The early eighties saw steel replacing iron as the material for shipbuilding and before the close of that decade the introduction of the twin-screw rendered breakdowns at sea more remote than they had previously been, at the same time giving increased safety in another direction, from the fact that the duplication of machinery facilitated further subdivision of hulls. Now the masts of the huge liners in vogue were no longer useful for their primary purposes, and degenerated first into derrick props and finally into mere signal poles, while the introduction of boat decks gave more shelter to the promenades of the passengers and removed the navigators from the distractions of the social side. The provision of train-to-boat facilities at Liverpool and Southampton in the 1890s did away with the inconveniences of the tender and the cab.