Boat to Miyajima from the Peace Park

I will be staying near the peace park in October and I want to visit Miyajima island.
I have read the you can take a boat from the peace park area.
Just wondering would it if it possible to prebook tickets or if you can just turn up on the day and purchase a ticket?
Not sure how busy the boats get so don't want to show up without prebooking and not be able to get on a boat. Any advice much appreciated.
Thank you

If you travel during peak seasons, such as the cherry blossom season, I strongly recommend to book at least a few hours in advance. The boat has become very popular.

During less busy times, chances are higher that you can just get a ticket ahead of departure.

Unfortunately, the web reservation system is available in Japanese only:
https://aqua-net-h.co.jp/heritage/reservation/form.php

Thank you for the information.
Do you know what happens if we got the boat there and then went to get the late boat back without booking and the boat was full?
I don't want to get stranded there but also not sure how long we want to spend on the island as we intend to walk up mt misen.

As long as it isn't super late, it shouldn't be a big problem to get the ferry and then the train. Looking at the website for the JR ferry (I know there is another company too), the last one is at 22:14.

https://jr-miyajimaferry.co.jp/en/timetable/

The ferry timetable Orangezorki posted above is the ferry between Miyajima and Miyajimaguchi, not the ferry between Miyajima and Peace Park.

But, since the ferries between Miyajima and Miyajimaguchi are very frequent, you may take this ferry from Miyajima to Miyajimaguchi, then change to the Sanyo Line train (frequent) heading toward Hiroshima station. You want to get off the train at YOKOGAWA (��川) station (2 stops before Hiroshima station), then follow signs to find tram line #7 to the Peace Park (or near your hotel).

The interval stops on the Sanyo Line train between Hiroshima and Miyajimaguchi are: HIROSHIMA > SHIN-HAKUSHIMA (新白島駅) > YOKOGAWA (横川駅) > NISHI HIROSHIMA > SHIN INOKUCHI > ITSUKAICHI > HATSUKAICHI > MIYAUCHIKUSHIDO > AJINA (阿品駅) > MIYAJIMAGUCHI.