Guess what I did this afternoon - big clue - half an hour after high water on a spring tide.
Right - I put her aground! On soft mud, in a river, but she is pretty firmly "parked" none the less and, whilst the weather is OK now, it is forecast to be vile tomorrow, so I am off down the river at midnight to try to sort it out.
Air temperature 28deg F (-2C). I should really know better.