Plans for a £100m underwater tunnel linking Orkney to the Scottish mainland are being considered.
A ferry service currently links Scrabster and Stromness
It is estimated the tunnel would cut travel times to mainland Scotland, with a seven-mile link between South Ronaldsay and Caithness.
The journey currently takes more than an hour by ferry.
The ferries used for the service between Scrabster and Stromness cost about £30m and have to be replaced every 20 years.
Proposals for a tunnel across the Pentland Firth were set out at Orkney Council's transportation and infrastructures committee.
The report, by director of development services Jeremy Baster, also suggested linking some of Orkney's outlying islands, such Shapinsay and Rousay, to its mainland by tunnel.
Mr Baster said: "Given the expense of ferry replacement, the infrequency of ferry sailings and their limited hours of operation and the susceptibility to delays and cancellations in poor weather, the theoretical attractions of a fixed link between islands and between Orkney and the mainland are self-evident.
"Undoubtedly there are major engineering challenges, and hence costs. However, in the context of a strategy focusing initially on an inter-island link, it would be worthwhile undertaking some further investigatory work.
"Of the inter-island possibilities, Shapinsay is considered to be the most obvious top candidate. It has a dedicated ferry - the cost of which could be avoided - and the shortest potential crossing.
"If the outcome was positive, the much larger-scale project of a Pentland Firth tunnel could merit further investigation over a longer time scale."
A council spokesman said: "Improvements to Orkney's transport system are a key part of the community plan and the council's corporate plan.
"Fixed links have always been seen as a possible way of achieving this aim and therefore further investigation of the practicalities of tunnels is consistent with policy."
Council members visited Norway in May 2004, where 24 sub-sea routes have been constructed through rock.
The budget for those tunnels, set out by specialist firm Sweco Groner, worked out at about £5,000 per metre.
Three main options for the mainland route will be considered by the council, which will now invite a Norwegian tunnel engineers to assess how feasible the proposals are.