Hatch cover maintenance

Technology

November 2022 Safety

Published on 03 Nov 2022

Hatch cover maintenance and operation requires a thorough understanding of basic principles along with type specific issues and requirements. Experience shows that hatch cover problems remain one of the predominant causes for accidents on board ships. Leaky hatch covers are associated with wetting damage and claims. Incorrect maintenance or operation can lead to injuries, loss of life or pollution.

Never underestimate the rigours of an ocean voyage. Hatch covers are designed to withstand the perils of the sea, but only well-maintained hatch covers will keep the cargo dry.

Nowadays, a wide variety of hatch covers are developed to accommodate the requirements of specific ships, trades and cargoes. The most commonly seen types of hatch covers are:

  • Folding hatch covers (general cargo and handysize).
  • Side rolling hatch covers (panamax and capesize).
  • Lift-away type pontoons (container).

Hatch covers are generally made of material that can withstand rough handling and does not need constant care and maintenance. However, modern hatch covers are high-tech equipment with very small tolerances and requires type-specific maintenance. Therefore, having a good understanding of working, maintenance and operation of hatch covers is very important.

The classification society regularly inspects hatch covers to ensure:

  • Ship staff has not altered, modified or changed the approved design of the hatch covers.
  • Hatch covers are still fit for duty.

Ship/office staff must inform class after carrying out on board (temporary) repairs to the hatch covers. All modifications to the hatch covers must be approved by the Class (and/or flag state) that originally approved their design.

International Convention on Load Lines (ICLL)

With regards to the ship’s hatch covers, the ICLL is the most important convention. However, from a Loadline convention point of view, the freeboard is of paramount importance as it determines the ship’s reserve buoyancy and safety. Under the Loadline convention, openings that are above the waterline must be weathertight. Water from green seas, sprays, and rain must not penetrate into the ship via these openings. To prevent water ingress, the ICLL requires the closures of these weathertight openings to be structurally sound and strong, tight and secured.

Carry out periodical tests to ensure that the sealing arrangements are in order. Additionally, carry out visual inspections to determine that the hatch cover structure and securing arrangements are in order. A test and a visual inspection are necessary to confirm hatch covers are weathertight and will remain weathertight throughout the voyage.

A satisfactory ultrasonic or hose test is generally sufficient to prove that the hatch covers are in order. However, a thorough visual inspection is necessary to confirm that the sealing capacity of the hatch covers can be maintained throughout the voyage. Inspect all parts that contribute in maintaining a tight seal (e.g. bearing pads, locators, stoppers, cleats, drains) as per manufacturer’s instructions and good industry practice.

Hatch covers must be strong to withstand the forces acting on them due to weather conditions and twisting and flexing of the hull during passage. The hatch covers are strong and rigid compared to the flexible hull. At sea, hatch covers will not move in unison with the hull, therefore relative movements can enhance the risk of water ingress.

These relative movements take place in the packing rubber and compression bar interface. A soft and flexible packing rubber in the hatch covers can compensate for these relative movements and prevent water ingress. However, the packing rubber alone may be unable to keep water out during extreme conditions such as hurricanes and freak waves.

In case of a (cargo) wetting damage claim, crew must ensure that the hatch covers can pass visual inspection and a hose or ultrasonic test. This will prove that the wetting damage was not because of improperly maintained hatch covers but due to extreme weather conditions.

Safety barriers in hatch cover design

The ICLL requires ships to maintain watertight integrity even in such extreme cases, preventing water ingress into the holds. To achieve compliance, manufacturers install drain systems (see figure) which consists of a:

  • Drain channel ‘A’, above the packing rubber / compression bar interface in cross joints.
  • Drain channel ‘B’, underneath the packing rubber / compression bar interface.

Drain channel A evacuates water from the inter-panel void space as soon as possible. Drain channel B evacuates incoming water escaping through the rubber / compression bar interface and prevents water from falling into the hold. During heavy weather, some water collected in the drain channels can spill over the edge of the drain channel into the hold.

Whilst the rubber packing and drains are important in keeping water out, the hatch cover steel plating keeps the majority of the water out. Assessing the condition and structural integrity of the panel (and coaming) plating is very important. The steel plating, sealing system and drain channel are the three safety barriers installed to reduce the risk of water ingress to acceptable levels.

Main hatch cover parts and their maintenance

Hatch panels and coaming plating

Advanced corrosion affects the strength of the structural members and plating. Good maintenance and proper (and timely) painting prevents corrosion. Visual inspection and thickness measurements can confirm sufficient plating thickness and strength.

Physical damage (such as cracks, holes, deformations) occur due to:

  • Stresses caused by twisting, hogging / sagging, coaming deflection, overloading / improper weight spreading, improper adjustment / alignment of the panels.
  • Stevedore damages that may also affect the structural integrity of the hatch cover.
  • Temporary repairs or shipboard made lashing terminal points such as stoppers and D-rings.

Packing rubbers

Packing rubbers are fitted in retaining channels that are part of the hatch panel. Packing rubbers must provide sufficient resilience to compensate for the relative movements between the panels, as well as the panels and coaming. Packing rubbers are flexible and able to withstand exposure to heat, cold, sunlight, cargo, and chlorides during their in-service life.

Well-maintained rubbers normally age slowly and easily remain in good shape for a five-year period. Various types and designs of rubber packing are available. Ordinary / box type rubber packings act on a raised steel compression bar, whilst the ‘sliding profile’ seal act on a flat steel mating surface.

It is important that the packing rubber is compressed to its correct design compression. Over-compression can lead to damage and permanent set of the rubber. Insufficient compression can cause the seal to lose contact with the compression bar in less severe weather conditions and allow water entry. For example, for a 70 x 40 mm packing rubber with a design compression of 10 mm, 5 mm of permanent set will be the limit for replacement.

Packing rubbers are normally correctly compressed up to their design by the weight of the panel and not by overtightening the cleats.

Bearing pads

To keep the packing rubber at the required design compression, steel-to-steel contact between the panel and hatch coaming is necessary. This is provided by the bearing pads consisting of a support pad on the hatch cover and a landing pad on the hatch coaming. Different designs with different materials for the mating halves are also available.

Bearing pads wear down due to type, age and loads acting upon them. As bearing pads wear down, the compression of the packing rubber increases. Regularly monitor the wear process by checking the skirt clearance using a ruler or feeler gauge. Information regarding the skirt clearance and maximum allowed wear on the bearing pads is available in the manual. Some mating surface designs include wear rings or marks that indicate the bearing pad wear.

Bearing pads play a crucial role in the sealing process and inspections must focus on:

  • Wear in way of the landing pads (resulting is reduced skirt clearance)
  • Lack of contact between the support and landing pads
  • Structural integrity of the bearing pads, coaming and deck structure
  • Correct steel for the landing (mild steel) and support pads (hardox)
  • Cleanliness and free movement between the landing and support pads

In hatch cover designs without bearing pads, the steel-to-steel contact is achieved through direct contact between hatch cover side plating and hatch coaming. In such cases, check the panel / coaming interface for damages such as corrosion, grooving, and thinning deformations.

Securing systems

The ICLL requires that hatch panels can be properly secured to the ship. This prevents panels from being pushed off or blown away, leaving the hatch and hold exposed. Securing of the hatch panels is done using quick acting cleats or holding down devices or by means of automated systems.

Regularly inspect cleats to ensure that cleats are fit for use:

  • Check for strength related issues such as corrosion, deformations and thinning of the different parts of the cleating system, coaming table and panel side plating.
  • Replace missing or damaged cleats as the required holding power can only be achieved when all cleats are in place.
  • The rubber washers must be flexible and in good condition (not painted over, no additional steel or rubber washers fitted).
  • Check alignment as if cleats are crooked or misaligned their holding power will be affected.
  • Tighten cleats to the correct tension considering the wear in the hatch cover (bearing pad) system.

Drain systems

Drain systems consist of a drain channel, drain hole in the coaming table and a drainpipe fitted with a non-return valve. The non-return valve prevents water from outside to enter into the hold (in case of heavy weather). Always keep drain valves open and free but keep the non-return valve closed with the fire cap in case of CO2 release or fumigation.

Whilst checking drain systems, focus on the following points:

  • Structural integrity of drain channels in cross joints and on the coaming.
  • Whether original type of drain valve fitted.
  • Drain system (drain channel, drain hole, drainpipe and drain valve) free and unobstructed.
  • Fire caps provided and available in a clearly identified space.

Compression bars

To achieve a weathertight seal, packing rubbers act against the compression bar. Choose the type of rubber depending on the type of the compression bar. This can either be a raised compression bar or a flat steel mating surface. The flat steel mating surfaces are easy to install, maintain and clean, and have no restrictions in movement.

Check compression bars for some important issues:

  • Structural condition: As packing rubber pressure and loads are considerable, compression bars must be structurally intact and strong.
  • Straightness: Straightness of the compression bars is important for even compression.
  • Smoothness: Smoothness of the compression bar sealing surface prevents abrasion of and damage to the packing rubber surface.

Frequent mistakes when testing and inspecting hatch covers

Common mistakes

  • Insufficient knowledge about hatch covers, resulting in improper reporting
  • Overestimating the capability of the ship’s crew for repairs
  • Omitting to call in specialists
  • Overlooking the importance of involving Class when shipboard repairs are carried out on hatch covers
  • Improper / temporary repairs by crew
  • Missing manual / drawings
  • No proper and detailed on-board instructions for maintenance
  • Hatch covers not included in SMS and PMS
  • Insufficient spare parts

Weather tightness mistakes

  • Ignoring discard / replacement criteria (over-compression)
  • Replacing rubber packing without addressing steel-to-steel contact issues
  • Installation of backing strips everywhere, even on top of rubber packing
  • Mix of new and old rubber
  • Using old rubber (from shipboard stock and ignoring shelf life)
  • Use of small pieces and filling-in of gaps
  • Improper maintenance of seals and rubber channel (painting)

Mechanical mistakes

  • Abnormal sounds / vibration during operation ignored
  • No greasing or greasing plan
  • Onboard repairs instead of landing panels ashore
  • Ignoring safety issues (heavy and moving equipment)

Hydraulic mistakes

  • Cleaning filters instead of changing
  • Improper filtering
  • Closing covers without using the pump
  • Changing of pipes without flushing
  • Valve positions incorrect during voyage
  • Ignoring leaks and pollution risks
  • Ignoring high-pressure risks

Source: Japan P&I

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