Hatch Covers

Hatch Covers

• Hatch covers are welded fabrications closing ship’s hatch and therefore they must have sufficient rigidity and mechanical strength.

Hatch Covers

• Usually they come in two types:• LIFT AWAY (lifted by deck or port cranes) or• FOLDING (opened and closed by hydraulic

cylinders).• Both types depending on the design might be

executed as “open” (with only upper plating) or “closed” (upper and lower plating and tested for tightness).

• Throughout the manufacturing process all hatch covers are subject to supervision by a classification society:

• PRS (Polish Register of Shipping),

• GL (Germanischer Lloyd),

• LRS (Lloyd’s Register of Shipping),

• BV (Bureau Veritas).

What is the fundamental importance of weathertight hatch covers to the safe and profitable operation of cargo ships?

Importance of Hatch Covers

• ‘Poorly maintained or secured hatch covers can result in total losses in heavy seas and are the principal source of the shipping industry’s $700 million annual cargo damage claims.

Importance of Hatch Covers

• The problems are particularly severe in middle-aged ships where poor maintenance seems to be a major factor. However, even a perfect hatch cover can, in a moment of carelessness, become the vehicle of a commercial disaster.’

Maintenance of Hatch Covers

• The necessary maintenance can be both labour intensive and logistically difficult to arrange between busy loading schedules. Sometimes hatches leak despite careful maintenance -- hatches that appear to be in satisfactory condition when a ship is in port and berthed in still water, may start to leak when the ship is in a seaway and subjected to racking stresses. It is however, true to say that if hatches are found to leak in port, they are sure to leak in a seaway. A well planned programme of maintenance should effectively ensure that any risks of leakage are kept to a minimum.

• Frequently, surveyors are instructed to attend ships and test hatch covers for watertight integrity and there is some debate as to how this should best be done.

• There are several options open to the surveyor wishing successfully to carry out such tests, and the best approach may be to follow a combination of several procedures.

Basic Testing Prosedures?

Basic Testing Prosedures

• 1. The simplest initial test may be to have the hatch battened down and then to enter the hold and look upwards. In some more drastic cases this test may demonstrate the existence of leaks, simply because daylight can be seen through the gaps in the seals or through wasted covers.

Basic Testing Prosedures

• 2. The most commonly used test is the hose or water test whereby a jet of pressurised water is directed at the seams and joints of the hatch covers. Systematically, all the vulnerable areas of the hatch cov ers are examined. The surveyor, during this test, is stationed within the hold, so that he can see if there is any leakage. It is clearly essential to ensure that the water, usually supplied from the ship's fire main, is supplied at a constant and sufficient pressure and that the hose is steadily directed in the proper direction. In some cases it may be appropriate for two surveyors to be engaged in the test, one on deck and one in the hold. Ideally the hose should be held at a distance not exceeding one metre from the joint under test, with a pressure not less than 20kg/cm squared.

• There are a number of disadvantages to this test apart from the fact that it is time-consuming. The first is that it may be difficult to ensure adequate water pressure. Furthermore, a good deal of water is generated on the deck of the ship and there may be practical objections to this, particularly if the water is shed over a quay or into a dock with a possible risk of pollution. If leakages are suspected, the test cannot be carried out when the ship is laden with cargo, for fear of wet damage.

Basic Testing Prosedures• 3. An alternative test which does not have these drawbacks, is

the chalk test. The aim of the chalk test is to verify whether there is good continuous contact between the rubber joints and the compression bar. Chalk is applied to the compression bars and the hatches are then battened down. They are immediately re-opened and the joints examined. When a clear, regular mark is observed on the joint, it is assumed that sufficient pressure exists between the joint and the compression bar. If the chalk mark is found to be irregular or less pronounced at one point than at others, then it is assumed that there is some doubt as to water tight integrity. However endless inconclusive results can ensue rendering the process time consuming and uncertain.

Basic Testing Prosedures

• 4. Ultra-sonic testing is the most reliable, precise and rapid method a vailable. Testing by ultra-sonic equipment gives the exact location and extent of any leakage, is easy and quick to operate, does not require assistance from crew members, and most importantly, can be used on laden or unladen ships without any risk of cargo damage.