is the amount, the ship can be flooded without the risk of sinking. i.e. the maximum length of the ship that can be flooded without submerging the margin line. The margin line is located 75mm below the bulkhead deck, providing a safety margin.

• A floodable length curve can be drawn for different permeability.
• It is used to test the after-bulkhead length so that the bulkhead length is sufficient to contain the flooding without sinking the vessel.
• Factor of subdivision = Permissible length / Floodable length

The factor of subdivision introduces a safety measure by reducing the size of the compartments to limit the effects of flooding. It ensures that the ship's draft or trim has less chance of touching the margin line during flooding or heeling.

Permissible Length Formula:

$$Permissible\:length=\frac{Floodable\:length}{Factor\:of\:Subdivision}$$

A smaller factor of subdivision leads to a smaller permissible length, requiring more numerous and smaller compartments. This reduces the potential for catastrophic flooding, as a smaller flooded area is less likely to exceed the ship's reserve buoyancy and cause it to sink. The factor of subdivision is determined by the ship's length and its intended service. The nature of service is quantified by a "criterion of service" (Cs) number, which considers the proportion of passenger and machinery spaces to the total volume of the ship. A higher Cs number (indicating more passenger space) typically results in a lower factor of subdivision and therefore smaller compartments.