II-C3B-5 Survey of Bottom External and Related Items
5.1 General Requirements
5.1.1 The interval of surveys of bottom external and related items is regulated in Section 2 Chapter 5 of Regulations on Classification of Inland Waterways Ships.
5.1.2 This section is applicable to surveys of all hulls and engine items below waterline of ship.
5.1.3 In survey of bottom external and related items, when necessary and practical, the outer plates and openings below waterline and the external components of related closing devices, steering gear and propulsion system are to be examined for satisfactory general conditions.
5.1.4 Surveys of bottom external and related items are to comply with the following conditions:
(1) Surveys of bottom external and related items may be carried out in drydock or slipway, or when ship is afloat. The survey in drydock or slipway is called as survey of bottom external and related items while the survey when ship is afloat called as underwater survey.
(2) When ship is afloat, the regulated underwater survey means may be considered but special consideration is given to the underwater survey of ships over 18 years. The surveys of bottom external and related items of oil tankers, bulk carriers and chemical carriers are to be carried out in drydock.
(3) During survey of bottom external and related items, when necessary, ship is to be placed on docking blocks with sufficient height and strength for possible inspection of ship's bottom.
5.2 Inspection items of bottom external and related items:
5.2.1 Examining excessive corrosion of outer plates like bottom plates, fore plates, plane keel, aft end and aft frame, side plates, etc. or defect due to collision or stranding as well as excessive deformation or buckling. Special attention is given to the plates of end structures (fore and aft) and the connection between bilge keel and outer plate. Unrepaired prominent sunk parts or other defects are to be recorded.
5.2.2 Sea connection appliances (including valve box, valve and fastener and inlet grid) and overboard discharge valves and their fasteners on hull are to be examined.
5.2.3 Examining visible parts of propeller, propeller boss, brackets and sealing appliances. Measuring and recording shaft clearance of water-lubricating propeller with reference to Appendix 4, Chapter 5 for limits of wearing gap. For other propulsion plants, examining tightness and locking device of securing bolts of propeller blades as far as possible.
5.2.4 Examining visible parts of rudder like rudder blades, rudder shaft, rudder stock and rudder pintle as well as bearings and aft structure, and if necessary hoisting or dismantling rudder to facilitate inspection of rudder pintle. Measuring and recording the gap between upper and lower rudder bearings, and testing steering gears. Refer to Appendix 3, Chapter 5 of Regulations on Classification of Inland Waterways Ships for limits of wearing gap between upper and lower rudder bearings.
5.2.5 Examining any corrosion, cracking, leakage, etc. of rudder blades with thickness measurement when necessary. If suspicious about rudder blade water tightness or after repairing, hydraulic test or inflation tightness test is to be performed. For hydraulic test, the test pressure head is to reach 2.4m height above ceiling plate (blade may be placed horizontally), and for gastight test, the test pressure is 0.02-0.03MPa.
5.2.6 Examining connection and corrosion between rudder blade and rudder stock, and repairing serious corrosion of flanges.
5.2.7 Examining rudder stock, rudder shaft and connecting bolts and nets as well as stoppage device of rudder pintle nuts.
5.2.8 In light with special survey, hoisting locally the rudder shaft or pintle or dismantling rudder shaft to check wear and corrosion of rudder shaft, pintle and bearing.
5.2.9 Performance tests of primary and auxiliary steering gears.
5.2.10 For revolving duct pipes, in additional to reference to the above inspections and tests of rudder facilities, examining whether clearance between inner ring plate and end of propeller blade is normal.
5.2.11 Besides external inspection of fixed duct pipe, checking the technical conditions of connections between its supporting arm and hull, and whether clearance between inner ring plate of duct pipe and end of propeller blade is normal.
5.3 Underwater Survey
5.3.1 General Requirements
(1) Underwater survey may supersede required survey of bottom external and related items provided that:
a. Ship complies with the required underwater survey conditions and survey interval;
b. No report of damage to underwater parts since the last survey of bottom external and related items, neither report of need to survey or repair underwater parts;
c. Rudder facilities equipped with appliance to obtain clearance underwater.
(2) For underwater survey, application is to be tendered to the Society with time and place of survey for consent of the Society.
5.3.2 Scope and requirements of underwater survey:
(1) For underwater survey, similar to normal survey of bottom external and related items, relevant ship's information is to be available as much as possible.
(2) Underwater survey is to be carried out in enclosed waters with proper draught of ship and good underwater visibility for proper inspection.
(3) Underwater testing is to be performed by the testing companies approved by the Society.
(4) Location means on Shell plates by divers and image display means are to be appropriate and effective dual-way communication means between Surveyor and divers are to be provided.
(5) The scope of underwater survey is to be the same as survey of bottom external and related items as far as possible, and provide the information generally available through bottom survey of bottom external and related items.
(6) Underwater testing company is to tender detailed examination reports including video record and photographic record of main parts of examination for confirmation by the Surveyor.
(7) During underwater survey, if any damage or defect that needs immediate treatment is detected, more complete inspection or necessary treatment is to be carried out in drydock.
5.4 Hull Test Items
5.4.1 Requirements on hull thickness measurement:
(1) For the first special survey, thickness measurement is generally not required unless prominent corrosion exists in local parts;
(2) For the second special survey, the scope described in C4.2.3 and suspicious areas may be randomly selected for examination and thickness measurement upon the request of Surveyor; for oil barge, each deck and two transverse sections within amidships 0.4L scope and the side outer plates within amidships 0.4L scope and part of draughts are to be included;
(3) For the third special survey, each strake of each side in C4.2.3 is to be selected two points for thickness measurement while suspicious areas and remaining parts all over the ship are randomly selected for thickness measurement; for oil tanker, thickness measurement is to include each deck plate and two transverse sections within amidships 0.4L scope and the side outer plates within amidships 0.4L scope and part of draughts; for oil barge, one extra section is to be measured on the basis of requirements of the previous special survey;
(4) For the fourth and following special surveys, two strake plates at the weaker section and primary longitudinal components within amidships 0.4L are selected for thickness measurement, with not less than two points of thickness measurement at each strake plate of each side; two places of each plate of outer plate, inner bottom plate, deck and watertight bulkhead plate within amidships 0.4L, and the bottom plate and side plate of fore and aft peak tank and deep tank serving as ballast water tank concurrently are to be selected for thickness measurement; suspicious areas and remaining parts all over the ship are randomly selected for thickness measurement. For oil tanker and oil barge, one extra transverse section within amidships 0.4L is to be added in each special survey on the basis of requirements of the previous survey, and each deck plate, bottom plate and side top strake plate within amidships 0.4L and the side outer plate between light and heavy weight draughts are selected for thickness measurement. The remaining parts throughput the ship are randomly selected for thickness measurement.
(5) Before thickness measurement, paint and stain on surface of steel plates or components to be measured are to be removed and cleaned. Drilling and ultrasonic instruments may be used for thickness measurement. If drilling is used, the accuracy of measurement tools is to be calibrated; if ultrasonic thickness measuring appliance is used, its accuracy is to be calibrated. Thickness measurement is to be performed by approved measuring companies, and thickness measurement record is to be filled up in the required format and tendered to the Surveyor for confirmation. The Surveyor may randomly sample and review thickness measurement results.
5.4.2 For ship with requirement on longitudinal strength, in case of any of the following conditions, the longitudinal strength of hull is to be verified in accordance with the requirements in C7 of this section:
(1) Total sectional area of strength deck and side top strake or bottom plate and bilge strake after corrosion is less than or equal to 0%/90% of the original calculation results;
(2) If longitudinal strength is suspicious due to serious corrosion or other causes, for plate thickness measurement and calculation of corroded area, two weakest sections of larger opening areas within amidships 0.4L scope are to be selected, and three connecting frame spacing for transverse framing ships are selected while floor plates of longitudinal framing ships are selected. After thickness measurement in accordance with the requirements in 5.4.1, the total longitudinal area after corrosion is calculated. In calculation, for the corrosions connected within three frame spacing along the ship's length, only the biggest corroded sectional area is calculated and added along the ship's circumference in accordance with the regulations in 5.4.2(1) to get the total sectional area after corrosion.
5.4.3 Extreme deformation of hull components
(1) The maximum permissible deflection of buckled or raised plates between frames on hull plate and strength deck is regulated in Table 5.1:
Table 5.1
self-propelled ship
Amidships 0.4L
6%S
Other parts
8%S
Non -self-propelled ship
Amidships 0.4L
7%S
Other parts
10%S
Where: L——ship's length, in m; S——frame spacing, in m
(2) For hull plate and strength deck, the maximum permissible deflection of common depressed deformation of plate and frame due to impact, grounding, etc. is regulated as below:
Amidships 0.4L: 0.04e, but not more than 100mm
Other parts: 0.06e, but not more than 150mm
Where: L——ship's length, in m; e―― minimum size of depressed plane, in mm
(3) Though deformation limits are not exceeded within deformation areas, any defect like broken frame, torn plate or beveled plate is to be repaired.
5.4.4 Requirements on hull repairing
(1) Deformation of outer plate, longitudinal component or strength deck within amidships 0.4L scope due to insufficient longitudinal strength, or deformation of transverse frame due to insufficient transverse strength is to be repaired and reinforced by proper measures.
(2) When considering corrosion of hull components, attention is given to stiffener rigidity and connecting bracket plate of stiffener nodes to guarantee integrity of horizontal and vertical frames. Any loose weld, tear or buckling instability of stiffener or bracket plate is to be repaired.
(3) Any serious corrosion or penetrating corrosion of decks at lower ends and relevant parts of superstructure and deckhouse is to be repaired.
(4) Any cracking or breaking of components at watertight or loaded part of hull is to be repaired.
(5) Repairing of corrosion of hull components is to be decided by the following corrosion states:
a. Pitting corrosion: if diameter of pitting corrosion is not more than 50mm with scattered distribution and little amount, and the residual thickness after corrosion is less than the maximum limit required in C7.2.1 or C7.2.2, grounding after welding is allowed. But for intensive corrosion pits, patching is required;
b. Local corrosion: a few corrosive areas formed by scattered or intensive pits;
① Within one frame spacing, when accumulated width of corrosion is less than 1/2 of plate width and the residual thickness after corrosion is less than the minimum limit required in C7.2.1 or C7.2.2, patching or cutting replacing is required.
② When accumulated with of corrosive area is more than 1/2 of plate width and less than 1/2 of plate length along the plate, and the residual thickness after corrosion is less than the minimum limit required in C7.2.1 or C7.2.2, local cutting and replacing is allowed; if more than 1/2 of plate length along the plate, the whole plate is to be cut and replaced.
c. Even corrosion: if the depth of most corrosion on surface of component is more than the limit in Table C.7.2.1 or C7.2.2, it is to be renewed.
(6) The parts that exceed the extreme deformation in C5.4.3(1) and C5.4.3(2), if no cracking or breaking on surface of steel plate or frame, may be locally leveled or otherwise cut and replaced.
(7) Butt weld with corrosion into surface of steel plate or crack, and loose weld of fillet weld are to be leveled and re-welded.
(8) Shell plates and frames of primary parts are not to apply doubler plate repairing; but in the following cases if consented by the Surveyor, local cover repairing is allowed (no doubler plate repairing of any part of oil tanker):
a. Over-aged ships that definitely withdraw from service soon;
b. Locations difficult to dismantle and replace shell plate and frame;
c. Doubler plate repairing techniques of sea damage as temporary remedy.
(9) The steel plates, structural steel, welding rods used in repairing and their mechanical performance and chemical components are to comply with the requirements of Rules with relevant certificates tendered to the Society.
(10) The weld seam disposition, class and welding technique used in repairing are to comply with the requirements of Rules and NDT detection of primary weld seams may be requested to shipyard.
(11) Repairs of Shell plates, decks, watertight bulkheads, watertight doors (windows), hatch covers of oil tankers, etc. are to have tightness test in accordance with Technical Regulation on Statutory Construction Survey of Inland Navigation Ships.
(12) If conversion or rebuilding of ship involves fire protection structure, the fire structure plans and fire protection material certificating documents are to be tendered to the Surveyor for review.
(13) The oil tank allowing thermal service is to comply with the requirements of Regulations for Survey of Purge of Flammable Vapors on Ships. Before and during engineering, the engineering unit is to measure flammable vapor of engineering area and its influencing area at any time, and adopt necessary fire protection means.
(14) Without consent of CCS Surveyor, all strength components, stanchions, girders, etc. of hull are not to be dismantled or moved during repairing, and no opening or expansion of opening area is allowed on freeboard decks, sides and watertight bulkheads.
5.4.5 Anchor equipment
(1) Extreme corrosion of anchor equipment
The average diameter of anchor chains, swivel chains and shackles (connecting shackles and anchor head shackles) after corrosion is not to be less than 85% of calculation result, and if renewal is necessary, the material grade of renewed spares is not to be lower than the original grade.
(2) Repairing and testing of anchor equipment
a. Deformation or crack of anchor fluke or stock is to be calibrated or welded and if carbon content is more than 0.23%, preheating is required before welding with annealing treatment after welding.
b. Any bending or twisting deformation of chain ring is to be thermal calibrated and repaired. Crack on surface of chain ring is to be grounded and removed to prevent dent of stress concentration. If the minimum diameter after grounding is less than corrosion limit, it is to be renewed or repaired by overlaying weld. If carbon content is more than 0.23%, preheating is required before welding with annealing treatment after welding.
c. For sand hole on cast steel chain rings, if the size of sand hole is not larger than the value in Table 5.2, weld repair after grounding is allowed with thermal treatment after welding. If the size exceeds the value, it is to be renewed.
d. For defects like loose or detached anchor chain cross bars, heat tightening is to be applied. If electric weld is used, only one end of cross bar is to be securely welded to chain ring and the repaired part is to be annealing treated.
e. Whether tensile test is required after repair of anchor is to be decided by survey department as the case may be.
Table 5.2
Diameter of anchor chain (mm)
Depth of sand hole (mm)
Circumferential width of sand hole along transverse section of chain rings (mm)
＜37
3
4
37～50
4
5
＞50
5
6
(3) Performance test
a. Engine-driven windlass
Anchor throwing test may be carried out in light with voyage test. Windlass with single chain wheel is required to throw and hoist individually portside and starboardside anchors and throw them separately but heave concurrently after lifting of anchors. The heave speed of single anchor after lifting is not to be lower than 9m/min, which is not lower than 12m/min at stream section that has special requirement on anchor heaving speed.
b. Manpower windlass
Portside and starboardside anchors are thrown and heaved separately. When anchor chain is released rapidly, windlass is to have braking test to check the performance of brakes. Anchor heaving is to be flexible and reliable with performance test of anti-return gears and chain stopper.
5.4.6 Duct pipes
(1) Intermediate survey/special survey
a. Examining corrosion of outer plate and inner ring plate of duct pipes, and serious corrosive area is to be selectively thickness measured by shipyard and owner together with the Surveyor.
b. Examining whether the gap between inner ring plate and end of propeller blade is normal.
(2) Extreme corrosion of duct pipes
a. The maximum residual thickness of corrosion of duct pipe outer plate and fore and aft inner ring plates is not to be less than 60% of regulated thickness.
b. The maximum corrosion thickness of inner ring plate of duct pipe is not to be more than 40% of original thickness or 6mm, whichever is smaller.
5.4.7 Repairing and testing of duct pipes
(1) The parts of duct pipe outer plates and fore and aft inner ring plates with residual thickness of corrosion less than corrosion limit may be patched and welded but not cover repaired. The surface after repairing must be kept smooth.
(2) The parts of inner ring plates of duct pipes with corrosion thickness not more than corrosion limit may be weld repaired with surface grounded. Before welding, rust and stain are to be removed with measures to prevent weld deformation. Weld quality must be good with no defect like gas pore, slag, lack of penetration, etc.
(3) For the inner ring plate of steel plate possessing weld, it is to be partly or wholly renewed when its corrosion thickness is more than corrosion limit. For the inner ring plate of cast steel, when corrosion thickness is more than corrosion limit, it may be repaired by possessing after weld or cover on boring holes.
(4) The gap between end of blade and inner ring plate is to be even and close to the original design gap. The minimum gap is not to be less than 0.4 times of the original design gap while the maximum gap not more than 1.6 times of original design gap.
(5) After completion of repairing, the duct pipe is to have gastight test with test pressure of (0.005d+0.25)Mpa where d is full-laden draught (in m). After 15min the weld seam may be covered by soap water to see any leakage. Test holes are to be sealed after test.