Bulging Merchant Ships

Bulging is the process of adding a new skin to an existing ship to regain strength, reduce draft, and increase stability. A previous 1989 ASNE paper was entitled "Bulging Warships" and by its very name announced that it would not deal with applying bulges to non-military ships. This paper reviews the history of bulges being applied to merchant vessels. Bulges are most often applied to merchant vessels when the traffic is better than expected requiring a quick increase in carrying capacity or when regulatory authorities demand an increase in the stability standard to allow continued service. Rather than enduring the long and expensive process of buying a new vessel, the owner will send an existing ship into the yard to be cut and lengthened or, in the case of ferries, have more passenger spaces added topside. Such modifications cause weight and stability growth that requires additional hull strength, buoyancy, and waterplane area that only a larger dimensions hull can provide. The paper includes an appendix updating the 1987 warship bulge history and a second appendix on the post-1987 attempts to bulge modern US Navy ships.