ES-TRIN, Article 19.03(3)(c) - Definition of the downflooding angle or φf
Up to the equilibrium position represented by the maximum heeling angle (φmom), all openings in the outer skin of the vessel have to be watertight, because it is a zone of immersion. Beyond this “watertight zone”, there is an additional safety margin defined of at least 3° between the maximum heeling angle (φmom), and a possible downflooding opening (see Article 19.03(3)(b)). This zone of at least 3° beyond the maximum heeling angle (φmom) is not a zone of permanent immersion of the outer skin of the vessel, but a zone of possible periodical and short-term immersion /splashing of the outer skin, caused by some additional dynamic disturbances (such as waves, wind gusts etc.).
Therefore, openings in this zone could in principle be accepted as being “only” weathertight and not mandatory watertight, as for short periods of time it is not expected that the considerable amounts of water (which may affect the stability of the vessel) can penetrate through weathertight openings being splashed/ shortly immersed.
However, Article 19.03(3)(c) gives the following definition: “φf the downflooding angle, that is the heeling angle, at which openings in the hull, in the superstructure or deck houses which cannot be closed so as to be watertight, submerge".
Why is the downflooding angle defined only by the “watertight” openings and not extended to “weathertight” openings?
The experts who developed the stability requirements included in ES-TRIN deliberately decided to consider only “watertight” openings for the definition of the downflooding angle. The reasons are the following:
- The definition of “weathertight openings” bears a higher risk of different interpretations (e.g. “no considerable amount of water”, accepted duration of immersion etc.) and might create a need for additional guidance. A conservative approach was taken to define the downflooding angle with reference only to openings which cannot be closed so as to be watertight.
- Reference to non-watertight openings only supports limiting the complexity of an already highly complex regulation.
CESNI/PT/Pax (21) 1, CESNI/PT/Pax (21)m 5, item 13.4
Working group for passenger vessels (CESNI/PT/Pax), openings, weathertight, watertight, stability, downflooding