UK P&I Club issued a report to provide a good understanding of hatch covers operation, as well as industry requirements, in order to help those involved in inspecting, testing and evaluating the weathertight integrity of hatch covers in making well informed decisions, and assist owners and crew in maintaining their hatch covers and closing appliances in line with industry standards.
Hatch cover design
In order to design hatch covers that comply with ICLL, and meet with customer’s demands and expectations, different issues have to be considered, such as:
- Hatch way dimensions
- Available deck space for stowing the panels
- Available stowage height for panels
- Required coaming height
- Required extent of opening
- Type of operation (opening and actuating mechanisms)
- Available power
- Required opening/closing time
- Degree of automation (available crew)
- Repair possibilities (availability of shore specialists/ship’s crew repair skills, spare parts)
- Carriage of cargo on hatch covers
- Required degree of tightness (weathertight/reduced weathertight and non-weathertight)
- Cost (min – max scantling, steel price)
- Required/Max. panel weight (ship’s gear, shore gear, power and rubber packing line compression)
- Construction type (open web, double skin) and required fittings (cleats, packing)
- Trading pattern (warm/cold, tropical rain showers/speed of closing)
In addition, the design has to be such that the cost (for manufacture, installation and maintenance) is low and that the in-service life (without failures) is long.
Hatch covers and tightness
Apart from being designed and developed by specialists, compliance with the ICLL needs to be further confirmed by the Administration/Classification Societies in the form of type approval.
In order to understand the difficulties related to design, it is important to know that ships are subject to different deformations when in port and at sea. These distortions are brought about by loaded/ empty/ ballast conditions as well as flexing and twisting of the hull as a result of wave action, which all have an influence on the hull form and eventually, the hatch covers. It is therefore important to understand the relationship between hatch covers and the ship.
In the first place, one has to think of a ship as a steel box, and in this context, it is useful to compare a ship with a box of cookies. Such a box will be quite rigid as long as the lid (comparable to the deck of a ship) is on. However, once the lid is removed, the box becomes very flexible as it has lost part of its structural integrity. Whilst on a ship, the deck is not completely removed, big openings (hatch ways) are created, which in turn leads to the structure of the ship becoming more flexible. An extreme example of this is the open hatch-type ship, which has large hatch openings and therefore, less deck space than an ordinary design. In order to maintain the vessels weathertightness, it is necessary to cover up these openings in the deck.
In a weathertight hatch cover system, the following three safety barriers will be required:
- A strong steel structure
- Packing rubber (flexible seal with design compression to compensate for known movements)
- Drain and collect any incoming water that passes through the joint in extreme conditions
Key parts
In a weathertight hatch cover system, various key parts need to work in unison in order to ensure that weathertightness is achieved and can be maintained throughout the voyage. These are:
- Packing rubbers: Developing packing rubbers that are fit for duty and retain their flexibility throughout their in-service life is not easy. Such rubbers also require proper and correct maintenance in line with manufacturer’s guidelines. Packing rubbers are designed to be compressed to a certain depth.
- Bearing pads: Bearing pads provide steel to steel contact between the panels and the coaming, and, as such, prevent the panels from sitting too low on the coaming, which would cause overcompression of the packing rubber, or panels from being pushed down under weather loads causing the cleats to be come disengaged.
- Locators: Locators guide the panel in its correct closing position and ensure that panels are kept properly positioned during the voyage
- Stoppers: The role of stoppers (restraints) is to prevent failing to control hatch cover movements, which would lead to excessive loads acting on component parts of the hatch covers with accelerated wear and damage as a result.
- Draining system: The drain system is the last safety barrier to water entry through the sealing system in a weathertight hatch cover system. If water enters the hatches it will be collected in the drain channel and expelled via the drain pipe.
- Securing mechanism: Another requirement under the ICLL is that the hatch cover panels should remain in place during the voyage to prevent he holds being left open at sea.
- Compression bars: In order to achieve a tight seal, packing rubbers need to be compressed up to their design compression and as such they need to act against a compression surface.
- Operating mechanisms: Depending on the hatch cover design, different types of opening/closing mechanisms are available, apart from the lift away type hatch covers.
- Hatch panels: the importance of the hatch panels should not be overlooked as it is still the steel top Improperly maintained or wrongly operated hatch covers can result in serious damages or accidents plate of the hatch panels that covers up the hatch opening.
As for hatch covers inspection, it is revealed that, when testing and inspecting hatch covers, the following typical or frequently seen mistakes are identified:
Common mistakes:
- Insufficient knowledge about hatch covers, not allowing for good inspections and proper, understandable reporting
- Overestimating the capability of the ship’s crew for repairs (maintenance and adjustment)
- Overlooking the importance of involving class when shipboard repairs are carried out to hatch covers
- Improper or temporary repairs by crew
- Missing manuals and drawings
- No on board instructions for maintenance
- No maintenance files on board (PMS)
- Hatch covers not included in SMS
- No understanding of the due diligence principle/issues
Weather tightness mistakes
- Ignoring discard/replacement criteria (overcompression)
- Replace rubber and not fix the pads
- Install backstrip rubber everywhere
- Mix new and old rubber
- Using old rubber (from shipboard stock, ignoring shelf life)
- Use small pieces and fill in gaps
- Not (or lightly) painting rubber channel
Mechanical mistakes
- Ignore abnormal sounds/vibration during operation
- No greasing, no greasing plan
- On board repairs instead of ashore
- Ignoring safety issues (heavy and moving equipment)
Hydraulic mistakes
- Cleaning filter instead of changing it
- Improper filtering
- Close covers without pump
- Change pipes without flushing
- Valve positions during voyage
- Ignore leaks and pollution risk
- Ignore high pressure risk
UK P&I Club concludes that deciding if the hatch covers are weathertight requires knowledgeable and professional people to carry out the test and advise principals, not only about the test results, but also about the overall condition of the hatch covers, their key parts and possible exposure to risk and water ingress.
Futher information may be found in the following report:
Source & Image credit: UK P&I Club