It seemed to me that I was gradually gathering together a fairly coherent body of text that looked exactly like an explanation of how a sailing boat works. It started as a piecemeal process when I wrote my book on the radio-controlled, model racing yacht and gradually expanded.
I have said that I have no experience of sailing and so it is inevitable that I cannot be familiar with the mind-set of those who do sail. They may even think that it is unfortunate that I ever started to put pen to paper. But there will be some readers who will find that my approach fits in with their own way of thinking and that it does not offend any of the established principles of physics.
My first version of this text attracted such comments as "this text is shaky but some of it is useful". It was not only shaky but in a crucial respect wrong. It was a mistake of interpretation of an observation. I withdrew it from the internet and set about rewriting it.
It has been very rewarding. For a long time I have been conscious that I did not know for certain how the coefficients of lift and drag for a sail varied with angle of attack and wondered whether my guess was valid. Whilst I was repairing this text I came across much more reliable data that I could use. It has permitted very considerable improvements.
I offer it to those who can make use of it.