Yes Eurostar needs a travelday

 you buy a reservation (seatplace)  and the Railpass (Interrail/Eurail) is your ticket :)

On ferries it depends some are for “free” you only have to pay the porttax and if you want a comfort upgrade in this case you need a travelday of your Pass (apllies for example for Superfast ferries at the Adriatic sea)

Others offer a discount on their prices. These wouldn´t need a travelday For example Tallink Silja at the Baltic Sea :)

Ferries with Interrail

Ferries with Eurail

Thank you for the quick response and information.

Since you are very early to plan, try to get a saver fare for the eurostar. the high reservation fee with interrail is not worth the price.

I am in agreement on this, with one caveat which is that, on balance, it is more likely to be worth it with a 1st class pass - in my experience Standard Premier seats on the Eurostar are more often than not up to double the price of 2nd class seats, but the reservation fee increase with Eurail is only €8.

Another thing that affects the value calculation is whether London and Paris/Brussels/Amsterdam/etc. are your termini, or if you will be catching any other trains at either end to get from/to your initial/final destination.

Finally, it’s worth pointing out that Eurostar return fares are always cheaper than singles.

In conclusion, whip out a calculator before deciding and you’ll be sorted!

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Since the introduction of the Eurostar to the pass, the number of UK-Continent ferry options discounted with Eurail has decreased. If you would like to travel this way (and it is nice seeing a new country hoving into view with a stiff breeze in your hair and the salty taste of sea spray on your lips) the only one that remains is Harwich to the Hook of Holland, which you get 30% off on. However, Irish Ferries have just begun a Dover-Calais link this year, which may also be discounted as all their other lines are. Alternately, do away with any 30% offs and make the saving by way of a combined sail-rail ticket, details of which can be found here:

https://www.seat61.com/trains-and-routes/london-to-paris-by-ferry.htm

https://www.seat61.com/trains-and-routes/london-to-amsterdam-by-ferry.htm

As these information pages explain, these options probably won’t save you money against an advance Eurostar ticket, but they might do well nearer to the time, and they offer more of a quintessential classic crossing experience.

Ferries are fine when the sea’s calm!

On the whole though, taking the train is far better for foot passengers as the ferries are mostly vehicle orientated.  Neither Dover Marine or Calais Maritime stations exist anymore so travellers have to make their way from the main town stations to / from the ferry ports.  I don’t think Newhaven - Dieppe’s any better, either.

Harwich to Hook of Holland is better, but a much longer crossing.  O.K. for those that don’t get sea-sick!  At least Hook of Holland still has a railway station, but it’s only a local train nowadays and you have to change somewhere or other to get a main line / long distance train to anywhere else.

So give me Eurostar every time!