Ventilation question

DRAWING

DNV D101 A105
On floating installations, ventilation inlets ans outlets shall be located not less than 4.5 m above freeboard deck.
Why ? How to interpret above words. Who could give your explanation ? Thanks

glittercai518

楼主，蹲在你边上和你一起等人来回答，学习一下！
会不会怕水或浪跑进来啊？
高手们，出现吧！

chinadragon

在浮动装置上，通风进出口应安装在不低于干弦之上至少4.5米。

DRAWING

At first , you must know what is the floating installation and free board deck.
Floating installation:
An offshore facility designed to provide hydrocarbon processing and/or hydrocarbon storage, and
offload hydrocarbons. The term Floating Installation is used to generically identify a buoyant facility
that is site-specific. This installation is securely and substantially moored so that it cannot be moved
without a special effort. The term includes, but not limited to Tension Leg Platforms (TLP), Spar
Buoy, Permanently Moored Shipshape Hulls and Semisubmersibles.
Freeboard deck:
The freeboard deck (reference deck) is defined as the lowest continuous deck exposed to weather and sea, which has permanent means of closing and below which all openings are watertight closed at sea.

DRAWING

Secondly, The Stability and Watertight Integrity shall be considered in this word.
Why does rule stipulate the distance between freeboard deck to inlet or outlet to be 4.5 m?
Below the lowest continuous deck above the damage waterline is water watertight line scale.
Which is minimum 7deg heel or trim situation at wind force and water flooding, 4 meters above it is weather line. in this area, all exposed structure shall be weather tight.
At last , You could know where does 4.5m come from.