GHS provides four methods of modeling water on deck including two methods for the purpose of modeling the effects of an extra burden of water due to waves.
1) Simple Spilling
This method models the deck area as an intact tank with a "spill point" at the coaming or major freeing port. As the vessel heels, the water not only moves to the lower side (moving the center of gravity of its weight) but some of it may also spill, thus reducing the burden of water on deck and therefore reducing the overall weight and displacement of the vessel.
2) Heeling Moment
In this method, a heeling moment function is derived which represents the moment produced by the water on deck shifting toward the lower side. GHS has a mechanism whereby the moment of the C.G. shift of a tank representing the deck area can be recorded as a heeling moment function. Thereafter a righting arm curve can be executed with the heeling moment so derived (and the deck tank empty).3) Added Volume
This method treats the deck area as a flooded (lost buoyancy) space but with a waterplane raised above the external waterplane by an amount such that the increased volume is equal to a given amount which is typically calculated from a height of water on deck at zero heel.
4) Added Height
In this method the deck area is treated as a "damaged" tank but with a given added head of water representing water which has come aboard from waves.