In over 100 masts sold, only a few have gone to windsurfers. As a kiter, I have marketed primarily to kiters through forums and word of mouth, and a lot of kiters have transitioned to winging so about 80% if my sales in the last 12 months were to wingers, with the rest surf and SUP foilers. Wing foilers appreciate the increased stiffness of the mast, and put a little more load on the foils without the additional lift of the kite and generally bigger boards. I have always known that windsurfers put the biggest load on their foils due to their extra wide boards and tall rigs. The only way to keep the foil stable in roll is get their weight as far outboard as possible, which creates a big bending moment at the board mount. I designed the mast with this in mind, but without knowing any windsurfers and with such limited test data I never knew how close to the edge these riders were pushing the setup. This winter, one of my Oahu based windsurf customers may have reached that limit, after bending the two bolts at the board mount. I also had evidence of bent screws in the mount of a hard jumping wing foiler.
Carbon doesn’t like out-of-plane loads (free composites 101 lesson here) which is why I don’t use a traditional collar at the top of the mast. Out-of-plane loads are forces that push into the surface of the material. Instead of inducing stress running along the direction of the fibers. These loads impart bearing stress into the epoxy resin, which isn’t as strong as the fiber. The joint of Project Cedrus relies on tension in the screws only, which is nice for a couple reasons. The first benefit to a metallic joint is a more benign (ductile) failure mode. Bending screws is a bummer, but at least the foil was not lost as typical with carbon foil failures, and with new screws my customers were back in business. To yield my standard 18-8 stainless steel flathead screw requires 5,000 pounds of tensile load. Considering there are two of them holding the mast to the mount, that means in takes 10,000 pounds of force to damage the standard lightweight plate mount screws of Project Cedrus. How does one achieve 10,000 pounds of force in these screws? Through a really big moment caused by a “short couple.” Basically, the edges of the mast bear against the mount in compression which puts the fasteners in tension. The resulting net force in the system is zero (static equilibrium), by the tensile load in the bolts, and bearing loads in the aluminum at the end of the mast are high. You can read about coupling moments here. Simply put, the rider weight in the photo above must be 2-3x the wind force because it is acting over a much shorter distance from the foil mast than the center of pressure of the wind. This rider weight is eccentrically loading the mast, imparting a huge moment at the mount.
As you may well be aware, there is a wide variety in the quality and strength of fasteners. While the 18-8 screws used in Project Cedrus are sourced from a reputable source to ensure good corrosion resistance and strength, the tensile strength of these fasteners is guaranteed to be more than 70,000psi. Remember the difference between tensile and yield strength? If not, read that blog entry here. I recommend McMaster-Carr for all your fastener needs.
Fortunately, there exists a class of bolts with a guaranteed tensile strength of 160,000psi that are compatible with my tuttle mounts, which is popular with the windsurfers. So to accommodate these in a standard track format, I developed the high-volume board mount with counterbored fastener holes and a thicker plate to ensure ultimate strength and stiffness of the joint. As expected, this plate is about twice the weight of the lightweight plate, but more than twice the strength. With the weight close to the board, and not at the end of the mast, it’s much less noticeable. Furthermore, the typical windsurf customer is already carrying a heavy rig and much higher volume board, so this weight will largely go unnoticed. This launch edition high volume board mount is available in gold anodizing.
If you plan to ride a wide board, windsurf, SUP, or prone… I highly recommend this new mount. Also, if you are jumping your mast with a wing, I also recommend this mount because the dynamic loads can cause a 200 pound rider to impart the load of a 600 pound rider at takeoff and landing. Please keep in mind that I have sold over 100 masts now and only bent bolts a couple times. Furthermore, I can’t even be entirely sure that the bent bolts is due to the yield stress of the fasteners or inadequate pre-tension or loctite. But to be extra safe, I wanted to introduce a beefier mount option. The average rider is not stressing the setup enough to warrant this mount, and I will continue to market the lightweight plate as the best option for 99% of my riders. I have 200 pound+ customers wing foiling on the standard setup with no issues, because you simply can’t get that much load into these bolts WITHOUT a super wide board and tall windsurf mast. Please don’t hesitate to reach out with any questions, especially if you’re on the fence about which mount to go with. I stand by Project Cedrus and all mounts and adapters, and have never had a structural failure of a mast or mount.