North Sea oil and gas explorer Ithaca Energy announced delays and higher costs in building a rig for a North Sea drilling programme, sending its shares down.Ithaca said construction works on its floating production facility (FPF) being built in Poland by Petrofac had taken longer than expected, meaning the vessel will be ready in the spring of next year.That meant Ithaca will be able to produce its first hydrocarbons from its Greater Stella area (GSA) hub in mid-2015, it said. Ithaca said the delays were likely to cost it an extra $5-$10m, but would not materially affect its funding.Chief Executive Les Thomas said: "While good progress has been made with drilling of the third Stella development well and the sub-sea infrastructure installation works, the delay in the FPF-1 sail-away schedule and consequently the impact on the timing of Stella first oil is clearly disappointing."We are working with Petrofac to expedite completion of the vessel modification and commissioning works and deliver start-up of the GSA hub as quickly as possible."Shares in Ithaca fell 15.5p or 10.2% to 136.25p at 12:41 in London.PW