Chris, it's a Shanty festival!

Quoting from the website:
a quality event is planned that will help to keep "Shantying" and maritime traditions alive in the City of Hull.

Perhaps if you do go along, you will find your statement There are only a limited number of shanties that people can sing along with or half know, without endless repetition, over an entire weekend to be very far from the truth- shanties, by their nature, are meant to be joined in with and easily picked up.

Also, you will see from the website that not all those appearing are shanty crews, for example the lovely Linda and Hazel of Hissyfit, the Davenports and the Evardsons, who sing sea songs rather than shanties.

There are plenty of festivals which cater for 'a mix of all types of folk music and song' as you put it. This shanty festival is an opportunity to focus on our oral maritime traditions which are deeply rooted in Hull and environs.

Wish I could be there!