America's Cup HY-80 keel failure

Used to illustrate that 130 ksi welded keel beam, four feet wide and eight inches thick, bent under sail loads — concentrating force in a single bending moment was beyond what HY130 could carry at that geometry. Tom names it as HY130 (the Navy submarine steel), not HY-80; the canonical cluster name may need reconciliation against other lectures.

They use it in the keel of the America's Cup yacht. This was about ten or fifteen years ago. In the America's Cup yacht keel beam, they'd used HY130, which was what the Navy wanted to use for submarines. But they built one and they went out and tested it and it bent. 130 ksi, like four feet wide, eight inches thick — a lot of force on those things, a lot of sail area, and you concentrate it all in a bending moment with a big knot. And I say keel — it's actually the piece that sticks down. It's not the rudder, but it's the centerpiece, and you want a bunch of weight in the bottom, down low.