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Tightness of hatch covers
In sailing vessels the cargo hatches used to be small, as small as possible, in order to preserve the integrity of the hull. Decks were often awash during ocean passages and the smaller the opening, the smaller the risk of flooding the holds. In the ships of today the cargo is no longer carried on board on the backs of strong men, and the speedy loading and discharge methods require much larger deck openings. Very large openings actually, but manufacturers have been able to design and build strong enough steel covers and closing devices to cope with the demand – strong enough and tight enough at the time of testing and delivery of the new ship, but as the vessel ages, however beautifully, the hatch covers are prone to suffer from wear and tear, and problems of tightness arise.
When leakages occur, ship managers may blame weather conditions rather than possible lack of maintenance of hatch cover tightness systems. One will often find, however, that there is evidence of both: bad weather and poor condition of hatch cover tightness systems.
A carrier’s liability for cargo damage relating to sea water ingress via the hatch covers often depends on whether he can demonstrate that he exercised due diligence to make the vessel seaworthy before and at the beginning of the voyage in question. Whilst this is an onerous burden of proof to meet, a carrier who can show diligent procedures and practices with regard to inspection, testing and maintenance will be less likely to encounter problems from the outset, and will be better placed to show that due diligence has indeed been exercised. Hence, Gard Services sees good maintenance and proper testing of hatch covers as a clear loss prevention issue. In the following paragraphs we look at some major points related to the tightness of cargo hatch covers of dry cargo vessels.
LAW AND ORDER
In addition, the class societies have rules for the construction of hatch coamings and hatch covers, and these have to be complied with in order to obtain a Classification Certificate covering the vessel’s hull.1
Hatch covers are inspected annually, by a class surveyor, for the purposes of the two certificates mentioned above, so class societies have a major influence on the degree of hatch cover maintenance needed as far as certification is concerned. The responsibility for maintaining a vessel’s hatch covers and locking devices lies with the owner and operator, but class and flag state are responsible for certifying compliance with classification and load line rules. Also, SOLAS regulations for the issuance of an International Cargo Ship Safety Construction Certificate touch upon the subject, and require openings on deck to have the means to be watertight.
The purpose of the International Safety Management (ISM) Code is to provide standards for the safe management and operation of ships. Its requirements include the creation of procedures for maintenance of the vessel and for inspections and reporting. When checking the text of such procedures, Gard’s surveyors often see that not much attention is paid to the vessel’s hatch covers. The hatch covers are important to the safety of the vessel, crew and cargo, but are often addressed in very general terms only, or hardly mentioned in the vessel’s maintenance procedures. Members are strongly recommended to include instructions from hatch cover manufacturers in the vessel maintenance program, including records of maintenance, tests and repairs.
WEATHERTIGHT OR WATERTIGHT?
Surveys for the issuance and maintenance of the class and statutory certificates do not always seem to be sufficiently strict to ensure that the cargo carried is safe from the ingress of water through the hatch covers. A few tons of water into a cargo hold may not represent a risk to the safety of the ship, but even very small amounts of water may for instance damage a sensitive steel cargo. Class surveyors are not particularly trained to care for the cargo, with the result that cargo hatch covers approved during a load line inspection may fail during a P&I condition survey. Class Societies have had different rules concerning the frequency of hatch covers tests in the past. According to the International Association of Class Societies (IACS)’s publication Care and survey of hatch covers of dry cargo ships – Guidance to owners,2 a special survey “shall, as a minimum, consist of checking the effectiveness of sealing arrangement of all hatch covers by hose testing or equivalent as necessary”. But how does a surveyor know if a hose test is necessary? It is certainly necessary to test hatch covers much more often than every five years, for the safety of the cargo, and class societies should encourage surveyors to do that. A recommendation to carry out a hose test of the hatch covers “as necessary” gives surveyors some freedom to omit the test when faced with practical difficulties (e.g., loaded vessel when no ultrasonic testing apparatus is available) and to carry out only a visual inspection.
HATCH COVER PROBLEMS
Rubber gaskets – When leakages occur, the rubber gaskets of the hatch covers are usually hard, deeply and permanently compressed, chafed or loose, and may even have sections missing. Gaskets may be of solid rubber, or have a hollow or sponge core. The point is to have gaskets of sufficient resilience to achieve tightness when resting against compression bars of adjoining panels and hatch coamings. The design compression for common gasket types is usually in the range of 10-15 mm, depending on the thickness, and a manufacturers’ rule of thumb is to replace the packing when a permanent impression reaches half the design value. This may seem a hard rule to live by for many superintendents, but that is how to avoid leaking hatch covers in bad weather. Gard’s surveyors often see hatch cover gaskets with permanent depressions around one third of the thickness. Such gaskets should definitely be replaced. When replacing gaskets it is important that the retaining channels be in good condition and maintained against corrosion. It is recommended to use original gaskets and to seek the hatch cover manufacturer’s advice. There are a lot of low quality rubber gaskets on the market. Cheap rubber gaskets will rapidly become permanently compressed and the loss of resilience may cause lack of tightness after a few months of service. When buying original rubber gaskets, the best price is normally obtained directly from the hatch cover manufacturer. Ship managers often leave the job of replacing the gaskets to the crew, with a variety of results. It is certainly cheaper than doing the job in a shipyard, but in all fairness the crew can not always be expected to do as good a job. At least some support from a skilled worker or supervisor is recommended. Pre-shaped corner sections should be glued in first and the straight lengths of gasket thereafter, slightly oversized in length. Gard’s surveyors often see gaps at joints of gaskets, as lengths are cut too short. Short pieces of gasket should be avoided, as they often fall out later. When gaskets are chafed or even clipped lengthwise by the compression bar, they must be replaced without delay.
Retaining channels – The gasket retaining channels are among the weakest construction parts of the hatch covers. Their maintenance is cumbersome and often neglected, and retaining channels are often reduced by corrosion and are thus not able to provide sufficient support of the gaskets. When gaskets are replaced, one should always use the opportunity to clean the retaining channels for rust and have them thoroughly coated. Retaining channels may be so reduced by corrosion that as the rust flakes are removed the new packing will fit in too deeply. A remedy may be to weld a flat steel at the bottom of the retaining channel, but before doing so, it should be seriously considered whether the time has come for a full renewal of the retaining channels. Heat applied by welding to a weakened steel channel may cause deformations, making tightness difficult. Retaining channels may also have been damaged by contact of grabs, wires for pulling, etc. Damaged corners are often noted in hatch covers of the single pull type on older vessels. Such damage may be a result of panels slamming against each other or against the hatch coaming top, during closing operations.
Steel to steel contact – One thing is fundamental to a good result when changing gaskets, and that is to check the steel to steel contact between the hatch covers and the hatch coaming top. Good and original gaskets may be rapidly damaged by over- compression if this steel to steel contact is not achieved. Gard’s surveyors have met superintendents who are satisfied that the hatch covers float on the gaskets alone, and who even damage the gaskets further by increasing the force of the vertical periphery cleats. The full weight of the hatch covers is not supposed to be borne by the gaskets alone, only to the extent that the correct design compression of the gasket is achieved, and then limited by the hatch cover resting steel to steel on the coaming top. For older vessels the steel to steel contact will often be affected by wear and corrosion of the resting pads, or if these are not fitted, by reduction of the lower edge of the hatch covers and by wear and corrosion of the contact area on the hatch coaming top. The solution is to fit new resting pads of adjusted thickness to achieve a correct design pressure of the gaskets. If that is necessary, the ship manager should consider whether his crew is qualified for the job, or whether it is necessary to go to a repair yard with specialists or to ask the hatch cover manufacturer for support. Gard’s surveyors have seen gaskets being replaced by crew every six months due to the steel to steel contact not being correctly achieved.
Compression bars – The compression bars on hatch cover panels and on hatch coaming tops need to be straight and the top edge must be well rounded and have an even surface. On older vessels they often have heavy scales of corrosion, and when the scales fall off in sections, the compression bars are left with high and low areas where compression of the gaskets will be unequal. Such compression bars should be chipped and maintained by coating. On some ships the compression bar consists of a stainless steel bar, welded to the top of a supporting flat steel. Such compression bar is preferred, as the surface stays always smooth and even.
For ship types with expected large movements between hatch covers and coaming while at sea, manufacturers may have designed gaskets not landing on a compression bar, but directly on the flat top of the coaming. For such type it is important that the landing areas are kept free of rust and debris and well maintained against corrosion.
Guiding of hatch covers – When hatch cover panels are placed in position there are, depending on the type, various means to guide them correctly into place. Wear and distortion of items like stoppers, guide rails, track ways, flanged wheels, etc., may allow the panels excessive sideways and longitudinal play and result in the gaskets landing off centre on the compression bars. Worn bearings and bent wheel shafts will also cause a lack of proper guidance for the hatch covers, with the same result.
Whenever closing of hatch panels includes “attacks” by crew members armed with heavy crowbars and sledge hammers, something is wrong both with the guiding of the hatch covers and with the general maintenance policy on board. If cargo hatches can not easily be closed due to operational problems, there is also the risk of cargo damage by rain water during times of loading and discharge.
Means of securing – There are various ways to secure the hatch covers once they are in place, depending on the type. Modern covers may be self cleating or secured by hydraulically operated cleats or wedges, but the most common type on older vessels is the manual quick-acting cleat, having a cam at the upper end, which is forced onto a snug on the hatch cover panels. A rubber disc between two steel washers at the lower end of the cleat has enough elasticity for the cam to be placed on the snug by using a portable lever. Thus the hatch covers are restrained from lifting, but are allowed some movement on the hatch coaming in the transverse and longitudinal directions.
Gard’s surveyors see a lot of poorly maintained cleats in older vessels, and the common problems are that the cleat is seriously weakened by corrosion or that the rubber disc is hardened and without elasticity. Nuts and treads may be so corroded that adjustments can not be carried out. The snugs, which are welded to the hatch cover panels, may be heavily corroded or damaged, offering no strength to the assembly. A well known problem on ships of some age is advanced corrosion around the passage of the cleat through the hatch coaming top plate. When all such areas of the coaming top plate are weakened, one risks losing the covers under extreme weather conditions.
When hatch cover panels are not sufficiently linked together by hinges, they also need cleats across the cross joints of the panels. These may be in the shape of wedges or screw-cleats. Surveyors often find such wedges to be missing, not engaged or not providing any force on the adjoining panel due to wear or distortions. In the worst cases, all the wedges have been removed and are nicely stored within the forecastle. Some covers may have internal cleats on torsion bars, operated manually or automatically. These are meant to save the crew some work, but when old, such arrangements may not provide sufficient pressure on the cross joint gasket due to wear, and water tightness may possibly not be complete. Such securing arrangements are more difficult to inspect than external ones.
Hatch covers may have distortions making it difficult to achieve watertightness of the cross joints by the original cleating system. Some owners may then choose to install additional cleats, like screw-cleats, to solve the problem, but it is then important to check that the additional cleats closing one joint better do not open the next one. It is always recommended to consult the manufacturer.
High stowing type hatch covers, like the folding type, are sometimes left unsecured in raised position. That represents a danger to the crew and stevedores, and the hatch covers themselves may be seriously damaged if they fall. Securing devices are often seen to be damaged and not functional, or are simply not engaged by the crew. Such mechanical safety devices should always be well maintained and engaged.
Gutters and drainpipes – Gaskets in good condition and regular maintenance and tightness tests of the hatch covers are a must to avoid water ingress into the cargo holds, but in the event that some sea water may penetrate the gaskets during heavy weather, it is important that the water does not enter the cargo hold, but drains out again. Cross-over joints between panels will have gutters fitted underneath the packing to catch small amounts of water penetrating. These gutters will drain the water to the hatch coaming gutters, and it is important to check that they are not fractured or damaged at the ends, so water drains down the inside of the coamings instead. The hatch coaming gutters will drain the water aft to drain pipes. These gutters are not always well maintained and may have layers of corrosion. They should be kept clean and coated in order to ease the flow of water, and all remains of cargo should also be removed before closing down the hatch covers. Often the inner edge of the gutters, being the top of the vertical hatch coaming plate, may have been chafed by wires, hit by grabs or reduced by corrosion. Such damage will allow the water to overflow to the cargo hold instead of being drained to the drain pipes, and should be repaired and always kept in good condition.
The drain pipes aft are often of small diameter, and are easily clogged up. The pipes need to be fitted with a non-return device, in order to avoid that green sea on deck finds its way into the cargo hold through the drains. Non-return valves easily clog up, so that they must either be frequently opened up for cleaning, or it may be better to fit a three-foot canvas hose to the drain pipe instead. The canvas hose must be of a pliable type and be well secured by hose clamps of stainless steel.
Temporary repairs – In older vessels there are often signs of rather desperate efforts to keep hatch covers tight by external taping, and by applying foams and fillers at joints between panels, etc. Gard’s surveyors have seen rubber liners glued on top of hardened and worn out gaskets, and tape glued on top of compression bars to build them up to improve compression. On one vessel the crew had run out of tape and tried to improve the watertightness of the cargo hatches by installing a rope covered with cement around the perimeter of the covers. Surveyors have also seen vessels with hatch covers in poor condition being fitted with tarpaulins, pulled down at sides by ropes fixed to any pipe or fittings on deck. Such remedies are often requested by cargo owners or charterers to reduce the risk of water ingress. The master of the vessel may choose such means, if he has doubts about the tightness of the vessel’s gaskets and has a sensitive cargo to carry. All such means are, however, only considered to be temporary repairs, and should not be allowed to replace a fully functional original tightness system. The effects of such remedies are also very limited if heavy weather is encountered. The bonding of the tape is not stronger than allowed by the surface condition of the hatch covers and any firm tightness around cleats, etc., is difficult to achieve. Tape may lose elasticity in cold weather and be ripped off by seas on deck. Tarpaulins will help against sea spray, but will be ripped off if all edges are not firmly wedged in against the coaming. The money spent on expensive tape and fillers could be better used if spent on regular maintenance of the hatch covers and on well planned renewals of the original gaskets.
From a surveyor’s point of view, the hose test also has the disadvantage of not being fool-proof: the surveyor will not be able to observe how the spraying is performed on the outside, while he is inside the cargo hold looking for leakages. If a hard water jet is not aimed directly at the hatch cover joints, the test may be worthless. The condition of the hose test can be improved by fitting rags at the outlets from the cross over joints, to contain the water in the spaces between the panels. Another useful trick is to fit plastic bags to the drain pipes from the hatch coaming gutters. If water has ended up in the bags following the hose test, it has passed the gaskets and drained by the gutters to the outlets. Using this method, a surveyor reduces his chances of being fooled by the crew if he chooses to observe the testing from inside the hold.
The latest and most accurate way of testing hatch covers is by using an ultrasonic apparatus. A unit emitting ultrasound is placed inside the cargo hold and the operator registers “leakages” of ultrasound through the hatch covers using a handled detector. Normally one will first measure “open hatch” values and establish 10 per cent of such as the lower acceptable limit with hatch covers closed down. The ultrasonic test method is easily carried out by a hired operator, and the location and importance of leakages are clearly identified in his report. The method has the great advantage that it can also be used on loaded vessels, by placing the transmitter on top of the cargo. Another advantage is that it can be used in cold weather. Major steel exporters may require satisfactory ultrasonic tests carried out on all ships, to reduce risk of damage to cargo. A satisfactory ultrasonic test, correctly documented by the professional operator, will carry some weight if a dispute about hatch cover condition should arise. Nowadays ultrasonic test equipment is available in all major ports, operated either by specialist firms, or by traditional marine surveyors. The only disadvantage with this method is probably that it is not always much liked by all ship managers, as “too many leakages” are detected. There is some truth in that, and the operator and his principals need to exercise some care in judging the results, as even quite small, insignificant “leaks” may be detected. Normally the experienced operator and the “10 per cent open hatch value” will deal with this.
Gard News is published quarterly by Gard Services AS, Arendal, Norway.