AdamCord

@Horton that's true, but I'm normally a believer in thicker is better in that regard. Skis that are too thin tend to shut down pretty hard at apex, which is where you need it to carry speed. Obviously there's a limit there because with carbon the ski can get way too stiff very quickly. That's why modern carbon skis tend to be thinner than old fiberglass skis. For this ski it was a bit too thin so I had to add extra carbon in the tail to get the numbers up. I'd rather avoid that.

So in order to make a mold from this ski I have to add a flange to it. The flange will create the geometry for the flat areas around the mold cavity. You can probably use a lot of different materials like plastic or sign board, but I had some 1/4" plywood so that's what I'm using. I'm not sure what type the wood is but it's got a very smoothe surface on one side so it should work well. Before attaching it to the ski I sealed the surface with some cheap home depot polyester resin. I just used a standard foam paint roller. Once it was cured I spent about 10 minutes with a palm sander getting it smoothed down, and now I have a nice flat surface. Here's the wood right after applying the resin: After sanding down the board I centered the ski on it upside down so that I could attach the board to the ski's top. I drilled ~20 holes in the board and ski and used wood screws to attach it. I want the new ski to be stiffer in the tail than the original. I could do this by adding layers of carbon to the layup when I build the ski, but it's better to make the ski thicker if possible. Stiffness increases with the cube of thickness so adding a little thickness goes a long way. I added some washers to the screws in the tail area to add the thickess: In order to make a clean edge at the ski parting line and to fill the void left by the shimming I did in the tail, I filled the seam between the ski and board with some bondo type body filler. This part is tedious but it's important to get this right, otherwise it'll screw up the mold or I could end up with an undercut, which would make the mold mechanically lock to the plug. That would not be cool. Next I'll sand that body filler down and *hopefully* be left with a nice clean edge.

Right now I'm in the middle of building the plug. You could try and build this from scratch but I never would. It would take way too much work to try and shape it by hand and the chances of ending up with a decent ski shape are pretty low. By far the easiest way is to build a plug using an existing ski. You could copy an existing ski shape if you wanted, or you could modify the shape of an existing ski. Modifying an existing ski is what I do. This allows you to test your modifications on the water before spending all the money/effort of building a mold and ski. What I usually do is take a shape that I like and start modifying it. That could mean splitting the ski to adjust the width, adding bondo and sanding, filing/sanding the bevels, heating it and changing the rocker, etc. Obviously you're going to ruin a ski or two doing this so it's not for the faint of heart, and I don't suggest you go out and buy a brand new ski to test with. What most manufacturers probably don't want you to know is there really isn't that much of a difference from skis built 5 or even 10 years ago vs. skis today. So use an old ski. The ski I'm using for this project was actually built by @adamhcaldwell. His shop is basically a mini ski factory with a pneumatic press and every tool you need to build skis. It's a sweet setup and I am very jealous of him. The shape itself is something he and I worked on together and then we had a plug cut on a cnc machine. So this shape isn't based on any production ski. I rode this ski for most of the summer and made some modifications to it, and now I will turn it into my plug. This ski was never intended to be "production quality" so it had some pin holes and blemishes, not to mention the cuts and other imperfections that I added by making changes to it. So what you can see below is the process of filling/sanding/painting that went in to getting a good surface finish. It's important to try and get the best surface possible now on the plug since any imperfections will get transferred to the mold. I will wet sand the plug and polish it to a shine before getting it ready to build the mold.

So the entire process will look like this: Build a "plug". A plug is basically the opposite of a mold and is used to build the mold from. Build the mold. I'll build this in a similar way to how a boat is built, by using gel coat and fiberglass. Build a foam core. The method I plan to try is a bit experimental so it may take a few tries to get right. Layup and "press" the ski. I plan to use a resin infusion method that I've been thinking about for a while. This is VERY experimental so there's a chance I'll ruin a few skis before I get this right. Ski finishing. This is pretty straight forward and involves cleaning off the flash edge of the ski, cutting a fin slot, and installing metal inserts to mount the bindings.

I was talking with @Horton and I told him that this winter I'm going to try and build some skis with a new technique in my garage. He suggested I post about it and that lead to me doing an entire How To / DIY ski build thread. So what I'm going to do is try and document the process here as I do it. For all the people who don't know who I am I'm an engineer that used to be in the watersports industry designing / building skis. I started really skiing competitively in college at Purdue in 2002, and have been obsessed ever since. My tourney PB is into 39 @ 36mph so I'm by no means a "pro" skier, but I try and get after it. After getting a real job I tried to just "ski" but I've found that I can't stop playing with ski shapes, fins, bindings, etc. I find it surprising that more people aren't experimenting with their own slalom skis. With all the DIY / Maker / 3D printing type stuff going on more and more people are building complicated products at home. There's even an entire forum dedicated to DIY snow ski building.(skibuilders.com) The only other "home" slalom ski builders I know of are @eleeski and @adamhcaldwell. I'm hoping that by showing in detail how to build a high quality and high performance scratch built ski at home I can inspire more people to get into the hobby. If nothing else this might take some of the mystery out of what goes into designing and building a slalom ski. It's turning to winter up here in NY so I'll hopefully have time to get this project done fairly quickly. My wife is about a week away from popping out our first kid so that might slow me down a bit but I'll do my best!

@Horton I'm going to have to start taking my laptop to the lake with me. Fin setups, flex changes, boot changes, bevel changes...even Zero Off setting changes and different drivers will be quantifiable now. This will take the level of nerdiness in this sport to new heights!

@dlokshin Thanks for getting back so quickly. With regards to the IMU: How can we use this data in a meaningful way? I assume you've developed the software to use it for other sports. Even if we could see the Gs in each axis as well as pitch/roll/yaw side by side with the speed and position data it would tell us a lot. Hell I'd be happy if I could just dump that data into excel.

I MUST have this! Super Cool. @dlokshin here are my questions: How is the video synced up with the data like that? Does your software do that if I have a video file of the pass? What is the sample rate of the data? We accelerate/decelerate quickly so wondering what the lag is and time between data points. Does this unit incorporate 3 axis sensors and accelerometers? It would be even more useful to have acceleration data as well as pitch/roll/yaw. Is there any way to make it work mounted to the ski? I know John initially had problems with losing signal when it went under water. If it's on the tip of the ski it could feasibly be kept out of the water at all times. Thanks in advance, I hope you guys sell a few million of these things.

@6balls - yeah we definitely lost some sales because of underbuilding. This was especially problematic with the Elite skis because they took so much longer to build than compression molded skis. The Connelly/HO/Obrien factory in Lynnwood, WA is set up pretty well now because they can print their own graphics and CNC their own cores which means they don't really have to wait for anything to start production on a particular ski. Their lead time is really low. I'm not sure what Radar has but I think they are in a similar situation. It becomes much more difficult to build the right amount of skis when you have long lead times for some of the materials. @Chef23 you've got it right, unfortunately I had to grow up and get a real job at some point!

@ShaneH has it right. You forecast, build it out, and hope you were right. The purpose of Surf Expo for the manufacturers is to try and get orders or at least forecasts from dealers/distributors that can be used to plan for production. Most of the new products at surf expo are one-offs that came in from the factory the day before, not something that's ready to go to production. That's why surf expo happens in September for the following year's product line, it gives the manufacturers time to build and deliver equipment before the next season starts (Feb/March timeframe). I assure you it's pretty rare that something ends up in dumpsters. I can remember maybe one time where we still had stock of some 6+ year old tee shirts and hats that no one wanted, so we scrapped them out. This definitely doesn't happen with skis. Normally if there are leftover skis, which is really rare, they'll go to a retailer like Overton's who will blow them out on their website really quickly by running a "sale". Most of the time we were building fewer skis than we needed, not more.

@BigC - Due to the changes in dynamic viscosity the ski will tend to ride a bit higher in cold water than it does in hot water. To compensate you need to make a fin change that will pull the ski down in cold water, or in your case let the ski ride higher in hot water. I've found that making small DFT and Depth moves tend to work best. As the water gets cooler I'll bump the fin back and deeper. As the water warms up you want to go forward and shallower. In your case it sounds like the fin is in about the right spot for cold water. When it's warm though the fin is too far back and deep, making the ski not want to rotate, and causing the slow turns and slack you're experiencing.

You missed the hard part about what he's doing. Do you have the 4 or 5 frames before that? That's the part to study.

If you want to try some things easily without destroying the ski you can put down some aluminum foil tape on the surface of the ski first. Then build up bondo or something like what Eric is talking about over that. Then you can shape away. If you hate it, just peel the tape back off. Works surprisingly well.

Having skied and worked with Cale quite a bit, I'm guessing the wording on this "tip" has been confused a little. What he's really talking about is staying connected and not letting the handle get pulled away from his body. There are several different ways to accomplish that, and for some people thinking about pulling in on the handle could help. In reality there's just too much load to pull the handle in, but if you're thinking about that it can certainly help keep the handle from getting pulled off your body. Also I've heard whatever he's skiing on is pretty amazing ;)

@thager Theoretically yes, so long as the shear loads are distributed in a way that it is carried fairly evenly by the carbon and there are no very high load concentrations. The Warp is a good example of how this could be done. I have not seen any of the newer Warp skis but I know some of the old ones had issues with cracking along the ribs in the ski (there are 3 vertical ribs running tip to tail, which along with the sidewall, are designed to support the top and bottom skins and carry the shear loads). I believe the cracking was a result of stress concentrations where the ribs meet the top and bottom surfaces. @walleye You love that orange koolaid, eh?

@kstateskier I'm glad I can spread some nerditude around the forum every now and then. @walleye I've heard multiple people say that about reverse flex. Do you know where that comes from? It doesn't really make any sense to me. A ski is basically a glorified sandwich panel with carbon laminated to both sides of a piece of foam. The only difference is that normally the top skin is made thicker to reduce the chance of breakage by buckling since carbon is not as strong in compression as it is in tension. So most skis will break more easily in reverse flex, but that doesn't mean that some amount of reverse flex will really speed up the breakdown on a molecular level.

Plastic Fatigue. @DW pretty much nails it. A ski has 3 main components: Carbon, Epoxy, and foam Core. The core and epoxy are both plastics, and plastics will fatigue over time with repeated strain. The shear loads on the core are very high, and many cycles reduce the elasticity of the core/epoxy and their bond. Some skis will last a long time because the laminate is better bonded to the core, meaning the shear load is spread over more molecules. Other skis that have a weaker bond to the core (meaning there is less epoxy attached to the core surface) will break down faster. The reason a ski like the Fischer will last longer is twofold: it has an almost perfect core-laminate bond (no air pockets) and also some of the shear load is carried through the sidewalls because of fiber orientation and how the core is wrapped over the flash line. Of course there are variables like type of epoxy, type of core material, UV exposure, temperature changes, etc, but that pretty much sums it up. The carbon fiber itself fatigues but those fatigue tests are in the millions of cycles. The core/epoxy will break down long before you get there :)

I've got the CAD files on a hard drive at home but I'm out of town so I can't give you an exact #. I would guess it's somewhere around 7.4-7.5" at the widest point.

The HO factory is no longer the HO factory. Obrien also sold their place. They have all moved into the Connelly factory up in Lynnwood. I don't believe they give regular tours but if you call Connelly and ask they might take you through?

@ral I think it all depends on what you're trying to emulate. Sure taking a snapshot of Nate or someone else at 41 off might show some interesting positions that you probably don't want to try at 28. But back up and look at the fundamentals of what allows those guys to run those passes and it's the same at 15 off as it is at 41. Generating speed with minimum load, staying connected until your release, taking your energy high on the boat, carrying as much speed as you can back to the line, etc. are fundamentals that work everywhere. Focus on those instead of trying to figure out what "posting" is (for example) and why they do it. It's just not important compared to the big picture ideas.

@horton that makes perfect sense. If he's staying connected with 2 hands and running a short line (38 or shorter) then the path he's on MUST be inside the buoy since the rope won't reach the buoy. What he's trying to do is release that energy high up on the boat. If he comes off the handle early he'll release that energy too soon and stop the swing up on the boat meaning he ends up not as wide and he doesn't run 41 like the rest of us run 28. @matthewbrown is right, there's definitely a limit to it and it's all about timing with your speed vs. where you are in relation to the boat. I can see how someone as good as @matthewbrown has pushed that limit too far. Most people don't even come close for a variety of reasons. Of course there's more to it than just "hang onto the handle!"...

Let me see if I can shed a little bit of light on this subject. @Horton's original question was something along the lines of "if a ski is fast, will that mean there is less load behind the boat and therefore does that make edge change and staying connected easier than with a slower ski?" - or something like that. First off for anyone like me who hates a buried lead, the answer is YES. Here's why: It helps if we consider the extremes. Let's say ski A is a 59" kids ski that's soft as a noddle and sits really deep. It takes half the lake of submarining to get up on ski A. Ski B is a 69" ski with small bevels and shallow concave. It sits really high in the water and you can pop up without getting your hair wet. On ski A: I pull out for my gates, turn in, and pull as hard as I can. What happens? Well the ski pushes deep in the water, it wants to go behind me, and creates a massive wall of spray. Do I go fast across the wakes? Of course not. But I'm pulling my brains out, so why can't I go faster? Remember that massive wall of spray? That's a LOT of water. Many gallons per second. Stop and think about how much energy it must take to move multiple gallons of water per second straight up in the air. It's a lot, and it's coming from the boat via your body. So all that load isn't generating speed. All that's happening is you're getting dragged down the lake sideways and you almost rupture a bicep. Now on ski B: I pull out for my gates, turn in, and pull as hard as I can. What happens? The ski lifts up as it gains speed, it moves in front of me, and before I know it I'm going mach 1. Is there more load than ski A? Not even close. In this situation I've converted much less energy to spray and I've been dragged down the lake a much shorter distance. My energy has been converted into cross course speed. The load through my legs behind the boat is no more than my body weight because my speed dictates that I'm no longer just plowing down the lake making spray. So it's not so much that a ski is faster and also has less load. A ski is faster BECAUSE there is less load. Clear as mud?

Thanks @Alberto Soares, I was able to get a hold of Carlos and get it setup. Hopefully the tequila helps with the soreness.

@Alberto Soares thanks for sending that! I'll try him today. @OB I'll be down there next week and it looks like the site isn't too far from the Guadalajara airport so I'm hoping to cruise over there after I land. Thanks

Thanks @OB, I tried emailing him and also Carlos (emails listed on the website) but never got a response.