Travelling from Norfolk to the Humber estuary

[answersplease]

Hello,

I'm new to this forum (and to boats) so please forgvie my ignorance. I should say up front that I'm not actually considering doing this journey myself, however I am writing a book where the main characters will be travelling from Horsey Gap in Norfolk to the edge of the Humber Estuary. I want them to travel in metal boat large enough to have a 'hold' below the deck. However, my problem is that I have no idea how long this kind of journey would take in a boat of this size. I have tried doing online calculations for shipping trawlers with displacement hulls, and came up with a figure of between 8-12hours. However, I've got no idea if:
a) this is the right kind of boat to be using
b) this is a reasonable amount of time for the journey to take.

I would really appreciate any wisdom you may have. It seems like a very easy thing to get wrong, but a very difficult thing to estimate (as a novice).

Thanks.