ssc - 419 supplemental commercial design guidance for fatigue ship ...

Supplemental Commercial Design Guidance for Fatigue• Ship description, including major dimensions• Intended operating conditions• Structural materials• Primary hull strength• Secondary loads• Fatigue strength• Special structure and structural details, Structural maintenance, includingmaintenance philosophy and preventive maintenance requirements• Structural drawings to be managed• Structural history, such as major modifications or upgrades to ships of the classFor each class of ships, a Naval Preventive Maintenance Schedule is prepared. Theseinspections are in several categories.Ship’s Staff Structural rounds are performed at 6-month intervals by formally trainedmembers of the crew. These inspections address areas most prone to defects. Examinations areintended for the early identification of potentially serious structural defects where theconsequences of failure are significant. Figures are provided identifying areas to be inspected.Typical areas of inspection include:• Feet of the mast structure• Foundations of radar and weapons• Intersection of the superstructure with the hull• Shear strake at the quarterdeck cut down• Specific door openings in longitudinal bulkheadsThe Hull Structures Progressive Survey provides for a 5-year inspection cycle. Thissurvey ensures that all ship’s structure is surveyed at least once during that time. The surveys areconducted by the Fleet Maintenance Facility, Engineering Division, Naval Architecture Officer.The survey document includes a list showing every compartment of the ship with an associatedschedule for maintaining a record on spaces inspected and planned for future inspections.Associated with the document are specific procedures for designated areas. These areas are:• Hull (Shell and Appendages) — These inspections must be performed when the shipis in drydock.• Decks — Specific areas are identified for inspection at 24 month and 48 monthintervals, such as specific deck openings and major butt welds in the strength deck• Masts• Hull Structure (Structural Tanks and Voids)• Bilge areasA review of structural and corrosion problems on Canadian destroyers was provided byHussey, 1982. Specific areas of the different classes of ships were described along withsuccessful and unsuccessful repair methods that were used. Areas of the hull that wereparticularly prone to corrosion were described, and suggestions made for design improvements8-6