The critical piece of hardware that makes windsurfing possible is the "universal joint" or "u-joint." The u-joint attaches the sail to the board but allows it to swivel and lean in any direction. This allows the rider to steer without a rudder and is the fundamental difference between windsurfing and normal sailboat sailing.
Picture from my old post, "Poor Person's Guide to Windsurfing"
The first commerically available windsurfers in the 1970s used clunky wood and metal u-joints. More compact and durable u-joints were developed in the 1980s and 1990s, along with lots of different systems for fitting them to the board and mast base. (
Joe Windsurfer has a blog post with pictures of the original wood u-joint and various other weird ones.) However, the u-joints themselves were all variations on two themes: 1) a bendy rubber "hourglass" or 2) a three-axis "mechanical" joint. By the 2000s, "Chinook" and a couple of other brands had more-or-less standardized u-joint and coupling systems, which made it easier to mix and match gear. The rubber hourglass u-joints were the most common type and seemed to work for 5-10 years before cracking and failing.
If the evolution had stopped there we'd be good, but someone had to come up with a "better" "tendon" design that has now mostly replaced the rubber hourglass joints. The tendon is a narrow, rubber-like cylinder that bolts into cups on both sides of the joint. The idea is that you can unbolt and replace the tendon easily without having to replace the longer-lasting parts of the u-joint. The problem is that you have to replace the tendons A LOT. Even the "good" ones don't last as long as the old rubber hourglass joints, and the quality of the replacement tendons on the market seemed to go way down shortly after everyone switched to using tendons. They can fail before showing any obvious signs of wear, even when they're brand new.
I discovered a new low level of tendon performance today when installing a brand-new one (Ruiqas brand, ordered from Amazon - should have gotten one from
my local Fort Myers windsurfing shop instead). I was a little suspicious of how the tendon had both bolt-holes in the same direction rather than orthogonal like the Chinook brand tendons. I was more annoyed when realized the ends of the tendon were too long to get the holes in the tendon to match up with the holes in the cups, no matter how hard I tried to jam the parts together. I looked up on the Internet that if that happens you have to cut off material from each end of the tendon using an X-Acto knife until it fits, which I did. It went together, but it seemed way less flexible than the original tendon joint. It snapped when I was positioning the board for a beach start, before I even sailed at all. GRRR. I could see a few little air bubble cavities inside the tendon where it broke through, but I think the real defect wasn't the air bubbles but simply that it was a lousy rubber/plastic formulation that lacked the flexibility and strength to do its job.
I still had one functional u-joint in the van, so the day wasn't a total bust. The wind had gotten too light to use the shortboard that I originally tried on, but I got a good session on my foil board with a 6.8 sail.
