A replica of a Viking ship believed to have been built in 1042 sailed triumphantly into Dublin after retracing the 1,000-mile path of the fleets of Norsemen who invaded Ireland more than a millennium ago. Over six weeks, the 100-foot ship, which carried some decidedly un-Viking-like equipment — global positioning systems, radar, radio, satellite weather forecasts and life jackets — crossed the waters of northern Europe from Scandinavia, around Scotland and into the Irish Sea.