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Hatch covers
Types of hatch covers- mechanically operated steel covers are of folding, sliding, rolling, etc. types, fitted with gaskets and clamping devices; steel pontoon covers with tarpaulins and battening devices or with gaskets and cleats; portable covers with tarpaulins and battening devices (usually wooden covers).Types of Steel hatch coversLift-away hatch covers Rolling hatch covers Hydraulic folding hatch coversPiggy-back hatch covers
Lift-away hatch covers
Lift-away hatch covers Single-panel covers:single-opening multi-opening
Single-panel types comprise one cover for each opening i.e. there are no joints. They are normally specified for bulk carriers in the case of single-opening , and for cellular container ships in the case of multi-opening configurations.
Lift-away hatch covers
Multi-panel covers:with longitudinal joints with transversal joints
Multi-panel covers comprise several separate panels for each hatch opening. They are used for cellular container ships in the case of longitudinal joints, and for multipurpose cargo ships and heavy cargo tonnage in the case of transversal joints.
Lift-away hatch covers
Rolling hatch covers
Side-rolling hatch covers stow in a transverse direction. The traditional side-rolling cover consists of two panels per hatch, each panel rolling sideways on a pair of transverse ramps, thus presenting a minimum obstacle when loading. In some cases both panels can be stowed together on one side to further enhance access when loading and unloading. A single-panel type where the panel stows transversally or longitudinally are mainly used on very large ore carriers (VLOCs), with sufficient free deck area.
Side-rolling hatch covers can have a variety of different drive systems. The two main options are rack and pinion, or chain drive. A combination of the two is also possible. The chain drive type can either be a two-sided chain system or a system with a single chain arranged The covers open by lifting to the rolling position and rolling out by the drive mechanism.
Rolling hatch covers
Piggy-back hatch covers are used on bulk carriers when the available deck space is insufficient to accommodate folding, side-rolling or end-rolling covers. This system always comprises two panels, with one panel being raised high enough for the other to roll underneath and to support the lifted panel on to its back. Both panels can then be rolled back and forth. The system can either be applied to a pair of hatches or to the two panels of a single hatch. If the number of panels exceeds two, the system is called stacking, and special high lifters are needed.
With ever more efficient cargo working in port being the objective, modern dry cargo vessels are tending to develop to a more open trend, i.e. the size of the hatches compared with the deck area is growing. This implies that there is less stowage space available for the hatch covers, which has made the high-stowing hydraulic folding covers very popular. Hydraulic operation results in smooth and positive control of the big panels during opening and closing of the cover. A major advantage with the hydraulic folding covers is the low number of panels. Fewer big panels are advantageous when designing the covers for container loads.
The name hydraulic folding cover refers, to a cover consisting of two panels which are connected by hinges to form a folding pair. In many cases the cover consists of two folding pairs. One pair is stowed at the aft end of the hatch and the other forward. The folding pair is operated by hydraulic cylinders acting directly on the end hinge arms which are connected at stools on the deck. When the cylinders push the end panel up from the closed position, the cover is folded and the second panel, fitted with wheels, rolls on the rails to the stowage position. The panels are usually secured in the open position by semi-automatic hooks interacting with the wheel arms.
The traditional sealing arrangement is made up of a water seal, which is pressed against the edge of a compression bar. For the arrangement to function correctly, there must be a suitable sealing force and the compression bar must be in the correct position in relation to the seal.
Battening down a hatch cover
Care and Maintenance of hatch coversThe ship owners and their crew should apply a programme of maintenance to ensure that the steel is not allowed to corrode, gaskets are periodically replaced, movable parts are kept properly lubricated and fittings periodically overhauled. The crew should also make sure, at each operation that the covers are sufficiently clean, especially at bearing surfaces, and that the drainage holes are clear. Most problems occur at the peripheral and cross-joint gaskets. This will involve not only the rubber but the compression bars, the locking devices, the cleating, load bearing surfaces, and the general condition of the coaming top plate to be checked.
Care and Maintenance of hatch coversIn addition, in cases where the hatch panels are moved by hydraulic means then the manufacturer's maintenance procedures must be adhered to in all respects.When hydraulic cleating or securing is arranged, means are to be provided to ensure that the covers remain closed and weather tight in the event of hydraulic failure.The crew should however bear in mind that in extreme cases hatch cover protection may have to be complemented by means of tarpaulins or adhesive tapes
Care and Maintenance of hatch coversThis is a decision to be made by the Master taking into account the nature of the cargo, expected sea-conditions, uneven load distribution on hatch covers and, above all, previous experience in similar circumstances. The use of tarpaulins on mechanically operated steel covers must be considered an emergency temporary measure.Containers and cargoes should not be stowed on hatch covers unless they have been designed for such carriage.
Care and Maintenance of hatch coversAdditionally, correct and adequate lashing systems are to be used at all times when stowing cargoes; this is equally important for cargoes stowed on tween deck covers and that battening down devices are correctly used to the hatch covers at the same time.All securing devices should be checked and tightened by the crew as appropriate especially in case where their ships may be subjected to unusually rough seas.The crew should also make sure that not only the deck cargo, but also the derricks, etc. are properly stowed and secured so that they will not be dislodged in a seaway and cause damage to hatch covers
Care and Maintenance of hatch coversGreasing of moving parts to be carried out at regular intervals.Before operation oil level in the system to be checked and toped up if required. The appropriate manufacturer's instructions with respect to the safe operation, inspection, maintenance and repair of the type of the hatch cover fitted on the ship should be complied with in all respects.To this end a "Record of the Maintenance of Hatch Covers" should also be provided by the Manufacturer together with the operation and maintenance manual to assist owners to carry out the appropriate maintenance.
