What function do mast risers (king posts) perform on a vessel?

Mast risers, also known as king posts, play a crucial role in directing vapors above the deck on a vessel. They are vertical structures that extend above the main deck, featuring openings at the top that allow vapor to escape safely into the atmosphere. This function is particularly important in preventing the accumulation of potentially hazardous vapors in the cargo area, as these vapors can be flammable or toxic, posing risks to crew safety and the vessel's integrity.

By allowing vapors to disperse upwards, mast risers help maintain safe operational conditions during the loading and unloading of cargo. This ventilation is essential when handling liquid cargo, especially hydrocarbons or chemicals, ensuring that any vapors generated during these operations are managed effectively and do not lead to dangerous situations such as explosions or fire onboard.

While drainage of excess cargo, throttling cargo flow, and reducing pressure are critical aspects of cargo management and handling, they do not pertain directly to the specific function that mast risers serve. This distinction reinforces the importance of mast risers in the context of vapor management and safety aboard vessels.