Fire monitor heel is a heeling moment imposed by the operation of fire-fighting equipment on board a ship. The total heeling moment is composed of two parts; the heel force exerted by a directed transverse spray of the ships monitors; and a countering thruster reaction force.
For most vessels, an evaluation of monitor heel is sufficient in the transverse direction only. Dedicated fire ships with complex fire fighting arrangements may also have to consider longitudinal forces, and rotational forces, on the hull. Once a force has been determined (based upon the flow rate and pressure at the monitors), the monitor heel force can be determined by;
The thruster reaction force is considered for a horizontal force equivalent to the force of the monitors; i.e., what would be required to prevent the vessel from being pushed sideways. As this force operates oppositional to the fire monitors, it adds to the heeling force exerted on the vessel.
The total fire monitor heel is taken as the sum of the monitor moment and the thruster moment;
For most vessels, evaluating only the transverse direction, this can be simplified;
As the reaction force and monitor force should be equivalent, the moments can be combined;