In 1974 the Avalon was selected as being the most suitable replacement for the Caledonian Princess on the Fishguard - Rosslare route.
At the North Shields yard of Swan Hunter her Lower and Main deck accommodation, mainly passenger and crew cabins, were cleared to make way for a vehicle deck accessed through a new stern door. At the aft end of the new vehicle deck was space for high vehicles. Mezzanine decks were provided port and starboard which could be raised to accommodate artics. Immediately forward, in the midships section, the headroom dropped to permit only cars while on the forward end of the ship cars were accommodated on two levels.
The de-luxe and special cabins on the boat deck were given over to the crew. On the Upper deck her accommodation was extended aft, a new cafeteria area being provided, thereby increasing her passenger certificate up to 1,200 in two classes.
In her new guise the Avalon offered capacity for 200 cars and eight trucks. The conversion had cost £1.75mn and on 15 July 1975 she began her new career as an Irish Sea ship.
Despite being a 'Fishguard ship', the Avalon spent much of her Irish Sea career at Holyhead, her first spell at the port beginning on 11th January 1976. Her time on the run was however marred by an unfortunate incident on 17th March. Arriving at Holyhead in dense fog with the 2045 sailing from Dun Laoghaire she made contact with the T-Piece on the Mail Pier, damaging some 20ft of starboard side plating. The service was subsequently suspended for three days, unheard of in the days of the mail ships, while a replacement ship was sourced. It was a complex affair, involving the movement of the Maid of Kent from Weymouth to Fishguard and the Dover moving from Fishguard to Holyhead where she took up service at 1545hrs on 20th March. After her repairs the Avalon was back on the run on 10th April and remained there until resuming at Fishguard on 25th June.
The Avalon was back in service between Holyhead and Dun Laoghaire on 4th October 1976, swapping with the Dover which in turn moved to Fishguard. This was also the day that saw the Hibernia stand down from service for the final time, laying-up pending sale. Once again she was to blot her copy book and on 17th October she failed with generator problems while alongside at the Irish port. Services were again cancelled until, in a repeat moved, the Maid of Kent was called to Fishguard from Weymouth to release the Dover which sailed north to restore Holyhead services.
Having returned to the Fishguard - Rosslare run for Christmas, the Avalon was to be found operating from Holyhead again from 1st March 1977, pending delivery of the new St Columba from Denmark. With the St Columba entering service on 2nd May, the Avalon returned south and so continued her routine, regularly switching between Fishguard and Holyhead as overhaul and emergency relief until in 1979 when she was replaced at the Pembrokeshire port by the Stena Normandica. At this point she was officially allocated to Holyhead for her final two years of Sealink service.
On 8th September 1980 the Avalon left Dun Laoghaire on her final commercial sailing under the Sealink flag. At the end of the month she sailed to Barrow for lay-up pending sale and three months later, with funnel painted black and the first letter of her name removed, she sailed to Pakistan. Despite being just 17 years old her thirsty turbines made her unattractive to any interested buyers and she arrived at Gadani Beach, on 22 January 1981. H.H. Steel Ltd commenced breaking immediately.