The planning reference is F/TH/11/0874 you need to go to the uk planning website http://www.ukplanning.com/thanet and put it into the search box if you want to view the council’s decision and report.
I would think the underlying problem here is that a bar and restaurant complex on the site is always going to be more profitable to the leaseholder than a boat repair business.
The problem for the council is I believe that the harbour - and it is important here it understand that the council derives a six figure income from the harbour - needs certain facilities to operate, the slipways being one of these facilities. Rather in the same way that the harbour needs an entrance to the sea to operate. Of course it would be much easier to run if it had no entrance to the sea, there would be no dredging problem, no problems with vessels and so on.