Condor Ferries hopes to minimise delays while it makes repairs by switching two of its ships on routes between the Channel Islands and the UK and France.
The swap of the Rapide and Vitesse for a week will see the Vitesse operate between the islands and France.
This will allow repairs to a fault in one of the engines to be conducted overnight while the vessel is in dock in St Malo.
Condor Ferries said the move minimised changes to their schedules.
Simon Edsall, managing director, said: "The majority of people travelling will see little difference aside of a different name on the ship."
He said the switch delivered more passengers to their destinations closer to the original schedule than might otherwise be possible with the Vitesse operating on reduced power.
Mr Edsall said those passengers affected had been informed of the changes.
The fault to be fixed was found in a piston's lube oil system.