Tuesday 3 December 2013

Docking Survey

１．Preface　

This document describes the general background of a "Docking Survey," which has an important role in a classification survey, and is meant to be used as a reference for surveyors before they carry out field inspections.
This document was prepared by Ichiro Ishikawa, former Chief Surveyor, and is based on the prerequisites described below.

1-1. Underwater inspection

An underwater inspection that replaces a docking or slipway inspection which is carried out by a company approved by the Classification　Society. The bottom shell, rudder and propeller should be inspected
indirectly by observing the television images transmitted by an underwater camera used by a diver.
Detection of abnormalities should fundamentally conform to the contents of this document; therefore,　details of underwater inspection are not specially described here.

1-2.Method of repairing damage

Various types of damage, such as damage due to stranding and contact with the bottom shell, may be detected during a docking survey. Such damage is usually repaired by the shipowner under insurance, but in this document details of repairing methods will not be described. These tems will be introduced in the separate home page describing "Damage and Repair" in futuer.

1-3.　 Propeller

The propeller and propeller shaft are inspected at the same time as a bottom inspection. However, shafts need not necessarily be inspected during a Docking Survey because "Propeller Shaft and Stern Tube Shaft Surveys" are independent from the Docking Survey under the responsibility of machinery surveyor but brief explanation is entered in this document.

1-4. 　Anchor and Chain Cable

An inspection of the anchors and anchor chains is not a requirement of a Docking Survey; these items fall under the purview of a Special Survey. However, as it is customary to inspect these items during a Docking Survey, they are covered in this document.

1-5. Damages in Bottom

Except for defects that occur because of stranding and contact with objects or the sea bed, defects in the bottom shell, such as deformation and corrosion almost never occur unexpectedly; they occur gradually over a long period. Because the most repairs to the bottom shell involve repairs to double bottom tanks, considering that the tank should be emptied and cleaned before starting repairs and hydrostatic tests carried out after repairs, the period for repairs should be estimated aproximately. Therefore, the data below should be collected before performing a bottom survey.

1-6.　Study the history of the ship

Before carrying out an inspection, have a look the survey report file submitted together with the survey request application, and check the recommendations and the precautionary items if any .And read old survey reports as far back as possible, at least until the previous bottom inspection. Dents in the bottom shell may be under- or over-estimated, or overlooked depending on the position to be inspected, increase or decrease in the intensity of light rays, and arrangement of blocks. Dents that have not appeared in reports in the last few years, may have been reported already in the past. There have been instances

1-7.　Working Schedule

The schedule for docking , undocking and sailing dates are determined by the shipowner's sailing schedule and the shipyard's docking schedule; therefore, these informations should be obtained for reference. If the docking period is as short as two or three days, both shipowner and shipyard are unlikely to carry out the big repairs to the bottom or side shell unless the shell is heavily damaged. The docking period gives you an approximate idea of the extent of the bottom shell works that is likely to be carried out. Information such as the time the ship will be docked/undocked , how many hours does it take the dock will be dry, and capacity of discharge pumps of the dock should be obtained for reference.

1-8.　Marine casualties

After the previous docking, instances where the ship hits the quay, or the bottom shell came in contact with the sea bed or floating objects, should be correctly entered in the log book. It is recommended to ask the superintendent or the Master about the instances of marine casualties before starting inspection . If there are any report of bottom contact, the bottom inspection should be carried out with special care; sometimes , In this case the major repairs to the bottom shell may be necessary. Another method of collecting data is to be request shipyard supervisor to show the specifications for repairs carried out to the ship, if possible.

Photo 1-1 ULCC in Dry Dock
One of the world largest ship, Piere Guillaumat in LISNAVE Margueira Yard in 1978 Dimensions Lpp 401.10 x B 63.01 x 35.92 m, DW 555,031t Built at the San Nazaire Ship Yard in France BV Class It takes more than 3 hours to carry out the bottom Survey.

2. Docking Survey

A　docking survey is also called a bottom survey. According to the "Protocol of 1988 relating to the International Convention for the Safety of Life at Sea, 1974", a bottom inspection is defined by a lengthy expression: thst is, "Inspections of the outside of the ship's bottom". Area of the hull under the water-line are always immersed in water ; therefore, the condition of damage in the event of the stranding or bottom contact can not be observed. The objective of periodical docking is to inspect the area of hull beneath the water- line. Offshore structures in conrtast to a ship, do not sail throughout the world and suffer neither from stranding nor contacting with other object. Conversely, docking an offshore structure is very difficult; therefore,　underwater inspection　by　an underwater camara inspection instead of docking is justifiable. There is no word corresponding to docking survey in the SOLAS Convention. But the Classification Sosieties request the periodical docking survey to the shipownes. According to their requirements ships must be in dry dock twice in 5years as shown in the following figure.
##
Before 1964 the docking survey was requested every year, because　at the Annual survey, docking was requested. Some shipowners put their ships twice in the year. But now the docking is only 2times　in 5years. The reason　of this relaxation was the improvement of paint. 　At that time the effectiveness of paints continued only one year or less. If the ship was not docked for more than one year, the paint would peel off and alrae and shellfishes would stick to the hull　under the water line, resulting in a drop of the ship's speed . For the shipowners at that time decreased speed was bigger problem than the expence of docking.









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Marine Survey Practice: Surveyor Guide Notes for Oil Tankers Survey

Marine Survey Practice: Surveyor Guide Notes for Oil Tankers Survey:

Surveyor Guide Notes for Oil Tankers Survey

An oil tanker, also known as a petroleum tanker, is a merchant ship designed for the bulk transport of oil. There are two basic types of oil tankers: the crude tanker and the product tanker. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally much smaller, are designed to move petrochemicals from refineries to points near consuming markets.
Oil tankers are often classified by their size as well as their occupation. The size classes range from inland or coastal tankers of a few thousand metric tons of deadweight (DWT) to the mammoth ultra large crude carriers (ULCCs) of 550,000 DWT. Tankers move approximately 2,000,000,000 metric tons (2.2×109 short tons) of oil every year. Second only to pipelines in terms of efficiency, the average cost of oil transport by tanker amounts to only two or three United States cents per 1 US gallon (3.8 L).
Some specialized types of oil tankers have evolved. One of these is the naval replenishment oiler, a tanker which can fuel a moving vessel. Combination ore-bulk-oil carriers and permanently moored floating storage units are two other variations on the standard oil tanker design. Oil tankers have been involved in a number of damaging and high-profile oil spills. As a result, they are subject to stringent design and operational regulations.

































Oil Tanker Double Hull Critical Area:





Double HullOil Tankers - Guidelines for Surveys, Assessment and Repair of Hull Structures
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Marine Survey Practice: Preparation for Survey

Marine Survey Practice: Preparation for Survey:

Preparation for Survey


Before starting survey work, authorization and scope of inspections are to be clarified, the necessary tools and personal equipment items to be prepared, and the safety precautions are to be arranged.
1. REQUEST FOR SURVEYS
It is important that the procedures listed below are observed when a survey request is received and that they are carried out before the ship is visited for the survey.
1.1 Nominated surveyors or those that belong to an organization recognized by the Administration should check who requests the survey and ensure that they are authorized to do so. For example, a survey request may be made by:
  •  the owner or master of the ship (or his agent), for a periodical survey, including a mandatory annual survey and an intermediate survey, or occasional survey in the case of damage to the ship's structure or equipment;
  • the port State, for clarification of possible non-compliance of the ship's structure or its equipment; 
  • the Administration of a State whose flag the ship is entitled to fly, for verification of the ship's condition.
1.2 Ensure that it is known which international requirements, which national regulations and which other orders and decrees are applicable to the requested survey.
1.3 If necessary, contact the Administration or organization responsible for issuing SOLAS-related certificates to which special requirements and/or instructions apply, such as: 
  •  national requirements laid down by the Administration which are additional to the international convention, e.g. regarding a dead-man stopping device at winch controls etc., the use of asbestos, which is banned by many authorities although there may be varying interpretations of this ban, a remote starting of fire pumps on ships having unattended machinery space etc., 
  •  exemptions from the international convention's requirements, e.g. fixed fire extinguishing system of cargo holds, 
  •  different survey methods and procedures accepted by the national authority, e.g. in-water survey (divers' survey) instead of the dry-docking of a ship, and non-traditional methods of surveying machinery such as surveys based on condition monitoring, 
  •  different procedures for reporting to the Administration, to be followed by the surveyor.
If the request for a survey is made by the port State authority, the surveyor should obtain the full background to this request, including the authority's point of view, before visiting the ship.
1.4 Check and study the drawings, data, past survey records and reports, as far as necessary and at hand.
2. TOOLS AND EQUIPMENT
For hull surveying purposes a few personal standard parts are necessary for the surveyor, whereas for special inspections additional tools or checking devices may be required.
Surveyors must be familiar with the equipment and tools used in hull survey procedures. Ship equipment can be used, and in addition, a shipyard may provide necessary devices. Before using measuring devices, calibrations and zero adjustments should be carried out, if necessary.
2.1 Standard Equipment Personal Property

  • suitable working clothes
  • safety shoes
  • safety helmet
  • ear protectors
  • gloves
  • notebook for recording and/or small dicta-phone
  • ex-proof electric torch
  • test hammer
  • pocket measuring tape
2.2 Other Tools and Equipment Used in Survey

Testing hammer:
Note that hammers made of steel must not be used in gas dangerous or gas suspected areas. Here the use of alloy hammers/tools is required to avoid that sparks are initiated by hammering or when tools slip out of hand and fall down.

Measuring tools:
Dial gauges, welding gauges, and feelers may be required for measuring clearances, welding seam heights, indents or deflections of hatches etc.




Portable oxygen and explosive content meters are necessary in areas where petroleum liquids or others are carried and where compartments with limited oxygen content shall be inspected. If ship's instrument is used, proper calibration of the instrument should be confirmed by a suitable testing method or by the latest calibration record issued by a recognized testing firm.







Thickness measurement instruments:
Such instruments use ultrasonic testing methods and calibration of the instrument is usually built in, otherwise it must be gauged separately.



















Vibration measurement equipment usually available through a shipyard or at major offices or testing institutes is to be used with reference to the relevant instructions and application procedures. There are numerous devices developed and suitable for hull vibration measurements and for recording vibrations exercised by running machinery.
Camera:
Photographs can greatly aid proper reporting if a suitable camera is available. The use of flashlights, however, is limited in areas where explosion risk exists.
3. SAFETY PRECAUTIONS
The surveyor must pay due attention to his own personal safety as well as to that of other persons on board. The following is i.e. an extract from "Guidance Manual for the Inspection and Condition Assessment of Tanker Structures" (pages 3 ff). Sections 3.2 - 4.5 may serve as a guideline for general safety aspects when tankers and product carriers are inspected.
Safety during surveys:
Before commencing any survey, the owner and all personnel involved in the survey must ensure that appropriate safety procedures are specified.
Safety standards often vary from owner to owner and vessel to vessel. While many owners maintain strict onboard safety procedures, survey personnel including Classification Society surveyors and subcontractors must still be aware of what constitutes minimum acceptable standards for tanker inspection to protect themselves from potentially hazardous working conditions.
The following are items of special importance to survey personnel and are included here to highlight the key items of on-board safety. These reflect the present practices and should be treated as a guide rather than a safety standard.
3.1 Safety Meeting - General Considerations
Before beginning any survey the survey team should ensure that a safety meeting is held to discuss all aspects of safety referred to herein with special attention being paid to gas testing procedures, command and communication links, and rescue arrangements.
In pump rooms where cargo vapors may occur due to leakages, pump rooms should be ventilated at least 15 minutes before entering or before the pumps are started.
As most cargo vapors are heavier than air, lower explosive limits (LEL) and/or toxic concentration measurements have also to be taken at floor level and below if inspections are necessary in this area.

Compartments normally not entered, as cofferdams, pipe tunnels, etc., which has usually no fixed ventilation system, should be ventilated by portable equipment.
Especially double bottoms in chemical tankers or product carriers were a risk of minor leakages from cargo tanks above always exists, the double bottoms should be opened at both manhole covers forward and aft and thoroughly ventilated before entering. Then the contents of oxygen, petroleum vapors and/or possible toxic cargoes should be tested before making final access.
The first person entering such a compartment should use breathing apparatus and a life line suitably attached for emergency rescue. A standby team should be trained for this purpose.

A good practice prior to inspecting those double bottom tanks is to fill them with seawater, keep them filled, and pump it out directly before entering.


3.2 Gas Testing for Tank Entry
Entry of tanks for survey should not be permitted until testing indicates that the following criteria are met:
  •  Gas reading 1% Lower Explosive Limit (LEL) or less (by Explosimeter).
  • Maximum Benzene (C6H6) 10 ppm (by Draeger Tube or equal).
  • Maximum Hydrogen Sulphide (H2S) 10 ppm (by Draeger Tube or equal) (this figure is under review and likely to be lower).
  • Minimum Oxygen (02) 21% by volume (Oxygen Analyzer).
    Note: the TLV-TWA for hydrocarbon varies depending on the cargo carried for gasoline the TLV is 300 ppm corresponding to about 2% LEL. Therefore if the TLV-TWA is unknown, a value of about 150 ppm should be used.
  • Maximum Hydrocarbons no greater than the Threshold Limit Value - Time Weighted Average (TLV-TWA) for the actual mixture encountered (by Draeger Tube or equal).
  •  Other limits specific to dangerous cargoes (chemical products), if applicable.
For vessels with inert gas systems, trace amounts of various toxic gases may increase the hazard of exposure for personnel. Normally, a steady 21% by volume of oxygen reading will be sufficient to dilute these gases below their TLV's. However, personnel should be aware of the following limits:
  • Maximum Carbon Monoxide (CO) 50 ppm (by Draeger Tube or equal).
  • Maximum Nitrogen Dioxide (N02) 3 ppm (by Draeger Tube or equal).
  • Maximum Nitric Oxide (NO) 25 ppm (by Draeger Tube or equal).
-    Maximum Sulphur Dioxide (S02) 2 ppm (by Draeger Tube or equal).
If gas readings are greater than 1% LEL (Explosimeter), or if other limits are exceeded, the survey team should be instructed not to enter the tank or, if already in it, to stop working and immediately vacate the tank. The Explosimeter used should be calibrated with a low level full scale reading of O to 10% LEL.
The team should arrange with the master to have the tank frequently tested for gas at several locations, say every 2-3 hours. In addition, a member of the team should verify the readings from time to time.
To aid the detection of any local pockets of gas, or lack of oxygen, team members should be encouraged to carry portable hydrocarbon and oxygen detectors with audible alarm features.
3.3 Tank Preparation
Continuous forced ventilation should be supplied to the tank during the inspection. An adequate number of deck fans should be used to supply this air. The fans should, where possible, be ducted to supply fresh air to the tank bottom. The vent fans should be stopped during atmosphere checks. The inert gas fans should not be used to provide fresh air ventilation because contaminants from the inert gas lines could be introduced into the tanks. Inert gas branch lines should be blanked off and the blanking flange interlocks checked at each tank if entry is required while inerting, or gas freeing of other tanks is taking place, or if any other tanks are inerted or contain hydrocarbons.
An alternative to pipe blanking would be to remove a section of the branch line.
All cargo pipelines leading to the tank should be checked for oil content and the valves secured closed, immobilized and signposted. Any oil present in the lines should be removed.
All adjacent tanks should be in the same gas free condition as specified above or fully ballasted. Alternatively, and with the knowledge and approval of the owners and the agreement of the survey team, adjacent tanks may be fully inerted or partly ballasted/remainder inerted but with pressure reduced to a minimum. The survey team should be aware of the danger of potential leakage of inert gas through bulkhead fractures or faulty valves.
3.4 Safety Watch and Safety Equipment
The survey team should not remain in a tank unless there is a safety watch by ship's staff with at least one individual stationed at the tank hatch throughout the inspection. The safety watch should have the authority to order the evacuation of a tank and should be responsible for registering the survey team entering or leaving a tank. Communication should be maintained between the personnel in the tank and the safety watch. When underway, the safety watch should maintain communication with the bridge.
Rescue equipment including breathing apparatus, resuscitators, smoke masks, rescue lines, a stretcher, etc. should be laid out at the tank hatch or, if more than one tank is being worked, at a suitable central location on deck.
3.5 Tank Cleaning
Tanks and spaces to be surveyed must be sufficiently clean and free from water, scale, dirt and oil residues to reveal excessive corrosion, significant deformation, fractures, damages and other structural deterioration. Tank cleaning can be performed with an existing Crude Oil Washing (COW) system.
Generally, tank surveys should be avoided in tanks in which de-sludging operations are taking place since these operations can potentially raise gas levels.
3.6 Ballast Transfer
The survey team should not enter or remain in any tank if ballast is being moved in or out of that tank. Consideration should also be given to ballast movement in adjacent tanks.
3.7 Maneuvering
The survey team should not enter or remain in any tank while the ship is maneuvering in congested or confined waters.
3.8 Use of Ultrasonic Measuring Equipment in Cargo Tanks
Most ultrasonic thickness measuring equipment is not intrinsically safe. Its use is allowed only in tanks with a “hot work” certificate or, alternatively, where agreed by the owner, in tanks with gas quality meeting the requirements of section 3.2 above.
In this case, surfaces within cargo tanks that are not sufficiently cleaned of cargo residues are unacceptable for inspection and should be avoided by the survey team. If ultrasonic measurements are essential in such areas, the surface must be cleaned free of all residues for a radius of 1 meter from each reading point.
3.9 Temperature Extremes
When temperature extremes are expected during a survey, the inspection team should review the procedures that the master or safety officer will follow to monitor the exposure of the team to guard against hypothermia, frostbite, heat fatigue, heat stroke, etc.
When the limit are reached or exceeded, the team, in consultation with the master or safety officer, should adjust its work/rest period for the conditions being encountered. In hot climates the survey should be scheduled to avoid the midday heat when the above limit is likely to be exceeded. Some cooling can be achieved by spraying the decks with water during very hot weather.
3.10 Lighting
Whenever possible, natural lighting should be provided in the tank during surveys by opening all tank hatches. Suspended lighting should also be provided to supplement any natural lighting. Each person should carry a torch of the high intensity beam type such as a Wolflite or Halogen light. Torches and lights should be of intrinsically safe design
3.11 Rafting Surveys
Inflatable or rigid rafts should be of a type with sufficient compartment that adequate buoyancy and stability is provided even with one compartment ruptured.
At no time should the water level be allowed to be within one meter of the deepest under-deck web face flat.
Under no circumstances should the raft be used so that it is isolated from a tank hatch. In the case of tanks with swash bulkheads where two tank hatches are not fitted, the survey may be carried out using two rafts. One raft will be in use while the other is secured at the swash bulkhead for emergency escape.
Rafting should not be attempted if there is more than a thin sheet of oil on the water.
Rafting or boating should be discontinued if the rise and fall of the raft or boat within a cargo tank (due to the motion of ballast water caused by rolling) makes the operation difficult or hazardous. In making this decision, the team should consider the degree and period of roll, the proximity of rafting to the deck-head or other structure (that could damage the raft), and expected maneuvering that could add to excessive motion of the ballast water. While it is difficult to set a limit, the rise and fall of ballast water should not exceed one meter, equivalent to about 1.5 to 2 degrees of roll per side on a V/ULCC.
Once the type of survey has been decided upon, it is necessary to consider the means of access available to achieve the goals of the survey.
The need for reasonable access to the upper parts of a tank structure has recently been reinforced by the introduction of the IACS Unified Requirements for the Special Hull Surveys of Oil Tankers. These requirements do not stipulate how access is to be achieved but have specific requirements for close-up surveys of deck-head structure and primary ring structure coupled with thickness determination in these areas.
The following options are available to aid access to the structure for condition assessment:
4.1 Climbing
In general, the free climbing height should be limited to about 3 meters above the bottom or any large stringer platform. If it is necessary to exceed this height, there should be a water bottom to provide a “cushion” or other provisions such as safety lines. The free climbing height above the water surface should not exceed 6 meters.
When climbing in tanks containing water, the surveying personnel should wear “flotation aids”. A flotation aid is a simple form of lifejacket which does not impede climbing.
4.2 Permanent Arrangements
Much can be achieved at the design stage of a vessel by the provision of manholes and ladders. The width of face plates, the location of stringers, the provision of manholes etc., can all contribute to the ease with which a structure may be surveyed and the condition monitored in service.
Some shipbuilders fit limited permanent walkways at the upper parts of the tank either for their own use or at the request of an owner. Often use of existing structure is made for permanent walkways with handrails added. The fitting of such walkways will however incur a cost and deadweight penalty for the operator especially as the walkways themselves and supporting brackets must be substantial enough for the corrosion environment. Walkways can provide sufficiently close access to obtain a general assessment of the condition of the structure and identify suspect areas for closer examination.
4.3 Temporary Staging
Conventional temporary staging within a tank to gain access to deck-heads and bulkheads structure is an option that may be attractive in some circumstances but, as the vessel gets older and survey requirements more stringent, the cost of such staging methods could become prohibitive.
The use of temporary staging restricts the survey to being carried out within the repair yard and does not facilitate a survey at sea for preparation of repair specifications and the like.
4.4 Mobile Platforms
The most common form of temporary staging other than conventional scaffolding is the mobile platform. This consists of a portable, self-elevating platform suspended from wires through holes drilled in the upper deck. If a sufficiently extensive grid of holes is provided, reasonable access to deck-head areas can be achieved.
Alternative designs of mobile platform are mostly based upon an articulated or telescopic arm principle. Such designs would typically incorporate a support turret suspended from a tank cleaning opening or from the tank bottom. The articulated or telescopic arm is supported by the turret and is usually operated hydraulical1y or pneumatically to bring the inspection platform to the desired position. The movement of the platform can usually be controlled by the inspector on the platform. Each platform should be capable of carrying two persons and would typically have an outreach from the turret of about 25 meters.
All forms of mobile platform are highly susceptible to the motions of the vessel and are therefore more readily usable in dry-dock or sheltered conditions rather than at sea. it should be noted that these platforms may have to be certified as complying with local factory inspectorate and International Labor Organization (ILO) requirements, particularly when used within a repair yard.
4.5 Rafting
Although limited in use for some structural configurations, survey of deck-heads from a raft or boat within a partially filled tank is fairly common practice with some operators and is likely to become even more popular as more stringent survey requirements are introduced.
The tank should not be filled beyond a level approximately 1 meter below the deck transverse so that the survey team is not iso1ated from a direct escape route to the tank hatch. This will mean that on larger vessels with deep deck transverses the inspector will still be some distance from the deck-head which may preclude close-up survey.
Filling to levels above the deck transverses should only be contemplated if a deck access manhole is fitted in the bay being examined to provide access to the raft and direct escape to the deck in an emergency.
Fitting of additional deck manholes (with access ladders and platforms) for this purpose should possibly be considered on future designs if rafting is planned as the main means of deck-head survey.
Safety is of prime importance during ratting surveys and likely motions of the vessel must be taken into account at all times.
(Note: above sections 3 and 4 are grouped under the heading "Safety and Access" in Chapter 1 "Survey Preparation Guidelines").
4.6 Opening of manholes
For access to double bottom tanks, pipe tunnels, wing tanks, etc., both manholes should be opened and prepared.
It enables natural ventilation and easier means of escape, if necessary.
In addition, inspections are easier to perform if the tank passage can be made in one way only and when light and tools and fresh air are to be reached from short ends.
Confined Space Safe Practice

Safe Use of Portable Ladders for Close-up Surveys

Ship Structure Access Manual 

Guidelines for Approval / Acceptance ofAlternative Means of Access - Rev.1 Jan 2011
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Marine Survey Practice: Hull Survey Methods

Marine Survey Practice: Hull Survey Methods:

Hull Survey Methods


Hull survey methods, are means and procedures to detect failure and damage at an early stage to avoid premature breakdown.

Hull survey methods are therefore not only comprehensive means of detecting deficiencies or monitoring structural condition, but also of defining schemes for inspection between the last overhaul and before the occurrence of failure.

Means of detection of defects and condition monitoring are inter alia:
  • Visual inspections
  • Non-destructive testing (NDT) and calibrating
  • Examination of tightness, function and centre of gravity
  • Measurements of thickness, vibration
Schemes of inspection are periodical survey requirements which by virtue of design and operational experience are envisaged to discover deficiencies completely and early enough before they may lead to breakdown.

1. MEANS OF HULL CONDITION ASSESSMENT

1.1 Visual Inspection

A major part of hull surveying work is carried out using visual skills to perform the examinations and to arrive at an opinion on the state of a vessel’s condition.
Such visual examinations can be carried out as:
  • Over-all inspections, a general sighting of a vessel's hull condition, followed by
  • Close-up examinations at 
  1. locations where discontinuities, ruptures or deformations have been found and 
  2. certain hull structures as stipulated by rules and/or requirements, for instance in way of cargo area of oil tanks.
  • Examination of areas of suspected crack and corrosion concentration.
The methods of visual inspection procedures may be applied as follows:

1.1.1 Visual over-all inspection

Examination of external hull body
Visual attention is to be focused on the vessel’s shapes, lines and curves for the detection of 
  • unusual deformation, 
  • misalignment of structures along bottom plating, side shells, bilge keels, decks.

As a result, permanent deformations of misshaped sections can be caused by:
  •  hogging
  • sagging
  • bagging
  • local deflections from the original structure.
     
 For measuring purposes, a wire or a piano line may be stretched out from forward to aft and gauging derived from such a zero basis.

Inside inspections in holds, tanks, hull parts

Similar visual examinations can be carried out inside of compartments:

Attention should be concentrated on the lack of straightness of structures, along side lines from forward to aft and from port to starboard, with regard to:
  • stringers and longitudinal frames,
  • walls, longitudinal bulkheads and corrugations,
  • platforms, transverse members and bulkheads,
  • frames, brackets, deck beams,
  • floors and attached stiffeners.


Lines and/or structures showing misalignment, deflection, buckling or other discontinuities, are an indication of existing defects requiring close-up inspection.

Docking inspections

When a vessel is dry-docked, attention has to be focused on:
  • discovery of deformations and/or discontinuities along keel plates, bottom, and side plates, bilge keels, and attachments,
  • checks for leakages from inside to outside, if the ballast
  • tanks have overflow prior to this inspection,
  • removal of the drain plug at the rudder blade. If water leaks out this is an indication that the blade has suffered water ingress (which may otherwise have remained hidden);
  • measurement of rudder bearing clearances by feelers can also be considered a visual approach to assess wear-down. Ditto calibration of anchor chain links by caliper slide,
  • condition of rudder flange; bolts or nut(s) must be absolutely tight;
  • condition of welding at seams and butts and in way of outlet openings.
1.1.2 Close-up examination
If indentations and/or deformations have been located, visual close-up examinations are necessary.
The area under scrutiny should be accessible for visual inspection within bodily reach.

Such inspections should be carried out with floodlight etc. A good torch and a test hammer should always be available, as well as a scraper to remove rust scale and debris to reveal the bare material underneath.
In case of deformation

Deformations that may have been produced as a result of external or internal forces should be carefully analyzed.

Without apparent extra loads along shell, deck, or bottom, likelihood of the following should be checked:
  • internal movement of cargo, liquids etc.
  • excessive flexibility of the structure.
  • local stress concentrations (point loads excessive).
Further examinations for fractures and incipient cracks may be necessary.
Also other identical locations should be examined to see whether similar defects exist or are developing.
In case of cracks
  • location of crack,
  • configuration of the structure/element,
  • starting point of the crack,
  • length and direction,
  • depth and width of the crack,
  • possible cause(s):
=        defective welding of assembled parts,
=        discontinuation of joints,
=        compression or tension of adjoining parts,
=        twisting motion,
=        reduced thickness,
=        type of corrosion, etc.
should be checked not only in the respective area, but also in other identical locations, especially at the opposite side.
1.1.3 Areas of concern for cracks and corrosion
Locations of stress concentration and crack raisers
On deck:
-        Corners of hatches on weather decks,
-        corners at deck connections to deckhouses and superstructures,
-        deck plating between cargo hatches, especially where plate thickness changes,
-        at bulwark stay deck connections.
Under deck:
-        Cutouts at webframes where longitudinal pass,
-        cutouts at bulkheads where longitudinal passages are closed,
-        tips of bracing plates (knee brackets) at bulkhead connections,
-        areas where longitudinal members meet vertical structures.
In machinery spaces:
As above in under-deck locations and especially
-        at areas of induced vibration (around oscillating machinery),
-        underneath of engine seats/along foundations,
-        at thrust bearing seats.
Locations where accelerated corrosion is likely
-        Generally where the coating is inadequate, defective, or poorly maintained,
-        corners and dead ends where water is restricted from draining or flowing away (i.e. bottom connection at aft bulkheads),
-        inside of scupper pipes, especially at the elbows where the scuppers are led into the shell,
-        at bulwark and coamings stays in way of deck connection,
-        along deck connections with coamings of hatches, venti1ation trunks, air pipes, etc.,
-        on top or underneath of air and ventilation pipes/trunks, especially where galvanized parts are fitted to steel.
At hatch covers:
-        between panel joints and especially along rain gutters, sealing bars, and rubber channels,
-        along underside of panel side walls in contact to hatch coaming,
-        in pockets of lashing points, etc.

At hatch coamings:
-        along sealing bar,
      -        along roller tracks.


Under deck (cargo holds/tanks):
-        along aft transverse bulkheads in way of deck/tank deck connection where water or cargo rests are likely to stay,
-        inside of bilge trunk,
-        base of sounding pipes (where doublers should be fitted),
-        base of suction pipe bell mouths,
-        in way of pipe clamps and fittings,
-        at the undersides of pipelines where condensate is dripping,
-        in ballast tanks along the area of air between filling level and tank top,
-        at pipes, especially along their outer rear side, fittings and outer undersides.
1.2 Non-destructive Testing Methods
The detection of cracks by visual methods is rather limited. Additionally internal welding seam imperfections or flaws in material parts cannot be discovered without suitable means of examination and instrumentation. To discover these suitable means of non-destructive testing (N.D.T.) are used, such as:
-        Dye checks with liquid penetrants
-        Magnetic particle checks
-        Radiographic checks, or
-        Ultrasonic measurements.
1.2.1 Liquid penetrant methods (dye checks)
One type of test uses a low viscosity liquid, containing a fluorescent dye. The area to be tested is sprayed or soaked to allow for penetration by capillary action, and after a time lapse is wiped dry. When viewed under ultra violet light, any faults will be shown by the glow of the penetrant in them.





Another test uses a penetrant containing a powerful dye. This is sprayed on the suspect area with an aerosol. After allowing time for penetration, the area is wiped clean and covered with a liquid which dries to leave chalky sediment (developer). The penetrant stains the developer along the line of the crack.
These methods are based on old chalk and paraffin tests but the penetrant can have a hydrocarbon or alcohol base. Some are emulsifiable for removal by water spray, others can be cleaned off with solvents to reduce possible fire risk.
1.2.2 Magnetic crack detection
This type of test is suitable only for materials which can be magnetized (cannot be used for austenitic steels or non-ferrous metals). After the test the component is normally de-magnetized.





A magnetic field is produced in the component by means of an electric current or permanent magnet and magnetic particles are spread on the surface. Cracks are revealed by a line of magnetic particles.
The powder used may be black iron oxide held in suspension in thin oil. It is poured onto the surface, the surplus being collected in a tray beneath. Colored magnetic inks in aerosols are also available and the dry method makes use of powder only and this is dusted on the surface. Powder tends to collect at a crack in the same way as iron filings will stick to the junction of two bar magnets, placed to end with opposite poles together.
1.2.3 Radiographic inspection
X-rays and gamma rays are used for inspection of welds, castings, forgings etc. Faults in the metal affect the intensity of rays passing -through the material. Film exposed by the rays gives a shadow photograph when developed.
There is a requirement for radiographic examination of many welds, particularly those in pressure vessels.
Defects such as porosity, slag inclusions, lack of fusion, poor penetration, cracks and undercutting are shown on the film.
Films of radiographic examination provide a permanent record of quality of welds etc. and must be identified by serial numbers or other location marks. Image quality indicators are placed on or adjacent to welds.
Radiographs are viewed by a radiologist on a uniformly illuminated diffusing screen. Training is necessary for the interpretation of film, both with regards to the faults in the part being examined and misleading marks that sometimes appear on film.
A skilled radiographer is required for the obtaining of photographs.
Exposure times for gamma rays vary with the type of material, its thickness and the intensity of the rays. X-ray machine voltage and exposure time are also varied to suit the material and its thickness. Distances between ray source, faults and film are important for image definition.
Rays are harmful either in a large dose or a series of small ones where the effect is cumulative. 
Monitoring against overdose is necessary with film badges, medical examination and blood counts.
Direct exposure is avoided by the use of protective barriers but there is a danger that objects in the ray path will scatter radiation.
1.2.4 Ultrasonic testing
Internal flaw detection by ultrasonic means is in principle similar to radar. The probe emits high frequency sound waves which are reflected back by any flaws in the object. Reflect ions are also received back from the opposite surface. The probe is connected to a cathode ray oscilloscope which shows the results in a simple way.
A single probe can be used, which combines both transmitting and receiving functions. Alternatively separate devices for transmitting and receiving the sound signals are available.
Any flaw in the material being inspected will also produce a peak.
The following details of "US Testing of Hull Butt welds" from BUREAU VERITAS Weld testing principle:
Transverse waves are emitted from an angle probe moved on the plate surface on either side of the weld.
The probe displacement should be sufficient for scanning the whole weld over a single or a double traverse, as shown on Figure 8.
As far as possible, and taking into account the plate thickness, scan from both sides of the weld, especially for detecting longitudinal defects.
-        The scanning operation depends on the type of plate edge preparation before welding and on the configuration of the weldment, i.e. on the difficulty of access for the probe.
-        The expanded time-base sweep should be chosen so that a triple traverse is displayed on the screen. The sweep may, however, be modified according to the difficulty of access and to the welded joint.
-        Scanning for longitudinal defects (aligned in the direction of the welded joint) is performed by a transverse displacement of the probe with respect to the axis of the weld. The lateral displacement of the probe, which depends on the dimensions of the transducer, should be such as to ensure the over-lapping of the scanned areas; see Figure 9.
-        When an anomaly has been detected, the weld may be inspected further by moving the probe parallel to the weld and swinging it back and forth by la to 30°. Then the speed of time-base sweep may be set for displaying an ultrasonic path equal to a double traverse.
-        For scanning flush welds one may place the probe on the centre line for the welded joint and direct the ultrasonic beam along the longitudinal axis of the weld.









1.3. Pressure and Tightness Tests
Pressure or tightness tests are required during ship construction and thereafter at periodical surveys or after repairs when the tightness of the respective section(s) has to be proved again.
For such tests the methods are different for either ship tanks and/or cargo tanks.
1.3.1 Basic requirements for tanks (except cargo tanks)
All ballast, trim, feed water, freshwater, and heeling tanks as well as oil tanks for fuel and lubricants, shall be pressure tested by water corresponding to a water column of 2.5 m above the upper tank level; under certain circumstances a pressure test with air followed by a later function test with the liquid is allowed.
Should the deep load line be higher than 2.5 m above the upper level of the tank, the tightness is to be tested with a water column corresponding to the deep load line.
In all cases the testing shall be carried out with a water column reaching to the uppermost level of the overflow or air pipe.
1.3.2 Pressure test of cargo tank
Pressure/tightness tests of cargo tanks of oil and chemical tankers, cargo tanks on dry cargo vessels, etc. are to be carried out as follows:
Prior to the vessel’s launching a tightness test should be carried out by water pressure in the cargo tanks and cofferdams. This test is to be carried out in such a way that the cargo tank bulkheads and the cofferdam bulkheads are tested at least from one side. The test shall be carried out prior to the application of the first protective coating.
Should the test with water not be possible during the vessel’s stay at the vessel 15 building place or dock, hydrostatic pressure test can also be carried out after launching.
For cargo tanks the test requires a water column corresponding to 2.5 m above the upper level of the tank. Any specific weight of the cargo above 1.025 t/m3 has to be taken into account.
For cofferdams a water level up to the upper edge of the access hatch is sufficient.
1.3.3 Tightness test of hatch cover
Weather deck hatch covers should be tested for “weathertightness”.
These tests should usually be carried out by hose testing using a fireline with a nozzle of 12.5 mm diameter at a pressure of at least 2.0 bar from a distance of 1.5 m.
1.4 Function Tests
Function tests or operation tests should prove by demonstration that the tested component
-        fulfils its respective purpose under the conditions for which it is designed, and that
-        all relevant aspects of safety are satisfied when the component is in operation, in open and/or closed position.
1.4.1 Basic requirements
Function tests shall be carried out with the Surveyor of the
Administration attending and the shipbuilder acting according to the following guidelines:
A definite testing procedure with details of all single tests is to be agreed upon, containing information on the duties and actions of all persons involved.
All relevant safety valves and/or pressure or temperature or flow control s should be readjusted and checked in the workshop before field installation and testing.
For reasons of safety the following should be considered and provided:
-        means of escape,
-        good lighting, including emergency lighting,
-        shipboard electricity in function and backed up, including blackout back-up,
-        means for fire fighting to be ready,
-        the persons engaged in testing shall be limited to a minimum number,
the testing director shall be selected and nominated.
1.4.2 Items to be tested
The following should be considered for each function and/or operation test:
-        Testing of all operational conditions under which the system should prove safe operationability (such situations may also be simulated ).
-        Testing of all relevant means of built-in control s, indicators, valves, and fittings; tightness of respective piping, admissible motor load, etc.
-        The minimum or maximum data expected; the relevant limits should be reached and demonstrated.
1.4.3 Hull function tests
Function tests forming part of hull surveys are inter alia:
-        anchoring tests
-        mooring winch tests
-        hatch cover operation tests
-        cargo gear load tests
-        maneuvering tests
-        bollard pull tests
-        heeling tank tests
-        accommodation ladder tests
-        pilot lift tests
-        cargo lift tests
-        cargo ramp tests
-        cargo door tests
1.5 Inclining Test
For each new building or after each modification of the vessel which influences stability an inclining test is to be carried out prior to sea trials for the vessel’s recommissioning into service. This test is to be carried out with the Surveyor of the Administration attending and under suitable conditions.
1.5.1 Condition for testing
-        Tanks should be empty and the vessel more or less in a completed state in respect of installation work and the equipment installed. Unavoidable tank contents should be concentrated to a tank with vertical side walls.
-        The additional weights on board shall not exceed 20% of the lightweight, provided no other stringent reasons request a higher percentage for additional weights.
-        Tanks should be completely filled up to 100%. Should a tank be partly filled, the free surfaces must be such that they do not change considerably during testing.
-        Vessels must be free of persons which are not actually carrying out testing and control measurements.
-        The vessel should be unlimited in movements, i.e. mooring rape free and no contact to quay walls.
-        Cooling water, fire fighting, sanitary, fuel, lube oil systems should be filled up to operational conditions.
Ditto boiler and cargo cooling or hydraulic systems.
-        Wind and current should not affect vessel' s free movement during the test.
1.5.2 Testing procedure
-        The inclination angles should be between 1.5º and 2.0º In any case limits of 1.00 and 2.500 have to be maintained. The inclinations to each side should be carried out twice. The zero points should be noted in the protocol.
-        The inclination test is to be calculated by using the hull form data for the actual waterline (buoyancy with trim correction).
-        Inclining tests can be omitted for sister vessels of the same type built by the same shipyard without deviation of building data which could influence stability, provided the test results of two previously built vessels produce comparable results. For this the written approval of the owners (and possibly of the Administration) is required, but a deadweight calculation is to be carried out in the presence of the Surveyor for the Administration.
-        If applied for, the inclination test can be omitted with huge tankers and bulk carriers of a length of above 250 m provided again the ship owner (and possibly the Administration) approves this in writing and the deadweight calculation is carried out under the attendance of the Surveyor of the Administration.
-      For vessels with built-in heeling moments, f.i. with cranes at one side only, also this moment is to be calculated in connection with the evaluation of the inclining test.
1.6 Thickness measurements
1.6.1 Anchor cables
Anchor chains are usually measured by using caliper slides.
Chain links in the vicinity of the chain ends should be measured in 2 cross sectional directions.
The locations for measurement must be chosen at the link ends where maximum wear and/or deformation is to be expected and/or visible.




1.6.2 Thickness measurements of hull scantlings
In general, thickness measurements are made by ultrasonic thickness gauges (see above 1.2.4).
If carried out professionally and in a representative way, measurements of the actual thickness of scantlings can generally reveal the actual overall condition of a vessel with respect to its structural strength.
The scope of the measurements required is determined by the rules of the classification society based on the type and age of a vessel under survey. The actual conditions of the structure, verified by visual observations, may request premature and/or additional measurements.
As a general rule, the smaller the thicknesses the more the extensive measurements have to be.
In areas of heavy corrosion testing is to be increased to show the extent of wear and to allow proper judgment if the area is to be renewed or otherwise repaired.
1.7 Vibration Measurements
Detailed vibration investigations should be made during the design period of a vessel to predict the vibration levels in accommodation and working spaces and to avoid damage by excessive accelerations to hull structures and machinery.
For vessels with slow-speed 2-stroke engines an overall vibration examination should be carried out for hull and superstructure.
Vibrations can be excited by periodical forces, such as the main engine (as a function of the firing frequency), the periodical propeller blade force s at blade frequency, and other free vibrating masses.
Tank sides and shell plating areas in way of the engine room and propeller area should be designed so that structural frequencies are higher than the respective exciting frequency.
For vessels with medium speed engines the possibility of propeller blade induced vibrations should be examined. This type of engine induces excitations with firing frequencies between 23 and 33 Hz. Calculations, of natural frequencies of local structures are therefore necessary.
Whether other systems as masts, rudder arrangements or shaft-lines are to be investigated, depends on the individual case.
Local structures should have' natural frequencies of about 20 - 25% above the highest main exciter frequency. Such calculations may be carried out by using simple formulas, or by the finite element (FE) methods.
FE models which are used for strength calculations may also be utilized for the vibration analysis.
Classification societies can greatly assist ship-owners or builders with such calculations which may avoid expensive modifications or structural alterations after unfavorable seatrials.
Vibration measurements are usually carried out in new-buildings during sea trials.
Occasionally these measurements are not sufficient and have to be repeated in a fully or partly loaded condition of the vessel and occasionally also under certain engine operation modes.
Measurements are then carried out by a special surveyor team, using vibration registration equipment positioned in specially selected locations to record simultaneously engine operation modes together with local structural excitation frequencies, amplitudes and acceleration in order to identify resonances.
2. INSPECTION SCHEMES
The recognized Classification Societies have developed systematic hull inspection programs which ensure that a vessel's structural parts, components and compartments are duly kept under control by periodical examinations and are subjected partially or totally to the above described visual inspections, testing and examination methods.
These survey programmes are:
-        Periodical Class Renewal procedures after 4 years, with a possible extension to 5 years if satisfactorily subjected to a class extension survey;
-        Continuous Survey procedures for Hull (CSH) with the renewal survey program divided into partial inspections of abt. 20% for each year) over a period of 5 years;
-        Class Extension Surveys
-        Dry-docking Surveys at intervals of at least 2.5 years.
All these scheduled inspection systems ensure that a vessels condition is regularly controlled and properly supervised within the respective survey system.
The respective inspection schemes are as follows:
2.1 Periodical Class Renewal Surveys (also called “Special Surveys”)
For the Renewal of the Class, the ship’s hull, machinery including electrical installations and the automatic/remote control systems are to be subjected to surveys at the fixed intervals.
A class renewal survey can, under special circumstances, be carried out in several steps. Here, the total survey period must not exceed 12 months.
A bottom survey within this period of time can likewise be recognized if the requirements for class renewal are fulfilled.
The examination of certain covered parts may be dispensed with at a Class Renewal Survey if the Surveyor is completely satisfied of their efficient condition, and if the Owner undertakes to have them exposed for examination within 12 months. A corresponding entry will be made in the Certificate of Classification.
Class Renewals Hull is to be effected in the sequence I, II, III, IV and subsequent to IV. The Class Renewal, No. IV and the following correspond to Class Renewal III.
2.2 Continuous Survey Hull – CSH
Instead of the Class Renewal procedure according to 2.1 the Owner may apply for Continuous Class Renewal for Hull and Machinery. The Class Renewal procedure can, however, also be adopted only for the hull or only for the machinery, including the electrical plant.
The required surveys under CSH extend over a period not exceeding
5 years. It has to be made sure that during the Continuous Surveys all parts of the ship’s hull and/or machinery, including the electrical plant, be surveyed at intervals not exceeding the periods normally required for the maintenance of class.
The Surveyor may re-inspect compartments or structures are deemed necessary.
At the end of the period of class the extent of survey of the hull depends on the scope of the respective class renewal due, I or II or III or IV.
Where both, a ship's hull and machinery, including the electrical plant, are surveyed in accordance with the continuous class renewal procedure, the 5 years' period of class is valid for both sectors. This is conditional upon the prescribed survey intervals and respective scope of survey required being observed.
Where either only the hull or the machinery, including the electrical plant, is subject to the continuous class renewal procedure, a 4 years' period of class is valid for both sectors. Class extension by 12 months is possible. Surveys according to the continuous class renewal procedure are performed al so during the period of class extension.
2.3 Class Extension Surveys
On Owners' request el ass can be extended by not more than 12 months after survey of the vessel - at least to the scope of the requirements for an Annual Survey afloat. Class may be extended only if hull and machinery, including the electrical plant, are in perfect condition and if, since the bottom was last surveyed, no incidents occurred resulting in damages expected to have been caused to the underwater body.
Ships having a character of classification different from 100 A 4 (highest GL class character) cannot have their class extended.
Dry-docking intervals are to be observed for class extensions.
At a Class Extension Survey the ship is to be inspected, if practicable, when it is not loaded, so that the hatches, the cargo holds, the tweendeck spaces, the watertight doors, etc. can be examined; if necessary, tanks will also be examined. In the case of oil tankers and ships carrying combined cargoes (e.g. OBO-ships) the ballast tanks located in the cargo area will be subjected to a general condition survey. An inspection of the machinery, including the electrical plant, is to be made to verify, in particular, satisfactory operation. Automatic/remote control systems are to be examined, taking into account records of operation.
2.4 Docking Surveys
Underwater hull inspections at regular intervals shall ensure that the outside and the steering facility of a ship remain in a satisfactory condition. Such inspections are also carried out for the control pf the propeller, the shaft-line bearings and seals. In addition inlet and outlet piping, valves, seachests and sea filters are examined.
A special type of underwater hull survey is the “in-water survey” which can be applied under special considerations.
For seagoing ships with character of class 100 A 4 an in-water survey may be recognized as a substitute for every second periodical bottom survey, provided
-        the required special equipment is available, documents have been issued and trial requirements complied with and if the survey is carried out as required and with approved firms and satisfactory results,
-        this survey is not part of a class renewal.
For ships of more than 10 years of age the intervals between dry-docking must not exceed 2.5 years.







Resolution A.997(25)E
Resolución A.997(25)S
Resolution A.1020(26)E
Resolución A.1020(26)S
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