It was late 1995 when I first traveled to the Western Isles and on my first trip on the Isle of Lewis there was a hell of a clatter every time a wave hit the bow! I also think the Loch Seaforth (photo below) is a far superior boat which seems to glide through even rough seas although I think they could also do with a freight service as well but it will be down to lack of money.
I was never on the Suilven but heard many stories about it, one from a friend who was a lorry driver and regularly traveled the route who left Stornoway and by the time they reached Loch Broom it was to rough for berthing in Ullapool they sailed back across the minch and it was to rough to berth in Stornoway, after sheltering outside Stornoway for 12 hours they sailed back across the minch to Ullapool and finally berthed after 30 hours
Here is a link of the Suilven when sailing as a freight boat in New Zealand don' look at it if your going to be travelling on a ferry soon!