The Steam Packet has suffered a setback in its plans to get its fastcraft running on full power.
Manannan was taken out of service on Wednesday for repairs.
But engineers told Packet bosses that it would take longer than anticipated to complete repairs to a damaged engine on the vessel.
Manannan, which is now back in service, has been running on three engines since a crankshaft failed. In the interim period the affected engine has been fully disassembled and the failed crankshaft has been removed.
Precautionary checks on the engine block, necessary before the crankshaft can be replaced and the engine rebuilt, have revealed more extensive damage than first expected.
It was hoped that the commitment and careful scheduling of additional resources over the next fortnight would allow repairs to be completed while Manannan was in port overnight.
The intention was to ensure no further sailings would be affected and the vessel would be back to full power for the Isle of Man Festival of Motorcycling.
However, because of the detailed inspection findings, Manannan will continue to operate on three engines during the Festival of Motorcycling, meaning journey times will be longer than advertised.
To minimise inconvenience to passengers during the busy festival period, the Steam Packet will be announcing details of a slightly revised schedule, on some peak days, shortly. There will also be schedule changes for afternoon and evening sailings for the post Festival of Motorcycling period.
Steam Packet chief executive Mark Woodward said: ‘The extent of the repairs needed could not be fully assessed until Manannan was withdrawn from service on Wednesday and engine specialists were able to have full and detailed access to the engine.
‘Unfortunately, the level of work required is greater than we had hoped and will require specialist machining of the engine block. This is a difficult repair which can only be carried out by a small number of specialist firms. We must now wait until these specialists are available to us.
‘We are working hard to ensure the repairs are conducted as quickly as possible, but we are unable to restore Manannan to four engines in time for the Festival of Motorcycling. This will lead to slightly longer journey times and we will try to minimise inconvenience by announcing a revised schedule as soon as possible, so passengers can plan their travel.
‘We are in the process of contacting all passengers affected by any schedule changes, which is why it is so important to ensure you give up-to-date contact details, for both home and while away, when making your booking.’
Last night’s (Sunday’s) sailing from Liverpool took the vessel five hours to complete due, in part, to bad weather.