I feel like an idiot now. Finally tides and work let me get on the beach to properly check the state of the weed growth
it was horrific. Took 2 containers of acid to wash it off (nice stuff to work with - make sure you wear old clothes). Took her out a hey presto almost all my lost speed returned.
So anyone with a moored boat not antifouled heed my warning and check the weed growth more often.
Unfortunately on the way bak in I developed fuel probs so I now have to work out if I have a blockage somewhere, water in the fuel (have a filter on BUT) or pump problems. Ah the joys of owning a boat