Watertight, tower-like structures called cofferdams are then built over the selected openings so that they extend from the hull of the ship to well above the surface of the sea.
Ukwakhiwa njengephondo okungangeni manzi okubizwa ngokuba zizithuntelo zamanzi xa kusakhiwa idama okanye ibrorho ziye zakhiwe ngaphezu kweendawo ezivulekileyo ezikhethaweyo ukuze zandise ukusuka kwisiqu senqanawa ukuya ngentla komphandle wolwandle.