The document by ferry operator Transdev warns masters that trials in early March showed that the new Emerald-class ferries became “airborne”,resulting in “tunnel slamming”,when the vessels sailed directly into waves or on a 45-degree angle to them at about 10 knots.
“This can be detrimental to the vessel’s integrity and the safety and comfort of the crew and passengers,” it states.
Tunnel slamming refers to water rising between the two hulls of the catamaran ferries,jolting the bridge deck which structurally joins the hulls together.
“Running ahead of the swell must be avoided,as this may cause ‘trapping’,which results in the vessel bow-diving or broaching,and a loss of control,” the memo warns.
The document – obtained by theHerald – advises masters that the safest and most comfortable course for passengers when crossing Sydney Heads is to have the swell directly on the beam of the Emerald-class ferries. The beam is the width of a vessel at its widest point.
Last weekend a 19-year-old teenager was rescued from the harbour after falling overboard from the Clontarf ferry several hundred metres from North Head. The Clontarf is one of the three Emerald-class ferries now used on the Circular Quay-Manly route.