Hatch covers are gateways to the major and core volume of a ship. Its dimensions depend on: type of ship; the kind of cargo that has to be handled; the intended gear that would be used; etc. Thus, on a bulk carrier the length or breadth may be 45 to 60% of length / breadth respectively of the hold in question. In case of container ship they would be bigger than hatch covers on other ships. The biggest responsibility on hatch covers being, they are strong deterrents against progressive flooding. They must be maintained in best of the health so that they do not give way when green seas board. Hatch covers must always be in smoothest state as far as opening or closing is concerned. Any problem in respect of opening / closing machinery must immediately be resolved.
Requirement of Survey of hatch covers and sealing systems
Article 14 of the International Convention on Load Lines, 1966, as amended sates that hatch covers and their coamings be surveyed annually. Bulk carriers and oil tankers are subjected to the enhanced survey programme as per resolution A.744(18), as amended). So it is imperative that the ship is kept ready from time to time for survey. In fact it is better to say the the ship should be always kept ready for any inspection that is in respect of safety.
There are many things common in Safety construction survey and the loadline survey. Where the loadline survey is more concerned about weather tightness issues, the safety construction survey deals with the structural strength areas. ESP aims towards ensuring that the fatigue and deterioration is kept under a strict monitor. The hatch covers must be inspected from both the sides, for condition, corrosion, thinning down, etc. A proper examination in the open as well as closed positions only, will provide the actual status.
The opening and closing of covers must be smooth. If a certain hatch cover on a ship is opened or closed by non standard ways or by emergency procedure, immediate attendance is a must. The kind of cargoes viz cement, woodpulp, agro products, etc. require immediate closing if it rains during the loading. This is the reason that all hatches must always be in the 100% state of readiness, at all times. At least 50% of hatch cover sets should be surveyed open, closed and in operation to the full extent in each direction, at each annual survey.
Any unhealthy sound from wheels, sheaves, hinges, winch, etc must not go untraced. A fault must get detected well before this stage. The full closing, commonly called as battening down of the covers should be carefully inspected. This is to confirm that all the securing units are uniformly contributing in causing the weather tightness. In the LL Convention, the forward 25% of ship and the freeboard deck is considered more exposed to weather. Naturally, these would be inspected more carefully.
A negligent approach by ship staff towards maintaining of hatch covers would be evident from the difficulty in opening / closing of hatch covers. If the cleats, channels, packings, etc are found in unsatisfactory condition, more number of covers will be tested as per the discretion of the surveyor. It should generally be evident from the tested hatches that the general condition of hatch covers is satisfactory. Partial replacements in cleating systems may pose imbalance between old and new cleats. Cleats partly may wear faster causing sequential loss. The replacement of cleats is therefore a tricky affair.
The survey of hatch covers and associated components will take following into consideration:
- Hatch Covers: Panels must be tested for corrosion, cracks, deformation. Stiffeners must contribute towards the strength;
- Sealing arrangements: cross joints, gaskets, flexible seals, gasket lips, compression bars, drainage channels and non return valves.
- Compression units: side cleats (for length, rubber packing, adjusting bolts, missing top wedges
- Opening / closing devices: wire rope, block, chain, hydraulic pipe lines, etc
- Mobility: condition of chain, pulleys, greasing points, eccentric wheels;
- Tracks: guides, guide rails and track, stoppers.
- Machinery: hydraulic or electrical parts including safety devices.
At annual survey, the coamings, with plating, stiffeners and brackets should be checked for corrosion, cracks and deformation. Hatch openings cause discontinuity in longitudinal strength and thus concentration of stresses. Any visible signs must be looked for.
Testing of hatch covers:
1. Hose water test used to be the most common method of testing water tightness. High pressure jet is applied at joints.
2. Ultrasonic test. Minutest of soundness can be detected by UV test. It is a very commonly used method for surveys. The test may be carried out in presence of most cargoes being within the hold.
3. Chalk test. One of the oldest methods whereby impression of chalk on the packing is studied. This gives idea about condition of packing rather than a certificate of weather tightness.
Maintenance of hatch cover system
- Rubber Gaskets tends to become dry and hard due paint or rust. Even the grease is kept away from a packing. A porous looking, hardened or deformed packing needs to be changed. A regular inspection of gasket is very important.
- Badly corroded gasket channels will spoil a replaced gasket again and hence must be replaced. This job is difficult for ship staff to carry out. This, because, it is inconvenient location wise. There are fire and safety issues too. It is invariably beneficial to send the hatch covers ashore where practicable. The repairs must not be skipped at the time of drydocking if the same were demanded then.
- Corrosion of Hatch Cover Structure must be closely monitored. Hatch coamings must be inspected for deformation and cracks. Coamings can be damaged during loading or discharge. Stevedore must be given timely notice of damage. Appropriate repairs must be carried out in consultation with a class surveyor, except when these are very minor.
- Compression Bars should be straight, undamaged and non-corroded. The purpose of compression bar is to provide due compression and must not over compress or under compress.Thus, the compression of the gasket should be correct when there is metal-to-metal contact on the hatch landing pad. Appropriate scantling, probably affirmed by a chalk test would be right thing to do.
- There is no substitute to a good seamanship. A new hand working on deck must always get trained continuously. Thus, any trapped water anywhere along a channel, trackway, etc should immediately be attended.
- Trackways can get weakened by corrosion and by wearing off. Any distortion in track can affect smooth rolling of covers. This may further lead to the malfunctioning and mis-alignment of wheels. Suitable build up of metal should be done to arrest deterioration
- Side cleats are important units of hatch securing system. A locking nut at base is provided to adjust compression capability. For doing the correct adjustment hatch must be first closed tight. The locking nut is adjusted until the compression washer touches the underside of the hatch coaming or its steel washer. The nut must not be tighten hard, though.
- Regular lubrication of hatch wheels, spindles and bearings will keep them in good order for long period of time. When the hatch cover is rested, the wheels should be free to rotate. Other components needing regular lubrication are hinge pins, toothed rack, etc. These components also need to be attended after a prolonged phase of shipping seas.
- The cleanliness and viscosity of hydraulic oil must be checked as scheduled. The hydraulic system is provided with bleed points from which samples can be taken. Hydraulic oil should be changed as per the maintenance schedule prepared on the recommendations of manufacturer. Hydraulic oil filters should be changed annually. Condition of hydraulic pipes, leakages must be duly attended. Pumps must be started, well in time, before taking load, particularly in cold conditions.
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