Consequences of CSR BC & OT on oil tankers
- Normally scantling increases due to higher minimum thickness requirements will be found in way of keel, sheer strake plating and non-watertight stringers in the double hull.
- Some of the plate thickness in way of tank boundaries does not satisfy local plate requirement due to increased internal tank pressure, as the design vapour pressure is now added on top of the liquid pressure for seagoing conditions.
- Longitudinal stiffener section modulus requirements in way of deck and upper part of longitudinal bulkheads are generally higher due to updates in the buckling requirement. This leads to scantling increase in most ships.
- Offered scantlings generally satisfy the prescriptive fatigue assessment requirements in accordance with CSR BC & OT. Some longitudinal stiffeners located in the bottom shell and the side shell have fatigue life in the order of 20 to 25 years and increased scantlings or improved connection details will be necessary.
- Finite element yielding assessment has limited impact but finite element buckling assessment leads to scantling impact for some members, such as: -- Hopper structure -- Inner hull upper part -- Longitudinal bulkhead upper part -- Horizontal stringers in the double hull -- Double bottom floors
- The Hull girder ultimate strength results for both intact and damaged condition were reviewed and no scantling increase was seen for the selected ships.
- The increased scope for FE analysis has a significant scantling impact in the way of the foremost and aftermost cargo holds, and also primary members connected to collision bulkhead inside fore peak tank and structures attached to engine room bulkhead inside engine room. Typical areas of concern are shown in the figure.
- CSR BC & OT requires standard structural details for fatigue critical locations and alternative design is not acceptable unless direct analysis proves equivalent fatigue capacity to the standard details. It is expected that this will result in more consistent quality of local detail design.