1. Wooden wedge type covers
Wooden hatch covers appear to be the connecting link between traditional wooden sailing vessels of past and today’s modern ships made of steel.
- Portable steel beams, wooden sleepers, tarpaulin, etc were used for weather tightness.
- This involved difficulties like placement of hatch sleepers, manual labour involved, closing difficulties in case of rain, etc
- Tween decks still have the system of hatch beams and sleepers on some ships.
- These type covers are practically obsolete.
2. Piggyback Covers
This type of hatch cover system accommodates folding, side-rolling or end-rolling covers. The piggy-back 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 top. The two panels can even be rolled back and forth. The system can either be applied to a pair of hatch openings or to the two panels of a single hatch opening. There may be more panels where they can mechanically stacke.
3. Folding type
Folding type hatch covers consists of two or more flat type topped panels, making one or two pairs of covers. These are heavier than the covers normally put on general cargo ships. They are operated via hydraulic arms. These are usually fitted on tween decks, even in case of smaller ships. A major advantage in the design of folding type hatch covers is its large size which means less number of panels. Thus, the stowage takes vertical space rather than horizontal.
4. Rolling type, Single pull cover
The pontoons (individual parts of the hatch covers) are connected to one another with chains and hinges and can easily and quickly be rolled into or rolled back on hatch top. The normal practice for the lengthwise opening of hatches involves an opening wire rope, snatch block and a winch.. The pontoons are also operable electrically or hydraulically with an endless drive chain doing the job. The wheels on the side on which the pontoons roll are eccentric in their construction thus when in the battened (lowered) position the clearance between the wheel and the trackway is minimum and the pontoon sits on the trackway, the rubber gaskets being compressed by the compression bar.
The cross wedges are used to ensure the pontoon rubber gaskets compress against the compression bars of the adjacent forward or after pontoons. The side cleats ensure that the pontoons stay compressed to the trackway compression bar. These hatch cover systems consist of various parts. A hatch cover should not be battened with cargo on top.
The Channels are to be swept prior battening so that the cargo remains do not cause a hurdle in weathertightness. The drain channel on the front of the hatch pontoons are to be cleaned prior closing the hatch. Usually drain channels are the first ones to get corroded. Once the wheels are turned, cross wedges are put and the side cleats are then fitted.Prior making a voyage the hatch cover sealing should be confirmed by a careful inspection. There should be no list when battening down the hatch. No one must stand on hatch covers as the covers are being opened or shut. People had died when the covers opened at a speed faster than expected due excessive trim, which was overlooked. Side cleats must share uniform tension for which adjustment on individual cleat may be necessary.
Opening and Closing Hatch Covers
1. Presence of a responsible person is a must.
2. Partial opening of hatch covers, leaving the cover on wheels is not safe as covers may roll down on their own.
3. Eccentric wheels are lowered for covers to roll.
4. A hatch cover should never be opened / closed with a load on it.
5. Hatch cover recess should be physically checked.
6. The track way should be clear of all ropes, portable light wires.
7. Status of all three securing items are checked, whether a cover is to be opened or shut.
5. Side Rolling Hatch Covers
The side-rolling hatch covers are apt for use on the weather decks of large bulk carriers. For ore bulk oil carriers (OBOs) hatch covers are designed to withstand large sloshing impacts. They would be best when deck space is available on the sides of hatch cover.
A side-rolling cover consists of two panels per hatch, each panel rolling sideways on a pair of transverse ramps. Side-rolling hatch covers can have a variety of different drive systems. The two main options are:
1. rack-and-pinion; and
The crucial areas being in respect of the drive system, the lifting system and the cleating system, which usually depends on the specified lifting system viz. rolling type with auto cleats or wheel lifters with manual cleats. MacRack, for example is an electric-drive system combines drive and lift operations for side-rolling hatch covers. It employs a combined rack-and-pinion drive and lifter system. Electric operation removes the need for hydraulic pipe work and other components.
6. Lift away type hatch covers
Lift away type hatch covers can be classified into two types:
a) Single panel covers,
b) Multi panel covers.
Single panel cover consists of a single cover for each opening, as seen on bulk carriers. In case of multi panel covers, a single hold is covered via multiple number of covers, like in case of cellular container ships in the case of longitudinal joints, and for multipurpose cargo ship in case of transverse joints.
7. Stacking cover type
These type of covers are used on ships having relatively smaller hatch cover. Many coasters in the European river are seen with this type covers. There may be a hydraulically powered lifting crane facility. It covers longitudinally and stack it together at one end or over any empty stowage compartment.
8. Slide hatches with smooth surface and walking strip
These are made of tread plate located in the ridge of the hatch. For small crafts, these covers are sometimes handled without power.
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