A Master’s Guide to Hatch Cover Maintenance

The Standard

A Master’s Guide

to Hatch Cover Maintenance

The Standard

Witherby

& Co Ltd

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British Library Cataloguing in Publication Data

A Master’s Guide to Hatch Cover Maintenance

ISBN 185609 2321

Contents

Introduction 02

1. Hatch Covers and their Function 03

2. Basic Advice 04

3. Common False Beliefs about Hatch Covers 06

4. Leakage Problems 09

5. Leak Detection Tests 13

6. Monitoring and Inspection 14

7. Maintenance and Repair 16

8. Heavy Weather Precautions 21

9. Safety when Working with Hatch Covers 22

Appendix 1 23

Procedures to Open and Close Hatch Covers

Appendix 2 24

Hatch Cover Condition Assessment Forms

NOTICE AND TERMS OF USE

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or otherwise howsoever in respect of any inaccuracy or omission herein.

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or inaccuracy or omission herein.

A Master’s Guide to Hatch Cover Maintenance

Introduction

It is generally accepted that leaking hatch covers are a principal cause of cargo wetting.

Hatches leak for a variety of reasons, but mainly because of poor maintenance or failure to close

them properly. Leaking or badly maintained hatch covers can lead to more serious consequences

than wet cargo – flooding, accelerated corrosion or even loss of the ship. These problems are

addressed in the guide.

During investigation and discussion we have found a degree of confusion throughout the industry

as to whether hatches are constructed to be watertight or weathertight. A watertight hatch cover

is a cover designed to prevent the passage of water in either direction under a head of water for

which the surrounding structure is designed. A weathertight cover, is a cover designed to prevent

the passage of water into the ship in any sea condition. Hatch covers are constructed to be

weathertight, which means that, in any transient condition, water will not penetrate into the ship

through the covers or the double drainage system. However, it is apparent that minor leakage into

a cargo hold during a hatch cover test is often erroneously considered to be within a weathertight

standard; in practice, no leakage is the requirement. For this reason, we include guidance on

procedures for conducting leak detection tests on hatch covers.

From our research we have the impression that many mariners think hatches are robust,

monolithic structures, thereby failing to appreciate the small tolerances on panel alignment

and gasket compression.

For example, 4mm wear on the steel-to-steel contact is sufficient to damage rubber sealing

gaskets beyond repair; 5mm sag along the cross-joint can cause a large gap between the

compression bar and gasket.

It is better to think of hatches as complex, finely-made structures, to be handled with care.

It is the aim of this guide to explain the key issues of hatch cover security and to steer mariners

towards active maintenance. It is less expensive to keep hatch covers weathertight by regular

maintenance and attention to detail, than to pay claims for wet-damaged cargo. It is crucial for safety

at sea and protection of the environment to maintain hatch cover weathertightness and strength.

This guide concerns steel hatch covers fitted with cleats, compression bars and gaskets.

Eric Murdoch

Director of Loss Prevention

Charles Taylor & Co. Limited

1st January 2002

Consultant

Mr Keith Taylor of Allworld Marine & Technical.

Suite 4, Pearl Assurance House, Chapter Row, South Shields, Tyne & Wear, England, NE33 1BN.

A Master’s Guide to Hatch Cover Maintenance

1. Hatch Covers and their Function

The purpose and function of a hatch cover and its coamings is to prevent ingress of water into a

cargo hold after a large opening has been cut in the deck for cargo access. Hatch covers are a

moveable structure designed to a weathertight standard.

Hatch Cover Construction

Typically hatch covers are lightweight steel grillages. Modern design methods using finite element

technology enable more efficient material distribution which results in lighter (thinner) structures.

Construction from high tensile steel results in even thinner plate being used. For this reason these

lightweight structures must be ‘handled with care’. Prevention of corrosion is essential – safety

margins are finite.

Hatch Cover Function

Hatch covers provide a primary structural and weathertight barrier to prevent water ingress into

cargo holds. Rigorous inspection, regular maintenance and prompt repair of damaged covers,

securings and supports are essential to maintain fitness for purpose and, in particular:

• to maintain sufficient strength to resist green seas landing on hatches in extreme weather;

• to maintain a barrier against ingress of water during normal seagoing weather conditions.

Failure to maintain hatch covers correctly can lead to physical loss of a cover in extreme weather

and hold flooding and possible foundering. Minor leakage can cause cargo damage and, if over a

prolonged period, damage to the ship’s internal structure. Long-term structural decline can lead to

structural collapse and total loss.

A Master’s Guide to Hatch Cover Maintenance

2. Basic Advice

There are procedures which will help to keep your ship’s hatch covers in good condition.

The following advice can be considered best practice.

Always

• carry out regular examination of the hatch covers, hatch beams and coamings to identify:

– general levels of corrosion (check with your classification society for corrosion allowances);

– localised corrosion at welded connections (grooving);

– cracks in joints and weld metal;

– permanent distortion of plating and stiffeners;

• call a Class Surveyor and carry out repairs as soon as possible when there are:

– indications of excessive corrosion e.g. holes or local buckling of the top plate;

– cracks in main structural joints;

– areas of significant indentation, other than localised mechanical damage;

• be particularly vigilant after heavy weather;

• rectify any steel-to-steel fault before renewal of rubber packing. Renewal will not be effective if

steel-to-steel contact points are defective, and expensive rubber packing will be ruined after

only a few months of use;

• replace missing or damaged hatch gaskets (rubber packing) immediately. The minimum length

of replaced gasket should be one metre;

• keep hatch coaming tops clean and the double drainage channels free of obstructions. (Open

hatch covers to clean coaming tops and the double drainage channels after loading bulk cargo

through grain or cement ports);

• keep cleats and wedges in serviceable condition and correctly adjusted;

• keep hauling wires and chains adjusted correctly;

• attach locking pins and chains to open doors and hatches;

• keep wheels, cleats, hinge pins, haul wires, and chain tension equipment well greased;

• test hydraulic oil regularly for contamination and deterioration;

• keep hydraulic systems oiltight;

• ensure the oil tank of the hydraulic system is kept filled to the operating level and with the

correct oil;

• clean up oil spills. If the leak cannot be stopped immediately, construct a save-all to contain the

oil and empty it regularly;

• engage tween deck hatch cover cleats when the panels are closed;

• give notice that maintenance is being performed so that no one tries to open/close the hatch;

• remember that continuing and regular maintenance of hatches is more effective and less

expensive than sporadic inspection and major repair.

A Master’s Guide to Hatch Cover Maintenance

Never

• treat temporary repairs as if these were permanent. The strength of the cover and ultimately

the ship will depend on the quality of repairs carried out;

• ignore serious corrosion, cracking or distortion in the covers and supports. These are signs of

weakness and are potentially hazardous;

• allow grooves to form in the coaming top, especially where the hatch side or end panel rests

when the hatch is closed;

• apply petroleum-based grease or paint to rubber packing;

• remove the rubber ball from a non-return drain valve;

• use anything other than the recommended hydraulic oil;

• leave cleats unfastened when proceeding to sea;

• attempt to open or close any hatch that has a load or cargo on it;

• open hatch covers at sea unless absolutely essential;

• leave open covers unattended when at sea;

• tighten down the cleats so that the hatch cover is unable to move on the coaming top.

Typical arrangement of a multi-panel hatch cover. The double drainage channel and ‘steel-to-steel’ contact are shown.

3. Common False Beliefs about Hatch Covers

• Hatch covers are non-load bearing – they are only there to keep

the water out.

Hatch covers can be subjected to very high pressure loadings during heavy weather. This in

turn induces significant in-plane stresses in the component plating, girders and stiffeners.

• Leakage is an inconvenience resulting in cargo wetting.

Leakage can, where unchecked, cause serious flooding and ultimately endanger the ship and

its personnel.

• Internal cracking at joints, corrosion/cracking in way of welds

and distortion of plating do not affect the hatch cover function.

Such problems change the way a structure works and can significantly reduce the load

carrying capacity.

• Hatch covers constructed of high tensile steel are more robust

than those made from mild steel.

This is not the case. A cover constructed from high tensile steel will normally comprise thinner

plating than one constructed from mild steel.

• It is the rubber seal that keeps the water out of the cargo.

The double drainage system is as important in keeping water away from cargo.

• Renewing a worn rubber seal is all that is needed to keep

a hatch weathertight.

Worn rubber is usually the result of worn steel-to-steel contact surfaces or a deformed

structure. Rubber renewal alone is futile unless the steel-to-steel contact surface is repaired.

Cross-section sketch of a multi panel

hatch cover illustrating the compression

bar gasket and cleat arrangement.

A Master’s Guide to Hatch Cover Maintenance

• The hatch cover side plate when closed should rest on

the coaming top.

If the weight of a hatch panel is sufficient to cause distortion of its side plate (hatch skirt),

then landing pads are fitted to the panel to transfer the weight evenly across the coaming top.

• Hatch covers will always leak in heavy weather.

Hatch covers are designed to withstand the rigours of the sea. Provided the cleats are correctly

adjusted, hatch gaskets are in good condition and the construction material sound, then hatch

covers should not leak, regardless of the weather.

• Screwing cleats down hard will ensure weathertightness.

No amount of tightening of cleats beyond their correct position will improve hatch cover

weathertightness. Hatch cover manufacturers usually test for weathertightness without

engaging cleats. The weight of a hatch is sufficient to create the required gasket compression.

• The use of hatch cover tape will ensure watertightness.

The use of sealant tape gives a false sense of security. Hatch cover tape is a short-term

temporary measure that can be used to stop water from entering cross or side joints. However,

the prolonged use of tape increases corrosion in the cross-joint and side plate. In bad weather,

sealing tape can and does wash off. Even when sealing tape is used with success a hatch

cover will only be weathertight.

• Drain valves are not important;

it does not matter if they are blocked.

Drain valves are an essential feature of the double drainage system as they allow water that

has penetrated the hatch gasket (rubber packing) to drain away. If the valve is blocked or

closed, water will spill from the drainage channel into the cargo hold.

• When carrying a cargo on top of a hatch cover it is not necessary

to fasten cleats.

Cleats prevent excessive movement of the hatch cover as a ship bends and flexes in a seaway.

They allow limited movement to ensure correct contact between the cover and its coaming,

preventing hatch cover damage. Cargo loaded on the hatch does not secure the hatch cover

to its coaming.

• Tween deck cleats are not essential because the tween deck

covers are not weathertight.

Cleats on tween deck covers should always be engaged when the covers are closed.

This is because they stop tween deck panels from jumping when a ship pitches, ensuring

maintenance of tween deck strength. When cargo is stowed on a tween deck panel, the panel

must be secured to the ship’s structure.

• Any rubber gasket can be used provided the gasket fits the channel.

No, use only the gasket type recommended by the hatch cover manufacturer.

A Master’s Guide to Hatch Cover Maintenance

4. Leakage Problems

Most leakage problems occur because of poor maintenance. Although robust, hatch covers will

leak if compression surfaces are not aligned correctly, if gaskets are damaged or worn, if there

are cracks or holes in the plating and if there is permanent overall distortion of the covers.

Maintenance of the Hatch Cover Structure

Corrosion reduces the strength of a hatch cover. Reduced strength gives rise to increased

deflection and possible loss of the steel-to-steel contact when a cover is loaded (green seas or

cargo). If advanced, corrosion can weaken a hatch cover to the point when normal loading causes

permanent deformation and permanent loss of the steel-to-steel contact. Good contact is an

essential prerequisite for weathertightness. Accelerated pitting corrosion leads to holes in the

top plate.

Maintenance of the Steel-to-Steel Contact Surfaces

Hatch covers are designed to make steel-to-steel contact between a defined part of the

hatch cover and coaming when closed. This steel-to-steel contact determines the amount of

compression between the hatch gasket and compression bar. Contact might be nothing more

than the hatch skirt sitting on the horizontal coaming plate, although some hatches are fitted

with metal landing pads.

When the horizontal coaming plate or hatch landing pad is worn, pressure on the hatch gasket

(rubber packing) increases. If this wear is greater than 4mm, increased pressure on the gasket

will cause damage. Landing pad repair is essential.

Typical defects that will cause poor sealing.

Factors affecting weathertightness:

Maintenance of Rubber Packing – Surface Damage

Rubber packing that is physically damaged, cut or chafed should be renewed immediately.

The minimum length of replaced packing should be one metre.

Maintenance of Rubber Packing – Permanent Set

Rubber packing that is permanently impressed to 75% of its design compression should be

completely replaced. The manufacturer will provide details of the design compression. A rule

of thumb to estimate design compression is to use 30% of the packing’s thickness. Permanently

impressed rubber packing indicates worn steel-to-steel contact surfaces. Never replace

permanently impressed gaskets without checking the steel-to-steel contact points for wear

and doing repairs if they are worn.

Maintenance of Rubber Packing – Aged Gaskets

Ozone will age rubber. It becomes hard and loses elasticity. The entire length of aged gasket

should be replaced.

A Master’s Guide to Hatch Cover Maintenance

Maintenance of the Double Drainage System

Hatches are designed to drain away water that has penetrated the gasket. Drainage channels

should always be cleaned before hatches are closed, and kept free from rust scale and cargo

debris. Damaged channels should be repaired immediately and then painted to prevent corrosion.

Drainage channels are located along the cross-joint and on the coaming between the

compression bar and the inner coaming.

Maintenance of Non-Return Drain Valves

Hatch coaming non-return drain valves are an essential feature of the hatch double drainage

system. They let water that has come through the hatch cover drain away. Damaged, missing or

defective non-return drain valves should be repaired or renewed.

Maintenance of Rubber Seals on Hold Access Doors, Access Hatches

and Ventilators

Water can enter the cargo hold through access doors, hatches and ventilator covers. Maintain

them in the same way as you would hatch covers.

Maintenance of Hatch Cleats

Cleats and wedges hold the hatch in position with adequate gasket compression. (Cleats are fitted

with a rubber washer or ‘grommet’ to aid compression). Compression of the washer determines

tension in the cleat. Washers are prone to both physical damage and age hardening (weathering).

When damaged or aged the washer loses its elasticity and should be replaced. Some operators

protect the washer and screw threads with a layer of grease or by application of ‘denzo’ tape.

Typical non-return drainage valve. The double drainage system.

Maintenance of Hatch Wedges

Cross-joint wedges require less maintenance than cleats and provided the wedge sidespring is in

place the wedge will work efficiently. Check the springs regularly and replace them if they are

damaged or missing. On a closed hatch, the wedge should make contact with its strike plate on

the opposite hatch panel. If there is a gap, it is likely that the panel is distorted. The steel-to-steel

contact may be worn. Repair and alignment of the hatch panel is necessary. Never repair the

strike plate by building it up with weld metal above its original design height.

Maintenance of Landing Pads

The size and dimensions of a landing pad are dependent on the size and weight of the hatch cover.

Landing pads are normally located adjacent to cleats. The pads are fitted to the top of the coaming

and to the side of the hatch panel. Landing pads should always be repaired to their original design

height. Correct adjustment of them can only be achieved during repair when the ship is out of

service. Some ships are provided with cassette type landing pads, which are easily replaceable.

Worn ‘steel-to-steel’ contact points.

A Master’s Guide to Hatch Cover Maintenance

5. Leak Detection Tests

The two most common leak detection tests are the water hose test and the ultrasonic test.

Ultrasonic testing is the preferred method because areas of inadequate hatch sealing are accurately

located. Chalk testing (another hatch test) gives only an indication of poor compression and potential

leaks. Chalk testing is not a leak detection test. Light testing is also effective but is potentially

dangerous because personnel are in a closed, dark hold looking for light infiltration between panels.

If hatches are found to leak during a test, make the necessary repairs, then test again.

Water Hose Leak Detection Test

Water hose tests are used to determine weathertightness of hatch covers. If correctly performed,

hose testing will show hatch joints that leak.

The general procedure for hose testing is to apply a powerful jet of water from a 20-50mm

diameter hose fitted with a 12mm diameter nozzle held at a distance of 1-1.5 metres from a

hatch joint, moving along the joint at a speed of 1 metre every 2 seconds.

The drawbacks of hose testing are:

• the hold needs to be empty;

• it cannot be performed in sub-zero conditions;

• it requires the deck scupper drains to be open (potentially causing pollution);

• the test cannot pinpoint leaks on the cross-joint or side joint accurately;

• two people are needed to supervise the test.

Care should be taken to avoid excessive nozzle back-pressure.

Ultrasonic Leak Detection Test

Ultrasonic leak detection is a viable alternative to the hose test for testing hatch covers, access

doors and access hatches for weathertightness, as it accurately locates potential points of

leakage. This test should only be carried out using class approved equipment and approved test

procedures.

The test involves placing (with hatches closed and secure) an electronic signal generator inside

the cargo hold. A sensor is then passed around the outside of all compression joints. Readings

taken by the sensor indicate points of low compression or potential points of leakage.

Ultrasonic testing overcomes the majority of limitations associated with hose testing and can be

carried out when holds are loaded.

The drawbacks of ultrasonic leak detection tests are:

• the equipment requires an experienced and specialist operator to interpret the readings;

• the equipment requires regular calibration;

• the equipment is not normally part of the ship’s equipment.

Chalk Testing

When performing a chalk test, the top edge of every compression bar is covered with chalk.

Hatches are then fully closed and reopened. The rubber packing is examined for a chalk mark,

which should run continuously along the packings centre. Gaps in the chalk mark indicate lack

of compression. Chalk testing merely indicates if hatch panels are aligned and compression

achieved. It will not show whether compression is adequate and therefore it is not a test for

weathertightness.

6. Monitoring and Inspection

Hatch covers and their fittings should be inspected at the end of every cargo voyage and all

findings recorded. The pro forma checklist (Appendix 2) can be used.

Inspections should be planned and held in time for repairs to be completed before the next cargo

voyage. Empty cargo spaces of all cargo and combustible material if welding torches are used.

Inspect and Check:

• condition. Covers and coamings should be well painted and free from significant corrosion,

cracks and distortion. During an inspection look for:

– holes and permanent distortion in the plating

– distortion of beams and/or stiffeners on the underside of the top plate

– corrosion around welded connections of beams or stiffeners

– cracking of connecting joints and welds

• hatch movement. This should be smooth. If violent movement is observed, investigate and

remove the cause.

• towing and backhaul wires. These should be free of kinks or broken strands. Repair or

replace damaged or worn wires. Use extreme care when handling wires to avoid injury.

• hydraulic system for leakage.

• hinge pins. Look for wear, particularly at cross-joints and hydraulic cylinders. Worn hinge

pins can cause hatches to slew and misalign at the cross-joint(s). Misaligned hatch panels

will leak.

• drive chain tensioners. Check their condition and adjustment.

• cleats and wedges. Check for physical damage, corrosion and tension when locked.

When closed the top of a hatch panel should be in line with the next panel.

A Master’s Guide to Hatch Cover Maintenance

Drive Chains; check their length

Drive chains and associated equipment are fitted in pairs, opposite one another. The side towing

chains, sprockets and hydraulic cylinders on opposite sides should match. Adjust the tension of

chains between panels so that the chains on both sides are exactly the same length. Do this by

removing or adding chain links. If the entire length of chain needs to be replaced, then replace the

chains on both sides at the same time. Always consult the hatch cover manufacturer for details of

chain length. As a rule, chain sag, measured from the assumed horizontal at mid-point along the

chain, should be a fist wide.

Steel Landing Pads; check for wear

Worn landing pads will damage hatch gaskets and cause hatch leakage. When newly fitted and

closed in the sea position, the top plates of adjacent hatch panels should be level. Any deviation

from level is an indication of landing pad wear or permanent distortion. If noted, investigate fully

and repair immediately.

End Stop Pads; check for damage

End stop pads prevent hatch panels from overrunning when hatches are fully open.

Look for physical damage.

Hatch Wheels; check for alignment

Hatch wheels should align squarely with the hatch trackway. If the wheel axle is worn the

wheel will loll. If it does, repair immediately.

Rubber Seals; check for elasticity,

mechanical damage and permanent deformation

When hatches are opened, rubber seals should regain their original shape. If they do not,

check for ageing. Permanent deformation should not exceed 75% of the design compression.

Locking Devices and Hydraulic Cut-Outs; check that they operate

Locking devices are often pins or hooks, these should engage when the hatch is open.

Look for physical damage, rusting and seizure. Hydraulic cut-outs should move freely.

Spares

Rubber packing and adhesive has a limited shelf life, so check the date stamp and discard if

beyond the use-by date. There should be sufficient spare parts (cleats, wedges and gaskets) to

complete planned routine maintenance. Always use manufacturers’ approved spare parts.

Two panels shown out of alignment.

7. Maintenance and Repair

Poor maintenance of hatch covers causes leakage leading to cargo damage and represents a

hazard to the ship and its crew. Although hatch covers are simple and durable, their sealing

gaskets are easily damaged. The quality of sealing is affected by lack of alignment and poor

gasket compression. When hatch covers are opened at the end of an ocean voyage, look for

signs of leakage such as rust staining or drip marks.

Regular adjustment and repair, by ship’s staff, will reduce the overall cost of maintenance.

Painting double drainage

A Master’s Guide to Hatch Cover Maintenance

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