Does anyone know of any sites that let you compare ferry prices across a month long period?

Looking specifically at Hull to Rotterdam but the P&O site seems to make you choose a date and give you a price and I would like to choose a price and get a date!

Not sure if it’ll do what you want but this is the one we use:
http://www.ferrybooker.com/

I just tried a few websites, they do seem to vary accross companies.
However, booking for tomorrow or next month seems to make little difference. try the less well known companies, I got Dover-Calais return for £59 (with car) with DFDS. The Portsmouth-St Malo rouute I wanted was over £400 with P&O! Worth the extra tank of petrol for the slightly longer journey.

Only really interested in the P&O Routes from Hull

I just want something like you get with airlines where you can see a spread of prices across dates

Only really interested in the P&O Routes from Hull

The P&O site is probably your best bet then 🙂

But it only lets you choose one date at a time, I thought there might be a comparison site that lets you compare prices across a range of dates. It’s pretty standard for most sorts of travel but doesn’t seem to exist for ferries.