House D.J. Ship Handling Theory and Practice

Подождите немного. Документ загружается.

3. Reduce the rpm and bring the vessel head to current. Let go the starboard anchor

and pay out the same amount of cable as on the port anchor.

4. Stop engines and bring the vessel up to four or five shackles on each anchor.

Dredging an anchor

On occasions it can be a practical option to dredge an anchor on the sea bed, usually

carried out when approaching a berth. The objective here is to let the anchor go at

short stay; definitely no more than twice the depth of water. The operation can take

one of two forms, namely:

a) to use the cable to act as a spring effect, turning the aft part of the vessel in

towards the berth (the pivot Point acting well forward), or

b) to position the vessel up tide, ahead of the berth, and allow the tide effects to

move the vessel astern, deliberately dragging the anchor backwards, allowing

the ship to fall back towards the berth (the rudder action being used to cause the

vessel to draw to a position parallel, alongside).

96 SHIP HANDLING

Dredging a single anchor to a spring effect on the cable. The offshore anchor is let go at short

stay, as the vessel approaches the berth. As the run of the cable is checked, the spring effect,

combined with rudder action, causes the stern to move towards the berth. The anchor would

probably be left deployed in the up and down position, to assist when letting go and depart-

ing the berth.

Dredging an anchor from an up tide position is an alternative option when berthing.

With a flow stream past the rudder, the helm can be applied to generate a parallel

closing movement towards the berth.

Ch03-H8530.qxd 4/9/07 9:49 AM Page 96

Anchoring large vessels, e.g. (VLCC)

When a large vessel like a VLCC intends to deploy anchor(s), the ‘anchor plan’

should include due consideration to the speeds of approach and the speed of the

vessel over the ground when walking back the anchor over the intended anchorage

position. A recommendation of 0.25 knots, over the ground, should be considered as

appropriate but such an estimate could be influenced by prevailing weather condi-

tions. It is also worth noting that monitoring the ship’s speed at such a low value

does have problems and may prove difficult even with updated equipment.

The ability of the vessel to retain such a recommended speed would lend to achiev-

ing a suitable lay of cable over the sea bottom, without placing undue accelerations

on the mooring equipment. The capabilities of ‘Band Brake Systems’ on larger ton-

nage would already seem to be operating at their upper limits and any increase in

the momentum of the running cable, caused by increased vessel speed, must be con-

sidered as undesirable. Any such increase could cause overheating of a braking sys-

tem and result in lost anchors and cables.

In the event that unrestricted descent of the anchor is allowed to take place, i.e.

letting go, then damage to the windlass gearing and/or motors may be unavoidable.

Speed limiting devices operating on the band brake may make the operator’s task of

control easier but overheating could still become a problem with subsequent loss of

braking efficiency. As such, over reliance on a restrictive speed, system should not

become the order of the day, and the principle of walking the anchor back all the way

should be adhered to.

It should be realized that 20 ton anchors are not unusual on large tankers and most

masters would generally not wish to use anchors if the vessel could be safely allowed

to drift in an area of clear water. Where an anchor is to be employed, turning the

ANCHOR OPERATIONS AND DEPLOYMENT 97

The offshore anchor is

let go at short stay,

usually no more than

1½ shackles.

Helm and engines can

be used while

dredging the anchor to

allow the vessel to

drop back parallel to

the berth

Dredging an anchor down to the berth, on a single right hand fixed propeller vessel.

Once alongside and moored the anchor would normally be drawn home, being at short

stay. If the anchor is left deployed, the cable would be walked back to the up and down

position.

Ch03-H8530.qxd 4/9/07 9:49 AM Page 97

vessel into the tide would tend to take the ‘way’ off the vessel providing an oppor-

tune time to commence walking back on the cable. Once the anchor contacts the sea

bed, the tidal direction would cause the vessel to drop away and astern from the

anchor position.

NB: Large heavy anchors limit the types of anchor operations that can be carried out at sea

by the ship’s crew. The ships are usually limited with the type of lifting gear and the Safe

Working Load of specific handling equipment, like shackles and wires. Invariably, where

maintenance or specific anchor operations may be necessary, the service of a Dry-Dock

would normally be required for such large vessels.

An estimate of ship sizes was issued in the Seaways Magazine in 1983 (see below).

This may provide some guidance as to the amount of scope expected for normal

anchor use.

98 SHIP HANDLING

Ship size Scope, general estimate

Deadweight Loaded Ballast

20,000–50,000 7  depth 9  depth

50,000–90,000 7  depth 9  depth

Over 90,000 6  depth 8  depth

The amount of cable employed will always be influenced by the prevailing

conditions.

A suggested approach to anchor a large vessel like a VLCC is shown opposite.

Ch03-H8530.qxd 4/9/07 9:49 AM Page 98

ANCHOR OPERATIONS AND DEPLOYMENT 99

Vessel approaches with anchor walked back to a position just

above the water surface

Tide Wind

Brought up

Stop windlass,

brake on

Veer cable

Stop engines

Stop

Hard a starboard

Vessel continues to turn into

the tide and wind

Let go (walk back anchor,

to sea bed) dead slow astern

Dead slow

ahead

Ch03-H8530.qxd 4/9/07 9:49 AM Page 99

Emergency use of anchors

Vessels make use of their anchors as a matter of routine as and when required.

However, there are occasions when they are required in emergency situations. Some

examples of these could be experienced if the vessel had to beach and run into shal-

lows, or hold off a ‘lee shore’ in the event of engine malfunction (not that anchors

are designed to hold the total weight of the vessel).

Where a ship might have to break her own cables – as with a foul hawse – then

such action would be considered as an incident which leaves the vessel vulnerable

until the situation is rectified. Similarly, a vessel with a fouled anchor may not be

able to deploy both bow anchors and, therefore, in certain circumstances may be

considered unseaworthy, until the foul is cleared.

Anchor work operations are, by their very nature, heavy duty type activities for

crew members and it is important that persons in charge of such incidents and emer-

gencies are conscious as to the safety requirements that are necessary to go along with

such demanding work. Risk assessments prior to carrying out any operation should

be considered as standard practice.

Deep water anchoring

Taking a ship to anchor in deep water is not usually conducted as a matter of choice

and Masters, Pilots and Officers in Charge of vessels intending to anchor should be

concerned with anchoring in a safe manner. It is normal practice when anchoring, to

employ a minimum scope of four (4) times the depth of water. Where excessive

depth is present such a minimum may, by necessity, become increased, bearing in

mind that a new windlass would have the capacity to lift 3.5 shackles of cable, plus

the weight of the anchor, when in the vertical. Older equipment could expect to lead

to a degree of lesser efficiency on the cable lifter.

In every case of deep water anchoring, the anchor MUST be placed in gear and

walked back all the way to the sea bed assuming that it is at a lesser depth than 3.5

shackles. Clearly, any length over and above this could well fall outside the control

of the braking system of the windlass and the capability to recover the cable length

and the anchor. Under no circumstances should the anchor be ‘Let Go’. Such action

in deep water could well cause the brake system to burn out and leave the windlass

without control.

NB. An exception to the above would only arise in the event that the vessel was in immedi-

ate danger of being lost. In which event, sacrifice of the anchor and cable length would be

seen as an acceptable exchange for the well being of the ship.

Pointing the ship

When lying at anchor your vessel may be required to provide a lee for barges to

work general cargo. This can be achieved by pointing the ship to create a lee for

barges/launches to come alongside safely. This operation is achieved by running a

stern mooring wire from ‘bitts’ aft, back up through the hawse pipe and shackling it

onto the anchor cable.

The cable is then veered to provide the vessel with a directional heading off the

weather and provides a lee for the operational use of barges or boats alongside.

100 SHIP HANDLING

Ch03-H8530.qxd 4/9/07 9:49 AM Page 100

Anchoring the vessel in ice conditions

The general advice on deploying anchors when inside ice conditions is: do not

anchor. Choose any other alternative, but do not anchor if another option is present.

Clearly, no Ship’s Master would willingly wish to put an anchor down in heavy ice,

but it is not considered good practice in any ice condition.

The adversity to deploying anchors in ice stems from the experience of those who

have tried in the past. Accumulation of surface ice between the hull and the anchor

cable, where it breaks the surface, can be considerable. Large floes can become

wedged and cause not only ice build up around the anchor cable but also down the

side of the vessel.

If the vessel is nipped at one end, namely the bow, ice concentrations will not

freely work themselves past the stern of the vessel and could accumulate down the

ship’s side. Such accumulations of possibly large ice floes along the side and in the

vicinity of the cable could expect to generate concentrated weight against the ship.

This weight in itself could cause the cable to part with excessive strain, or at the very

least, come to play on the anchor and cause it to break out. Dragging anchor at any

time is not a good experience, dragging anchor in ice conditions must be considered

particularly hazardous.

ANCHOR OPERATIONS AND DEPLOYMENT 101

Anchor cable, veered

Mooring wire

from aft

Anchor cable

Area of lee

Ch03-H8530.qxd 4/9/07 9:49 AM Page 101

Where anchors and windlasses are being employed in extreme cold climates it is

always advisable to leave the windlass running during periods of non-use, to ensure

machinery does not freeze up. Prior to entering ice regions, it is always considered

prudent to ensure that pipelines are adequately lagged with insulation, especially

pipes leading to deck machinery like mooring winches and windlasses.

Anchor parties, if required, are usually going to be exposed to extreme climates if

the anchors are to be deployed. Such conditions, even when men are adequately

clothed in protective, insulated wear, are not ideal and working conditions on slip-

pery decks must be seen as a continuous hazard. If anchoring can be avoided, avoid

it. You do not expose the crew, and the risk of problems with a fouled or frozen

anchor is eliminated.

Alternative to use of anchors could be to revise route planning and/or adjust

speed so as not to arrive at the necessity to anchor. A second alternative would be to

steam up and down, hopefully in clear open waters away from ice infestation. A

third option would be to consider a lay-by berth, but such an action could incur Port

and harbour dues.

Use of mooring boats

Mooring boats are employed for many routine, as well as for the more unusual,

operations. When engaged in running long drifts in mooring ropes, possibly from

securing to non-conventional quaysides, it may be considered a routine duty for a

mooring boat, compared to more unusual operations like mooring to single buoy

moorings (SBMs) or passing slip wires to mooring buoys.

Whatever the task in hand, clearly operations with small boats, especially in poor

weather conditions, must be considered somewhat hazardous for the personnel so

engaged. Apart from the potential of interaction occurring between the parent ves-

sel and the small craft, the exposed boat and the respective personnel are, in the

majority of cases, very close to the water at a low freeboard. The working of the craft

also tends to involve the handling of heavy warps and/or specialist equipment, in a

confined deck area.

Personnel are also often expected to jump buoys for the securing of moorings,

passing slip wires or securing anchor cables. Whatever the duty, personnel in this

capacity, especially when expecting to ‘jump the buoy’, should always wear lifejackets.

These would normally be available from the parent vessel if requested or if own crew

members are involved. Positive communications should also be available at all times

between the Bridge of the parent vessel, the mooring deck controlling officer and the

mooring boat coxswain.

102 SHIP HANDLING

Ch03-H8530.qxd 4/9/07 9:49 AM Page 102

Non-standard mooring operations

Not all mooring operations are regular or conducted with standard mooring decks.

Specialized vessels, certainly in the Offshore environment, are often engaged in moor-

ing to SBMs or Floating Storage Units. Specialized moorings are usually employed to

secure the ship prior to commencing cargo operations with pumping stations.

Moorings tend to be of a heavy variety combining heavy duty warp and/or moor-

ing chains. A ship’s mooring deck is likely to be fitted with Auto Kick Down (AKD)

stoppers and special leads to accept chain moorings, while the operation of recovering

the moorings is often by pick-up buoys. Special fitments on shuttle tankers are

designed for securing the vessel safely for a limited time period to complete cargo

and permit speedy release.

ANCHOR OPERATIONS AND DEPLOYMENT 103

A mooring boat engaged in securing chain mooring recovery buoys for a shuttle tanker moor-

ing to a Floating Storage Unit (FSU).

Ch03-H8530.qxd 4/9/07 9:49 AM Page 103

Some of these ships often incorporate a forward conning position, remote from

the bridge, to permit precise, close manoeuvring to the installation.

104 SHIP HANDLING

The offshore moorings from a large shuttle tanker to a Floating Storage Unit. The moorings

are recovered via pick-up buoys with the chafe chains held by AKD stoppers, prior to pass-

ing the floating oil pipe seen at surface level.

Mooring chain stoppers. A type of chain mooring arrangement for use when securing shuttle

tankers or supply vessels, often used, known as an AKD stopper to hold the chain moorings.

It is normal procedure to have a stopper to each chain, to port and starboard; mooring ropes

may be an additional optional mooring.

Ch03-H8530.qxd 4/9/07 9:49 AM Page 104

Mooring to buoys – by anchor cable

Several ports around the world specifically require ships to moor up to buoys using

the anchor cable of the vessel. It has to be said that this is not a common occurrence,

but does happen from time to time. The ports in question are usually those that are

regularly threatened by tidal surge or bad weather conditions often generated by

monsoon conditions or within the Tropical Storm latitudes.

Many oil exporting countries also make use of the buoy mooring facilities offshore

by bringing large tankers into SBMs or making connections to Floating Production

Storage and Offshore systems (FPSOs). Specialized mooring arrangements secure the

vessel, while floating pipelines are drawn on board to effect cargo transfer.

ANCHOR OPERATIONS AND DEPLOYMENT 105

A chain mooring is sent away through a ship’s lead to an SBM; once connected, the floating

pipeline would be engaged to effect oil transfer.

Mooring to buoys (mooring lines)

The possibility that a ship may be required to moor between two mooring buoys is

common practice in many ports of the world. The mooring may employ the use of

the anchor cable or not, but more often employs the use of mooring ropes secured

directly to the buoy. The basic needs require the use of a mooring boat, with a ‘buoy

jumper’ wearing a lifejacket and additional securing equipment to join the rope to

the ring of the buoy.

Methods of securing the ropes to the buoy vary but common practice is to send

either a mooring shackle with the rope eye, or a length of about three (3) metres of

rope lashing to secure the two sides of the eye, under the bight of the rope.

Ch03-H8530.qxd 4/9/07 9:49 AM Page 105