Cargo storage spaces of any type of vessel, need to be well protected in order to preserve the cargo and prevent any kind of spoilage. A cargo space needs to be air and water tight for conserving the cargo goods for a longer time. If the cargo that is carried contains perishable food items, then it becomes extremely important to protect it from moisture and adverse weather conditions, especially rain. Inability to do this not only results in spoilage of goods but also produces chances for spreading diseases. Hatch covers come to the rescue in this situation and can be compared to the lid on a box
Cargo Hatch Covers
Hatch covers are used to cover and protect the cargo in the cargo spaces. Hatch covers close off the hatch opening and makes it water tight. In the days of wooden ships, the hatch covers were made of wooden planks, beams and boards and were covered with tarpaulins. Wooden hatch covers had many drawbacks. Mainly, they used to get spoilt due to continuous exposure to the moisture laden sea winds. Rain and sea water also used to produce detrimental effects on the wooden hatch covers. But with the advent of steel, the wooden hatch covers started disappearing. Nowadays, mostly steel hatch covers are used. The most common type of hatch cover used today consists of a number of steel covers linked together. The design of a hatch cover changes according to the size and design of the ship, but most of the designs are made to make the opening and closing of the covers as quick as possible in order to facilitate faster cargo handing process.
One such type of hatch cover is a MacGregor, single pull hatch cover, shown in the figure. In this type, the hatch cover moves on rollers attached to tracks fixed on the hatch coaming. The hatch cover is not one steel structure but a series of steel covers linked together by chains. When the cover is opened, the individual steel covers ride up and tip onto a stowage tank at the hatch end. Most of the hatch covers found on board a ship are controlled hydraulically by a hydraulic power unit operated from a control box fixed near the hatch cover. Hatch covers can also be operated with the help of a crane or a winch, though these systems are today obsolete .
Moreover, the hatch covers are made watertight, using a compressible jointing strip at the place where the cover sits on the hatch openings.The covers are pulled down on this compressible joint strip with the help of cleats, which can be hand or automatically operated.
Tween Deck Hatch Covers
For hatch covers that are to be fitted below the weather decks, the covers are arranged flush with the deck. A hydraulic system consisting of a reservoir pump and a motor is mounted into the hatch covers for controlling the opening and closing of the same. The controlling of the doors can be done from any place nearby.
Hatch covers should be properly maintained by regular inspections and periodic routine tests. The hydraulic system of the hatch covers should be tested and the hydraulic oil level should be checked at regular interval of time.