Types of Hatches:
- The Conventional Hatch Covers:
Now obsolete except with small coastal vessels or on river barges. This type of hatch was covered by ‘hatch boards’. The ridged ‘King Beams’ with a ‘Queen Beam’ set midway underside of the boards held the boards.These were then covered by three canvas tarpaulins respectively, tabled, and tucked into a side coaming, with a wedged cleating arrangement.
- hatch beam, portable beam,
- hatch coaming,
- wooden hatch boards,
- wooden wedge,
- hatch bar, hatch batten,
- Cleat, king beam, sister beam, beam bolt.
- Steel Hatch Covers:
The present day cargo vessels are equipped with one of the many types of steel hatch covers which are available. The advantage with this type is mainly the speed of operation and the saving on the number of personnel required for the operation.
The type of hatch covers can be broadly divided into
- Folding type
- Lift Away type and
- Side rolling type.
- Folding type:
Folding type hatch covers are basically used on general cargo ships. Drum stowing rolltite hatch covers also form a part of the folding type.
Folding type hatch covers consists of flat pontoons which are operated either by means of a hydraulic ram or in the older designs by means of a wire and pulley arrangement, also called the direct pull type.
The hydraulic ram arrangement is simple to operate however, if the system develops a leak, the operation could result in delays and in some cases may even damage the cargo.
The hatch covers (pontoons) are designed to move on wheels along a track which forms a part of the hatch coaming. The sections of the hatch covers (pontoons) are connected with chains and ride up a raised part of the trackway until they finally stow in an area at the end of the hatch.
To open the hatch in the pull type arrangement, securing devices such as side securing lugs, wedges on the hatch tops, cleats etc. should be cleared and the pull wire connected to the forward most or leading hatch cover through a lead block. The trackways should be cleared and the wheels of each pontoon jacked up after unlocking them. The locking pin of the wheels must be secured to prevent accidental fall off. Ensure that the area around the hatch and the pontoon stowage area is clear of personnel and heave on the pull wire gently taking more weight to pull all pontoons on the hatch into the stowage area one by one. After all the pontoons are in the stowage area, they must be secured to prevent accidental movement. For closing the hatch cover the reverse process is to be followed except that the pull wire is led to the winch through two lead blocks; a lead block located at the forward end of the coaming as seen in the figure and through the lead block which was used for opening.
2. Lift away type or lifting type:
The Lifting type (lift away type) hatch covers are generally designed for use on container ships, and may be of the single panel type or multi-panel type. In order to open or shut the holds the ships crane or shore crane will need to be used along with a spreader.
The individual pontoons when removed can be placed on top of adjacent pontoons.
3. Side rolling type:
The side rolling types, operated hydraulically, are used on bulk carriers and operate/stow in a transverse direction. The pontoons move on a pair of transverse ramps.
Closing /Securing Arrangements of Hatch Covers:
Hatch covers of ships are designed to protect goods from damage due to ingress of water, dampness and at the same time provide an efficient securing arrangement coupled with ease of operation.The covers also provides a structural barrier while maintaining sufficient strength.
The various types or hatch covers that are mainly used on board depend on the service for which the ship was built.
Components that make a hatch watertight:
Watertightness of the hatch covers is achieved by the following components:
- The single pull hatch cover: (Figure) consists of a number of transverse pontoons which cover and span the hatch opening and are linked together by chains.
- When the hatch is in a closed position, the pontoon sides are designed to align and rest firmly on a horizontal steel plate attached to the top of the hatch coaming. Just inside the side pontoon is a rubber gasket housed in a channel on the underside of the hatch cover and which sits firmly on a steel compression bar to form a weathertight seal (Figure).
- When closed the covers are held on to the seals by a series of peripheral cleatswhich are the quick release or the screw type as seen in the figure.
- Rollers are attached on the sides of the covers to facilitate opening and closing.
To open the hold, cleats located on the sides of the pontoon must be unlocked first and each pontoon is raised off its compression bars by hydraulic jacks.
The rollers or wheels, which are arranged on eccentrics, are rotated through 180 deg and locked into position. The jacks are then removed and the cover can be pulled backwards or forwards as required.
- The trackways on both sides at the end of the hatch coaming are designed in such a way that they facilitate in turning the pontoons into an upright position in the stowage space that is provided.
Detail of single-pull cover showing scaling arrangement and
- jacking system (The Henri Kummerman Foundation)
CLEAT LOCATED ON THE SIDES OF A PONTOON
Cross joint cleats or wedges located on the top of the pontoon are provided to batten down the covers once they are closed and cleats are fastened. These wedges are hammered in manually.
WEDGE LOCATED ON THE TOP OF A PONTOON.
INSPECTION OF COMPONENTS:
- Compression Bars:
If the compression bar is damaged, or excessively corroded, effective sealing will not be possible. If such a condition is evident then the compression bar should be repaired or replaced and while doing so the alignment must be maintained. A chalk test will be of help prior, during and after repair.
2 Drain Channels:
The top of the hatch coaming particularly the area that forms the drain channel must be rust free and clean. The cross joint channels should also be free of loose rust. The drain holes must be clear. All these checks will facilitate proper drainage of water. The Non return valve fitted on the drain must be checked for proper operation.
3 Securing Cleats:
Cleats are provided with means to adjust the compression. The compression on all cleats must be checked and if required adjusted together in such a way that the pontoon is not overtight.
4. Sealing Gaskets:
Gaskets must be clean and free from rust clinging’s and paint. Check for physical damage or a permanent impression and if required replace sections. It is always a good practise to renew lengths of about a meter at a time. If in doubt, check the manual provided by the manufacturer.
While checking the gasket, it is equally important to check the retaining channels for heavy corrosion or damage. This can cause the gasket to lose its adhesive property and go adrift. If required the channel must be repaired.
Wedges must be checked for misalignment and excessive corrosion. The securing pin must be checked.
TESTS FOR DETECTION OF LEAKS:
When testing hatch covers for leakages, the two most common leak detection tests are the water hose test and the ultrasonic test.
- The ultrasonic test detects weather tightness of the holds by placing a signal generator inside the hold and a sensor held on the outside with the hatch cover in the closed position. In this test areas which are inadequately sealed can be detected. Although this test is the preferred choice it requires an experienced person to conduct the test.
- The water hose test is a very common test conducted by many class societies with variations in their requirements. The general requirement however is a 2-3 kgs/cms2 pressure requirement applied through a hose of 20 to 30 mm dia and a 12mm nozzle held at 1 to 1.5 mtrs distance moving along the joint seal at about half a meter per second.
- Chalk testing on a cargo hold will indicate areas of poor compression. This uneven compression could possibly cause the hatch cover to leak.A Chalk test should not be considered a leak detection test.
- Testing with the help of a light can be an effective method however it has some drawbacks concerning the safety of the personnel conducting the test. The concern is due to area of darkness in which the test is conducted.
SAFETY PRECAUTIONS WHILE OPERATING HATCH COVERS
- Instructions from the manufacturer with regard to the safe operation, inspection, maintenance and repairshould always be followed.
- Prior undertaking the operation all hazards should be identified and controls put in place to mitigate them.
- Conduct a tool box talk and keep personnel clear of the area.
- Ensure that the pontoon wedges, securing cleats are released while opening.
- Ensure that the stowage bay for the pontoons is clear prior opening.
- While operating the hatch cover to open or shut DO NOT STAND on the pontoons.
- If for any reason hatch covers need to be opened while at sea ensure to first check the securing arrangements provided and also in addition drop the wheels into the guide slots. In addition where applicable keep the wire secured.
- DO NOT STAND on the hatch coamings during the operation.
- While operating side rolling type covers, additional lashings to secure the pontoon in place will help and prevent movement.
- Ensure that the securing cleats are released and correctly stowed such that the trackway is clear.
- Check eccentric wheels where applicable, are secured by the pins provided.
- Ensure where applicable that all wheels are properly jacked up and in position.
- The hatch locking pins or preventers of rolling hatch covers should not be removed until a check wire is fast to prevent premature rolling particularly considering the trim of the vessel.