Bluebridge can't say for sure when its Connemara ferry will be back in service

The Cook Strait vessel's under investigation after losing power during a sailing last week, having to be towed back to Wellington Harbour.

Maritime NZ has been inspecting the ferry.

A Bluebridge service alert states safety is its highest priority, and its working to ensure the problem's sorted, but does not have a confirmed timeframe for when that will be.