TOPIC THREE 3.1 Manoeuvring Flashcards

Question 1

Q

(a) Demonstrate with models the ability to manoeuvre in the open sea, approaching rivers and harbours, to anchorage or to pick up a pilot, to a berth alongside a quay or jetty, to single buoy mooring and to leave from buoys and other SBM’s

Answer

A

Take Into Account

Transverse Thrust -Single screw right hand turning propeller cants stern to port when coming astern.

Kort nozzles- negate transverse thrust, concentrate thrust.

Side thrusters, bow and stern.

Windage. Current. Draft and deadweight.

Interaction, bow waves and bank cushion and suction.

Precautions with CPP and fixed propellers. (Ropes, creeping, clutch delay, minimum power with CPP as opposed to fixed power with clutch engines.)

Rudder types and independent rudders.

Approach plan according to available thrusters and conditions

Interaction when passing close to ship mooredAlongside.

Ship 'A' should have her lines tended during the passage of 'B', and the latter should proceed as slowly as possible in order to keep her wave-making to a minimum. Ship 'B' must also be kept well clear of the other bank so that she does not take a colliding sheer into 'A'.

Ship’s pivot points

The pressure of the water that acts on the bow or at the stern brings about a shift in the position of the pivot point.<img></img>

Ship stopped: No forces are involved and the ship has a pivot point coinciding with its centre of gravity approximately amidships.

With Headway:Two forces now come into play.Firstly, the forward momentum of the ship and secondly longitudinal resistance to the forward momentum created by the water ahead of the ship.These two forces must ultimately strike a balance and the pivot point moves forward.

As a rough guide It can be assumed that at a steady speed the pivot point will be approximately 25% or a 1/4 of the ship's length from forward.

With Sternway: The situation is now totally reversed.The momentum of sternway must balance longitudinal resistance this time created by the water astern of the ship.The pivot point now moves aft and establishes itself approximately 25% or a 1/4 of the ship's length from the stern. Although not intended some publications may give the impression that the pivot point moves right aft with sternway.This Is clearly not correct and can sometimes be misleading.It should also be stressed that other factors such as acceleration shape of hull and speed may all affect the position of the pivot point.

Effects of the wind on ship

When movingahead, the pivoting point in most ships is well forward, so that the pressure on the greaterexposed area abaft this point tends to turn the ship into the wind.

When goingastern, the pivoting point moves aft and the stern tends to fly into the wind.

The degree to which these effects are felt depends largely on the shape and disposition of the ship’s superstructure.For example, a ship with a very high forecastle is not affected a great deal when going ahead, but her stern seeks the eye of the wind rapidly as soon as she gathers sternway.

Wind effects are felt more strongly when speed is slow, and when she is lightly laden.

Using a current in ship handling

Effects of current are important especially when the ship is under the effect of on shore winds, near off shore platforms, while maneuvering in narrow channels and open seas, or in inland waters or harbors.

When the ship is in harbors or inland waters and the current is at constant strength and direction, the ship’s handling becomes considerably easier.

Currents are usually complex, with varying rates and directions that can change hourly. Current from ship’s ahead will reduce the ship’s speed over ground, improve ships response to the rudder, and also give more time to assess and correct developing situations.

A berth should be approached bow into the current in order to give the advantage of relatively high speed through the water with a reduced speed over the ground. Consequently, steerage at low ground speed is improved by the good water flow over the rudder. The ship will be easier to stop.

The current can be used to push a ship alongside. Position the ship off the intended berth but at a slight angle towards it. Then allow the current to produce a sideways movement of the ship towards the berth.

A ship making headway into a current, but stopped over the ground, will have a forward pivot point.

Using a current when berthing

Stem the current. (Bow into the current). Approach at a shallow angle. 
Too large an angle between the berth and the direction of the current will cause the ship to move rapidly sideways. Unless corrected, contact with the berth may be unavoidable.

If during berthing the bow’s angle to the berth is over-corrected then the ship could move away from the berth as the wedge of water between ship and berth becomes established. This may cause the ship’s stern to strike the berth.

Once alongside, care must be taken to prevent the ship dropping astern before back springs and head lines are set.

Points to remember: 
• In many places a counter current flows in opposition to the main current close to the bank. Only local knowledge will provide this information. 
• Current can vary with depth of water and large deep draught ships can experience different current effects at differing parts of the hull. Caution is needed. 
• When close to the berth in a head current, there is a danger that flow inshore of the ship becomes restrictedand the ship is subject to interactive forces. These forces can cause the ship to either be sucked towards or pushed away from the berth. Local knowledge will help anticipate this phenomenon.

• As speed is reduced, take care that the increased proportion of the ship’s vector which is attributable to current does not set the ship close to obstructions.

• Always make a generous allowance for current. Its effect on the ship increases

Question 2

Q

(b) Demonstrate the use of anchors and cables both for manoeuvring a vessel and berthing a vessel with or without currents and wind

Answer

A

<ol>
<li>Outboard anchor let go parallel to berth, used topull bow off when unmooring.</li>
<li>Mediterranean Moor.</li>
</ol>

Question 3

Q

c) Describe various manoeuvres such as running and standing moors, Mediterranean moor

Answer

A

Mediterranean:

Advantages: Allows for best use of limited space in crowded harbors. Allows for each ship to have a brow to the pier; strong moor.

Disadvantages: Possibility of fouling anchors exists with adjacent ships.

Place two anchors about 100 - 150 meters apart on line parallel to the pier, and equidistant on either side of the position of the ship when moored.

Place anchors at an angle of 20 - 30 degrees off the bow for each chain, allow for 120 meters off the pier in addition to ship's length.

Planned positions of the anchors should be marked on the harbor charts.

Shiphandling and execution.

Approach should be made parallel to the pier and towards first anchor point.

Position A - Reduce speed to bare steerageway. Drop anchor about fifty meters before bow comes abreast of assigned point on the pier

Position B - Ship should apply full rudder to steer towards second drop point, and keep the chain clear of the ship. Chain is veered to the first anchor as the ship heads to the second point.

Position C - Passing through the second point, the second chain is dropped with slight sternway.

As stern moves towards pier, chain is veered or taken in to locate the bow 90 degrees from the pier where stern is to be located.

As the ship comes into line, it is backed against catenary of the chain to locate at desired distance from the pier.

Once stern lines secure, chains are adjusted to keep stern safely off the pier.

Getting back underway, the last anchor dropped should be the first recovered. Stern line should be retained as long as possible to keep the stern under control

Running Moor:

Head to stream or wind

When both are present, head to one has stronger effect.

Let go starboard anchor on run, when vessel is 4 shackles and half of ship's length, position -1.

The cable is rendered as the vessel moves upstream.

The cable is not allowed to be tighten, as bow will cant to starboard.

The cable is rendered or veered to 9 shackles as the vessel movesto position-2.

In position-2, port anchor is let go.

The vessel moves astern.

The vessel is then brought up on her riding cable at position-3.

Five shackles on the lee (starboard) cable

and five shackles veered on the riding cable.

Standing Moor:

The ship is to anchor on the line AB. The stream is as shown.

Head to stream or wind

When both are present, head to one has stronger effect.

With sufficient headway, take vessel to position 1.

Position-1 is roughly 5 shackles minus half ship's length beyond line AB.

Let go port anchor.

The vessel drifts downstream,renderport cable to nine shackles, the sum of two lengths.

She is brought up on her cable.

Then the starboard anchor is let go at position-2.

Vessel then moves to the position 3 by going ahead andrenderingor veering the starboard cable and heaving in four shackles on the riding cable.

Engines may be used to reduce stress on the windlass.

Question 4

Q

(d) Describe precautions before entering heavy weather, entering close waters and entering or leaving port

Answer

A

Entering or Leaving Port:

a.Ensure passage plan allows for safe passage through pilotage areas and does not terminate at pilot station only.

b.Check most recent weather reports and navigation warnings regarding conditions in area and plan accordingly.

c.Calculate under keel clearances and times of high and low water.

d.Ensure all departments are kept up to date and that necessary personnel are available on stations, the anchors are walked out and ready to let go and that bridge team is informed as to the planned sequence of manoeuvres.

e.All watertight doors to be closed and the ship is flying the correct flags.

f.Ensure the master/ pilot information exchange card has been correctly filled out and that the pilot is informed early of any deficiencies in equipment and specific manoeuvring characteristics of the vessel (eg. Nomzi speed at dead slow ahead was 7 knots).

g.Ensure that the planned manoeuvres have been discussed with the pilot

h.Allow for safe anchorages in the event of an emergency, or alternate routes to clear any dangers if practicable.

i.Ensure the pre-arrival or departure checklist has been completed and that master is aware of problems or deficiencies.

j.Ensure communications between various departments and from ship to shore are satisfactory.

Entering Close Waters:

a.Ensure passage plan allows for safe transit through area and includes contingency plans such as safe anchorages in the event of emergencies.

b.Close all watertight doors and inform all departments of entry into close waters.

c.Have engines on standby and thrusters available or on standby for immediate starting and use.

d.Calculate under keel clearance and take into account the effects of ship speed on squat and shearing, as well as bank suction and cushion effect.

e.Prepare anchors for immediate use and post a watchman on the foc’sle if deemed necessary.

f.Ensure bridge team are aware of intended route and conversant with all contingency plans. Make sure positions are plotted using all available references and plotting intervals are shorter.

g.Check echo sounder is on and settings are correct, engage hand steering if necessary and as a minimum

Question 5

Q

(e) Describe the routeing and handling of a vessel in the vicinity of a TRS

Answer

A

RSs form in both the northern and southern hemispheres. In the Northern Hemisphere in the early and late season a TRS will likely form between latitudes 5-15 degrees north. At the height of the season a TRS will likely form between latitudes 10-25 degrees north. In the North Atlantic Ocean a TRS, throughout the season, will commonly form between latitudes 25-30 degrees north. In the Southern Hemisphere, a TRS commonly forms between latitudes 5-18 degrees South. For a TRS to form, aside from being in the appropriate location on the Globe, high air temperatures, high sea temperatures (the minimums sea temperature required from research is 27 degrees Celsius) and high humidity are all required.

The seasons of TRSs and their regional names around the world are:

		<p><strong>Name</strong></p>

		<p><strong>Area</strong></p>

		<p><strong>Season</strong></p>

		<p>Hurricane</p>

		<p>North Atlantic/West Indies</p>

		<p>May-December</p>

		<p>Hurricane</p>

		<p>North-East Pacific</p>

		<p>May-October</p>

		<p>Cyclone</p>

		<p>Fiji, Samoa, New Zealand</p>

		<p>November-March</p>

		<p>Cyclone</p>

		<p>Australia</p>

		<p>November-March</p>

		<p>Cyclone</p>

		<p>Bay of Bengal</p>

		<p>April-November</p>

		<p>Cyclone</p>

		<p>Arabian Sea</p>

		<p>April-June, October-December</p>

		<p>Cyclone</p>

		<p>South Indian Ocean</p>

		<p>November-March</p>

		<p>Typhoon</p>

		<p>North-West Pacific</p>

		<p>May-December</p>

If within any of the areas mentioned or in the seasons in which TRSs are expected to form, the OOW must be fully aware of the signs of a TRS being in his or her vicinity.

Some of the important characteristics of a Tropical Revolving Storm (TRS) that are:

<ul>
<li>They appear smaller size than temperatedepressions</li>
<li>They form near theInter Tropical Convergence Zone, a zone of instability</li>
<li>They have nearly circular isobars</li>
<li>No fronts occur (boundary between two air masses, distorted by warmer air bulging into the colder air)</li>
<li>They result in a very steep pressure gradient</li>
<li>They have great intensity</li>
</ul>

The following changes in weather indicate the presence of a TRS:

<ul>
<li>An appreciable change in the direction and strength of the wind</li>
<li>A long low swell originating from the centre of the TRS</li>
<li>As the TRS approaches large amounts of Cirrus clouds, followed by Alto Stratus and then broken Cumulus</li>
<li>If, once corrected, the barometer reads 3hpa below the mean for the time of year (found in the Climatic Atlas or the appropriate volume of Admiralty Sailing Directions for the location) this should arouse suspicion that a TRS is in the vicinity</li>
<li>If, once corrected, the barometer reads 5hpa below the mean for the time of year then avoiding action must be taken as a TRS is almost certainly present</li>
</ul>

Coriolis force, weakest at the equator and strongest at the Poles, is also required for a TRS to form. This is the apparent force caused by the rotation of the Earth and causes the TRS to rotate. Without Coriolis force a TRS can’t form and this is why a Tropical Revolving Storm will not form below 5°N/S.

To monitor for the signs of changes in wind and pressure readings, it is good practice to log the wind direction and force along with the pressure readings every hour whilst suspicious that a TRS may be in the vicinity. This allows for patterns to be spotted within the hourly observations that may match with the above warning signs that a TRS may be approaching.

With reference to ‘Figure’, after a TRS forms they usually travel Westerly then North Westerly in the northern hemisphere and South Westerly in the southern hemisphere. They then usually recurve (known as ‘recurvature’) within a latitude of around 20 degrees. After this they usually head to the North East in the Northern Hemisphere and to the South East in the Southern Hemisphere. It must be noted though that recurvature may not take place. Previous TRSs have looped back onto their original track and if two TRSs meet, they sometimes interact and start rotating around each other. The tracks that a TRS takes, shown in figure one, should only be used as a guide as all TRSs are different and can behave in different and potentially unexpected ways.

There are two sides to a TRS. The dangerous semi circle and the navigable semi circle. The dangerous semi circle is so named as the wind in the dangerous Semi Circle moves in the same direction in which the TRS is travelling. Therefore in this half of the TRS very strong winds will be experienced as the combination of the movement of the storm plus the already fast moving winds cause stronger winds than elsewhere in the TRS. The navigable semi circle is the safer half of a TRS. In the navigable semi circle, if the TRS was to recurve, the TRS would recurve in a direction away from the vessel. The navigable semi circle will still be dangerous due to strong winds and heavy seas, but the wind and sea state will be less severe than if within the dangerous semi circle. The winds in the navigable semi circle will also push the vessel out of the path of the storm whereas the winds on the dangerous semi circle will push the vessel into the path of the TRS.

The dangerous quadrant is the most dangerous area in the TRS. This is because if the TRS was to recurve and the vessel was in this quadrant, the vessel would have limited options as to how to escape the TRS as the TRS would be recurving around the vessel.

Action to avoid a TRS

In the Northern Hemisphere:

Wind veering (changing direction in a clockwise direction), vessel is located in the dangerous semi-circle

Wind backing (changing direction in an anticlockwise direction), vessel is in the navigable semi-circle

If the wind is steady, the vessel is located in the path of the TRS,

In the Southern Hemisphere:

If the wind is veering, the vessel is located in the navigable semi-circle

If the wind is backing the vessel is located in the dangerous semi circle,

If the wind is steady, the vessel is located in the path of the TRS

Once aware of the vessels location in relation to the TRS actions must now be taken to avoid the TRS –

In the Northern Hemisphere:

a.If the wind is veering the ship must be in the dangerous semi-circle. The ship should proceed with all speed with the wind at 10 - 45 Degrees (depending on the speed) on the starboard bow. As the wind veers (anti-clockwise direction) the vessel should alter course to starboard, thereby tracing a course relative to the storm.

b.If the wind remains steady in direction or nearly steady so that the vessel shall be in the path of the storm or nearly in the storm of the path she should bring the wind well on the starboard quarter and proceed with all available speed. When well within the navigable semi-circle she should act as in (c) below.

c.If the wind backs (clockwise direction) the vessel is well within the navigable semi-circle. The ship should bring the wind well on the starboard quarter and proceed with all available speed, altering course to port as the wind backs.

In the Southern Hemisphere:

If located in the dangerous semi circle, put the wind on the port bow and alter course to port as the wind backs

If located in the navigable semi circle or the path of the TRS, put the wind on the port quarter and alter course to starboard as the wind veers

Actions When in the Path of a TRS:

1)Plot the position of the storm centre.

2)Plot the likely path of the storm from Navigation Warnings.

3)Compile report as per SOLAS 1974, which requires that the Master of a vessel is obliged to report to other vessels in the vicinity and the nearest Coast Radio Stations regarding the TRS. The report should contain the following:

- Position of storm as best as it can be ascertained and time (UT) when it was encountered.

- Position of the vessel, course and speed at time of encounter.

-Barometric Pressure, uncorrected.

- True direction and force of the sea.

- State of the sea.

- Height, direction and period of the swell.

4)Update storm details as and when reports arrive by email, fax or sat-c.

5)Check watertight integrity of vessel and instruct crew to batten vessel down.

6)Reduce free surface and attempt to increase GM of vessel.

What is the Mariner's 1-2-3 rule?

The Mariner's 1-2-3 rule, also referred to as the Danger Rule, is an important guideline mariners follow to keep out of a tropical storm or hurricane's path. It refers to the rounded long-term National Hurricane Center (NHC) forecast errors of 100-200-300 nautical miles at 24-48-72 hours, respectively.The danger area to avoid is constructed by accounting for those errors and then broadened further to reflect the maximum tropical storm force (34 knot) wind radii forecast at each of those times by the NHC.

Question 6

Q

(g) Demonstrate with models the turning circles and manoeuvring data of ships

Answer

A

Merchant ships usually turn in a circle having a diameter of about 3–4 times the length between perpendiculars (LBP). The larger the rudder, the smaller will be the Turning circle diameter(TCD). During the TCD manoeuvre, the ship will experience transfer, advance, drift angles and angle of heel (see Figure ).

The maximum angle of heel must be recorded. If the ship has Port rudder helm this final angle of heel will be to Starboard and vice versa. Again, this is due to centrifugal forces acting on the ship’s hull. 
This manoeuvre is carried out with the ship at full speed and rudder helm set at 35°. The ship is turned completely through 360° with say Starboard rudder helm and then with Port rudder helm (see Figure ).

Turning circle diameter :There will be two TCD of different diameters. This is due to the direction of the rotation of the propeller. For most single screw Merchant ships, the propeller rotates in a clockwise direction when viewed from aft to forward part of the ship. It does make a difference to the Turning circle diameter (TCD). 
It should be observed in Figure that at the beginning of the Port turning manoeuvre, the ship turns initially to Starboard. There are reasons for this. Forces acting on the rudder itself will cause this move at first to Starboard. Larger centrifugal forces acting on the ship’s hull will then cause the vessel to move the ship on a course to Port as shown in this diagram. 
Ship model tests and Ship Trials have shown that the TCD does not change if this trial is run at speeds less than full speed. If these trials had been carried out in shallow waters, the TCD could have been double that measured in deep-water conditions.

Advance:

Distance the vessel’s centre of gravity will travel ahead through a 90 degree change in course.

Transfer:

Distance the vessel’s centre of gravity will travel athwart ships through a 90 degree change in course.

Tactical Diameter:

Distance the ship’s centre of gravity travels athwartships through a 180 degree change in course.

Factors Affecting the Turning and Manoeuvring of Ships:

Speed - the faster the speed the larger the turning circle.

Water Depth - in shallow water the larger the turning circle and the longer the stopping distance.

Engine Use - short bursts of engine help the turn but minimize the headway of the vessel.

Draft - the deeper the draft the larger the turning circle.

Structural design and length of the vessel.

Draught and trim of vessel.

Size and motive power of main machinery.

Distribution and stowage of cargo.

Even keel or carrying a list.

Position of turning in relation to the available depth of water.

Amount of rudder angle required to complete the turn.

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TOPIC THREE 3.1 Manoeuvring Flashcards

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