Ballast Water Management

The Convention requires that vessel should conduct ballast water exchange:

•At least 200 nm from the nearest land and in water at least 200 m in depth; if this is not possible

•As far from the nearest land as possible, and in all cases at least 50 nm from the nearest land and in water at least 200m in depth.

•In sea areas designated by the Port State.

All local and / or national regulation should be taken into consideration as they may specify other depths and distances from land.

A ship will not be required to deviate from its intended voyage or delay the voyage in order to comply with any particular requirement as stated above.

In addition if the master decides reasonably that an exchange would threaten the safety or stability of the ship, its crew or its passenger because of adverse weather, ship design or stress, equipment failure, or any other extraordinary condition he is not required to comply with above paragraphs.

Purpose

Ballast water is essential to control trim, list, draft, stability, or stresses of the ship.

However, ballast water may contain aquatic organisms or pathogens, which, if introduced into the sea including estuaries, or into fresh water courses, may create hazards to the environment, human health, property or resources, impair biological diversity or interfere with other legitimate uses of such area.

The selected methods of ballast water management take into account the need to ensure that ballast water management practices used to comply with this convention do not cause greater harm than they present to the environment, human health, property or resources of any state and the safety of the ship.

It is estimated that at least 7,000 different species are being carried in ship’s ballast tanks around the world.

Studies carried out in several countries indicated that many species of bacteria, plants, and the animal can survive in a viable form in the ballast and sediment carried in ships, even after journeys of several months’ duration. Subsequent discharge of ballast water or sediment into the waters of port states may result in the establishment of harmful aquatic organisms and pathogens which may pose threats to indigenous human, animal and plant life, and the marine environment. When all factors are favourable, an introduced species may establish a reproductive population in the host environment, it may even become invasive, out-competing native species and multiplying into pest proportions. Although other media have been identified as being responsible for transferring organisms between geographically separated water bodies, ballast water discharge from ship appears to have been among the most prominent.

As a result IMO has developed guidelines for the development and implementation of a ballast water management on board ship aiming to assist governments, appropriate authorities, ships masters, operators, owners and port authorities, as well as other interested parties, in the preventing, minimizing and ultimately eliminating the risk of introducing harmful aquatic organisms and pathogens from ship’s ballast water and associated sediment while protecting ship’s safety.

Good record keeping is critical to the success of a sound ballast water management program.

The appointed ballast water management officer is responsible for ensuring the maintenance of appropriate records and that ballast water management and / or treatment procedures are followed and recorded.

The function of the ballast water management plan is to assist in complying with IMO guidelines and quarantine measures intend to minimise the risk of transplanting harmful aquatic organisms and pathogens from ships’ ballast water and associated sediments while maintaining ship safety.

Operation of the Ballast Water Management System

Ballast water exchange in open water and the need to for exchange should be carefully examined and prepared in advance, in a similar manner to the preparation of a cargo plan for a loaded voyage, and with the same degree of thoroughness.

There are three methods of Ballast Water exchange which have been evaluated and accepted by the Organization.

The three methods are the sequential methods, the flow-through method and dilution method. The flow-through method and the dilution method are considered as “pump through” methods.

Sequential Method

The “Sequential Method” is a process by which a ballast tank intended for the carriage of ballast water is first emptied and then refilled with replacement ballast water to achieve at least a 95% percent volumetric exchange. In each tank, all of the ballast water should be discharged until suction of the pump is lost, and stripping pumps or eductors should be used if possible. This is to avoid a possible situation, where organisms are left in the bottom part of the tank, the tank is refilled with new water which may allow re-emergence of organisms.

The sequential method requires careful planning and monitoring by the ship’s staff to mitigate risks to the ship in respect of:

• longitudinal strength
• dynamic loads
• excessive trim
• bottom forward slamming
• propeller emergence
• intact stability; and
• bridge visibility

At the same time ship stuff should be taking account ship’s position in relation to the land, navigational hazards, shipping density, current and forecast weather, machinery performance and degree of crew fatigue, before proceeding for exchange. If any factors are considered unfavourable the ballast exchange should be suspended or halted.

Flow through Method

Flow-through Method is a process by which replacement ballast water pumped into a Ballast tank intended for the carriage of ballast water, allowing water to flow through overflow or other arrangements to achieve at least 95% percent volumetric exchange of ballast water.

Pumping through three times the volume of each ballast water tank usually shall be considered to meet the standard described above. Pumping through less than three-time volume may be accepted provided the ship can demonstrate that at least 95% percent volumetric exchange is met.

The flow-through method has the advantage that it can be used in weather conditions which would be marginal for the use of the sequential method since there is little change to the condition of the ship and is relatively easy to follow by ship stuff. However, the Flow-through method introduces certain other risks and problems which may be considered before using this procedure.

The disadvantage is that not all tank are designed with a head to the top of the overflow. Moreover, some tank configurations can be difficult to flush through effectively, in particular, cellular double bottom spaces and peak tanks. There is a danger of over pressurisation of tanks and there can be an accumulation of water on deck, which in sub-zero temperature conditions make the method impractical and dangerous for the crew.

In addition pumps and piping will experience an increase in workload. Where peak tanks are partially filled, the flow through method should be avoided unless any inadvertent exceeding of the design partially filling levels will not result in hull girder bending moments and shear forces exceeding the permissible values.

Dilution Method

Dilution method is a process by which replacement ballast water is filled through the top of the ballast tank intended for the carriage of ballast water with simultaneous discharge from bottom at same flow rate and maintaining a constant level in the tank throughout the ballast exchange operation to achieve at least 95% percent volumetric exchange of ballast water.

Pumping through three times the volume of each ballast water tank usually shall be considered to meet the standard described above. Pumping through less than three times the volume may be accepted

Treatment Systems

The BWMS includes Ballast Water Treatment Equipment, all associated Control Equipment and Sampling Facilities.

Ballast Water Treatment Equipment is equipment which mechanically, physically, chemically, or biologically processes, either singularly or in combination, to remove, render harmless, or avoid the uptake or discharge Harmful Aquatic Organisms and Pathogens within Ballast Water and Sediments.Ballast

 Water Treatment Equipment may be operated at the uptake or discharge of ballast water, during the voyage, or at a combination of these events. Ballast water management systems installed on board should ensure in addition to compliance with the convention requirements, to be type approved and relevant certificates to be readily available on board. When such a system is fitted on board it should be operated in accordance with the system design criteria and manufactures operational and maintenance instructions as contained in the relevant booklets. When the system encounter failure and / or malfunctions, these are to be recorded in the ballast record book.

Ballast Water Sampling Points

Compliance monitoring may be undertaken by authorized officers (e.g. Port State Control), by taking and analyzing ballast water and sediment samples from the ship.

There is unlikely to be any need for crew members to take sample except at the express request, and under the supervision, of an authorized officer. Authorized officers must be advised of all safety procedure to be observed when entering enclosed spaces.

Where ballast water or Sediment sampling for compliance or effectiveness monitoring is being undertaken, the time required to analyse the samples shall not be used as a basis for unduly delaying the operation movement or departure of the ship. When sampling for research or compliance monitoring, authorized officer (e.g. Port State Control) should give as much notice to the master as possible that sampling will occur, to assist the Master in planning staffing and operation resource to assist. The Master has a general obligation to provide reasonable assistance for the above monitoring and information pertaining to ballast arrangements and sampling points.

Port State Authorities should indicate to the master or responsible officer the purpose for which the sample is taken (i.e. monitoring, research or enforcement). Port State Authorities may sample or require the sample to analyse ballast water and sediment, before permitting a ship to discharge its ballast water.

Precautionary Practices

a. Minimizing uptake of harmful aquatic organisms, pathogens and sediments.

When loading ballast, every effort should be made to avoid the uptake of potentially harmful aquatic organisms, pathogens and sediment that may contain such organisms.

The uptake of ballast water should be minimized or, where practicable, avoid areas and situations such as:

• area identified by the Port State in connection with advice relating to :
• areas with outbreaks, infestations or known populations of harmful organisms and pathogens.
• areas with current phytoplankton bloom (algal blooms, such as red tides):
• nearby sewage outfalls :
• nearby dredging operations :
• when a tidal stream is known to be the more turbid : and
• areas where tidal flushing is known to be poor.
• In darkness when bottom-dwelling organisms may rise up in the water column ;
• in every shallow water ; or
• where propellers may stir up sediments.
• If it is necessary to take on and discharge ballast water in the same port to facilitate safe cargo operations, care should be taken to avoid unnecessary discharge of ballast water that has been taken up in another port.
• Minimize departure and arrive ballast quantities but always within the Constraints of safe navigation.

b. Non-release or minimal release of ballast water

In the case where ballast exchange or other treatment options are not possible, ballast water may be retained in tanks or holds, should this not be possible, the ship should only discharge the minimum essential amount of ballast water in accordance with Port State’s contingency strategies.

c.  Discharge to reception facilities

If reception facilities for ballast water and / or sediment are provided by a Port State, they should, where appropriate, be utilized.

Procedures for disposal of Sediment

Where practicable routine cleaning of the ballast tank to remove sediments, should be carried out in mid-ocean or under a controlled arrangement in port or dry dock.

When sediment has accumulated consideration should be given to flushing tank bottoms and other surfaces when in suitable areas, i.e. outside 200 nautical miles from land and in a water depth of over 200 meters. The volume of sediment in a ballast tank should be monitored on a regular basis.

Sediment in ballast tanks should be removed on a timely basis and as found necessary always taking into account safety and operational considerations addressed in this manual. The frequency and timing of removal will also depend on factors such as Sediment build up, ship’s trading pattern, availability of reception facilities, the workload of the ship personnel and safety consideration. Removal of the sediment from ballast tank should preferably be undertaken under controlled conditions in port, at a repair facility or in dry dock. The removed sediment should be preferably be disposed of in a sediment reception facility if available reasonable and practicable. Flushing by using water movement within a tank to bring sediment into suspension will only remove a part of the mud, depending on the configuration of an individual tank and its piping arrangement.

Removal may be more appropriate on a routine basis during scheduled dry dockings. However, flushing at sea may be a useful tool on some occasions such as when a ship changes its trading area.

When sediment is removed from the ship’s ballast tanks and is to be disposed of by that ship at sea such disposal should only take place in an area outside 200 nautical miles from land and in a water depth of over 200 meters. When ballast tanks have been cleaned to remove sediment, a record should be entered into the ballast water handling log.

Duties of Ballast Water Management Officer

Duties of the appointed officer in charge of ballast water management:

• Ensure that ballast water management and / or treatment procedures are follow and recorded.
• Where ballast exchange is required, follow the applicable Ballast Exchange Sequence(BES), or develop a new BES on the basis of ship’s assessment criteria, the condition of hull, equipment and weather forecast.
• Ensure adequate and enough personnel and equipment are available for the execution of the BES and / or treatment.
• Ensure that the steps / sequences of the BES are followed in the prepared order.
• Inform the shore management on commencement / interruption / completion of ballast water exchange, using the Notification Form.
• Maintain the Ballast Water Record Book and all other relevant / applicable documentation.
• Prepare the appropriate national or port Ballast Water Declaration Form prior to arrival at destination.
• Assist the port state control or quarantine officers for any sampling that may need to be undertaken.
• Undertake familiarization and training of crew in ballast water management requirements and applicable shipboard systems and procedures.
• Other duties specified by the Company.

The Master must ensure that the ballast Water Management Plan is clearly understood by the appointed officer and by any other ship stuff that may be involved. The duty officer must keep the Master advised on the progress of the plan from time to time. Should there be any doubt, or if the management plan does not keep to the schedule, Master shall be advised accordingly.

Safety Procedures for the Ship and the Crew

Exchange at Sea

The exchange of ballast water in open sea has to be distinguished from ballast operation carried out in ports or sheltered waters.

Ballast water operation at sea has the potential to be more hazardous than ballast water operations carried out in port.

A decision should be made at the completion of each sequence, taking account factors such as the ship’s position, weather forecast, machinery performance, stability, strength, the degree of crew fatigue, before proceeding to the next sequence.

If any factors are considered unfavourable, the ballast exchange a decision should be made if exchange operations should be suspended until conditions become favourable or halted. Contingency procedures for situations which may affect ballast water exchange at sea, including deteriorating weather conditions, pump failure and loss of power ; time to complete the ballast exchange for each tank or an appropriate sequence thereof ; continual monitoring of the ballast water operation ; monitoring should include pumps, level in tanks, line and pump pressures, stability and stresses.

Safety considerations

Ballast water exchange has a number of safety considerations these include but is limited to:

• avoidance of over and under-pressurization of ballast tanks ;
• sloshing loads in tanks that may be slack at any one time ;
• maintain adequate intact stability in accordance with an approved trim and stability booklet taking into account the free surface effects on stability;
• permissible seagoing strength limits of shear forces and bending moments in accordance with an approved loading manual;
• torsional forces
• forward and aft drafts and trim, with particular reference to bridge visibility
• propeller immersion;
• minimum forward draft
• wave-induced huh vibrations when performing ballast water exchange;
• watertight closures(e.g. manholes) which may have to be opened during ballast exchange must be re-secured ; crew safety is paramount during this operation. Provision of discharging pipe head on the manhole cover is suggested.
• maximum pumping / flow rates – to ensure the tank is not subjected to a pressure greater than that for which it has been designed.
• internal transfers of ballast;
• admissible weather conditions ;
• weather routeing in area reasonably affected by cyclones, typhoons, hurricanes, or heavy icing conditions;

Sequential Method

• Hull girder damage due to insufficient longitudinal strength.
• Adverse effects on ship’s stability due to free surface effects resulting in a reduction of ship’s GM while emptying ballast water tanks or holds originally in a filled or partially filled condition in order to achieve exchange.
• Structural damage to ship bottom forward caused by insufficient forward draft,
• Impermanent of manoeuvrability and / or ability to make headway; caused by insufficient after the draft, as a result of emptying after ballast water tanks or holds originally in a filled condition or filling partially filled forward water ballast tanks in order to achieve exchange.
• Reduction of bridge visibility forward caused by insufficient forward draft, as a result of emptying forward ballast water tanks or holds originally in a filled condition or filling partially filled aft water ballast tanks in order to achieve exchange.
• Structural damage to topside and hopper side tanks caused by inertia loading, as a result of a full of a full ballast hold with empty adjacent wing tanks.
• Structural damage to partially filled ballast water tanks or holds caused by sloshing as a result of resonance with ship motion.

Flow through Method

• Accumulation of water on decks which can cause a safety hazard to crew working on deck.  (Effect on stability may be negligible)
• In order to avoid over and under-pressure of the ballast tanks, the Master should ensure that the Air Vents of the tanks are at all times properly maintained and in good operating condition.
• Where the flow through method is to be undertaken and there are slack ballast tanks in the certain ballast condition, the appointed Ballast Water Management Officer should first ensure that accidental filling of the partially filled tanks does not result in hull girder bending moments and shear force exceeding the permissible values.
• In order to avoid over and under-pressure of the ballast tanks, the Master should ensure that the manholes of the specific ballast tanks are opened prior to the commencement of the flow through method of the ballast exchange for the top side tanks, as mentioned in the Ballast Exchange Sequences.

Care should be taken that the manholes are closed after termination of the flow through of subject tanks.

Conditions under which ballast water exchange at sea should not be undertaken

This circumstance may result from critical situations of an exception nature or force due to the stress of weather, known equipment failures or defects, or any other circumstances in which human life or safety of the ship is threatened.

Ballast water exchange at sea should be avoided in freezing weather conditions. However, when it is deemed absolutely necessary, particular attention should be paid to the hazard associated with the freezing of overboard discharge arrangement air pipes, ballast system valves together with their means of control, and the built up of ice on deck.

Consideration must always be given to personnel safety, including precautions which may be required when personnel are required to work on deck at night, in heavy weather, when ballast water overflows the deck, and in freezing conditions. These concerns may be related to the risks to the personnel of falling and injury, due to the slippery wet surface of the deck plate, when water is overflowing on deck, and to the direct contact with the ballast water, in terms of occupational health and safety.

Ballast exchange at sea should not be carried out or, if under progress, interrupted under the following conditions.

• When wind strength exceeds Beaufort 4 and sea state exceeds moderate.
• When there is an indication that weather and sea conditions will deteriorate prior to completing ballast exchange program or a step thereof, adequate time margin should always be included in such cases.
• When sailing in an area which is known to be seasonally affected by cyclones, typhoons, hurricanes, or heavy icing condition.
• When any part of the power or ballast system (generators, pumps, level indicators, etc.) is inoperative or gives a sign of under-performance.
• When due to other important duties on board, not enough trained officer and crew are available to perform the ballast exchange safety.
• When abnormal vibrations of the vessel’s huff or equipment are experienced while progressing on a certain step of the ballast exchange.

Precautionary advice to Master when undertaking Ballast Water exchange operation

Master should take all necessary precautions when undertaking ballast water exchange sequences that involve periods when the criteria for propeller immersion, minimum forward draft and bridge visibility cannot be met.

(1) During ballast water exchange sequences there may be times when, for a transitory period, one or more of the following criteria cannot be fully met or are found to be difficult to maintain:

• bridge visibility standards (SOLAS V / 22)
• propeller immersion; and
• minimum draft forward
• emergency fire pump suction ;

(2) In planning a Ballast Water Exchange operation that includes sequence which involves periods when the criteria for propeller immersion, minimum draft and or trim the following should be taken into consideration:

• the duration and time(s) during the operation that any of criteria will not be met;
• the effect(s) on the navigational and manoeuvring capabilities of the ship ; and
• the time to complete the operation.

(3) A decision to proceed with the operation should only be taken when it is anticipated that;

• the ship will be in open water.
• the traffic density will be low ;
• an enhanced navigational watch will be maintained including if necessary an additional look out forward with adequate communication with the navigation bridge ;
• the manoeuvrability of the vessel will not be unduly impaired by the draft and trim and or propeller immersion during the transitory period; and
• the general weather and sea state conditions will be suitable and unlikely to deteriorate.

Factors affecting choice of ballast water treatment systems

From the moment the Ballast Water Management Convention was adopted in 2004, shipowners have been well aware that at some point they would need to fit a ballast treatment system to new and existing vessels unless the ship in question was to be scrapped before the implementation date.

Some others would have been aware of the possibility that an exemption might be possible under the Same Risk Area rules but will have been frustrated to see little official action in this regard. Because of the different regulatory regimes, owners that trade to the US will already have been obliged to fit ballast treatment systems but the number of such ships represents only around 10% of the world fleet.

Even taking into account the unexpected extension allowed by the IMO in 2017, it is now time for their owners to consider choosing a system and take account of the many factors that will influence the final choice.

With such a wide choice of systems and technologies there is almost certainly a system available that could be fitted to any vessel affected under the IMO Convention or the US regulations.

However, not every system is suitable for every ship and owners must bear in mind several factors when looking for a system. Which factors are most important will vary depending upon the individual circumstances of both the owner and the ship. For some owners, mere compliance with the rules will be sufficient regardless of whether or not the system chosen is best matched to his particular needs. For others, a much more considered approach will be to look at the whole life cost of the system and its reliability.

Most systems will be sold as complete packages but it should be recognized that many of the individual components will almost certainly be sourced from sub-suppliers. There should not be much difficulty in replacing simple components such as piping unless the pipe profile is unusual and designed to be a key element of the disinfection process.

UV lamps, power supplies and rectifiers, automation control panels and other parts may however be more difficult to replace and although it may not be top of the list of concerns, potential purchasers of systems may be wise to undertake some investigation into the background of suppliers and their service and supply network. This is especially important for systems with US type approval as each component is considered as being part of the type approval. If spare parts become unavailable, the approval status may be in jeopardy.

Capex and Opex

As with any new equipment cost will feature high on the list with upfront capital expenditure likely to be prominent for most operators. Very few makers quote list prices so there is a large degree of shopping around to be done. Most attempts to establish a typical system price will fail  because of the wide range of sizes needed by different ship types and because of the different technologies used. The cost range has been said to be between $500,000 and $5M but with so many players in the market, competition may well reduce those figures although installation costs could be inflated for supply and demand reasons especially in the early retrofit era.

Fleet operators with many vessels could well be able to negotiate deals for multi-ship  installations but factors such as ship type and ballast capacities may mean that a single manufacturer does not have suitable systems for all vessels in a fleet. In the case of new buildings, prices will tend to be relatively small compared to the final ship price especially if the ship has been designed with installation of a particular system in mind.

UV Ballast Water System

In a retrofit situation, the capital cost may be similar but installation costs higher due to modifications needed to other systems in order to create space for the treatment system.

Operating costs also have to be considered. Regardless of the method of disinfectant all systems will require pumps just as they always have. In new builds the pumps will be matched to the system requirements from the outset. On existing ships it may be possible to reuse the original ballast pumps to save some of the cost but if the pumps cannot maintain the flow rate demanded by the new system or are deficient in some other way they may have to be replaced.

The opportunity to explore more efficient alternatives to old pumps that will save running costs should not be overlooked Power costs are likely to be highest on systems that employ electrolysis or related technologies.

Considering that the systems could well be operating alongside when the ship is relying on harbour generators the power demand may need to be given a lot of thought. Across the whole  range of systems, the power required to treat a ballast flow of 1,000m3/h varies from just a few kW to over 200kW. Most fall within a band from 50kW to 150kW. For UV systems, the cost of replacement lamps may be a small additional outlay over the life of the system and it is the cost of power for the lamps that is likely to be the biggest running cost.

The costs of consumables for systems that use chemicals for treatment and neutralization on discharge are likely to be higher than any power requirements those systems may have. For those that make use of electrochemical or similar methods, the anodes and cathodes will need replacement at some point. In systems that include a filtration step, replacement filter elements also have to be factored in to cost calculations. In all systems service and maintenance time is also a factor to consider.

Costs will be dependent on the number of ballasting and de-ballasting operations that are performed. Ships which make small numbers of long voyages will be using the system less than those which run on numerous short voyages.

The issue of cost will be tied in with the value of the vessel in the S&P market. Few potential buyers will want to pay the full asking price for a ship that has no ballast treatment system unless they intend to operate it exclusively in a SRA or if there are shore-based reception and treatment facilities available.

Hidden hazards

Although ballast systems would not ordinarily appear to present many risks, several of the various treatments available can potentially cause problems if the system malfunctions.

Systems relying on electrolysis or Electrochlorination will produce hydrogen and chlorine gases as part of the treatment process.

Although the systems are designed to safely deal with these gases some very unusual circumstances might arise under which levels might become elevated. 

The type approval

process should be robust enough to identify such risks at the design stage and make provision to prevent a problem arising under normal circumstances. This is now a requirement under the new G8 type-approval guideline.

Even so it might be a prudent measure for gas detection devices to be made available for monitoring machinery spaces and for crew obliged to enter ballast tanks or void spaces which might be affected by leaks from the ballast tank. Some ship types such as tankers may present problems of their own but several manufacturers have recognized this and are producing explosion-proof versions of their systems. An owner requiring an explosion-proof system will find that there are sufficient models available to be able to select from a number of different technologies.

Area of operation

There are two factors to be considered here; the need for a system to be installed and the water qualities likely to be encountered. There is little doubt that eventually all ships will be subject to ballast water treatment regulations but presently the only major area with a  regulation in force is the US. Under the US rules both US-flagged ships and foreign vessels  trading in US waters need to be fitted with a ballast treatment system unless they come under  one of the few exemptions allowed.

Now that the US has type-approved a number of systems with more expected soon, the AMS rule that permitted some IMO type-approved systems to be installed will eventually be discontinued. New installations of systems under AMS are still considered by USCG as an acceptable method of complying with the regulations – but only if it has been determined that a USCG type-approved system is not appropriate for the particular vessel.

From a practical point of view the salinity of the water taken for ballast and its temperature may cause problems for some systems particularly those making use of electrolysis or certain chemicals.

Ships trading worldwide may face different problems at any number of ports so no system may be better than any other, but for ships with a more confined operational range it is  sensible to ensure that the system is capable of functioning correctly under the environmental conditions likely to be encountered.

Ships that make very short voyages may find that a UV system which treats ballast during the ballasting operation is a better alternative than one which requires a long tank holding time for chemical treatment to be effective. The question of organism regrowth in vessels on long voyages is one that also needs to be considered.

Installation program

Each year of delay in the ratification process of the IMO Convention has added thousands of vessels to the 60,000 or so that would have been obliged to retrofit a treatment system under the initially intended program. However, the possibility of regional exemptions and  containerized and shore-based treatment system does mean that an as yet unknown number of ships will be removed from the fleet needing to be retrofitted.

Owners will need to ensure that once the need arises they can arrange to have a system fitted within the time span allocated to vessels. Some system makers claim that their products can be fitted in very short time spans but a prudent owner may do well to consider planning an installation schedule sooner rather than later because of the pressure on dry-dock or yard slots.

Even those system makers who claim a quick installation is possible are often talking about a period of around 10 to 14 days. Such a time span is in excess of the usual time needed for a  periodic dry docking therefore it may not be possible to install a system during the time when a vessel will be out of service.

Some manufacturers have said that initial work can be done by riding squads. However all this  may well be true the men who would make up such riding squads are most likely to be needed to be working on ships in dry dock.

Size and space matter

Not all systems are suited to every vessel type because of limitations on rate of treatment.

Large tankers and bulk carriers commonly take ballast at rates in excess of 6,000m3 per hour and there are a limited number of approved systems that can meet this requirement.

Installing multiple systems may be an answer and would provide some degree of redundancy in the event of system failure. In retrofit situations the issue of pressure drop also needs consideration.

Space on board ships is normally at a premium and while it should be relatively simple to design for the installation of ballast treatment systems on new builds, there could be real  problems in retrofit situations. Some manufacturers have been very innovative is limiting the space requirements of their systems and allowing for a variety of configurations of component parts, in some instances it is even possible to house the system on deck or at any convenient location in the ship. 

Consequently, the footprints of systems with similar capacities can vary enormously and for older and smaller vessels can preclude some systems. Explosion proof  versions of some systems have been developed especially for extra flexibility of location on tankers and gas carriers.

When calculating space for the system itself thought may need to be given both to access for maintenance and storage space for any chemicals used in the treatment process. Some of the containerized versions are so designed that the skid-mounted components need to be pulled from the container for servicing.

Enjoy, be Safe...

Source [www.cultofsea.com] & Carlos Agulhas (revision) @ Sokhna Port - Egypt