I am about to fit a folding propeller, and have decided on the Flex-o-Fold. See my enquiry 'Foling propellers' of 11 January. (I am not good at typing or proof reading). The reply I had was the this is a very effective unit, with the only slight drawback that if you are going astern with the boat moving ahead, you need a good burst of revolutions for the centrifugal force to open the blades. A view expressed to me at the boat show was that the flex-o-fold unit was more robust than the Gori, although I have no means of checking this. The Flex-o-Fold is marketed in this country by CQR of Southampton and costs less than the Gori. You might still be able to get the Boat Show offer prices.
Be a bit careful because I asked if I should replace my existing 18" fixed with an 18" Flex-o-Fold and was told yes. I then checked with the builder, NAJAD, who said fiit a 17". On discussion this recommendation came from YANMAR who built the engine, so it might be worth checking with the builder, to see what they recommend,and the engine manufacturer to ensure you do not over stress the powerplant.
Thanks. I was originally offered a Maxprop but now a Gori. I went to
the Gori website and entered in my boat details. The response was a) My boat engine was too small to achieve hull speed and 2) the reduction ratio needed altering to avoid cavitation at rpm above 3268! The size of prop is NOT the one the yard is proposing! All too hard.........
That is quite surpricing. Unless you have an unusual reduction gear. What's the ratio and engine HP you gave to gori?
Try the prop spreadsheet from the westerly-owners site: www.westerly-owners.co.uk/html/downloads.html
See what it tells you. In my case it came pretty close to what I actually have, and that works well.
And let flex-o-fold do the same sizing for you.
The 2.63 ratio for the Yanmar is probably the right assumption for a boat like yours, it is the most common for sail boats in that range, and is what I have too.
The quick calculation shows you need about 89HP for practical max hull speed of 9.72 knots. The prop would be around 21x15. This does all look pretty reasonable, I have a 22 x 13 on the same engine and gear ratio, but my boat is a bit heavier.