This site is an absolute treasure trove of technical material on sail and hull design, with a focus on model yachts but most of the physics scales up. It covers aerofoil theory (momentum, circulation, lifting line), sail twist, downwash, planform effects, Reynolds number, hull resistance, appendage design, VMG, and more.

Lots of spreadsheets and practical calculators too—bulb shape optimization, wetted surface area, simple VPP models. If you're into sail performance modeling or yacht design, this is one of the best resources out there.

Nice to see an enthusiast/engineering site that is putting cutting egde design ideas into the public domain. Grew up with boat builders on the south shore of Nova Scotia, and knew and learned from some of the last people to build and crew working schooners, that were also raced, I a boy, and they proud old men. Also know current builders and restorers of blue water boats. A few years ago I stumbled onto footage of a big hydrofoil cat that was the first boat to break the 50 knot barrier, you could tell that any celebrating was waiting and would largely be to celebrate still bieng alive, big seas, 50+kn, and quite clearly nothing but flinders left if anything broke and they plowed into a wave.,..,........they were standing on deck

Yeah, I miss the days when a higher proportion of this Internet was content like this.