Normandy - getting there from Portsmouth

We're doing something very similar next year - catching the morning ferry from Portsmouth that arrives in Ouistreham (Caen port) at 3 PM local time. Rather than worrying about getting off the boat and into the town before the rental car offices close, we plan to relax, spend the night in the town, and then collect our rental the next day - also for a few days in Bayeux.
For info, Brittany Ferries also has a night crossing that day: departing Portsmouth at 11:30 PM and arriving at 6:45 AM ... taking 7+45 for the trip. You could conceivably book one of their cabins and just sleep on the way over. By the time you disembark at Ouistreham and make your way into town the rental car offices will likely be open or, if not, you could grab breakfast while you wait.

As an alternative I wonder about flying Southampton to Paris Orly with Eastern Airways and picking up a car there, as an alternative to the ferry.
The Caen ferry is the route I would take to Bayeux but the flight may better suit you.

Either bus or train from central SOU to the Airport, or taxi if you prefer.

Check out aquacars.co.uk, based in Portsmouth, to fetch you from Southampton to near the ferry terminal in Portsmouth. The heart of British naval history, Portsmouth is certainly worth a day. We did just that and took the ferry to Quistreham and a short bus ride to the Caen railroad station where most of the car rental agencies are located. About 20 miles or so to Bayeau. With a car you can explore the D Day beaches and even drive to Mont St. Michel, about 90 miles or so via a motorway. Easy peasy. We returned from MSM via the back roads, drifting along and stopping to buy local cheeses, sausage, etc. and the ever present Calvados. Good luck.

Thank you all for the helpful information. I am curious to know if anyone has taken the overnight ferry. If not, how is the daytime crossing? It seems like it would maybe be better to sleep while on the ferry vs 'wasting" a day on the Channel.

https://search.ricksteves.com/?button=&date_range=2y&filter=Travel+Forum&query=southampton+ferry&utf8=%E2%9C%93

Though we haven't yet taken the ferry, all of my research in preparation for our own trip indicates that the vessels are quite nice, stable, and that the crossing is usually a pleasant one unless you get extremely unlucky with some bad weather. The on-board cabins look pretty good too - not to mention being an extremely cost-effective way to pass the night..
Would think the overnight ferry would be a good option for you: could spend the day in Portsmouth seeing the sights (including a very good D-Day museum apparently), saving yourselves the cost of a hotel room during the crossing. Once arrived at Ouistreham you'd be well rested and ready to go. Would effectively add an extra day to your itinerary by doing it that way.

I once took this overnight ferry by chance. I had originally booked a ferry from Poole, UK to Cherbourg, but when I arrived in Poole, the ferry has been cancelled due to some sort of French strike (surprise?) in Cherbourg. So the ferry company sent us by taxi to Portsmouth where they re-booked us on the overnight ferry to Ouistreham. This was 15 years ago, so my details may be sketchy. But they also put me in a taxi on arrival from Ouistreham to Caen where I picked up my rental car (Hertz). It is about a 20-minute drive between the ferry terminal and the train station where many of the rental offices are located. Keep in mind that many rental car offices are closed on Sunday. Other than these variables, the idea of ferry travel to Normandy has always interested me. At night you don't see much, but if the ferry runs, it is a nice way to travel and you can factor in one night less in hotels. But I would only do it if I had a "plan B," and if my schedule and time off was very flexible. The ferries are notoriously unreliable.

I've booked five Channel ferries between St.-Malo, the Channel Islands and England. Two of those five ferries were cancelled, one of them for three days in a row. That happened in 2017; my other cancelled ferry was many decades ago. Both of those trips fell between May and September, so winter weather wasn't a factor. I think I was unusually unlucky, but still I would be cautious about creating an itinerary that depends on a ferry connection. Will you be able to recover if that ferry is cancelled?

Questions for those who have had to deal with ferry cancelations:
1. What was the reason for the cancelation, ie strike action, weather, mechanical ?
2. How much advance notice did you receive from the operator, ie last minute or a day or two in advance ? Tx

Questions for those who have had to deal with ferry cancelations
(sic):

1. In my case, I was told that the strike was due to the French fishermen in Cherbourg—but I have no way of really knowing.

2. This was in 2008, before I traveled with a phone I could use in the EU. so I didn't know until we arrived at the ferry terminal. I was actually cooling my heels in a local pub while my traveling companion went to check on the ferry status since we didn't see it, and she showed up in the pub with someone from the ferry company. They said they had tried to call our U.S. number, but no one there could reach us.