Transporting equipment from Ireland to France by Ferry

There's another clause further down the list that might catch you out - this type of vehicle must be booked as freight…

• all vehicles registered in the Republic of Ireland, and classified and taxed for Irish Motor Tax purposes as a Commercial Goods Vehicle. VAT, if applicable, will be applied to vehicles of 7m or more in length. Express boarding and disembarkation is not available for vans or horseboxes over 7m in length

If your van is taxed as private then it's down to what they mean by 'commercial'. You're gong to a trade show with display equipment so I would say it would be reasonable to categorise your cargo as commercial. As in, you're not bringing furniture to your new house in France. The fact that you are carrying kit which is not for sale might be significant when it comes to motor insurance but I don't think it will be a material fact here.

It's open to interpretation. Whether you declare it as commercial or not would depend (in my book) on whether you think someone from Stena will ask to inspect the contents of your van or they'll just wave you onboard.

Is the van taxed as commercial? If it is, there's no issue to be resolved, you have to book it as freight.

An interesting fact I noted when i looked at the page the OP linked to above. Stena seem to care more about the length of a car whereas with Irish Ferries, it's the height. Stena list off several models that are between 4.7m and 6m in length, preumably it costs more to being them on their boats. For example, the Skoda Superb and Merc E-Class models are listed by Stena as being longer than 4.7m. Irish Ferries just ask that your car be not more than 1.9m in height, they assume that all cars and SUVs are within their limits.