Hatch cover maintenance for bulk carrier

C Q1: Defective hatch covers are particularly associated with vessels of which of the following age brackets?
A: 10-20 years

C Q2: In a side-opening rack and pinion hatch cover arrangement, what is the function of the “pot lifts”?
A: To raise a short section of rail to bring the rolling wheels up to the running level

C Q3: What technique do automatic cleats employ to hold the hatch firmly in place once closed?
A: Wedges on the hatch cover engaging mechanically in matching wedges on the coaming

C Q4: In order to understand the basic principle hatch cover design, how must the hatch be considered?
A: As a dynamic (mobile) object on the coaming

W* Q5: If it is assumed that the covers have been properly installed, which of the following lead to the majority of the problems of accelerated wear of hatch seals? (Select all applicable answers)
A:
– Over-compression caused by corrosion or breakdown of the steel-to-steel contact
– Blocked drain channels or non-return valves
– Loads coming from inside the hatch covers, such as those due to sloshing water ballast

W Q6: In which of the following operational conditions would a solid rubber seal commonly be used? (Select all applicable answers)
A: Where there are very heavy hatch covers,
On vessels with large open hatchways, where coaming movement will be a problem
For oil cargoes on an OBO vessel
Where the vessel trades in Arctic conditions

W Q7: In terms of the sealing of a hatch cover, what are the design requirements? (Select all applicable answers)
A: The seal must be resilient or elastic enough to make up for hull and coaming deformations
The seal must be easily maintained
The seal must be suitable for expected weather conditions
Seal material must be compatible with cargo carried
Water must be kept out of the ships holds – obvious requirement but often not met
Cargo must be kept inside (relevant in case of OBO in particular when carrying oil)
– Water must be kept out of the ships holds
– Seal material must be compatible with cargo carried
– Cargo must be kept inside the holds
– The seal must be suitable for expected weather conditions
– The seal must be resilient or elastic enough to make up for hull and coaming deformations
– The seal must be easily maintained

Q8: Which of the following is the definition of “weathertightness”, as given in this program?
A: In any sea condition water will not penetrate into the ship. Sealed against fluid coming from one side of seal.

Q9: In terms of the safety of hatch covers, which of the following are appropriate considerations? (Select all applicable answers)
A: They must be able to be fully secured in the open position and released without endangering personnel
They must be able to be operated without endangering personnel up to the maximum angles of heel and trim which are specified
All fittings used for routine or emergency operation must be of adequate strength

C Q10: In determining when a hatch cover seal has reached the point when it needs to be replaced, what general “rule of thumb” is commonly applied?
A: When permanent set reaches half the design compression

Q11: What general rule does this program suggest designers of hatch covers, those who maintain them and those who operate them should direct their efforts towards?
A: To defend the thin line where the compression bar and the seal rubber meet

C Q12: If personnel are in, or could be in the vicinity of a hatch cover, what should you do before you open or close it?
A: Use all available means of communication to notify them that a hatch cover movement is about to take place

C Q13: Why is a chalk test considered to have limited value in establishing the watertightness of a cargo hatch cover?
A: Because it gives no indication of the amount of seal compression that exists when the ship is actually underway in a seaway

W Q14: As quoted in this program, which are the features listed below, render all hatch covers potentially dangerous? (Select all applicable answers)
A: They are manoeuvred by heavily-loaded wire arrangements, hydraulic cylinders or chains and often make use of gravity, particularly when closing
Securing devices are considered unnecessary by many crews and changes in draught during loading can cause them to move rapidly and unexpectedly

Q15: In an ultrasonic test, what is the severity of a leak referenced to?
A: The open-hatch reading

C Q16: Who performs the statutory annual survey on the hatch covers?
A: A classification society surveyor

C Q17: When de-ballasting is about to start, why is it necessary to have the vents on water-ballast hatches open?
A: If they are closed, the tank may collapse under vacuum

C Q18: It is February 3rd. You have just loaded a cargo of gravel in Trondheim, Northern Norway. You anticipate that, if you close the cargo hatches, the rubber hatch seal may stick to the compression bar. What can you do to prevent this?
A: Spread a non-organic grease or commercial glycerine on the compression bar prior to closure

W Q19: Which of the following are among the CRITICAL hatch cover spares to be carried on board, as recommended in this program? (Select all applicable answers)
A: Running wheels and bearings
Cleats
Lengths of hose for temporary drain “socks”
Seals

C Q20: Which of the following must there be a comprehensive record of, in order to be able to demonstrate “due diligence”?
A: Regular maintenance
All associated classification survey histories
Testing
Repairs
Inspections

Q4: Which of the following is a description of the function of periphery cleats around a hatch cover?
A: They provide horizontal restraint, control the cross-joint seal compression and ensure the edges of the hatch cover panels at the cross joint remain firmly pressed or held together and that the cross joint seal rubber remains properly compressed

Q5: Which of the following may be considered as key design elements of hatch design? (Select all applicable answers)
A: Strength
Safety
Support
Security
Sealing

Q6: After defective seals, what is one of the largest causes of serious cargo damage resulting from ingress of water, as highlighted in this module?
A: Blockage of the drain channels, non-return valves or socks by cargo residue

Q7:- Strength
The structure must be strong enough to withstand loads from inside hatch covers (such as sloshing water ballast), outside hatch (such as seawater over decks), and cargo loaded on top of hatch covers
– Hatch cover must not experience any main hull girder stresses, rather it must ‘float’ on the coaming as the ship bends and twists at sea

Security
– Means fitted to prevent hatch cover sliding longitudinally or athwartships when at sea
– Means of keeping hatch cover in contact with coaming (cleats)
– Cleats need to be resilient to allow for small horizontal and vertical coaming movements at sea

Support
– Hatch cover need to be supported on sufficient number of steel-to-steel supports
– Support pads need to allow for sliding as hull and coaming deform at sea

* Geometry of seal compression depends on, and is controlled by steel-to-steel contact. Hatch cover rests by side plate/support pads having steel-to-steel contact with the coaming. Leading to exact geometric relationship between compression bar and seal rubber. When side plate/support pads become corroded or worn, the relationship breaks down and leads to rapid seal breakdown and water ingress.
* Compression bar: Usually 40~50 mm height x 16 mm width. Preferably top edge made of stainless steel round bar welded to supporting flat bar.
* Job of cleats is to maintain with some resilience, that steel-to-steel contact

Weathertightness depends on precise penetration of hatch cover seal rubber by compression bar.
Too much: Quickly damage seal rubber and cause rapid failure
Too little: Allows seawater to get past the seal, especially when ship is rolling and pitching

W* Q1: Industry statistics clearly indicate a high proportion of reported cargoworthiness defects as being caused by which of the following areas of operation?
A: Maintenance

Q2: How does a side-rolling, chain-drive “piggy-back” hatch cover work?
A: A dumb panel with no wheels is lifted by hydraulic lift cylinders fitted to the coaming, a rolling panel is moved underneath it and the dumb panel is lowered onto the rolling panel, which is then driven to one side as the hatch is opened

W* Q4: In which of the following operational conditions would an extruded hollow section seal commonly be used?
A: Where the vessel trades in Arctic conditions

W* Q: In which of the following operational conditions would a seal with a sponge core with an outer skin made of nitrile rubber commonly be used?
A: On side-rolling cover fitted to a bulk carrier

Q: If coaming movements are expected to be significant, what type of seal will the designer commonly consider fitting?
A: A sliding rubber seal

Q: What type of hatch cover is frequently fitted with an indirect cross-joint cleating arrangement, where wedge-shaped battening devices attached to the covers engage in coaming sockets, causing the panels to be forced together as they are lowered onto the coaming?
A: Side-rolling covers

Q: Which of the following are common patterns of cross-joint cleat? (Select all applicable answers)
A: Manually-operated cross-joint wedges, screw cleats, hydraulically-operated swings seals

* Cross-joint cleats: ensuring hatch cover panels at cross-joint remains firmly held together and cross joint seal rubber remains properly compressed
– Wedge bolt, knocked into place or released by a hammer. Holds the hatch panels in a vertical direction
– Screw cleats, threaded bolts manually tightened, hold the hatch panels together in a horizontal direction
– Hydraulically-operated swing seals, less common, limited life span and difficult to maintain

* Peripheral cleats:
– Manual cleats: Basic design, minimal maintenance, effective seal
– Quick-acting cleats: “Common” or “saddle” type, rubber washer positioned between two steel washers
– Automatic cleats: Automatic operation as the hatch closes, matching wedges lock the hatch in place once closed
– Hydraulically-actuated cleats: Labour saving, may be used for heavy cleats, various designs but all tighten using power from hydraulic cylinders

Q: You are onboard a bulk-carrier, in ballast, at sea. You are to clean and examine the inner faces of the side-rolling hatch covers on no 2 hold. What particular safety measure is required?
A: Safety fencing, consisting of portable stanchions with an upper and lower safety wire, should be in place’

Q: Before attempting to open the hatch covers, what should happen to all cross-joint cleats and wedges?
A: They should be disengaged

Q: Which of the following is checked at an annual survey? (Select all applicable answers)
A: – Evidence of any significant changes to the hatch cover system since the last survey
– The condition of seals, compression bars, tracks, cleats, stoppers and the panel structures

* Special survey
– That class approval has been given for any and all repairs to the hatch covers and attendant structures and fittings
– Thickness measurements of plate and structural stiffeners
– Documentary evidence of monthly inspections by ship’s personnel

* Insurance survey
– Watertightness, as established by a hose test of equivalent

Q: What is the minimum length of any straight piece of rubber seal inserted during a repair, as recommended in this module?
A: 500 mm

Types of seals
1. Sponge core seal with outer skin
– Multi application
– Sponge rubber core, outer box of neoprene or nitrile rubber skin
– 80 x 40mm, designed compression 10 mm +/- 3 mm or 90 x 50 mm, designed compression 13 mm +/- 3mm

2. Solid rubber seal
– Special applications, e.g. heavy hatch covers, arctic conditions
– Variety of sizes

3. Hollow section
– Side-rolling cover fitted on bulk carrier
– Standard sizes, designed compression 12 mm +/- 3 mm

4. Sliding rubber
– Container ship, or other vessel with large open hatchways, where coaming movement will be a problem
– Allows more movement between hatch cover and coaming
– Typically 70 mm square, with designed compression of about 12 mm, +/- 8mm

5. Double lip seal
– Special seal for vessels with specific operational problems, e.g. OBO
– Variety of sizes and designs

Drainage system
Most covers have double drainage system.
– Cross-joint primary designs are sloped to each side so that water flows to holes in the hatch cover side plates and then drains freely to deck. The secondary drain channel leads any water to the peripheral channels. Peripheral channels are formed by the compression bar and coaming upstand, the continuation of coaming plate above top of the coaming bar. Forming a small gutter and prevents any water from going directly into the cargo hold.

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Locators/Restraints
All types of hatch covers have restraints or locators fitted to them to absorb longitudinal and athwartships forces that be experienced due to ship motion when at sea.
The hatch opening does not generally stay in a flat rectangular shape when ship is acting in a seaway. It twists and stretches back and forth. The extent of this coaming movement is most severe on ships having long and/or wide hatch openings.
Purpose: Keep seals and hatch cover in correct alignment with compression bar and coaming.
But there must be enough clearance in the locators to avoid the hatch covers picking up main hull forces when ship is at sea.

TOP 10 Hatch cover defects
1. Seal permanent set beyond point of replacement
2. Seal rubber tor, displaced or missing – including cross joints
3. Poor quality or temporary seal ‘fixes’
4. Wastage of steel support pads or coaming side plates -> over-compression of seal and subsequent damage
5. Blocked drain holes in hatch covers and coaming corners
6. Wasted cross joint drain channels
7. Cross joint cleating or alignment faulty
8. Cleats and cleat support stools wasted or missing
9. Wear on centreline wedge devices on side-rolling covers – causes cross joint to open when at sea
10. Holes in steel plating caused by corrosion, possibly localised

• This topic was modified 2 years, 1 month ago by icedcappucino.
• This topic was modified 2 years, 1 month ago by icedcappucino.
• This topic was modified 2 years ago by icedcappucino.
• This topic was modified 1 year, 11 months ago by Admin.