – fixed propeller

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Ship’s behaviour

• Fixed pitch

• Right handed (Rh) • Engine ahead

• Engine astern

• Left handed (Lh) • Engine ahead

• Engine astern

• Variable pitch

• Right handed engine ahead as fixed Rh pitch, engine astern as fixed Lh

• Left handed engine ahead as fixed Lh pitch, engine astern as fixed Rh

Explain the movement of the stern of a vessel equipped with a

Ship’s behaviour

CONCLUSIONS:

• The direction of the movement of the stern of the vessel is the turning direction (wheeling) of the propeller

• The wheeling effect with engine ahead is hardly noticeable, on astern however the influence is significantly

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α

Ve

(speed)

Vrpm

Lift force

Thrust

(stuwkracht)

Drag

(weerstand

Propeller and Bernoulli

• Engine full ahead • α = (optimal) angle of inflow • Lift perpendicular on inflow • Forward thrust

Water inflow

Cross section topblade RH propeller seen from above

-α

Ve

Vrpm

Lift

- Thrust

Drag

Stopping on the Lift Engine slow ahead

• Engine slow ahead, speed still high

• Negative inflow angle • Lift perpendicular on inflow • Gives a stern thrust

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-α

Ve

-Vrpm

Lift

- Thrust

Drag

Fixed RH propeller engine astern

• Engine half astern, speed still forward

• Negative inflow angle • Lift perpendicular on inflow • Stern thrust

-α

-

Ve

-

Vrpm

Lift

- Thrust

Drag

Propeller and Bernoulli

• Engine half astern, stern speed

• Negative inflow angle • Lift perpendicular on inflow • Stern thrust

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Type of propellers (also see book)

Type of Propeller - Azipod

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Type of Propeller - Propeller Duct

Type of Propeller - Water jet

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Type of propeller- Voith Schneider

Tugs and Ferries

Bow Thrusters

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Bow- and stern thrusters

Bow- and stern thrusters

• Bow- and stern thrusters can only be used at lower speeds. WHY?

• Moving backwards, the bow thruster is a great help in steering. Why?

• Your vessel is equipped with both stern thruster and bow thruster. While proceeding foreward to the berth, you like the bow to move to starboard. Which thruster do you use to achieve this movement?

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Bowthruster and steering torque

.

.

P

P

P= Pressure point Short and long arm of a couple

RUDDERS Workings

• Effectively wake bent

• Minimal drag = small rudder angles, achieved by a wing shaped profile giving a Lift force

vertical foil

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Rudder types – Spade rudder

Rudder types – Flap rudder

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Rudders - Mariner Semi Balance Rudder

Upper part: Wing Profile (compare with

Oertz rudder)

Lower part: Balance

Rudders – Fishtail Rudder

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Rudder and forces

• What movements makes a vessel after giving starboard rudder

• Leaning shortly over to starboard

• Turns to starboard

• Tranverse movement to port (kick)

• Leaning to port during turn

• Loss of speed

• Explain with the book these movements of the ship

Manoeuvring data

• Turning circle difference deep and shallow waters !

• Stopping distance in the formular: mv2 !

compare with advance turning circle !

• Speed tests • MOB manoeuvres tests Williamson turn test on bridge

• Zig zag tests For checking course stability

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Turning circles – stopping distance

Know the expressions. Explain why diameter turning circle larger in shallow water. Explain speed reduction. Why speed reduction less in shallow water? And so on

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Speed reduction

Crash Stop

Crash stop vessel Full ahead-full astern Speed 12 knots Q: In how many minutes stopped? (7½ mins) Q: In what distance? (1100 meter) Q:After how many minutes speed 4 knots? (4½ mins)

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Controlled stop with engine and low frequency rudder cycling (only effective on deep water)

stopped

By using the Stopping on the Lift principle(reduce revolutions of the propeller step by step) as well as speed reduction by the drag of the rudder and vessel. The final astern manoeuver should be given to stop the vessel and to turn the vessel into the original heading (depending left/right prop)

Chapter 4 Standing and handing over the Watch

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The watch

• Standing the watch is taking care of navigation and act when needed

• Warn the captain instantly upon any doubt as to safety

• The watches 0-4 middle watch

4-8 morning watch

8-12 forenoon watch

12-16 afternoon watch

16-20 evening watch

20-24 first watch

The watch

• Handing over the watch • be in time to consider the oncoming navigation

• Handling over: al relevant information as course(s), speed, drift, ships, lights, dangers, and so on

• Heading and course both given in figures 150 = one five zero • What’s the difference between heading and course

• REPEAT ALL and what does it means • Hard a starboard Starboard a bit Starboard a bit more

• Starboard 30 Ease to 20 Midships

• Steady Steady as she goes Course 3 4 5

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GRADE 2 TWIN SCREW

• Twin propellers (two screws) improve 1. operating reliability and 2. maneuverability.

• With twin props the shafts mostly are at equal distance from the center line. The further the shafts are away the easier the ship will turn

• The propellers can be inturning or outturning . Fixed or variable.

• Most vessels are equipped with outward rotating fixed propellers, or inward rotating variable propellers. WHY?

• The maneuverability is improved when the vessel is equipped with two rudders and a bow thruster

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Outturning fixed propellers - one rudder • Port propeller left handed

• Starboard propeller right handed • Turn over starboard with port engine

ahead and sb engine astern • Two momentums are effecting the

propeller: • One because of one propeller

reversing while the other one is still in forward gear

• The other one due to wheeling propeller effect.

• Both momentums together will increase the turning.

• With slow speed the rudder to starboard has none or little effect

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Inturning fixed one rudder • Port propeller right handed

• Starboard propeller left handed

• Turn over starboard with port engine ahead and sb engine astern

• Two momentums are effecting the propeller:

• One because of one propeller reversing while the other one is still in forward gear

• The other one due to wheeling propeller effect but now counteracting

• So both will oppose each other and therefore making turning more difficult or even impossible

Mooring and unmooring twin screw

• Fixed inturning

• Fixed outturning

• Variable pitch inturning

• Variable pitch outturning

• With • one or two rudders

• bowthruster or bow-and sternthruster

• bowsprit

• Non parallel propeller shafts

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Unmooring 2

conventional twin screw ship fixed-outturning

starboard port

right handed propeller

left handed propeller

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one propeller (sb) working ahead

one propeller (sb) working astern

wheel effect

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one propeller (sb) working astern, the other propeller (port) ahead

wheel effect

when the rudder force is also applied the vessel will rotate even faster

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Inward turning fixed pitch propellers

starboard port

right handed propeller

left handed propeller

Inward turning fixed pitch propellers one propeller (sb) working on astern

wheel effect

When the vessel has inward turning propellers the momentum between the two propellers is outweighed by the wheel effect

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Traverse with outward turning propellers without bow thruster

Port engine/prop/rudder pushes stern to starboard Starboard engine /prop pulls the stern backwards and to port Only with little or no wind!!

Traverse outturning fixed props with the aid of a bowthruster

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2 x Traverse inturning fixed props with the aid of a bowthruster