Good to hear that you're making progress, Paul.
The only thing wrong with using PVC was that I found it difficult to tap M6 into it, it tended to crumble, so I had to drill out the eyeplates to accept M8. If I did it again, I'd go for black nylon 66 for greater strength and toughness, and I certainly would go that way for your larger rig. It would be fine to buy a 250mm length and bury half of it in the tube, leaving 125mm to screw to.
I dug out and scanned an ancient photo of my Sadler 25 to remind myself of the mast position. For my wingsails with less balance area than you'll have, it shows that I put the mast through what would normally have been the hatch area, but I only cut out a smaller hatch aperture through the forward part of it. At this distance in time, I don't remember what the helm balance was like, so I can't guess how a SJR with the mast in the same position will compare. Also I don't remember how I reinforced the deck area, but it wouldn't have been much. I think you'll be OK bolting 18mm plywood where the 500mm square hatch was, without cutting away any headlining. At that time, I was working for M S Gibb, and got the foundry to cast me a mast partners fitting, then the machine shop to bore it out for a 5in diameter mast. I guess your mast partners are going to take up more space, and will end up being a little further forward.
(Also in the photo, I see that I put in a peg at the bermudan mast position, for the foot of a derrick for mast stepping)
When you've got her into commission, please could I invite myself for a ride, for old time's sake to remind myself what a good little boat the Sadler 25 is, and to compare and contrast your new SJR with my barely remembered wingsail on the same hull? assuming that travel is permitted by then, of course.
