Trinity Hotel in Dublin to ferry to Holyhead

Assuming you are taking Irish Ferries, their website says:

Dublin
Dublin Ferryport is situated 2 miles from the centre of Ireland's vibrant capital city, and is positioned at the heart of Ireland’s road and rail network. Dublin Port Tunnel is situated within the port complex & provides quick access to the M50 & M1 motorways, the main routes to the North and South of the country.

A public bus service operates from the terminal building to the main bus station in Dublin City Centre.
The GPS co-ordinates for Dublin are:

53 20 45 N/6 11 39 W

https://www.irishferries.com/uk-en/frequently-asked-questions/our-ports/

With luggage etc., I would take a taxi.

I do public transportation a lot but on this route (Trinity College to the ferry) I took a cab. It was an easy ride and really enjoyable conversation. I honestly can’t remember how much but it wasn’t ridiculous or anything.

The way I do it depends on my mood and the weather.
Either the LUAS tram to the last stop at The Point and then about a 25 to 30 minute walk-
I also pray at the statue of Mary at the Dock Gate- a very Irish thing!
And yes I have done that with luggage. They invented wheels on suitcases for a reason.
Before LUAS it used to be almost an hour walk to Connolly or the Busaras.
Or the LUAS to the Busaras, then the #53 bus right to the terminal as detailed in the Irish Ferries blurb (you may of course be using Stena). It's a good and very under used service since Nolan's started the transfer to Tara Street.
I don't use Nolans on principle.
Nowadays you mainly encounter dock workers on the #53.

Thank you fellow travelers! A cab sounds like a plan to get us there on time and in the right spot.

by that time, or even much sooner we hope, the storm damage to the moorings in Holyhead will be repaired and everybody back to a full schedule

I hope so too! Thank you.