DRY DOCK - VESSEL SHELL INSPECTION

Inspection Procedure from Fore to Aft

1) Front view
(1) A bend in the stem by comparing the port and starboard sides, or a bend due to contact of the stem with some object can be detected only when viewing the ship from the front.
(2) Dents in the shell plate at the bow and corrosion due to the anchor chain rubbing
(3) Shell plate near the bell mouth
Dent in the shell plate where the anchor fluke strikes around the shell plate.
(4) Is the hull resting correctly on the blocks? Although this point is not related to the Docking Survey, you can judge the Dock Master's skill in docking work. If the hull is offset excessively to one side, the keel might be damaged.
2) Oblique forward part 

The bow of the hull is as shown in the figure. Stand in oblique forward position and examine the locations listed below.
1) Condition of side shell at the forward region Check for dents in the shell from this position. Dents frequently occur in the fore flat portion of the hull at the bow when the ship comes in contact with the quay while berthing.
2) Area of shell chafed by chain
Carefully observe corrosion due to chafing with chain . Use a ladder for inspection, if necessary. Corrosion mainly occurs in the hatched areas shown in the figure below; instances of grooved corrosion have been frequently observed. If corrosion is severe, these area should be gouge the welded beads and re-weld. If the ship is to operate in coastal water routes and is likely to anchor frequently, a half-round steel bar fitted near to the seam will prevent chafing
3) Contact with anchor fluke
Examine the area around the bell-mouth from this position.
Weather three points, that is, both anchor fluke ends and crown, are well fit to the shell plate 　 If one is not contact to the shell plate, the clearnce is to be filled up providing a doubling plate.
　
4) Forward end of the keel
Confirm that the keel is sitting correctly on the keel blocks. If there is clearance between keel and blockl, the forward bottom may be lifted or the top surface of keel block is not correct.
(3) Forward bottom 

1) Carefully Inspect for dents that might occur in the keel or A strake because of panting.

2) Watch the area between keel blocks where the keel plate will be corroded.
Because during previous drydocking top of blocks ware not painted
The welded joints of the keel are likely to corrode easily. 

A. Chain rubs against the shell plate and peels off paint on the welded beads
B. The portion of the beads where paint has peeled off and subjected to be corroded.
C. Corrosion progersses
D. Appearane of grooved corrosion

(4) Bilge keel fore end
Aftre walking under the bottom shell, go to the sip side, and look through the all bilge keel from fore end to the aft end. We can easily find out the deformation
of bige keel . 




1) Simultaneously check the fore end of the bilge keel. Sometimes the crack appears at the fore end. Ensure that the crack (if it exists) does not extend to the bige strske. Also check for corrosion, because corrosion frequently occurs at the front of the bilge keel.

2) Inspect the side shell in this area.

Sometimes the crack of bilge keel propagates to the side shell.

3) Cracks often happen at the local joints of the bilge keel and extend to the side shell. The bilge strake above the bilge keel is often corroded excessively.

(5) Midship Part
We have to continue the inspection of the bottom. The main points of the hull mid?body are listed below. 

1) Condition of shell amidships
When the ship has the side ports, as in a refrigerated cargo ship, check at the four corners carefully. Cracks happen at the corner because of shearing force.

2) Check the freeboard mark, The mark might have been disappered or there might be a mistake in the characters. Also check the draft marks

3) Check for abnormal corrosion in the bilge strake. Corrosion occurs in the side shell of a ship that has been moored for a long period at a quay, because of the electric potential difference between the quay and the hull corrosion frequently occurs in the bilge strake.

4) Inspect the deck scupper opening.

5) Engine room area
In case of the ship with midship engine, the followings are to be examined.
1)Sometimes crack appears at the corner of sea chest and valves.
These items are carefully examine after erecting of stagings and cleaned.
and also look into the inside of the distance peaces.
2) Corrosion often appears in the shel plate behind the boiler blow -off opening.

(6,7 and 8) Oblique stern part
1)　Aft end of bilge keeel
the same as (4)
2) Shell plate
Inspect the shell in the aft region. The thickness of the shell plate in this region is less than the mid ship region. In aged ships small holes appears　because of wear and tear.
3) Engine room
Please refer to Midship part.

(7) Stern part
Not only hull construction we have to examine the rudder and propeller.
1) The clearance between the keel blocks and the keel
examine the clearance carefully. The stern frame might be raised because of hitting the bottom or impact with other objects. Details of the stern frame damage and repair works will be introduced in the other home page in future.
2) Propeller and rudder
Although the propeller falls under the responsibility of the Machinery Surveyor, but the Hull Surveyor has to inspect the propeller during bottom survey. The Machinery Surveyor starts his inspection after the sea chest cover is removed and staging have been erected around the propel for inspection. Thus the inspection by the Machinery Surveyor might be a few days later than the inspection by Hull Surveyor. Major damage to the propeller blade or the guard 

ring can be easily detected; observe the conditions of the propeller and guard ring and if we find abnormalities, report them to the Machinery Surveyor after the Bottom Survey. Because the date of undocking of a ship is fixed, if repairs to the propeller are required, they should be carried out at an early stage.
The following points including propeller should be examined.

1) Is the shoe piece raised ?
2) Is there an abnormality in the stern frame ?
3) Is part of a propeller blade missing ? Are the blades deformed ?
4) Has a guard ring been fitted ?
Inspectons of stern frame and rudder are described in the following sections

(8) Aft View
Inspect the stern and the rudder from this position.
1) Whether the rudder is amidship position ?
2) Is the rudder centred ?
3) Whether　the shoe piece is not twisted ?
4) Are the propeller blades normal ?

Bottom survey should be carried out after the bottom shell is cleaned after removal of the barnacles ,algae and shell-fishes and with the bottom shell is in the dry condition. However when the damge to the bottom is suspected after any accident in the previous sailing, It should be inspected immediately after the water in dock is discharged, then, the repair methods and the scope of repair should be decided as soon as possible. the scratch or small indents in the bottom shell are re-inspected after the bottom shell is dry and cleaned.

1) Side and bottom shell
2) Bilge keel
3) Stem and Stern frame
4) Rudder (measurement of bearing clearance)
5) Openings (sea chest, side port)
6) Scuppers, discharge ports and their valves
7) Stern bearing (measurement of clearance in stern bush or wear down of propeller shaft)
8) Stern seal
9) Propeller (dye penetration test for blades if deemed necessary)
10) Sea valves (both in dock and also in engine room)

Procedure for Bottom Survey

Similar to other inspections, a bottom survey is a kind of visual inspection.
Tools used during a bottom srvey are a test hammer, light, measuring tape, and a stretched string for measuring the depth of dents. A large hole or indent in bottom shell can be detected easily by anybody, but it is very difficult to
find any small indent or cracks while walking around the dock. The bottom survey is hard work; if we get tired, we are likely to overlook large dents. Procedures for detecting defects in the hull when the ship is docked are described below.

 Inspection of Bottom Shell in Dry Condition
If we inspect the shell immediately after water is discharged from the dock and when the hull is still wet, we cannot see the water on the shell if there is a leakage of ballast water through fine cracks in shell plate or remaining water. In the same way a bottom inspection is extremely difficult during the rainy season and on damp days because a large amount of dew remains on the shell plate due to the difference between ambient and shell temperatures. If major damage due to stranding or contact is known beforehand, even if the shell plate is
still wet and uncleaned, we should inspect damage as soon as possible to decide repair method and extent. In this case the bottom should be inspected again after the shell plate is dry and cleaned.

 Inspection before Painting
Shell plating is to be inspected before re- painting. Because in a wet painted condition we cannot detect fine cracks. If you refuse bottom inspection on holidays or weekends, and carry out the inspection on the following working day, there is a possibility that painting will have already commenced and small cracks will be covered with paint.

 Symmetrical Examination
Notwithstanding the bottom survey, the hull structure is generally symmetrical about the centreline. With the exception of local damage, such as dents due to contact and cracks, if we find a crack on the starboard side of the hull, there is a high probability of finding a similar crack on the port side at the same location, although there are exceptions to this case. We need to check both port and starboard sides paying attention to both sides.
 Dirty Spots
On both bottom and side shells, if we find spots that are dirtier than the surroundings, there is a possibility of a flaw in the vicinity. The area where the paint has peeled off due to abrasion must be carefully examined.
Generally, such an area will be badly corroded.

Wet Locations
If we find partly wet spots in a dry shell area, small cracks may be concealed. After cleaning the shell plate, sometimes algae or barnacles remain at wet areas. Such locations often develop cracks. From this point of view, the bottom inspection should be carried out when the shell is completely dry.

 How to Detect Dents
Large local dents can be easily detected but it is easy to overlook a dent that extends over a wide area. In particular, dents in the curved shell plate in the bilge, fore and aft peak parts are difficult to identify. If the side shell plate is viewed directly from the dock side, dents can be overlooked easily
because of the effect of light rays striking the plate at this area. There was an instance of a large dent being detected in the side shell plate after all inspections and repairs were completed and the ship was just about to sail.

1) Side shell plate
If the side shell plate is inspected by looking at it from various angles or by looking up from the dock , dents can be detected easily. Locations that are suspect may be observed later by looking down and inspecting the shell plate from the deck. A dent in the plate can be overlooked if the shell plate is examined from position A. The plate must also be viewed from position B to check for dents. 

A dent in the plate can be overlooked if the shell plate is examined from position "A". The plate must also be viewed from position "B" .
Have a look the side shell plate in the vertical and fore-aft directions.
Side shell
The followings are the example of the defects in the side shell.
1) Corrosion
2) Dents and fracture due to contact with quays or floating objects
3) Cracks in the longitudinal or transverse direction as a result of development of cracks in the internal members
4) Wear to the shell due to internal corrosion in addition to the above defects
5) Cracks migh occur in the side shell due to shearing force　caused by inappropriate jumping loads. however, no cases of damage to a side shell due to shear caused by loads in the longitudinal direction have been reported

(2) Dents and fracture due to contact

1) Both forward and aft ends of flat parts
Dents and fractured openings are likely to appear in these parts when the ship comes into contact with the quay when berthing. These defects are often observed in car carriersand ships operating in narrow waterways, such as the St. Lawrence waterway are also observed to have dents at these area.

2) Fore and aft body near the waterline
Dents appear in these area when the ship is pushed by a powerful tug boat while berthing.

3) Stern
Deformation apperas at the stem when the ship hits floating objects. Sometimes it is difficult to find such a derormation just looking frome side. It is better to examine from just in front of the ship.
Indent of the shell is difficult to distinguish so sometimes it is better to examin　from the deck looking dowawards .

4) Near the bell-mouth
Dents and fractured openings are caused when the anchor fluke frequently hits the side shell.

5) Range of abrasion by chain
Grooved corrosion due to chafing by chain appears in the area of spurling pipe opening.

6) Near the hatch openings
In ships that load/unload cargo from/to barges, dents are often caused when the barge or the cargo comes into contact with the ship.


2) Bottom shell 

(1) Bottom scratches and Dents
Most damage to the bottom shell is due to contact with objects on the seabed. Bottom scratches are slight damages. Such damage happens when the ship operates in shallow waters In many instances, bottom damage due to contact starts from the forward part and disappears around midship.
Because of scratches, the bottom paint has peeled off and corrosion occurs. In this case, remaining paint and rust should be cleaned by shot blasting and properly re-painted . When the bottom has had contact with a coral reef or rocky seabed, large dents and/or holes appear with scratches. In this case, as a matter of fact, fractured shell plate should be cropped and renewed with damaged internal members. If the dents are relatively small, they may be left as they are with some effective internal reinforcement.
If we find a large fractured opening during the bottom inspection, naturally we should recommend repairs. However, there have been many instances where the shipowner has believed that there were no abnormalities and dents were found during the bottom inspection, which naturally gives the shipowner a headache. The shipowner usually decided sailing schedule beforehand, they hate prolonging docking period because of major repairs, they persists in putting off major repairs, and try to carry out simple repairs within the drydocking period. That is why sparks usually fly between the Surveyor and the shipowner's representative.
Regardless of experience of bottom inspection, the surveyor always feels uneasy before docking survey. 

 Small dents in the bottom shell plate can be detected easily if we bend our waist and look backwards to view the bottom shell between legs, thereby lowering your line of vision. When the beam of light is projected parallel to the bottom, a dent, if present, can be detected as it will appear dark. However, in a ship of riveted construction, the lapped parts of the bottom shell appear shaded and are likely to be mistaken for dents. 

If we find a clearance between the keel block and the keel, a dent is likely to exist in the keel.
When

the big and widly repairs works to the bottom are carried out , in the next docking widly dent may appear in the same area.

In case the floating dock , the dock itself may deform as the same as bottom. In this case a clearance between keel blok and keel may not be appeared.
Lower our line of vision, If we inspect the side shell by looking down from the deck,we can easily detect dents 

Measuring and Recording of Dents
If the dent is minor and repair is not necessary at that time , it may be recorded in the survey report without outstanding recommendation. At the next docking survey the same atra should be re- measured. if the size of the dent is increased, repairs should be recommended. 

 How to Measure Dents
Measurement using a stretched string is easier. Use two magnets for securing both ends of the string to the bottom shell, and measure the dent using a scale. This measure-ment can be performed single-hand. The measurement using transit is also useful, 

6.7.2 Precautions during Measurement
Because the measurement is to be carried out to determine whether a dent has increased in depth by measuring the same location again during the next docking, care should be taken to record the measurement points and the reference points for measurements correctly, so that the dent can be measured at the same location and compared to the previous measurement. As shown in the figure below, A and C are taken as
reference points, and the depth of the dent is recorded as PR. During the next measurement, if A and B are taken as reference points and the
depth of the dent is taken as PQ, it indicates that the dent has reduced. The fwd-aft position and position in the breadth direction of the reference points should be recorded for future reference, as shown in the figure below. The reference points should preferably be taken at bulkheads or other locations where movement is considered to be minimal. In the case of a double bottom, record whether the tank is empty or full during the measurement.

 Bend in Bilge Keel
Although no requirements for bilge keels are prescribed in classification rules, if bilge keels are fitted, they should be inspected. Bilge keels might bend because of contact with the sea bed or contact with floating objects.
If we view the bilge keel from end to end, we can easily detect a bend.
Damage to the bilge keel is as follows;
(1) Bilge keel dropped off, a part of bilge keel ripped off, kinks in bilge keel
The bilge keel is a member that does not need to conform to classification society rules. However, if it is damaged, it is normal to repair the bilge keel, usually under insurance.

(2) Cracks at ends
Aged ships which constructed with rivet not weld. Rivets at the ends of the bilge keels often worked loose. In a welded ship, the welds at the both ends are provided with large leg lengths, but sometimes cracks are found at the ends.

(3) Local joints of the bilge keel
The block butt in the hull becomes a local joint in the bilge keel. If welding at this location is defective, cracks appear in the joint. If the crack progresses and reaches the bilge strake, water penetrates into the hull. In case of tankers, this defect leads to marine pollution. During a bottom survey, check the side shell plates at the location of the bilge keel　join.

(4) Box-type bilge keel
In fine and high speed ships, box-type bilge keels are frequently used. The box structure is watertight, but water sometimes penetrates into the box through small cracks in the welds of local joints. If the local joint is wet, there is a possibility that water has penetrated into the box. In such cases, carry out the air test, find locations where leaks start and recommend welding repairs.

(5) Corrosion of the bilge strake
Although not directly related to the bilge keel, when we inspect the bilge keel, check for corrosion of the bilge strake above it. Bige strake above the bilge keel
is corrosive than other strake.

 Damage to Internal Members
Cracks in the sheer strake at the ends of superstructures
Cracks sometimes appear at the sheer strake at the fore and aft ends of the superstructure (Bridge) of "Three Islander" ship and long Poop or long F'cle ships because of hoging and sagging.
Sheer strake at the break of the superstructure should be carefully examined



 Shell plate in way of the the aft peak tank
In ships with a long aft peak tank such as ocean tugs boats or some car carriers, aft peak above the rudder is flat and wide. sometimes crack because of stern vibration appears in the APT and may propagate to shell plate. Care should be taken.

Vicinity of bulkheads
Cracks may also occur in the vertical direction along the bulkhead due to the difference in rigidity of the frame and the bulkhead. these cracks propagete to　shell plate. This situation is shown in the figures below. Shell plate In the vicinity of bulkhead should be carefully examined not only outside but in the hold side.especially in aged ships 

Crack in rudder plate : known after pressure test if not visible.

Bilge part
Cracks at the lower ends of frames in cargo holds sometimes extend to the shell plate. Cracks 
Even a minor dent of bottom shell plating it may accompany a damage of internal members such as frame, bulkhead or floor.

 Aft end of collision bulkhead
A large number of internal members, such as frames and stringers, are provided in a relatively small area of the fore peak tank. It means that the fore peak tank is a rigid constructioncollision. While the hold adjacent to the fore peak tank is a large, broad space with a small numbers of internal members per unit volume. Moreover, this region is often subject to large wave impacts, which cause cracks in No. 1 hold.
As the reinforcement against panting, classification rules request side stringers or brackets in the region between the collision bulkhead and 0.15L from the bow. But at the end of these members crack appears and develop to the side shell. Therefore, the vicinity of the ends of these members should be carefully inspected . Initial cracks appear in the vertical direction and have a length of 50 mm to 100 mm. 

(2) Dents due to panting
When the ship sails in rough weather without reducing speed, dents might occur in the keel and A strake starting from the fore peak tank to the middle part of No.1 Water Ballast Tank , because of the relation between ship speed and curvature of the forward bottom. In the worst case, the floors in the tank and bottom stiffeners buckled.
Naturally, the Surveyor should recommend repairs to the shell, as well as the internal members.

(3) Corrosion of keel and adjusent A strake
Re-painting of the area on the keel block is impossible. So after undocking and also long boyage, these unpainted area is much more corrosive than painted area. the corrosion of welded beads is more heavy than the plate itself.
At the bottom survey previous un-painted area which we can find easily because of much rust should be carafully examined espacially welded beads. When the beads is excessively corroded, rust should be removed and it is necessary to re- weld and after well painted. 
Corrosion
The shell plate is generally painted when the ship is in drydock but in the hold it is not well painted. In the following area shell plate is thinner than other area. If necessary the tickness should be measured in aged ships. Locations to be checked carefully .


(1) Chain locker bottom 

Ventilation of the chain locker is not enough and bilge water accumulates in the bottom, resulting in the rapid onset of corrosion. In large ships, the chain locker is isolated from the shell plate, corrosion does not appear in the shell plate. However, in the normal ships, the shell plate forms a part of the chain locker, side shell plate corresponding to chain locker bottom should be carefully examined. 
(2) Tank top
Corrosion at the sides of the tank top plate proceeds faster than other area, but it is not faster than in chain locker. If corrosion at the sides of the tank top plate in the aged ships is neglected, it extends to the shell plate and sometimes it leads to corroded openings appear in the shell plate. In ships where the sides are raised, such as bulk carriers, this problem does not occur.
(3) Aft end of 'tween deck
In ships with a 'tween deck, bilge water generally accumulates at the aft end of the deck and causes corrosion that extends to the shell plate. This is not a major problem, except in aged ships.
(4) Near the forecastle aft bulkhead
Bilge water in the forecastle accumulates at the aft end on both side. Therefore, forecastle end wall on both lowest corners to be carefully examined .
(5) Corrosion below side scuttles

Starting with Special Survey No. 2, it is mandatory to measure the thickness of the shell plate below side scuttles. Rules prescribe inspections of the condition of the shell plate below side scuttles after removing the lining during Special Survey No. 3. In practice, the space below the side scuttle is narrow and is covered with lining boards. Sea water often enters through open side scuttles; the humidity is so high, and corroded fracture openings gradually appear in the shell plate. Because this area is above the waterline, we need not be excessively concerned about the danger of water flooding into the ship immediately.
 when we entering the dock, check the plate below the scuttles on the super-structure from the dock floor or dock sides and compare the condition with the surrounding shell plate. If rusting is excessive, enter the cabin after completion of the bottom inspection and ask to remove the lining and examine the state of corrosion in the superstructure side plate.

(4) Corrosion of beads
Grooved corrosion, which at first glance looks like cracking often occurs in heat affected zones of seam and butt weld. It means the both side of beads. The corroded beads should be gouged and re-welded.
(5) Wrinkled corrosion
Small craft and ships adopting the transverse system of framing might develop wrinkles in the transverse direction in the midship area of the bottom shell. These wrinkles are considered to occur because of buckling. If possible, it is better to fit the transverse carlings in the double bottom tank to prevent buckling.
(6) Sea chest
After removing the grating of the sea chest in way of the engine room or the pump room, climb onto the staging and inspect the internal parts of the sea chest. The sea chest forms a discontinuity with the rest of the bottom shell; therefore, cracks might apear at fillet welds of girders and floor plates.

  Plate Terminology and Shell ExpansionPlan
Refer to the Shell Expansion Plan when we want to check the size, type and thickness of a shell plate in which damage has occurred. The Shell Expansion Plan shows the bottom shell

 and side shell on one sheet of drawing with a 1:2 scale for units in the longitudinal and transverse (vertical) directions. That is, if the scale in the length direction is 1:100, the scale in the width direction is 1:50. In addition to shell data, the positions of holds and tanks, frame spacing and dimensions of all frames are also shown in this drawing. Plates on the shell are named as follows: 

K for keel plate; plates adjacent to the keel starting from the garboard strake are named sequentially as A, B, C, D, E, F, G, H, J, L (not K as "K" is used for the keel plate; not "I" as it is likely to be misunderstood for some other symbol). The topmost strake (sheer strake) is named S (using the initial letter of sheer strake). For the same strake (say H-strake), the plates are numbered 1, 2, 3, and so on, starting from aft and proceeding forward. The fore and aft parts of the hull are slender, and the plates are narrow; therefore, at the stern, the plates adjacent to the C strake and nearer to the centre are divided into two strakes, C and D, while at the bow, the C and D strakes are combined to form the C strake. The tank top and bulkheads that fall on the side shell are indicated by broken lines; the frames are indicated by single dot and dash lines. The number above mark is the plate thickness to distinguish it from other values. Class D, Class E, etc. indicating the kinds of stee,such as D class steel etc. The mark (<) shows a joint in the breadth direction of the plate; a long S shows a joint in the length direction or a block joint.

 Repair symbol mark
There are 5 international repair marks. The origin is unknown.

How to Predict Defective Locations
If defects such as dents are found in the side shell plate or the bottom plate, the location of the part where the defect has occurred should be recorded. However, a hold or tank with a dent cannot be identified from the outside. This has to be judged later by observing the Shell Expansion Plan, but the methods described below may be used to confirm the approximate　position of the defect

(1) Judging the position of dent by the mast or crane post
If the dock is wide, move the dock side so that　we can see the mast or crane post on the deck. These are usually installed on a bulkhead. For instance, you can judge whether the dent is between No. 2 Hold and the No. 3 Hold. However, if the width of the ship covers almost the entire width of the dock, this method cannot be applied. 

(2) Judging the position of the dent looking for the bottom plugs In double bottom tanks, bottom plugs are installed at the aft end of the tanks near the centreline of the ship for draining residual bilge in the tanks when the ship is docked. These plugs are coveredwith cement; therefore, if you observe a raised part similar to a small dish, it is a bottom plug. From the bottom plugs, you can aee the approximate position of the aft end of each tank and estimate the position of the damage.

Sea Valves

If a sea valve and the distance piece are holed, water enters into the hull
and may cause a major casualty such as sinking of the ship; therefore, the inspections should be
 Hull
"Sea inlets and overboard discharges below the waterline are to be examined and valves and cocks together with their fastenings to the hull are to be dismantled and examined. Dismantling may be dispensed
with at the discretion of the Surveyor, provided they were dismantled and examined at the last Docking Survey."
Machinery
"All openings to the sea including sanitary and overboard discharges in the machinery spaces and pump room with valves and cocks are to be examined internally and externally. The fastening of valves and cocks to the hull are also to be examined."

 Position of valve
The weather deck discharge pipes are fitted above load water line without any valves but most of discharge and inlet pipes are in stalled below the load water line directly to shell plate through the distance piece or the sea chest
 Damages of valves and distance piece
 Storm valve
In aged ships storm valve should be completely opened up and inspected.
If the cover protruding from the valve body, it should be removed and completely opened up.
(1) Blockage
When the valve is opened up, you might sometimes find toothbrushes or combs etc. came down from the washing basin which block the flow in the valve. In such cases, the valve plate will not operate, and the valve will not function as a non-return valve.
(2) Corrosion
If the casing or the valve plate is excessively corroded, there might be corroded hole and if the arm to the hinge is also corroded and worn out, the valve plate should be renewed.
(3) Wear of gasket
The gasket of the valve plate and the gasket fitted to the cover might be worn out and thickness reduced. If the cover is worn out, naturally water will leak.
(4) Wear or missing hinge pin
The hinge pin might be too much corroded or missing. If the hinge pin is missing, the valve plate works loose.
(5) Missing counterweight
Sometimes the lead counterweight fitted to the valve plate is lost . In such a case, the valve will remain open permanently and will not function as a non- return valve.
(6) Defective spindle and handle
In the screw-down type stop valve, sometimes　the spindle and the handle　are broken
Other defects in valves (1) Corrosion and cracks
A major problem in valves is a corrosion of the valve body. In old ships, openings appear suddenly because of corrosion, water floods into the engine room and in bad case the ship sinks.
Examine the thickness of body by hammering; if it feels thiner, open the valve completely
 and inspect thoroughly the internals . If a rubber lining has been provided, corrosion will be small; however, if the rubber lining has partly peeled off, concentrated local corrosion occurs. 
Even if other area is is satisactory, holes might develop at the peeled off spots.
In angle valves and globe valves, corrosion in valve body, valve stem and valve seat can be carefully examined, in addition to corrosion in the
casing, sometimes, cracks are also detected in the casing.
In Sluice valve, the grooved disk guide is provided on both sides of the casing. It prevents horizontzl movement of the valve disk. When this guide　is heavily corroded valve disk do not move smoothly.

(2) Valve connection bolts or studs
Bolts or studs used for securing the valve to the sea chest do not have any problems when they are made of stainless steel. But if they are made of mild steel they rapidly corrode because they are immersed in bilge.
If the base of the valve is, corrosion progresses rapidly. In some cases, bolts head is disappeared.

(3) Damage and wear to the valve seat
When the valve seat is damaged and the contact between sest snd valve disk is defective, watertightness will not be maintained even if the valve is closed. If such defect is found , it should be taken to the machine shop
and repaired to obtain the proper seating.

(4) Leakage from gland
When the gasket through which the valve stem passes is deteriorted,
the tightness is not kept. The basket is the important parts.

 Distance Piece 

Generally valves are not directly fitted to the shell plating, but short piece of pipe which is called distance piece, is used between valve and shell plate. If a hole is made in this distance piece due to corrosion or crack,sea water runs into the engine room.
We have to carefully examine the condition of distance piece. If corrosion is suspected, the plate thickness should be measured.
Not only corrosion sometimes crack appeas at the bracket end.
If the paint in the distance piece is partly dirty, there is a possibility of hole or crack.
The scupper pipe on the exposed deck is the same as the distance.
piece.
Check point of distance piece is as shown in the following figures.