The ferry terminal Liverpool will be closed on the weekends of March 14 and 15 and March 21 and 22 for essential works, the DoI has announced.
The closures will allow for the reinstallation of a modified dolphin fender as part of an ongoing repairs programme.
The work follows issues identified during berthing trials for the Manxman and Ben-my-Chree, where mooring lines clashed with the fender at lower tides.
The DoI said the closures are weather-dependent and form the next phase of modifications first announced in October last year. A mooring hook at the terminal is also scheduled for modification in the autumn, with further details to be released when finalised.
It apologised for any inconvenience caused and thanked passengers for their patience while the work is undertaken.