trunk deck ships had a low net tonnage (an approximate measure of cargo space) in comparison to their deadweight tonnage capacity (weight of cargo). net tonnage is a computation of volume, and the method of measurement used at the suez canal to determine tolls was based on a measure of net tonnage which excluded the cargo spaces in the trunks of these unconventional hulls. trunk deck ships therefore paid less in tolls. in 1911 the toll measure changed at suez, and construction of the type ceased.