ClassNK has investigated behaviour of waves acting on windows located considerably above the freeboard deck of ships where the navigation bridges are located forward of the midship, such as onboard Ro-Ro cargo ships. Based on the investigation results, ClassNK has issued amendment of rules for ship windows.
It has been found out that there is possibility waves can hit the windows located considerably above the freeboard deck due to waves rolling over the foredeck and running up along the front walls, even though the wave height may not be so high that the wave directly reaches the windows. In fact, cases have been confirmed in which navigation bridge windows seem to have been damaged by the aforementioned phenomenon.
ClassNK amended the relevant Rules to provide the minimum design pressure for windows located considerably above the freeboard deck and forward of the midship.
This amendment is intended to enhance the structural reliability of windows on the front walls of deckhouses and superstructures located forward of the midship, such as the navigation bridge windows of Ro-Ro cargo ships. Even so, the possibility still exists that pressure from waves might exceed the design pressure stipulated by the amended Rules, depending on the sea state. Consequently, it is suggested that operational guidelines for safe navigation already established and implemented by each shipping company, management company, and relevant institutions should be steadfastly maintained even if such windows provided on your ships satisfy the amended Rules.
Furthermore, this amendment applies to ships the keels of which have been laid or which are at similar stage of construction on or after 30 June 2016. Meanwhile, the potential for waves to hit the navigation bridge windows as described above also exists onboard the existing ships to which the amendment does not apply. Therefore, ClassNK recommends to pay continuous attention and to keep strict observance of the operational guidelines for safe navigation for existing ships.