As this a large boat so I will use standard 3/16″ Props, as these a easy to get and come in lots of different sizes and pitches.
The only trouble is they are normally used on fast racing power boats and they tend to use flex shafts.
This makes it very hard to find a solid 3/16″ prop shaft, so the only option is to make them.
I used 5/16″ Stainless tube with a 3/16″ stainless shaft running in some brass bushes that I turned up on the lathe.
Made the support struts out of scrap brass & tube.
The couplings also needed bushes in them for the shafts.
Now all I need to do is fit them in the hull.