CHAPTER No 5 – BALLAST MANAGEMENT
REGULATIONS GOVERNING BALLAST MANAGEMENT
Before considering the ballasting processes in detail it is worth recalling the restrictions which are placed upon ballasting operations.
These restrictions have two objectives to
(1) protect the ship from damage and
(2) to preserve the marine environment.
The appropriate “in port” and “at sea” limits for shear forces, bending moments, and hard girder torque, as specified by the class and stated in the Loading Guidance and Stability Information Manual, must never be exceeded. To ensure that they are not exceeded the values must be calculated and taken into account when ballasting is planned..
Vessels which have the option of ballasting to a
(1) light ballast draught or
(2) heavy ballast draught must ballast to the heavy ballast draught when adverse weather is expected.
A minimum forward draught for the vessel when at sea may be specified by the class. This figure will probably be 0,025 L. (In a bulk carrier with L=200m the minimum permissible forward draught would be 5 meters)
Adequate positive stability must be preserved throughout the voyage.
Ballast holds and topside tanks must not remain part filled throughout the sea voyage.
Ballast tanks must not be over-pressurized.
The ballasting pressure will be too high and damage will occur if tanks are filled faster than the water can overflow from the air pipes when the tank is full.
Such damage can occur if two pumps are used to fill a single ballast tank or if ballast tank air pipes are damaged or blocked.
Ballast tanks must not be under pressurized.
If tanks or ballast holds are emptied with air pipes and ventilators closed the resulting vacuum can cause severe damage to the deck structure, and hatch covers in the case of ballast holds.
On January 2008, the SOLAS requirements – SOLAS as amended V 22 IMO 2009 – entered into force consideration, is given when changing ballast, to increase blind sectors which might impede a good lookout, that the exchange is in accordance with the ship’s ballast water management plan and that the ballast exchange is logged.
Τhe IMO Guidelines – Guidelines for the control and management of ships / ballast water to minimize the transfer of harmful aquatic organisms and pathogens / Resolution A.868 (20) IMO, November 1997 – specify how and where ballast should be taken, exchanged and discharged, the precautions to take and the ballast records that must be maintained.
These guidelines are strengthened and made mandatory by the international convention for the Control and Management of Ships Ballast Water and Sediments the requirements of which, depending on the willingness of the IMO member states to ratify the Convention may be coming into force between 2008 and 2010.
Some Authorities have their own requirements, which are mandatory and are more exacting than those of the Convention. Details of these can be found in National Directories and Port Information on the internet, on the BIMCO homepage or Vessel CD, or in Guides to Port Entry.
Details of the requirements at the intended ballast discharge port can also be provided by Ships Agents in that port and should be studied before taking ballast to be sure that all relevant requirements can be satisfied.
SHIPS BALLAST LAYOUT
A. Ballast pipelines
Each ballast tank is connected to the engine room by a ballast pipeline running from tank to engine room, through which the ballast water, passes as the tank is filled or emptied.
Each tank may have its own separate line, or all starboard tanks may be connected to one common ballast main and all port tanks to another.
If there is duct (αγωγός – tunnel) keel the ballast lines will run along it.
Certain bulk carriers are provided with ballast ducts formed by the double bottom structure, instead of ballast pipe lines.
Such ducts are approved as suitable for use with a stated static head of water which must not be exceeded in service.
In the ballast tank the line ends in a bell mouth, an enlargement of the line which terminates to the lowest part of the tank about 3 cm above the tank base.
In the engine room the line can be connected to a sea inlet (στόμιο) by a choice of pipeline systems served by one or two ballast pumps, and general service pump, so that the most suitable pumping option can be selected.
In most cases, particularly in larger vessels, the line is also connected in the engine room to an eductor of stripping pump for final stripping.
Alternatively a separate stripping line is fitted.
This shows that each wing tank and double bottom ballast tank has its own separate suction / filling line connected to one of the main ballast lines and is also connected to one of the stripping lines. The forepeak and the after-peak tanks benefit from the tapering (narrowing) shapes and are connected only to the main ballast lines.
The plan states, in effect that in the double bottom tanks the suctions are to be placed inboard in the starboard, and outboard in the port tanks so that the most efficient drainage of the tanks can be achieved by listing the ship a little and, of course keeping her trimmed by the stern.
Achieving Good De-ballasting…
Keeping ship upright:
If the ship develops a list when loading and de-ballasting the effect may be caused by
(1) bad distribution of cargo, or
(2) it may be a fault with the de-ballasting, causing one of a pair of tanks to discharge more slowly than the other.
– If the fault is in the de-ballasting, the soundings will show that one tank is more full than the other and the fault must be found and corrected.
– If the list is the result of unbalanced loading of the cargo, the operator of the ship loader must be instructed to distribute the cargo so as to keep the ship upright whilst loading.
An unplanned list will make de-ballasting more difficult and is likely to cause uneven discharge of ballast, thereby encouraging unbalanced loading of the cargo and exposing the ship’s hull to additional stress.
Β. Duct keel
In smaller ships the ballast pipelines to the forward tanks pass through the after tanks to reach the forward ones.
In larger Panamax and Cape-sized vessels a duct keel – a tunnel running fore and aft to contain ballast and other pipelines – is likely to be installed below the holds on the ship’s center line/
This provides space for all pipelines and for all pipelines and for most of the valves serving the holds and forecastle, and allows access to them for repairs and maintenance.
The duct keel is entered from the engine room via a watertight door and on larger ships is likely to be provided along its length with one or more additional access from the upper deck.
C. Air pipes
Each ballast tank is provided with at least one air pipe, and usually two – one forward and one aft – to allow air to escape as the tank fills, regardless of the ship’s trim.
The air pipes extend to sheltered positions on the upper deck.
They come in variety of designs which allow
(1) the passage of air,
(2) the overflow of water, and
(3) will not permit water to enter.
It is essential that this non-return arrangement (often a float) is well maintained and adjusted, if necessary, to ensure that the accidental flooding of ballast or fuel tanks cannot take place.
Inspection of the non-return arrangement in all the air pipes is a Load Line Survey item, and every air pipe should be regularly checked between surveys by ship’s staff.
The position of the air and sounding pipes of can be seen on the “Air, Sounding and Filling pipe plan” .
D. Sounding pipes
Every ballast tank is provided with a sounding pipe, normally located at the after end where the greatest sounding will be obtained provided the ship is trimmed by the stern.
At the base of the sounding pipe is a striking plate, a small section of doubled plating which protects the ship’s shell platting from the wear caused by the impact of the steel sounding rod, or the pipe may continue to the ship’s shell, with openings cut near its base.
Striking plates must be examined whenever tanks are inspected and renewed when they are wanted, as they protect the shell plating from damage.
E. Tank gauges (μετρητές)
Ballast tanks are often provided with remote reading indicators which show
(1) whether or not the tanks are empty or
(2) with gauges which show the volume of ballast which the tank contains.
Such devices are useful indications of the progress of ballasting or de-ballasting but must never be trusted completely Upon completion of any ballasting process the tank contents must be measured with sounding rod or sounding tape to obtain a reliable measure of the contents.
If there is any suspicion that the sounding rod has not reached the base of the pipe, which may be blocked by an old sounding plumb or by scale or sediment
the ullage should be measured by taking the reading at deck level when the rod is at the deepest sounding.
The ullage can then be compared with its known or listed value which, on large ships, is likely to be the same as that for a number of other tanks.
F. Centralized ballast controls
On modern ships the ballast controls are likely to be centralized in a single position, perhaps with duplicate controls elsewhere.
Such controls are likely to include remote switches for the valves in the ballast system and for the ballast pumps, along with gauges or indicators to show the contents of each ballast tank.
The centralized controls may be found in a cargo control room, in the engine room control room, on the bridge, in a mast house or within a watertight box on the open deck )
G. Double-bottom ballast tanks
It is normal for the double bottom ballast tanks to extend in to the lower hopper spaces, creating a tank with a tank top which rises to a greater height in the wings beneath the lower hoppers.
Alternatively, in double hulled vessels, this area may be part of the wing ballast tanks.
These double bottom tanks are subdivided for strength purposes into small steel cells formed by vertical steel plates running athwart-ships (κατα μηκος το πλοιου) and fore and aft The athwart-ships plates (called floors) and the fore and aft plates (named side girders) have lightering holes cut in them at intervals to reduce the weight of steel used and to allow access.
Drainage holes are provided at the base of the vertical plating to allow complete drainage of the tank, whilst similar holes at the top of plating allow free circulation of air.
Movement through the tank for inspection or cleaning purposes is difficult in the smaller mini – and handy sized vessels, because of the limited dimensions, though it becomes easier in large bulkers.
H. Top side ballast tanks
The topside, saddle (σελα-σαμαρι) or upper hopper ballast tanks strength along the length of the ship’s side and occupy the upper corners of the ship’s hull.
There are several ways in which these tanks can be filled and emptied, and the method varies from one design of ship to another.
The simplest method to describe is similar to that found in other ballast tanks a ballast line runs to each topside tank from the engine room and is used to pump ballast water into or
out of the tank from or to the sea, via the engine room.
The usefulness of the topside tanks increased when they are fitted with DUMP VALVES / drop valves (πετάω-αδειάζω) – (their openings are usually sited below the light waterline) Dump valves (drop, or screw down overboard drain valves) are ship’s side valves, usually one to tank, which are used to discharge the ballast from the topside tanks by gravity directly into the water alongside the ship.
There is very useful when there is a requirement to discharge a lot of ballast quickly.
A further advantage is that no pump is needed for the discharge.
One exceptional situation in which dump valves are useful is when refloating a vessel after grounding.
If all topside the topside ballast is dumped (αδιαζω) at one time the draught decreases rapidly and the prospect of overcoming the suction and refloating from a muddy bottom is increased.
The facility is equally useful in routine de-ballasting when rapid de-ballasting is required, as is so often the case.
On older vessels when de-ballasting by way of dump valves, care must be taken not to discharge ballast into barges lying alongside or on to the quay where sensitive equipment power lines or stocks of cargo are located. Where available and where required chutes (αγωγοι) should be used to guide discharged ballast water down the ship’s side.
On modern vessels the dump valve discharge openings are usually sited below the light waterline where they will cause no flooding.
Precaution when de-ballasting
When ballast is discharged from topside tanks by way of dump valves otherwise known as drop valves the process looks after itself.
This is convenient for ship’s personnel, but is thought to have resulted on numerous occasions in personnel forgetting to close the dump valves after all ballast has been discharged.
This can result in water re-entering the topside tanks, and flooding from there into the double bottom tanks in ships where topside and double bottom tanks are joined.
At the worse this could result in serious difficulties or loss of the ship.
At least it could cause the carrying of unnecessary ballast, and reduction of the cargo lifted.
It is recommended that the closing of all dump valves immediately on completion of the de-ballasting be checked and logged.
I. Integrated top side tanks
The topside tank in this system is simply an extension of the lower hopper and double bottom tank. Some topside tanks are fitted with no separate ballast lines, and with no dump valves, but are simply joined to the adjacent lower hopper and double bottom tank by trunking (κορμός).
Τhis system is clearly the cheapest to install and maintain, but is least useful.
This top side tank in this system is simply an extension of the lower hopper and double bottom tank. It can only be filled when the lower tank has been filled, and the double bottom tank cannot be emptied until all the ballast has drained from the top side tank.
When there is a need to keep the lower tank empty for any reason – for example, to make the ship less stiff by raising the center of gravity, or because the lower tank is damaged and leaking – the upper tank must be left empty too.
An improved version of the combined double bottom tank is achieved when a gate valve is fitted in the trunking between upper and lower tanks.
This permits the upper tank to be kept full while the lower tank is emptied.
BALLAST PUMPING ARRANGEMENTS
Most bulk carriers are provided with at least two main ballast pumps Normally one is used on starboard ballast tanks and the other on port ballast tanks, but these arrangements can be varied.
The port pump can be used on starboard tanks, and the starboard on port tanks, and both pumps can be used together on large tanks such as ballast holds or the fore-peak tank.
For emergency use if ballast pump fails there are usually other pumps such as a general service pump which can be used to pump ballast. In addition to the main ballast pumps most bulk carriers except the smallest are provided with a ballast stripping system.
This relies on the low capacity pump or educator to pump out the stripping ( the last few centimeters of ballast water ) from the ballast tanks.
On Cape-sized or larger vessels a separate stripping line to each tank may be provided but this is rare in other bulkers.
More often on Cape-sized, Panamax and handy sized vessels the stripping is done by way of the main ballast line ( ιδια γραμμη / σωληνα, διαφορετικη αντλια ).
Mini bulkers may be provided with no separate stripping pump or system, all the ballast being discharged by careful operation of the main ballast pump.
QUANTITY OF BALLAST REQUIRED FOR VOYAGE
Most bulk carriers have a light ballast condition for use in fair weather , with all double bottom, hopper, topside wing and peak non-fuel tanks filled.
The displacement in light ballast condition is typically 40 – 50% of loaded displacement. Most bulkers also have heavy ballast condition for use when rough weather is expected or met.
In this condition the above tanks are filled and in addition one hold or several holds are, flooded giving a displacement of 50 – 65% of loaded displacement.
It is possible to change the amount of ballast which the vessel is carrying during the course of the voyage, but the matter should be considered beforehand (εκ των προτέρων ) since a ship with, insufficient ballast will be showed by weather and may suffer damage, whilst a ship carrying too much ballast will be incurring extra expense as her fuel consumption will be higher and her speed may be reduced. When strong winds particularly strong adverse winds and heavy swell are expected it is prudent to carry maximum ballast to prevent the
(1) bow slamming and
(2) propeller racing when the ship is meeting the swell.
In fair weather, significant savings in fuel consumption can easily obtained, it is claimed, by carrying minimum ballast, and a major study of this subject has identified the optimum minimum ballast condition.
The propeller need be only immersed to 90% of its diameter when the vessel is at rest, since the stern wave will immerse the propeller fully when the vessel is underway.
The optimum forward draught in fair weather is more difficult to specify.
It is necessary to strike a balance between the benefit of reduced forward draught and the loss of efficiency which results from increased trim.
In addition, there will usually be a loss of propulsive efficiency at the draught at which the top of the bulbous bow breaks the surface.
The study suggests that a ship provided with a reliable and accurate (1) fuel meter and (2) speed log can become its own test bed to tune draught and trim in varying weather states so as to “maximum meters per liter”.
The benefits of tuning are likely to be greatest in fair weather conditions, whilst in moderate or heavy weather the vessel should be ballasted down.
The transfer of bankers is a more efficient way of improving trim than is the taking of additional ballast, since the former alternative requires no increase in displacement but seafarers will treat this option with caution in view of the possible penalties for a mistake whilst transferring fuel.
A further study by one of the same authors concluded that a very flexible and adaptable system of ballasting could be achieved if the ballast hold was always filled on ballast passages with most other ballast tanks being kept empty except as required to avoid excessive bending moments and shear forces, to achieve optimum trim, or increase displacement in the event of meeting adverse / weather.
An additional benefit of this method of operation would be the reduction of sediment taken into double bottom tanks.
This system of ballasting, with the ballast hold or holds always filled on ballast voyages, is only attractive in trades in which the hold or holds can become available for ballasting some time before the completion of discharge and where loading can proceed in other holds whilst the ballast hold is prepared for loading.
It is particularly attractive for bulk carriers which have restrictions on filling or emptying ballast holds while at sea due to the risk of sloshing.
On some ships the filling of all ballast tanks for a ballast passage is forbidden because the longitudinal stresses are excessive when ballast holds, and adjacent ballast tanks are all full.
Such a ship is permitted to sail in the light ballast condition with all double bottom and topside tanks full and the ballast hold empty or alternatively in the heavy ballast condition with the ballast hold or holds filled but with specified adjacent topside tanks empty.
Some bulk carriers have restrictions on the filling of their fore-peak tanks, in particular in the light ballast condition, where it would cause excessive hogging.
Any such requirement will be plainly stated in the ship’s loading manual.
BALLASTING WHILST DISCHARGING
Preparations for ballasting
A full ballasting plan, consistent with the cargo discharge plan, complying with shear force and bending moment limits and taking account of any draught and air-draught limits must be prepared in advance in compliance with the BLU Code.
Before commencing of ballasting it is necessary on some ships to open the ballast tank ventilators or air pipes to allow air to be exhausted as the ballast water enters the tank.
It is also important to note where ballast water may overflow.
Ballast water which can overflow into part-filled cargo holds or over the ship’s side into barges or on the quay can be a source of substantial claims, with the ship even being accused of causing pollution. For this reason when tanks are ballasted in port pumping must always be stopped before the tank overflows.
To ensure that this is achieved the ballast pumps should be singled up, or reduced to minimum speed, when the tank is nearly full and an officer should be stationed by the tank air pipe sounding pipe with a walkie-talkie radio, which gives him direct contact with the ballast pump operator.
When the officer sees from the sounding, that the tank is about to overflow or when he sees or hears the water nearing the top of the air pipe or sounding pipe he must instruct the pump operator to stop the pump.
Alternatively, provided that the tank gauges are reliable filling can be stopped when the gauges show the tank to e 95% full.
To prevent sloshing the filling of such tanks should be completed – ie the tank should be “pressed up” when the vessel is at sea.
It is important to remember that hold structures are regularly damaged by grabs during discharge.
If a hole has been punched in a tank during discharge then ballast water will pour on to the cargo in the hold when the tank is ballasted.
Before ballasting is started the holds should be inspected as far as possible to ensure that no damage has been sustained, and the tank boundaries should be regularly viewed to detect any leakage of ballast water whilst ballasting continues.
Precautions whilst ballasting
Instances have been recorded in which the internal structures of ballast tanks have been damaged as a result of ballasting at too high rate.
Damage can occur when a full tank is over pressurized, a condition which arises if water is pumped into the tank faster than it can overflow out of the tank through the air pipes.
This is most likely to occur if the tank has an air pipe which is
(1) blocked through freezing,
(2) two, pumps were used to fill a single tank,
(3) an air pipe were damaged.
Risk of damage will be reduced if tanks are always topped-off at a reduced pumping rate.
When berthed in a river ballasting is best done on the flood tide, when there is less sediment in the water.
This will result in less mud in the ship’s ballast tanks.
Other factors that may affect the quality of the ballast are,
(1) shallow water,
(2) nearby sewage outlets,
(3) toxic algal blooms,
(4) cholera in the locality and
(5) the hours of darkness when bottom dwelling organisms rise to the surface. Often these circumstances cannot be avoided but the should be recorded.
Ballasting – the 1st stage
It is normal to commence ballasting by filling double bottom tanks, and this can be done by gravitating opening the sea valves in the ballast system and allowing the water to flow through the ballast pipes and into the chosen tanks under the effect of gravity.
The speed of filling will depend upon the head of water this corresponds to the draught of the ship.
In the early stages gravitating may be faster than pumping.
If the draught of the ship is less than the height of the tops of the lower hopper tanks, then the tanks can never be completely filled by gravitating and it will be necessary to complete the filling by pumping.
The benefits of filling a tank by gravitating are threefold (τριπλα).
(1) There is no possibility of the tank overflowing and causing damage,
(2) no power is required so there is a cost saving, and,
(3) the filling will stop naturally when the level of the outside water is reached so it is not necessary to monitor the process continuously.
The sequence (αλληλουχία / σειρά) of filling the double-bottom tanks will be decided by the sequence of discharging the cargo holds.
When all holds are discharged simultaneously and where the cargo is of low density, (stowage factor is bigger from 0,56 m3 / ton ) the longitudinal stresses will be low and will be possible to adopt any reasonable sequence of filling the double bottom tanks, as will be apparent when the details are entered in the loading instrument.
Another factor to bear in mind is the vessel’s trim.
It is always preferable to maintain a trim by stern so that reliable soundings can be obtained, for purposes of efficient drainage throughout the ship, and for the convenience of the engineers.
Where possible this trim should be ensured by a suitable cargo discharging program, but ballast may be needed to assist the process.
Where all holds are not discharged at the same time / simultaneously and some remain full it will usually be necessary to reduce the longitudinal stresses by taking full ballast in the double bottom and topside tanks surrounding the holds which are first discharged.
Ballasting – the 2ndt stage
As the remaining quantity of cargo diminishes, and once the double bottom tanks have been ballasted, the topside tanks must be filled.
They are at too great a height to be filled by gravitation so must be pumped full, taking the precautions already mentioned for the double bottom tanks.
The forepeak tanks will be filled as required during the first or second stage of ballasting.
Ballasting – the 3rdt stage
The third state of ballasting is the filling of the ballast holds of ships which have them.
Ships with no ballast holds are fully ballasted upon completion of second stage of the ballasting.
Most other ships will, on completion of the second stage, be fully ballasted to the light ballast condition. Filling the ballast hold or holds is usually optional and is undertaken to achieve the heavy ballast condition.
If this condition is chosen each ballast hold must be prepared for ballasting.
When the hold has been cleaned as circumstances require an blanks and cover plates must be removed from the ballast line to allow ballasting and de-ballasting and the bilge line must be blanked off to prevent the flooding of other compartments.
Some classes prohibit ships Masters from operating their ships with ballast holds filled between 20 – 90% of capacity, and holds if ballasted at sea should always be fully ballasted to avoid damage from sloshing.
At the commencement of the voyage the ballast holds should be filled to the coaming, process which is often achieved with the hatch covers still open for easy observation of the filling.
When filling has been stopped the hatch covers must be closed and well battened down.
The ballast hatch covers on some ships are provided with four (4) pressure vacuum valves which must be open when ballast carried.
Ballasting – the 4th stage
Certain large bulk carriers are equipped with some additional ballast holds which can be ballasted only in port to reduce the air draught.
The bulkheads of such holds are not strong enough to allow the holds to be fully ballasted, and they can only be filled to a stated level, perhaps half the capacity of the hold.
Soundings are often painted on the end bulkheads of such holds so that the water depth in the hold can be easily seen.
The ballasting reduces the vessel’s air draught, so that the grabs and bulldozers can clear the coaming when being lifted in and out of the working holds.
The ballast must be discharged from these holds before the vessel puts at sea.
Ballasting rates
Officers will quickly become familiar with the ballasting rates which can be achieved with one or with two ballast pumps or by gravitating.
Normal ballasting and de-ballasting rates, based upon installed pump capacity and ballast capacity, vary considerably from ship to ship, but a nominal (πλασματικό) time 10-15 hours is typical for the full de-ballasting of a large range of ship sizes.
Actual times are longer for operational reasons, though it is reported to be common for terminal operators and charter party clauses to require a vessel to de-ballast completely within 24 hours.
Some Cape-sized vessels have ballast pumps with pumping capacity of 2000 m3 / hour or more, allowing two pumps to discharge ballast at more than 4000 mt / hr when assisted by stripping pumps as is necessary for vessels with a ballast capacity of more than 70000 m3 de-ballasting time is speeded when ships are fitted for gravity discharge through separate lines from topside tanks and ballast holds.
BALLAST MANAGEMENT ON PASSAGE
Whilst on the ballast passage it is tempting to ignore the ballast tanks in the belief that nothing can go wrong with them, but this is not a prudent attitude to take.
Ballast tanks when full should continue to be sounded or ullaged at least once a day as a means of sounded detecting any leakage, and the soundings should be recorded as measurements not simply as “full”.
Leakage from ballast tanks into (1) holds will usually be detected during hold inspections, but leakage from ballast tanks into (2) void spaces or through the (3) ship’s side into the sea is not easily detected by any means other than the monitoring of soundings.
During the course of the voyage it is likely that a small part of the contents of ballast tanks will slop out of the tanks by way of the (4) air pipes, particularly if the ship moves in a seaway.
For this reason it is common practice to press up (ie., fill and overflow), all ballast tanks before arrival in the discharging port.
However, the pressing up of tank does not guarantee that it is full, and it is still available to sound all tanks, to apply the appropriate corrections to the soundings and to take account of the density if the exact weight of the contents required.
During the course of a ballast voyage there are several possible reasons for changing ballast.
(1) Is the requirement existing in a number of loading ports for ballast to be changed in mid ocean in accordance with the IMO Guidelines before arrival in the port because the marine life can be harmed by the release of ballast water from another region.
(2) When the ballast carried is fresh or almost fresh water and the ship is going to a loading port in a cold climate, where fresh or brackish ballast water is liable to freeze in the tanks and to block sounding and air pipes and ballast valves.
Before reaching freezing conditions fresh water must be exchanged for salt water.
(3) When a ballast hold has been filled at the start of the ballast voyage with dock water which is dirty or sediment laden and a clean hold is required in the loading port, for the carriage of grain for example, the hold should be emptied, cleaned and refilled at sea provided that the vessel is steady and it is safe to do so.
(4) Individual ballast tanks may be emptied or filled during a ballast passage, provided (a) sloshing, (b) stress and (c) stability considerations permit, for purposes of adjusting (a) draught, (b) trim and (c) list or tank (d) maintenance.
When changing ballast in the open ocean a ballast water management plan which ensures that the at sea stress limits are never exceeded and that adequate positive stability is maintained at all times must be used.
All ships are supplied with such a plan in compliance with the IMO Guidelines, the plan normally being approved on behalf of the flag state by the ships class.
Sequential and Flow-through ballast changing
Two methods of making a full ballast change are recognized.
They are the sequential method and the flow-through or continuous method.
In the Sequential method the ship’s ballast tanks are emptied and refilled one or two at a time in a sequence which has been planned to ensure that the ship is not overstressed or unfavorably trimmed at any time.
The benefits of this method are first that
(1) it removes most of the pollutants from the ballast tank,
(2) it requires less power,
(3) takes a shorter time than the flow – through method,
(4) it does not require the overflow of ballast water onto the vessel’s decks,
(5) it minimizes the risk of over pressurizing ballast tanks and,
(6) does not require the unshipping of the ballast tank manhole covers – ( on ships which were not designed and built for flow-through ballast change )
Disadvantages of the method are:
(1) it increases structural stresses for the duration, of the ballast change and
(2) it requires more supervision and management.
(3) It is important to minimize the sloshing of water in part-filled tanks and holds.
This requires that the changing of ballast is undertaken in the calmest weather available.
Since swell is even more difficult to predict than wind, and since a full change of ballast may take 36 – 48 hours of continuous work, which may be spread over (4) four normal working days, this will sometimes be a difficult requirement with which to comply.
(4) The ballast change program should be as simple as possible to execute, for the convenience of the ship’s personnel responsible for the process. The Flow-through method keeps the ballast tanks full by pumping water into each full tank and overflowing it continuously.
Its benefits are
(1) no increase to the structural stresses
(2) less supervision than the sequential method.
Disadvantages of the method are:
(1) On ships which were not designed and built for flow-through ballast change the ballast tank manhole covers must be unshipped to allow safe overflowing. Local structural damage to ballast tank ventilators or structures can occur if these precautions are ignored and tanks are over-pressurized.
(2) It is necessary to pump three times the tank capacity through the tank to achieve an acceptable standard of renewal of the tank’s contents. Trials have shown that the flow-through method does not achieve a complete change of ballast. Even after exchanging three tank volumes some 5% of the original water and up to 25% of plankton sediment is likely to be retained.
(3) This process takes longer and uses more fuel than the sequential method.
(4) Another disadvantage is that for the 3 – 4 days which the process requires the decks are awash with corrosive salt water, preventing maintenance work on deck and causing deterioration of deck coatings.
Despite these disadvantages the flow-through method is nowadays preferred by most operators because it avoids increased structural stresses.
A successful ballast change requires:
(1) deep water,
(2) as far as, possible from any land and,
(3) sufficient time to complete the task.
A sequential ballast change also required (4) calm weather but this is less important for a flow-through exchange.
When exchanging ballast the ballast tank sounding pipe caps should be removed to ensure that the ballast in the sounding pipes is exchanged. Neglect of this precaution could result in false samples later being obtained from the sounding pipes.
A ballast tank on the port side and the matching tank on the starboard side should be emptied or filled at the same time. No.2 starboard double bottom tank should not be pumped out at the same time as No.4 port double bottom tank, even if they have the same capacity. The ship will remain upright, but the uneven distribution of weight about the ship’s center line will risk twisting her hull and damaging her.
Restrictions on the discharge of ballast
Many ports and Administrations place restrictions on the discharge of ballast water in port or coastal waters
In some ports ballast water samples are taken by the local authority before de-ballasting is permitted. Before discharging ballast in port or coastal waters it is essential to find whether permission is required.
If written permission is required it must be obtained.
DE-BALLASTING
De-ballasting before berthing
A full de-ballasting plan, consistent with the cargo loading plan, complying with shear force and bending moment limits and taking account of any draught and air draught limits, must be prepared in advance, in compliance with the BLU Code.
When planning de-ballasting of their vessel, the Master and Chief mate will take account of the possible need for permission from the authorities to discharge ballast – an important matter – and of several significant operational considerations.
Important among these is the height of the loading arm – the height of the loader above water level, or the air draught in the berth.
If the ship discharges too much ballast before she commences loading she will rise too high in the water, and the loading arm will be unable to extend over the coaming to commence the pouring of the cargo into the hold.
The height of the loader, taken in conjunction with the ship’s dimensions and trim, and the anticipated height of tide, will decide the maximum amount of ballast that can be discharged before arrival.
In many instances the Master will decide to do no de-ballasting before berthing, to ensure that the vessel preserves a draught and trim which is safe for maneuvering in all circumstances.
Stress and stability must be considered, as in all cargo and ballast operations, and if the ship has reached a sheltered anchorage or layby berth where she is not exposed to swell.
Then it is permissible to use the in-port stress limits for the calculations.
A stern trim is essential for the taking of accurate soundings and for the efficient stripping of ballast tanks and must be maintained throughout the loading.
Other factors will also influence the Master’s decision as to how much ballast, if any, is to be discharged before berthing at the loading berth.
If the winds are strong and the berth is not well sheltered or well orientated he may require to maintain maximum draught for the berthing maneuver.
The port regulations may specify minimum draughts, trim, and propeller immersion.
On the other hand, a loading plan which calls for the loading of cargo in a ballast hold will require that the hold to be de-ballasted and prepared for loading quickly. When sheltered waters can be guaranteed and an adequate draught can be maintained may be possible to de-ballast the hold before berthing.
If other factors permit the discharge of ballast before berthing, it is always in the interests of a speedy loading that some ballast should be discharged.
Loading at most berths can be accomplished faster than the de-ballasting rate, so de-ballasting delays can be reduced or eliminated if the ship is partly de-ballasted before loading.
Since it is sensible to meet and resolve problems as soon as possible, the best tanks to de-ballast before berthing are those which are most likely to present difficulties for the ship.
These are the ballast holds, if they are to be loaded fairly early in the loading sequence, and then the double bottom tanks.
The topside and peak-tanks taper steeply to the tank bottom, which assists drainage, but the double bottom tanks have extensive flat bottoms in which a small sounding (say, 15cm) can represent a considerable tonnage of ballast.
These double bottom tanks are usually the most difficult to de-ballast and it is helpful if some or all can be pumped out before berthing when this can be done without risk to the ship Some of the factors mentioned above are reasons for the discharge of some ballast before berthing.
Others are reasons for retaining ballast until the ship is berthed.
The Master must seek to strike the correct balance in each loading port, having regard to the circumstances of the case.
De-ballasting sequence
The de-ballasting sequence has already been indicated and is dictated by the requirements to limit stresses, maintain a stern trim and an acceptable air draught.
(1) Ballast holds, where provided and full, will be discharged first.
(2) Double bottom tanks will be discharged next.
(3) Topside tanks will be discharged after double bottom tanks, except where stress considerations or ship design dictate that they are discharged at the same time as the adjacent double bottom tanks.
(4) Peak tanks will be discharged last.
Within this framework it will generally be the case that double bottom tanks and topside tanks will be discharged when the adjacent hold is being loaded.
Keeping the program
A variety of operational problems can cause the speed of de-ballasting to slow particularly with inexperienced operators and / or older ships.
When this happens there is a danger that the de-ballasting will get out of step with the loading.
This must not be allowed to happen, the de-ballasting must continue in step with the loading to ensure that the ship is not exposed to stresses which have not been calculated and that longitudinal stresses are not exceeded.
If a de-ballasting step has not been completed the loading must be stopped until the de-ballasting is again in step although, if the quantity of ballast remaining in the tank is small, it is acceptable to move to the next step in the program and to return to finish de-ballasting the uncompleted tank at a later stage.
It will always be easier to keep to the de-ballasting program when that program is a realistic one. When preparing the program it is best to assume the highest possible loading rate and a moderate de-ballasting rate.
This should ensure that there is adequate time for each de-ballasting step, even if minor problems are met
Stripping ballast
When No.5 port double bottom tank has been pumped put, a small, quantity of water (the stripping) will remain in the tank.
All but the smallest bulkers have a stripping pump or eductor (εξαγωγή) to remove the stripping.
Eductor rely upon Ventouri principle. They have no moving parts, and are operated by a powerful water jet which is passed through the educator, and which sucks the ballast water with it.
An eductor requires no filters and can be used to discharge water which is laden with sediment and mud.
Another advantage of the eductor is that once it has been started it requires very little attention and will come to no harm if left to run on an empty tank / tripping / cut off – switch off.
On ships with stripping eductors the stripping is similar to the main pumping but uses pumps of lower capacity.
Two (2) problems may be met with stripping pumps which do not occur with eductors.
The pumps are equipped with strainers to prevent damage to the pumps by mud and grit which could enter them.
If the ballast water is dirty the strainers may become blocked.
This slows the pumping rate and the strainers must be changed or cleaned.
When a stripping pump is being used it must be watched in order to adjust its settings as the pressure changes and the tank must be watched to detect when it is empty, since the pump will be harmed if it continues on an empty tank (stripping) for more than a few minutes.
In this case the stripping process requires more supervision than with eductor.
Gravitating ballast
Gravitating ballast is the process of letting ballast which is high in the ship run out into the sea under the influence of gravity, without the need to use the pump.
The same process can be used to fill tanks which are below the water line from the sea.
ACHIEVING GOOD DE-BALLASTING
Opening of air pipe cowls – (καλυπτρα)
Before de-ballasting can commence, the ballast tank air pipes must be open.
Aboard modern bulk carriers the air pipes usually designed to be always open, but in older vessels the air pipe cowls may need to be raised, or opened, to admit air into tank.
If this is forgotten the ballast pumps will begin to labor as they try to remove water from a sealed tank, or the structure of the tank may be damaged as a vacuum is created within it.
Keeping ship upright
If the ship develops a list when loading and de-ballasting the effect may be caused by
(1) bad distribution of cargo or
(2) it may be a fault with the de-ballasting, causing one of a pair of tanks to discharge more slowly than the other.
If the fault is in de-ballasting, the soundings will show that one tank is more full than the other and the fault must be found and corrected.
If the fault is the result of unbalanced loading of the cargo, the operator of the ship loader be instructed to distribute the cargo so as to keep the ship upright whilst loading.
An unplanned list will make de-ballasting more difficult and is likely to cause uneven discharge of ballast, thereby encouraging unbalanced loading of the cargo and exposing the ship’s hull to additional stress.
Optimum trim and list
It is almost impossible to pump dry all the ballast tanks of a bulk carrier, but when such a vessel is carrying a deadweight cargo or is restricted to a limiting draught at some point in the voyage she ought to be carrying only the absolute minimum of ballast water, since the more stripping she carries, the less cargo she can lift.
Achieving a good discharge of ballast requires a combination of competence, thoroughness and good organization, and also a clear understanding of the physical positions of the ballast suction and the sounding pipe within the tank.
The ship’s pumping plan can be useful in providing an understanding of the layout of the tank, but a conscientious officer will seek an early opportunity to enter some of the ballast tanks to view the pumping arrangement for himself.
It is normal for the ballast suctions in double bottom tanks to be situated in the inboard after corner of the tank.
To achieve the max discharge of ballast from No.2 double bottom starboard wing ballast tank the vessel should be trimmed by stern thus tipping any ballast which remains in the tank towards the after end where the suction is located..
Damage can be further improved if the vessel is listed (to port in this example) but this is not recommended.
Ships should not be listed for stripping purposes when close weight cargoes are being loaded because it is likely to lead to unbalanced distribution which could overstresses the ship.
When loading low density cargoes such as grain or coal which will eventually fill the compartment unbalanced cargo distribution is less likely to be a problem, but there is less need to minimize the stripping if the vessel is not loaded to her marks.
The sounding pipe should be situated close to the ballast suction so that an accurate measure of the depth of water at the suction can be quickly obtained.
The factors which govern the de-ballasting and stripping on most bulkers are the following:
• The ship should have a good stern trim through the de-ballasting.
• The ship should be kept upright through the main discharge and stripping of ballast.
• On most bulkers stripping can only be done when main pumping is finished or interrupted, because both processes use the same lines.
• Stripping can usefully continue so long as the tank sounding shows water.
• A list to port or starboard for the purpose of stripping is not recommended.
Good stripping of the double bottom tanks takes time and cannot be done effectively at the end of loading when the ship is normally trimmed even keel or nearly so
Every opportunity must be taken during interruptions to the main ballast pumping to continue with the discharge of the stripping, to reduce them to a low level before final stripping.
By the time that the final double bottom is stripped dry more water will probably have trickled through the tank floors and side girders to the suction in the first tank stripped.
Any double bottom tanks which are again showing a sounding should be stripped for a second time.
The topside and peak tanks taper down to every small area at the base of the tank where the suction is situated and normally present no problems in stripping.
( το double bottom μεγαλη επιφανεια .. “βαση”) Whilst loading and de-ballasting the ship should never be allowed to go by the head.
In this condition the discharge of ballast is more difficult, final ballast stripping cannot be pumped out and accurate soundings cannot be obtained.
Preventing ballast pumps from tripping
“On most occasions the pump trips because the water cannot flow to the suction fast enough for the speed at which the pump is operating” Bulk carrier ballast pumps are usually centrifugal pumps driven by electric motors, with
capacities appropriate to the size of ship, a Panamax vessel probably being provided with two (2) x 1000 tons / hour pumps, and a handy-sized vessel with two (2) 500 tons / hour pumps. When ballast pump is given a tank full of ballast water to pump out it will operate efficiently until the tank is nearly empty, provided that its performance is monitored and adjusted necessary.
To maximize the pump discharge the load (the pump amperes) should be monitored regularly – say every half hour – and maintained at the makers recommended value by adjusting the pump outlet valve.
When depth of water in a double bottom tank is reduced to 15 – 20 cm the flow of water to the suction will start to be interrupted, as the ballast water cannot flow fast enough across the base of the tank, though the drain holes in the floors and inter-costals. In consequence the pump will begin to pump a
(1) mixture of air and water.
Modern pumps are fitted with degassing devices which enable them to keep pumping when air is mixed with the water.
The degassing is effected by a vacuum pump which may serve one or several ballast pumps.
When air starts to pass through the ballast pump the vacuum pump is switched on automatically and removes it When the ballast pump is again pumping water the vacuum pump is switched off automatically.
The older vessels, where the ballast pumps are not fitted with degassing devices, the pumps will race and then trip (cut out or switch off) when they gas up.
If the pump frequently cuts out, the de-ballasting becomes very inefficient and there are several methods by which the problem of gassing up can e reduced.
Another cause for the ballast pump to trip (cut out or switch off) is the ballast suction in the tank becomes (2) blocked with mud – the sediment which has settled out of the ballast water in the tank.
Sediment in tanks can build up to substantial levels during a period of months or years.
Where sediment is suspected of being the cause of the stoppage of discharge the quickest way to clear sediment from around the suction is to flood back into the tank from another tank with a good head of water or from the sea.
The rush of water into the tank, will wash the sediment away from the suction but this of course is only temporary solution.
When sediment is causing problem in a tank, traces of mud will probably be seen on the sounding rod.
Leaking ballast line
A less common cause for difficulties in de-ballasting is a (3) hole in a ballast line.
So long as the hole in the ballast line is below the level of water in the tank, the system will perform normally, but once the water level has dropped below the hole, the system will start to take in air and the pump is liable to gas up and trip.
Some vessels have (4) expansion joints in the ballast lines, and if an expansion joint leaks the effect is the same as if the line has a hole in it.
Such a leak should be suspected (1) if difficulty is regularly experienced in pumping out the last 0,5 – 1,0 meters of ballast in tank, and (2) if the sounding in an after tank falls slowly whilst a forward tank is being discharged, or rises slowly whilst the forward tank is being filled.
The leak can quickly be found by inspecting the ballast line within the after tank whilst the forward tank is full and the tank valve is open. Under these conditions water will be squirting out through the leak.
Repairs to a leaking expansion joint can be effected by tighting or renewing the bolts, or by wrapping the joint temporarily in plastic sheeting.
An unusual explanation for difficulties should only be considered once the common explanations have been tested and discarded.
On most occasions the pump trips because the water cannot flow to the suction fast enough for the speed at which the pump is operating, or because mud is locking the suction.
Investigation of de-ballasting problems.
When difficulties with de-ballasting are experienced, time is often spent trying to deduce the cause of the problem.
It is sometimes impossible to make a physical inspection and then it is necessary to rely upon experiment and experience, both of which are useful tools.
Physical inspections are also valuable.
Example. Aboard a mini bulker which had not stripping pumps and where all de-ballasting was done with the main ballast pumps, the pumps would lose suction when the sounding was still 40cm – the height of the bottom of the lightening holes.
The engineers believed that the drainage holes in the floors and side girders were blocked with mud. The tank was opened up and the pump was started with the water height 40 cm, and true problem was immediately seen.
When the pump was pumping at full speed it emptied the small bay where the suction was located in 2 or 3 seconds, much faster than the water could flow into the bay through the drainage holes , which were not blocked.
The only way that the tank could be pumped dry was by reducing the pumping rate.
Precaution when de-ballasting
When ballast is discharged from top side tanks by way of dump valves – (the usefulness of the topside tanks is increased when they are fitted with dump valves) otherwise known as drop valves the process looks after itself.
This is convenient for ship’s personnel, but is thought to have resulted on numerous occasions in personnel forgetting to close the dump valves after all ballast has been discharged.
This can result in water re-entering the topside tanks, and flooding from there into the double bottom tanks in ships where topside and double bottom tanks are joined (integrated topside tanks).
At the worst this could result in serious difficulties or loss of the ship.
At least it could cause the carrying of unnecessary ballast, and reduction of the cargo lifted.
It is recommended that the closing of all dump valves immediately on completion of de-ballasting be checked and logged.
Whilst de-ballasting, the object of the Chief mate and his colleagues is to ensure that every ballast tank is empty or as close to empty as is humanly possible, by the time that loading is complete.
The prospect of achieving that objective will be greatly improved if each duty officer is competent (ικανος) thorough and methodical.
Communication with the loading foreman and with the ship’s pump man, if there is one, should be prompt and efficient.
Records of soundings obtained and of stages in the de-ballasting should be carefully and accurately recorded, so that they can easily be checked by colleagues.
When the de-ballasting of tank has been started the air pipe should be checked to verify that air is being sacked in, thus confirming that water is being pumped out.
Tanks which have been de-ballasted and recorded as empty should be rechecked at a later time, preferably when there is a good stern trim. (1) Water which was lying undetected at the fore end of the tank may have flowed to the after end, or (2) the tank may have been partly refilled by mistake. Often a draught surveyor will accept well presented records of this sort, so that the true ballast tonnage – measured accurately when there was a substantial stern trim is used instead of the less accurate tonnage obtained from soundings taken when the vessel is near even keel.
Typical ballast residues for well run ships in the laden condition, as measured by accurate surveys, are approximately mini bulkers 20 tons, handy 50 tons, panamax 100 tons, cape 200 tons.
MAINTENANCE OF BALLAST COMPARTMENTS – remove mud
Requirements for maintenance.
The maintenance required for ballast compartments includes
(1) the removal of sediment (mud),
(2) the removal of scale,
(3) the repair of leaks and,
(4) the renewal of coatings.
Anytime that mud-laden ballast is loaded into ballast tanks and held there for longer than a few hours, mud will be deposited on horizontal and near horizontal surfaces within the tank.
A ship which regularly discharges and takes ballast in mud-laden rivers such as the Maas, the Mississippi or the Chinese rivers will quickly accumulate heavy deposits of mud.
It is not unusual for such mud built up over a period to a depth of 10cm.
Mud accumulated within a ballast tank
(1) reduces the ship’s cargo lifting capacity,
(2) makes inspection of the tank for the damage more difficult ,
(3) makes the condition of coatings worst, and,
(4) makes draining of ballast from the tank a slower and more inefficient process.
These are all good reasons for removing mud from ballast tanks and for preventing the build-up of mud as far as possible.
Entering ballast tanks
Entering any enclosed space can be dangerous and the procedures recommended by the IMO and contained within the company’s SMS should be followed when entering a ballast tank.
Immediately after a tank has been de-ballasted it is reasonable to expect the air within the tank to be as healthy as the air on deck, since all the air in the tank will have been drawn from on deck whilst the tank was being de-ballasted but the Permit to Enter procedures for entry into enclosed spaces must always be followed.
Removal of mud by shovel and bucket
There are several methods of removing mud.
The most labor-intensive option is to remove mud by bucket and shovel.
This is only a practical option when plenty of time, as might be the situation in dry dock or in layup.
It may be worthwhile to remove mud from positions close to the ballast suction by shovel and bucket.
Hosing of topside and forepeak tanks.
In compartments in which it is comparatively easy to move about, such as forepeak and topside tanks, the mud can be hosed towards the ballast section and pumped out.
Since these tanks can normally be entered at any time except when water is being shipped on deck this work can be undertaken at almost any time that the tanks are empty and the discharge of ballast is permitted.
However the hosing of mud from topside and forepeak tanks remains a slow and labor intensive job because of the time required to wash all the mud to the vicinity of the suction, and the possibility of problems in keeping the pump running when the supply of water to the suction is small and uncertain.
Hosing of double bottom tanks
The limited height and confined space within the double bottom tanks of all but the largest ships make the hosing out of mud from these spaces, using a wash deck hose, not normally a practical proposition. However, the hosing out of the double bottom tanks of a Panamax can take place in dry dock a number of holes can be opened in the ship’s bottom so that the mud could be hosted into the dock bottom, thereby reducing the distance the mud had to be hosed through the tank’s and avoiding shipboard pumping problems.
Since double bottom tanks of handy sized and mini bulkers are normally entered from the holds it is only possible to enter these tanks when some at least of the holds are empty.
This will occur in port, at anchor, during ballast passages or whilst part cargoes are being carried.
The double bottom tanks of Panamax and Cape sized bulkers can normally be entered from the stool spaces.
On some ships this allows access to the double bottoms at any time that tanks are empty.
High-pressure hosing of double bottom tanks.
The hosing out of very cramped (πιασμένος) double bottom tank in a handy might be achieved using a portable high pressure washing machine, connected to a long lightweight hose no larger or heavier than the cable used with oxy acetylene welding equipment.
The work was illuminated by gastight torch lashed to the probe (καθετηρας) of the high pressure hose.
Washing was commenced at the after end of the tank, nearest to the suction, so that drain holes were cleared, permitting the liquid mud created by the washing to flow aft to the ballast suction.
Use of sediment remover
Sediment removers are liquid compounds which hold mud in suspension, preventing it from settling on the tank surfaces and permitting it to be discharged with the ballast in which it was loaded.
They remain efficient indefinitely.
Since any chemical additive is expensive it is important to obtain the best value for money spent.
To ensure that best value is obtained there are a number of practical considerations to take into account.
The most beneficial time to use a sediment remover is when the following conditions can be met.
• A double bottom ballast tank is heavily coated with mud.
• The passage can be made with the ballast tank 20% full / maximum agitation (ανακάτεμα)
• A swell is anticipated (αναμένεται), to make the ship pitch and roll.
• The ship can be brought to even keel.
• The tank can be emptied after a period of rough weather.
It is seldom / rare that a passage can be undertaken with a part-filled double bottom ballast tank, since longitudinal stresses or loaded draught often prevent it. Nevertheless opportunities do arise – for example, when the ship is carrying a full low density cargo (0.56 m3 / ton) such as grain, fertilizer, coke or coal, and is not loaded to her marks, or when she is loaded to winter marks, but passing through a summer or tropical zone.
In addition, stresses calculations may show that certain double bottom tanks can be left empty, or part empty, or part filled during a ballast voyage.
One reason for wanting the tank only 20% full is that this will permit the maximum agitation (ανακάτεμα) of the water over the deposited mud as the ship pitches and rolls, thereby taking the greatest quantity of mud into suspension.
In addition, the quantity of sediment remover to be used depends upon the quantity of ballast in the tank.
A tank which is only 20% full can be treated more efficiently, and much more cheaply, than a full tank. A tank which is half full ( 50% ) is more liable to suffer damage from sloshing.
The scouring (σαρώνω / τρίβω) effect of the water in the tank, induced by the ship’s motion, will be most effective when the water is surging in the same direction as the framing in the tank.
Where longitudinal framing is fitted, a pitching motion will be more effective in raising the sediment than will rolling.
For best results it is important that the ship be exactly even keel when under way after the tank has been filled to the required level.
This must be remembered that bulk carriers usually trim by head when underway and allowance should be made for this. If the ship is not even keel whilst the sediment removal is taking place, it will be found that one end of the tank will be cleaned whilst the other end which the water has hardly reached, remains thick with mud.
Every effort should be made to ensure that this is thoroughly mixed with the ballast water in the tank.
This is normally achieved by pouring a little by little into the tank by way of a spunding or air pipe adjacent to the ballast suction whilst the tank is filling. Inspection of the tank before and after treatment is strongly recommended, to assess the results achieved and to gather information on how the process can be improved.
Removal of scale from ballast tanks
If the coatings in ballast tanks are allowed to deteriorate either generally as a result of old age or locally as a consequence of mechanical damage loose (χαλαρό) scale will be deposited and will tend to accumulate around drainage holes and near the ballast suction.
Deterioration of tank coatings is aggravated – επιδεινώνεται – by mechanical damage.
The tanks which are most at risk depend upon the size and the trades in which she is engaged.
The topside tanks of mini bulkers generally suffer most from grab damage and contact damage whilst berthing, whilst Cape sized vessels sustain most of their damage in the tank top which tops the double bottoms.
The loose scale will tend to reduce or prevent the flow of water to the ballast suction and should be removed.
The only practical way of removing loose scale is with shovel and bucket to be passed to the deck when filled.
Provided that this process is done regularly the quantities to be removed will not be too great.
Patching – μπάλωμα – of leaks in ballast tanks – RAM NEK
It is quite common for small leaks to develop in the steel plating which forms the boundary between the holds and the top side tanks.
In smaller bulk carriers such leaks are often the result of berthing impact on the vessel’s port shoulder because such vessels normally berth port side – to.
They occur primarily in the vicinity of the forward hold and appear to result from the transmission of the impact load through the transverse internal members of the topside tank.
Whatever the cause, small leaks in topside tanks interfere with the efficient operation of the vessel.
If the leaking tank is filled a spray of water spurts in to the hold which will not be dry when presented for loading.
The leak may be sufficient to induce gradually a list into the vessel over a period of one or two days, which is inconvenient.
Alternatively, if the affected pair of topside tanks are left, empty, the forward draught may be unacceptably small, requiring the ship to slow down or causing her to pound. In larger vessels the longitudinal stresses may be excessive, making it unsafe to leave the tank un-ballasted.
The appropriate response to leaks of this sort is a professional repair undertaken by a qualified welder, but ……find hereunder a method of quick temporary repair for small cracks and pinhole leaks.
The method involves the use of patches of heated RAM NEK high adhesive plastic tape.
The equipment required is a scraper (ξύστρα), a blowtorch (καμινέτο), a length of Ram Nek high adhesive (κολλητική ταινία) plastic tape.
Τhe tank must be safe to enter (το ΡΑΜ ΝΕΚ τοποθετειται απο μεσα) the required tests for oxygen and hydrocarbons having been completed. Within the tank the surroundings of the leak are scraped clear of loose paint and scale and a Ram Nek patch, measuring about 15 x 15 cm, is centered over it, perhaps being held in position with the scrapper.
A second Ram Nek patch, similar in dimensions to the first, is placed conveniently to hand.
The patch which has been placed over the leak is heated to a molten, bubbling state with the blowtorch, and the second patch is then pressed firmly into place over the first.
Provided that this is done quickly the patch can be pressed into place before the heat passes through it, making it too hot to touch with comfort.
This forms a robust, flexible patch which seals the leak until a permanent repair can be made and which, unlike a poor run of weld, will not fracture, again. Proper full repairs should, of course, be undertaken as soon as possible.
MAINTENANCE OF COATINGS.
In most bulk carriers all the steelwork within the ballast tanks will have been coated when the ship was built and the coatings should be maintained in good condition through the life of the ship, to prevent excessive corrosion of the steel work forming the tanks.
It is now a new SOLAS requirement that the coatings in all dedicated seawater ballast tanks and double side skin spaces in bulk carriers built since 1 July 1998 are maintained in accordance with an approved ship maintenance system.
Ships’ personnel cannot hope to renew the coatings of ballast tanks without very specific support and assistance in the form of labor and materials from the ship operators since the job is big one.
However – coatings – within ballast tanks will deteriorate as a result of
(1) local mechanical damage caused by contacts with fenders, jetties, and tugs, and
(2) damage caused by cargo, grabs, and mechanical shovels.
Damage of this sort can be made good without great effort and any opportunity should be taken to (1) clean, (2) prime and (3) repaint any damaged areas, using the same (4) paint system as was used previously.
For an example of what can be achieved by a well organized ships crew, the case of a 16 –month – old Panamax on laden passage from East Coast of USA to China can be quoted.
The vessel had sustained approximately 15% breakdown of tank coatings, mainly below the double bottom tank top and lower hopper sides.
All mechanical damage in all double bottom and topside tanks was
(1) scraped clear of rust and
(2) flaking paint,
(3) wiped clear,
(4) coated with rust inhibitor,
(5) primed and
(6) painted with a recommended tank coating.
The entire operation took days and involved six men working eight hours per day a total 1.872 man / hours.
INSPECTION OF BALLAST TANKS
All of ship’s ballast tanks should be inspected regularly, say twice yearly or as required by the owners management system, by competent ship’s personnel, mindful of all the points which have been mentioned in this chapter.
Matters to be noted and recorded are the condition of internal fittings such as
(1) ballast suctions,
(2) sounding pipes,
(3) air pipes, and
(4) other pipe work passing through the tank,
quantities and locations of (5) scale and (6) sediment, condition of tank coatings and
(7) percentage break-down of coating, and details if any (8) structural damage observed.
The findings of ballast tank inspections should be recorded, and copies should be sent to the ship owners managers.
When ballast tank inspections are required as part of the Enhanced Survey Program they are best done in conjunction with hold cleaning, at times when crew members are available to open and close manhole doors.
The manhole recesses can be washed out at the same time.
Closing of ballast tanks
On completion of work in, or inspection of, ballast tanks care must be taken to ensure that they are properly closed with watertight seals to ensure that water cannot subsequently leak out of or into, the tank.
Correct sealing of manhole covers will be achieved by the use of a gasket which is in good condition and by ensuring the gasket and the steel surfaces of manhole and manhole lid are absolutely clean, smooth, and free of particles of scale or cargo.
Once closed and sealed, the water-tightness of the ballast tank should be tested by filling it and inspecting the closed manholes for signs of leakage.
