How can you go from Paris to l'Ile d'Yeu?

Since the OP wants to minimize travel time and assuming they are at CDG, another fast way to go from CDG to L’Île le d’Yeu:

1. Take a flight from CDG to Nantes (1h)
2. Take a taxi from Nantes airport to Fromentine helipad (1h). You could try to book it ahead.
3. Take an helicopter from Fromentine helipad to L’Île d’Yeu (20min). Video.

Add around between 1h30 to 2h for check-ins, walking between connections and baggage retrieval. Add more time to wait for the plane and helicopter depending on when you’re at CDG.

• Assuming you are arriving at CDG.

In France, TGV is the best option for city center to city center travel, and is great fun.

However, to get from CDG to Fromentine or St Giles, rent a car.

France largely invented modern cars and roads, the whole nation is car-centric, and the nature of France is the rural essence (for which you run around in a car), not the big cities.

To go from Paris and L’Ile d’Yeu, you will first need to get to Nantes (the biggest city near Yeu).

This can be done using TGVs (High speed train) from Gare Montparnasse in Paris taking 2 hours

Nantes

At Nantes, you have two choices, you can either go to Fromentine or go to Saint-Gilles-Croix-de-Vie.

The trip between Nantes and either ports take around the same time of an hour either by train to Saint-Gilles or by car (bus) for Fromentine

But due to the crossing being far more frequent in Fromentine (if you miss your boat due to train/bus delay, this will help, but, remember that all tickets are reserved and are only valid for the booked ferry, so you will need to re-book if you miss your boat), this is my recommendation, and the only way if you have more than a few piece of luggage (see below.)

Fromentine

The main port to the island is Fromentine (La Barre des Monts), from there you can, as stated by the tourism office, either take one of the two ferry companies or take the helicopter.

To go there, the regional Aléop bus line 13 (timetable) will take you from Nantes Bus Station (linked to the railway station, follow the signs to Gare routière) to the port.
They are time-matched to most TGV from Paris and also to the onward crossings from Yeu-Continent, see bottom paragraph, and can be bought together with your train ticket online if you choose La-Barre-des-Monts as the destination of your ticket from Paris (they can also be bought onboard with the driver cash only)

If you choose to take the helicopter, you need to check the linked timetable if your bus stops at BEAUVOIR-SUR-MER Fromentine Héliport (not all buses does, if it doesn’t, change your ticket to have the correct bus) and get off the bus there.

For the ferry crossing, you will get off the bus at Fromentine Gare Maritime (this is not the terminus !)

For the Ferry company, you can either choose between the faster (nicer in my opinion, but fully enclosed) catamaran by the Yeu Continent company doing the crossing in 30min or the open-air smaller boat by the Compagnie Vendéeene doing the crossing in 45min.

Either way, you MUST be at boarding at least 30 min before the scheduled ferry departure (on either way), non-validated tickets are cancelled (with no refunds) and put back up for sale 15min before departure time.

Baggage

The only company that will accept more than 2 pieces of cabin luggage on board is Yeu Continent which only starts at Fromentine

If, and only if, you choose Yeu Continent, you need to put your luggage (you can have a cabin luggage inside, drop them off only if you have more than one such cabin luggage) in the luggage racks that are brought up near departure time.

You can easily spot them when getting off the bus, by locating the huge sign that says BAGAGES DEPART (Departure Baggage, no. 2 on the map) (it is alongside the BAGAGES ARRIVEES sign (which is for arrivals)) (if there aren’t any, just wait a little bit and they will arrive eventually).

Put them on those racks and look at the side of the one that has your luggage for the number of the rack and the color linked to the side, you will need it if you want to retrieve your baggage without doing Where’s [my baggage] Wally? along the crowd on arrival.

In this example, you will need to remember that your luggage is on the luggage rack 44 on the Red side

Ticketing

Tickets prices for all of the crossings, are fixed and don’t change over time, are either bookable online on the operator websites Yeu Continent Compagnie Vendéene (Green Réserver button in the top left corner), and directly at their ticket offices in Fromentine (YC and CV) or Saint-Gilles (CV)

If you take an onward crossing in the mid-afternoon (~12am-4pm) or near mid-August, pre-booking in advance is really the only realistic way you will get a ticket.
At other times, you can keep a look at the respective numbers of available tickets on their websites and go at the respective ticket office to grab a ticket if you don’t want to pre-book.

If going back from Yeu in a week-end, It is really important that your pre-book your tickets.
On a weekday, you will likely be able to get your ticket without prebooking at the ticket offices in Yeu (Directly inside Gare Maratime for YC and here for CV)

I would recommand always prebooking, especially as a > 1 month before departure booking with Yeu Continent saves €4 per person.

Boarding

After dropping your bags, walk towards the left end of the glass walkway.
The building attached to the walkway is the ticket office, buy your tickets inside if needed.

Once you have a ticket, walk right through that walkway to head to the terminal.

Once in the terminal seating area :

• If you take Yeu Continent‘s NGVs, your gate will be no. 2 located on the left of the terminal.
• If you take Compagnie Vendéene, it will be gate no. 3 just at the right of where you come from the walkway.

Pass ticket check, and board the ferry.

Tip : On the catamaran, stay on the upper floor to be able to leave faster, being downstairs slows that down

Arrival

If you have taken Compagnie Vendéenne either from Saint-Gilles or Fromentine, go right out off the ferry onto the bridge then on the ground, the center is along the marina on your right.

If you have taken Yeu Continent, you will arrive a little bit further from the center.

The disembarkation procedure for Yeu Continent is :

Leave the ferry and follow the flow downstairs.

If you have dropped-off luggage, after the last flight of stairs, go on your right and wait (Warning: it can be really crowded), you will see the racks come by heaps.
Identify your rack by the number and the side by the color taken at drop off, take your luggage from it and leave.
The center of the town is on your right following the marina. Note that you also have most of the rentals (bike, car…) shops in the ferry station area if that’s of interest.

Note about the helicopter :

If you choose to take the helicopter, either to do the crossing or to do a tour flight, from the heliport you will need ~10min walking to town center and ~15min to the rental shops, all along the marina.

Return

Either way, you MUST be at boarding at least 30 min before the scheduled ferry departure, advisable to be 45 min ahead for the NGVs, non-validated tickets are cancelled and put back up for sale 15min before departure time

For the return leg, you will find the Compagnie Vendéene embarkation point here, the gare maritime for Yeu Continent here and the heliport here.

• For Compagnie Vendéene :
  Providing you have a ticket, you can just show up at the embarkation point, pass ticket check and get on the ferry

• For Yeu Continent :
  I really advise you to be quite early, there is always a long queue to board, and all the seats on the top deck will likely have filled out before you go in if you are too far down the queue, and if you have a connection, it is not advisable to be downstairs.

The baggage racks are, again, under the BAGAGES DEPART sign, on your right when you arrive at the station (on the side where the catamarans are) and the same procedure that you need to have identified (number and color) your rack applies here.

Go up the stairs/escalators and go inside, on your right you will have gate no. 2 (signs with NGV) where you will board (and a somewhat long queue).

As you did inward, pass ticket checks, and board.

If you have a connection, stay on the top deck

Return Arrival

After arriving, you will be guided to the terminal from where you boarded inward, and you just need follow Sortie through the glass walkway.

Once outside, go grab your bags (alongside of where you put them on departure and no. 6 on the map) and then head straight for the bus stop (you will see quite a lot of buses, yours is line 13 to Nantes and likely in Aléop livery and should occupy the same deck as when you arrived.

Note about Yeu Continent :

[1] : They are a public company and the only company for which the regional buses are time-matched.
For ex. if you choose Compagnie Vendéenne, you might have issues regarding time matching (like having to wait 2h for a crossing, where the corresponding NGV will depart 45m-1h earlier), you may also be re-booked on a later ferry if the bus has a delay that makes you miss the boat

There are two fleets for the island, the NGV catamarans (Navire à grande vitesse, aka high speed boat).

And the cargo ship Insula Oya II, which is a combi cargo/passenger ship (that used to run alone the link before the NGVs), open air, but it takes 70min.
On the return leg, you might benefit from better headroom before connecting on your bus, if boarding the Oya instead of the NGVs and I recommend taking it just for the open air deck.

When booking on the YC site :

• the NGVs crossings are identified with a blue 30min logo
• the Oya II’s are identified with a orange 70min logo

Préférentiel pricing is for a passenger of 60 yo or more, holding a French student card (an ISIC might work though) or the famille nombreuse (large family) card from SNCF

If you so choose, some minor differences :

• The luggage racks will not be as pictured above but something akin to a 5 ft. container will be brought up where all the baggage are put in. Usually only a single one is brought up, you don’t need to remember anything on those ones.
• Boarding at Fromentine, you will likely still board from Gate 2 downstairs, but then be guided to the correct gate when upstairs.
• Boarding at Yeu, look for the ticket offices inside and on your left you will have Gate no. 1 for the Insula Oya II

Other guidance still applies on either ferries

St Gilles Croix de Vie seems to have far better connections than Fromentine, which lacks a station. So although Fromentine has more, and slightly shorter, ferry crossings, St Gilles makes more sense.

Google can route you by train from Paris Montparnasse to St Gilles Croix de Vie, with the majority of the journey on the fast efficient TGV. The whole trip takes about 4 hours. You can book in English at SNCF.com.

Unfortunately to catch the midday ferry means an early start: the 0743 TGV, with a short walk to the port, gives you half an hour to buy your ticket and board. That should be enough based on my experience of similar services, but isn’t guaranteed. The previous departure is 0642. There’s then a gap until the evening ferry at 1830, though St Gilles itself looks like a nice place to spend a few hours.

Times are based on travelling tomorrow, taken from Google maps, so check on sncf.com before booking.

Even if you’re starting from the airport (CDG) there are a few direct TGVs to Nantes, where you’d be changing trains anyway. RER+Metro+TGV takes a similar amount of time from CDG, despite the TGV being really very fast (up to 320km/h) and almost always the best option for long-distance travel in France.