Irish Ferries owners Irish Continental Group (ICG) in a statement released to coincide with its AGM said "generally positive trends' outlined in a May Interim Management Statement were continuing.
"The recent closures of Irish airspace have reinforced the strategic importance of sea access to the island of Ireland for both passengers and freight," the company said.
"The reaction from first time customers who used our services during the recent air disruption has been very positive and we are hopeful that this will lead to repeat business, particularly for summer car traffic."
The company said its passenger numbers were up by 11% year to date at 570,000 passengers.
It also carried 124,800 cars, a 4% reduction on the same period last year, 2% lower on the Irish Sea and 13% lower on the Ireland-France route due to a two month later start of the service following winter vessel refit.
ICG said its Roll on Roll off freight market was showing signs of modest growth for the first time in approximately 18 months, although excess RO RO shipping capacity continues.
In the year to date Irish Ferries carried 74,400 RO RO units, a reduction of 13% on the previous year.
Container freight volume was meanwhile up 10% to 179,000 twenty foot equivalent units.