It is not possible for me to describe the emotions after receiving an email from a customer with the subject line “mast problem.” I am not a skilled enough writer to communicate the immediate feelings of fear, sadness, frustration, and even anger that something I poured my heart, soul and savings into has somehow failed to live up to my exceptions or the customers. This is what happened last week, after a recent customer found himself in a coast guard boat getting a ride to Crissy Field after his new Moses wings almost fell off his mast.
This is the 3rd iteration of the Moses adapter, and fortunately only 1 was delivered with the 2nd waiting in inventory for masts to be delivered to a customer in Europe. I have been working to reduce drag and increase consistency among my adapter designs, as a significant portion of total foil drag comes at the interface to the fuselage. To be honest I don’t perform detailed structural analysis on these parts, solid chunks of 6061-T6 machined to spec should have excessive strength for this application. I guess even I have suffered from the effects of poor carbon design in the sporting goods world, as most people think carbon is weaker than aluminum. Carbon is much stronger and stiffer and aluminum, so when a mast fails, it is due to bad design, not the material.
In the last 3 years, foil wings have gotten bigger and bigger, and new forms of foiling (eg. wing foiling) have increased loads on the foil without the additional lift of the kite and faster maneuvers on the water. Project Cedrus has finally found her position in the market, satisfying customers looking for something stiffer for these big wings, especially Lift and Moses. Unfortunately, I pushed the design of this adapter a little too aggressively, and a combination of hole positioning and fatigue led to a fracture while wing foiling under the Golden Gate for a 205lb (dry weight) rider.
Based on my analysis, it took about a 3.5G maneuver to cause stresses above yield strength to propagate through the thickness of this part. As seen in the above graph, the adapter deviates from the linear elastic region around 3,000N/675lbf which is a dynamic load case. According to Alex, this did not sound unreasonable… heading down the face of big windswell in 20+ knot winds only to pump up the next leeward swell. Fortunately, the front of the adapter hung on to the mast, and no wings were lost. I am so grateful for the Coast Guard support off of Crissy Field and that I didn’t have to buy Alex a new set of really expensive wings!
I’ve redesigned the adapter with 2-3x higher strength. Is this enough? I’m 99.99% certain. Do I have concerns about this adapter or any of my other designs? No. I am confident that Project Cedrus with adapters is stiffer and stronger than any mast on the market. In fact, this failure further proves the design and sizing of the mast, with no structural failures to the carbon or edges, but some slight (repairable) yielding to the aluminum. I have nothing to hide, and want to share this failure as an example of the learning experiences that make product design so challenging and rewarding at the same time. I was quick to ship Alex my demo mast and a V1 Moses adapter to get him back on the water. I’d like to thank him again for his patience and understanding, and for being the type of customer that makes this whole project worth it.
“While I was obviously disappointed about the failure and it created a tough rescue situation, everything worked out well. We push our gear hard and sometimes things fail. I am really happy with Kyle’s quick response to the issue and working with me to get everything right and get me back out on the water.”
Thank you to Alex and all of my supportive customers. Good winds! Kyle