As you will read on that page, even Jeckells seem to have hand drawn the sail logo and it has subtly changed over the years - gradually degrading. I would just examine a number of images found on the site and decide for yourself what size to have it made. There is not a definitive "right" answer.
Graham did register on the forum within a fortnight of it being launched. However, he has never posted here, although he was active on the YahooGroup that the site used before then. I also know he sold his SeaHawk soon after he registered.
What this means is that I have no idea whether he still uses the address that he used to register here and that is the only way I have of contacting him. It must be worth a try. See his profile page!