Void Space Calculation (OW, OH)

Out-of-gauge (OOG) cargo, in which the cargo protrudes from the Flat racks or Open tops upon loading, will result in VOID Space when loaded onto a container ship.

VOID space may vary depending on the nature of the cargo and the loading situation on the ship, but carriers generally calculate it as illustrated in the table below in order to secure space on the vessel and reflect the void charge in the ocean freight rate.

	OW (Over-width)	OH (Over-height)	OW+OH (Full Void)
20’ Flat Rack	2 TEU	1 TEU	5 TEU
40’ Flat Rack	4 TEU	2 TEU	10 TEU
20’ Open Top	N/A	1 TEU	N/A
40’ Open Top	N/A	2 TEU	N/A

As depicted in the image below, when the yellow cargo is loaded onto the flat rack, the part of the cargo that extends outside of the container prevents the container ship from loading other containers in that slot, thus leaving it as VOID space. 

This slot is preserved as VOID space to preclude the loading of other containers, and vessel loading planning and actual loading operations are conducted accordingly.

[Void Space of OOG Cargo]

The photo underneath demonstrates an OOG cargo of steel structures on a 40' flat rack, stowed in the under-deck position of a container ship.

On both sides of the 40' flat rack, the yellow dimensions I've indicated show where the Out-gauge, Over-width, extends, and these slots cannot be occupied by other containers, so they are considered as VOID space.

Although not shown in the image, there's also an Over-height extension upwards. Therefore, this shipment is an OOG cargo with both Over-width and Over-height. 

The Void space results in a total of 10 TEUs, saying 'Full Void' occurs.

[OOG Cargo - Full Void]