I’m about 2 weeks into Project Cedrus as my full time job. So far the experience is much different from my expectations. For the last few years, this has been my side-hustle, or “part time” job. I figured with it now being my only job, I would suddenly have a ton more free time. Time to exercise again, be a dad, maybe even kite foil on a windy day. Ha! Turns out now that this is my primary focus, I’m realizing all the things I could be doing better! I need a new website, better packaging, youtube videos on assembly, user manuals, terms of service, better accounting tools, and overall business and manufacturing optimization. Notice that nowhere in there is actual product design or engineering, which is what attracted me to this in the first place. I love challenging engineering and design problems, and while the mast may seem like a really simple structure, I wanted to share the challenges that I encountered when I designed the original Project Cedrus almost 5 years ago and why the mast is the way it is today.
When a client pays a deposit for a mast, they are directed to a questionnaire which is intended to get a background of their foiling style and their goals for the custom foil. The opening half of the survey asks them to rate the importance of 5 main mast characteristics: Strength, weight, stiffness, drag, and universality. If you’ve been following this project for a while, you know you can’t have it all. To achieve the the stiffness, weight, strength and compatibility aspects of Project Cedrus, I sacrificed a little hydrodynamic drag. At times I wonder if I’ve been too open about this, because anyone who actually owns a Project Cedrus claims to not notice or mind any increase in overall drag. Thanks to my friend Cody at Inde Foil, analysis shows the effects on overall top-end speed of a 19mm thick mast to be about 2-5% vs. a 12mm thick mast (I actually don’t know any masts that are 12mm thick). One data point lacking from this analysis is the subsequent effect on stiffness when going from a 12mm thick mast to one that is 19mm… and it’s orders of magnitude bigger than the impact to drag. Because stiffness is related to thickness cubed, that 2-5% sacrifice in speed can allow for a 400% increase in stiffness! So next time you hear someone whining about 2-5% more drag, feel free to educate them of the non-negligeable impact in stiffness, strength, and foil control.
This is a real engineering challenge
Back to the survey, this morning I woke up to a new client in Australia who ranked every characteristics as “most important” to him. With his weight somewhere between 200 and 250lbs, I can see why strength and stiffness are critical to him. However, he’s also requesting a mast that is extremely light weight and also very fast. If I were designing a car, I would basically need to mash a pickup truck with a race car to satisfy this client. Impossible. Fortunately, I’m designing a mast and what I am offering him will satiate 4 out of his 5 needs. I have a 285lb client in Florida who’s broken every mast he’s ridden, but very happy with his Project Cedrus. On the other hand I have 100lb clients who are grateful for a mast that is so light and easy for them to maneuver on and off the water. The group of foilers who may be less satisfied are those looking to race or set speed records. Fortunately there are plenty of other thin carbon masts out there for this group of foilers.
To illustrate the challenge of engineering and multi-disciplinary optimization, I’m going to compare Project Cedrus to another very high-quality, US-made, super stiff foil mast. This week a client sent me their F4 high modulus mast from which to design a new adapter. Please do not take this comparison as anything negative towards the designers at F4, this a simply an apples:apples comparison of two somewhat similar, but different products. This F4 mast is thin, with my calipers I measure 14mm. It’s stiff, based on my very basic testing, actually 7% stiffer in bending than Cedrus. But it’s heavy: 52% heavier than Project Cedrus. And it’s expensive, over $300 more.
A stiff and strong monocoque mast mount comes at the expense of weight and cost
If you are racing, or truly riding small wings down 30kt+ swell, the F4 high modulus mast may be for you. Thinner means less drag, and a longer chord length further improves resistance to ventilation at high speeds and aggressive angles of attack when powered by a kite or wing. This isn’t subjective, these are facts based on engineering principles which is why I am so open about them. F4 is based in the Bay Area, and came from the world of race fins. It’s obvious why they’ve chosen to stay thin and focus on speed, and I fully respect their design decisions and the products they produce.
At the expense of speed comes weight: a thinner mast must be solid to maintain equivalent stiffness and strength to a thicker hollow mast. A solid mast means more plies of carbon, which adds significant material labor costs. Project Cedrus is 13plies. The Axis carbon mast is publicly claimed to be 80, and I assume this F4 mast has a similar amount of material. Again, the F4 mast is over 50% heavier than Project Cedrus, at 5lb 11oz vs. 3lb 10oz. For some, this may not matter. But for me, and many of my clients, weight is important for a variety of reasons from air travel to actual ease of use of the foil.
My basic 3-pt bend testing involves laying the mast on its side and standing with full body weight at mid span. I measure deflection of the middle point, which gives me a rough estimate of bending stiffness but tells me nothing about torsion. Mounting the mast horizontally to a wall and pushing on the end is NOT a proper method for assessing mast stiffness. You are primarily stressing the mount when you test this setup, which gives inaccurate insight into the overall stiffness of the mast. I suspect this is why so many brands taper their mast, as the reduced stiffness near the fuselage does not show up in this test method. Anyway, based on my measurements, the F4 mast is about 7% stiffer in bending than Project Cedrus.
Measuring Deflection of a 3 Point Bend Test
If you’ve read my composites 101 blog entry, or listened to my podcast, you’ll remember why I designed my board mount the way I did. This mast provides another reinforcing example. Look at how much material F4 needs up near the plate to reduce inter laminar tension stress at the board interface. Inter-laminar tension stress occurs when curved fibers want to straighten. Managing this type of composite state of stress adds significant cost and weight, which is why the mount for Project Cedrus is aluminum. Aluminum is an isotropic material with much higher strength than epoxy, allowing me to design a lighter, cheaper, modular mount system than a traditional monocoque carbon mast.
I hope this illustrates the fun and challenge of multi-disciplinary optimization. Honestly the mast example is quite simple, as there are only 4 variables (strength, stiffness, weight, drag) with levers that I get to pull in the overall design. But I hope it’s clear that you can’t have all 4, at the most pick 2-3 important ones and live with the lowest priority. I could have made Project Cedrus thinner, but it would be heavier, or less stiff, or weaker, or some combination of all of those! If speed is absolutely critical to you, there are a number of solid, thin carbon masts out there to chose from. But if you are a heavier rider, riding big wings and boards, and desire the universality of Project Cedrus, the impact of added thickness is in the noise for non-negligible increases in stiffness and strength.
With modern aircraft design, there may be 10+ levers to pull. With consumer products like iPhones, you’d be surprised at how many engineers are involved optimizing features like audio quality, screen size, camera quality, battery life, weight, strength, cost, and more. It’s been the most fun aspect of my career, working with all these engineers to come to a solution that satiates everyone’s needs. It can be very challenging at times, for both technical and personal reasons, but in the end it’s incredibly rewarding when it all works out.
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