many thanks taitharris - it seems a four stroke in the 50/60hp range is ideal for these conditions. I have a working knowledge of the rowing code, so the rowers don't bother me too much. and, dare I say it, I've rowed a few times before, so I have experience of the "dark side".
John Kennett - love that kayak story - thanks.
I may end up with a dory or fast fisher of some kind. Where I live, it makes sense to leave it in the water, and something hard might be more robust and easier to put a cover on.