Section 4 Construction Monitoring

4.1.1 The Construction Monitoring (CM) notation may be assigned if extended controls on structural alignment, fit-up and workmanship standards are applied to critical areas, as identified during the design of the ship. Construction Monitoring is applied primarily to verify the quality of workmanship required to improve the fatigue resistance of critical details, though other construction quality requirements can be specified in the CM plan.

4.1.2 The fatigue life of structural details can be adversely affected by a variety of factors, including workmanship defects. Criteria for workmanship defects can be considered in the CM plan. The most common factors that impact on fatigue are:

1. Misalignment of structural members; i.e. poor fit-up;

2. Welding defects;

3. Materials defects;

4. Stress concentrations resulting from incorrect geometry of structure, inadequate plate edge finish or generally poor manufacturing;

5. Erroneous cut-outs due to inappropriate routing of systems;

6. Discontinuity of structural members.

4.2.1 A critical area is generally a structurally significant item or structural joint that has been subjected to an enhanced calculation or assessment. As a consequence, the performance of the item or joint will be influenced by the workmanship and fit-up in the building yard. In some areas, where there are high cyclic stresses, an enhanced workmanship and alignment standard is required in order to achieve the specified design hull fatigue life.

4.2.2 Critical areas will be identified by LR from the following assessments:

1. Structural Design Assessment (SDA), specified in Vol 1, Pt 3, Ch 6, 2 Structural Design Assessment;

2. Fatigue Design Assessment (FDA), specified in Vol 1, Pt 3, Ch 6, 3 Fatigue Design Assessment.

The CM notation is mandatory if the SDA or FDA notations are applied.

4.2.3 Critical areas may also be identified by LR from one of the following optional assessments. In general, these will be associated with reinforcement and alignment of specific critical joints; they will not be associated with general deformation criteria:

1. Extreme Strength Assessment (ESA), specified in Vol 1, Pt 6, Ch 4, 3 Extreme Strength Assessment, ESA;

2. Residual Strength Assessment (RSA), specified in Vol 1, Pt 6, Ch 4, 4 Residual Strength Assessment, RSA;

3. Whipping Assessment (WH), specified in Vol 1, Pt 4, Ch 2, 6 Whipping.

4.2.4 In addition, critical areas may be identified by the designer, Naval Administration or Owner from one of the following:

1. Known areas of high stress identified by structural engineers;

2. Areas that have experienced failure on similar ships in service;

3. Structures with specific alignment requirements; e.g. masts, shaft brackets.

4.2.5 The critical areas, locations and assessment criteria are to be detailed in the Construction Monitoring plan. The plan should also contain templates to be used to record specific alignment requirements. The CM plan may be supported by a high-stress key plan identifying critical regions on the ship.

4.2.6 Development of the CM plan is the responsibility of the designer; LR will identify the critical locations to be subjected to monitoring, following appraisal of the assessments identified in Vol 1, Pt 3, Ch 6, 4.2 Identification of critical areas 4.2.2 and Vol 1, Pt 3, Ch 6, 4.2 Identification of critical areas 4.2.3 above. In general, areas with stress ranges greater than σ_ws, see Vol 1, Pt 6, Ch 4, 2.2 Bending strength 2.2.3, and areas where general or detailed fatigue analysis has been undertaken will be listed in the appraisal documentation. LR may develop the CM plan on behalf of the designer, if so requested.

4.2.7 It is recommended that the areas for Construction Monitoring be identified and the criteria developed in a workshop with the Owner, Naval Administration, Builder and LR.

4.3.1 Critical areas are to be assigned an alignment criterion, as given in Vol 1, Pt 3, Ch 6, 4.3 Construction monitoring criteria 4.3.2, based on the significance of the item and requirement from which it was derived. LR will review and agree the criterion assigned before construction commences.

4.3.2  Normal alignment is assigned to structure which requires an enhanced level of survey above the normal survey requirement but does not require enhanced levels of alignment above the agreed production standard, such as the Naval Survey Guidance for Steel Ships:

1. Structure will be inspected by the Builder, before welding, for compliance with the general shipbuilding tolerances laid down in the agreed production standard.

2. A representative sample of alignment measurements will be undertaken by LR during the survey to confirm compliance with the agreed production standard.

3. Where there are non-compliances, the relevant shipyard department will be requested by LR to undertake full measurements and to produce a report for review by LR which details the non-compliances.

4.3.3  Enhanced alignment is assigned where critical areas have enhanced alignment requirements to maintain structural performance:

1. The relevant shipyard department will be required to provide a report, based on templates in the CM plan, detailing the achieved alignment at each location.

2. LR will review the alignment report and request check measurements as necessary to confirm the results.

3. The maximum allowable misalignment between the interconnection of structural members is to be 15 per cent of the thinner of the members being connected. This alignment criterion is to be applied where longitudinally effective structure is butted; e.g. plating at ring butts, longitudinal butts, see Figure 6.4.1 Alignment criterion.

4. For all cruciform joints, the maximum allowable misalignment between the interconnection of structural members is to be 20 per cent of the thinner of the members being connected. This alignment criterion is to be applied where there is alignment through a thickness; e.g. intercostal longitudinal bulkheads through a transverse bulkhead, bilge keel plate alignment with internal structure through shell plating, see Figure 6.4.2 Cruciform joints.

Figure 6.4.1 Alignment criterion

Figure 6.4.2 Cruciform joints

4.3.4  Specific alignment is assigned where there are specific alignment criteria identified by the designer which need to be verified by LR:

1. the relevant shipyard department will be required to provide a report detailing the achieved alignment at each location;

2. LR will review the alignment report and request check measurements as necessary to confirm the results;

3. the alignment criteria and templates, where appropriate, are to be defined by the designer for each critical area defined.

4.3.5  Close-up inspection is assigned to structure which has no specific alignment requirement but requires an increased level of inspection; for example, to verify correct plate thickness or maximum permitted plate deformation. Close-up inspection may be required to verify a particular or unusual structural feature:

1. Structure will be subject to an enhanced close-up visual inspection by LR Surveyor(s).

2. Dry surveys should identify where units or compartments contain construction monitoring points. These are to be identified by the Builder as a specific witness point.

4.3.6 Non-destructive examination, in addition to the general levels of NDE required in Vol 1, Pt 6, Ch 6 Material and Welding Requirements, may be specified by the designer for critical areas, which LR will verify:

1. The relevant shipyard department will be required to undertake the additional NDE required at each location and record the results.

2. LR will review and audit the NDE measurements as necessary to confirm the results.

4.4.1 Construction Monitoring is a process for monitoring workmanship standards and alignment in critical areas. It is the Builder’s responsibility to carry out the necessary checks and document the results for relevant critical locations, irrespective of the Surveyor(s) attendance at hold points. Shipyard personnel are responsible for the inspection and recording of all CM requirements, in accordance with the approved CM plan.

4.4.2 LR will provide third party inspection to confirm that the critical areas to be covered by CM conform to the required/agreed standards based on check inspections and audit activities. Where LR undertakes a CM inspection to verify the implementation of the CM plan, it will cover:

1. weld specification in terms of type, size and finish/treatment, including:

   1. fit-up and alignment before commencement of welding;

   2. alignment after application of first root run;

   3. back gouging;

   4. final welding and alignment;

   5. stress relief grinding of weld profile (where required for enhanced fatigue performance);

2. the continuity of structural members, where required;

3. plate edge radius and roughness;

4. joints for radius and tapering;

5. openings and penetrations for radius corners.

4.4.3 LR will review all of the specific CM records, as defined in Vol 1, Pt 3, Ch 6, 4.3 Construction monitoring criteria, and in a few cases request that measurements be presented. It is not intended that the attending Surveyor(s) witness each stage of the fabrication process for every critical area, except during the early stages of construction whilst the process is being established.

4.4.4 CM activities will generally be undertaken in conjunction with routine dry surveys required for all construction units. A few specific CM items require measurement by the shipyard; these are described as Enhanced or Specific Alignment.

4.4.5 Non-compliances will not be permitted in the critical areas identified within the CM plan. Where defects are identified within defined critical sections, LR is to agree the remedial action to be taken with the Shipbuilder before rectification is commenced.

4.4.6 On satisfactory completion of all surveys and measurements, LR Surveyor(s) will recommend the assignment of the CM notation.