I have been collating the statistics on shipping for the various Sussex ports of: Littlehampton, Newhaven, Shoreham and Rye, and have done so for a couple of years now. Only Shoreham used to publish details of cargoes carried/discharged and which cargoes were to be loaded. This cargo information was published on a weekly basis, and was prone to inaccuracy, but it was the best that could be done at the time. This ceased some 18 months ago and in line with what other ports have done is not to publish such information, as has been stated it is commercially sensitive.
But there are other ways of getting the information, by using a port map and getting to know what wharves are used to receive say timber, aggregates, etc one can build up basic picture of what cargo is arriving where. Also other useful internet applications to use apart from Marinetraffic are: Twitter and Facebook.
As Littlehampton, Newhaven and Rye, do not publish anything but the Harbour Masters at Rye and Littlehampton use Twitter. When commercial shipping arrives sometimes details of the cargoes are reported, again these are worth investigating, as a tweet gives you direct access to the Harbour Master or his assistant, all you have to do is explain what you need to know and where the info is going.