The 'How to Build a Water Ski at Home' Thread

AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
edited November 2014 in Skis Fins 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.( 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!


  • thagerthager Posts: 4,447 Mega Baller
    Ahhh! So that is where @Horton got the email pic!! I might have to give this a go this winter. Been a long time since I built Indy car wings but the process sounds very similar.
    Stir vigorously then leave!
  • lcarneslcarnes Posts: 114 Solid Baller
    I'm going to have fun watching this process over the winter!
  • rq0013rq0013 Posts: 552 Baller
    This is awesome. I love it! I would think making the plug would be the hardest job. I've been wanting to build a slalom ski but it seems so complicated with all the variables. So I built 2 trick skis out of pvc foam and carbon, uni and bi directional. Rides great, but a slalom ski is a different story.
    Rob Quetschke
  • AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
    edited November 2014
    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.
  • HortonHorton Posts: 27,217 Administrator
    I am surprised that you are using thickness to tune stiffness. I would have thought that thickness needs to be tuned for ride height.

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  • AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
    @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.
  • JASJAS Posts: 246 Solid Baller
    Maybe an unspoken topic but what keeps a ski company from building a plug off of a successful ski made by another company? A change to top skin cosmetics and most of us would never know difference.

  • Chef23Chef23 Posts: 5,899 Mega Baller
    @JAS there are rumors that other companies have used other ski designs as the foundation for their skis. Other people may know better than I do.
    Mark Shaffer
  • HortonHorton Posts: 27,217 Administrator
    edited November 2014
    @JAS all good ski designers look at other designs. There is more to a ski than pure shape. Two skis of the same shape but built by different factorys will generally ski nothing alike.

    Support BallOfSpray by supporting the companies that support BallOfSpray

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  • Mateo_VargasMateo_Vargas Posts: 833 ★★★Triple Panda Award Recipient ★★★
    DIY skis are cool but how about a DIY gasoline thread for the winter?
    Success is failure that just hasn't happened yet
  • skier2788skier2788 Posts: 726 Crazy Baller
    edited November 2014
    @Mateo_Vargas did that in college. Not hard to get 48 octane but to go further than that gets difficult. We ran an old ford van on it. Ran like a diesel. This DIY ski project is cool have tried a couple different times to no success played with bondo and old skis some.
    Travis Torley
  • Mateo_VargasMateo_Vargas Posts: 833 ★★★Triple Panda Award Recipient ★★★
    Well I guess I'll keep watching Moonshiners on Discovery Channel for tips or throw a diesel in the old MasterCraft like this guy in Turkey.
    Success is failure that just hasn't happened yet
  • eleeskieleeski Posts: 3,818 Infinite Pandas
    Adam, very cool!

    One advantage of homebuilding is freedom from marketing driven finish. You can finish as a work of art without regard to cost. On the other hand, you can ignore the finish and its weight. You can use sawzalls, grinders and rough bondo to experiment. There's a good chance you'll end up doing a LOT of post molding work. Don't stress too much on the finish of the plug. Pick up some Superfil from Aircraft Spruce and lots of sandpaper to finish the ski to taste.

    @Horton‌ Cap molding techniques can control flex control thickness without affecting the edge profile. Plus an edge built up with Superfil will not add too much stiffness. Thickness is a very useful tool to adjust stiffness.

    @Mateo Vargas Homebrew fuel might be more fun in other applications than in your gas tank.

  • AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
    @JAS there's nothing stopping a manufacturer from copying someone else's ski. That's how a lot of startups get going. I know of at least one popular ski on the market that's a blatant rip off of another company's ski...

    @eleeski I think we have two different ideas on this. I could build something ski shaped and then spend time tuning the shape in. Or in this case I can tune the shape first using an existing ski and then build a plug/mold from that shape. There are advantages/disadvantages to either way but I already spent the summer playing with this shape and I know it's really good. If I spend time now getting the plug perfect then I won't have to spend much time at all working on the ski after it's molded.

    Also my motivation for this project is more about trying a new manufacturing technique that as far as I know hasn't been done. We did RTM at Obrien but that was a faster process that uses highly specialized equipment. The way I plan to do this ski (Resin Infusion) is a slower process that uses almost no specialized equipment (vacuum pump), but can theoretically make a better part.
  • Stevie BoyStevie Boy Posts: 1,919 ★★★Triple Panda Award Recipient ★★★
    Kewl, I watched a video on resin infusion, looks very good way of doing it.

    I appreciate you are going to go through various stages, but these are some of the areas of the process, where people could come unstuck.

    Question # 1 I take it there will be some sort of core material, that you wrap the carbon fibre around

    Question # 2 is it going to be difficult, drawing resin, through the mould evenly.

    Question # 3 the product of resin infusion, comes out pretty slick with a high gloss finish, surely that is not what you want on the underside of a ski.

    Question # 4 regards flex, how do you know where and how much extra carbon, to place, to get your desired flex, I take it you use extra carbon and not some other material.

    "Getting Harder/Getting Positive”

  • AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
    edited November 2014
    @Stevie Boy all good questions, I'll try and answer them as clearly as I can:

    1. For this ski I am going to "cast" the core from 2 part polyurethane (PU) foam. This is the same type of foam that is used on lower end skis and that Connelly used for years in the F1/Prophecy. Now all high end skis on the market use a PVC or similar foam but that can't be cast, it has to be machined on a CNC. Since this is the DIY/at home version I won't be using a CNC. To get the same strength properties as the PVC I'll have to run a higher density PU, which means this ski will be about ~1/2 pound heavier than it would be with a PVC core. Not a big deal in my opinion. Some of the best skis I've ever ridden barely floated.

    2. I've never used resin infusion to build a ski but I have some ideas on how to do it. I think I can figure out a way to make it work consistently, it just might take a few goes. @tap is a composites engineer that I went to Purdue with and he's been very helpful in determining the best way to do it.

    3. Not necessarily. Take Horton's beloved Warp as an example. Your wife could do her makeup using that ski as a mirror it's so glossy. Surface finish definitely changes the way the ski rides, but I don't think one is better than the other, it's just different. Also it's easy to change. A few minutes with some sand paper and I can put a "textured" bottom on this ski.

    4. Honestly this is just a combination of trial and error and experience. I've tried several times in the past to come up with a way to calculate the stiffness of a ski based on layup, but the geometry on the bottom of the ski is so complex that it just never really works. (If someone thinks they might know how to do this accurately please do share!) What I normally do is take a guess based on past experience but aim for the ski to come out a bit soft. Then I can add carbon to the top of the ski to bring the stiffness up to the desired level. Then I can base the layup of the next ski off of what I learned from the last ski.
  • gsm_petergsm_peter Posts: 732 Crazy Baller
    In case this helps anybody
    2 cents for DIY on how to vacuum a laminate.

    Have a friend that made model plans.
    Wing was 2 m wide (6,7 feet) at 250 g weight (half lbs).
    Did break at 50 kg load (+100 lbs) on the middle.
    Carbon fiber, epoxy, foam. Laminated with use of vacuum and later high temp.

    Vacuum was created by
    - Putting the mold with wet laminate on a piece of window glass (very flat)
    - Create a ‘plastic bag’ around it using thick plastic and tape (towards the glass)
    - Put in a thin metal pipe with many small holes parallel to the object.
    - Use a water hose connected vacuum pump to gradually create the vacuum.
    - Use a soft rubber piece to ‘massage out’ un-needed resin (poor down outside of the mold)
    - The water driven pump only need some gallons per hour and will create a pressure of almost 10 000 kg / sqr meter. (type 2 000 lbs / sqr feet)

    Best luck!
    Life is too short not to enjoy every day!
  • Chef23Chef23 Posts: 5,899 Mega Baller
    Very cool thread. I have read it a couple of times now and I will be interested to see the results. It is way beyond my abilities but interesting to follow.
    Mark Shaffer
  • eleeskieleeski Posts: 3,818 Infinite Pandas
    Adam, I completely understand your motivations and unique methods. And I commend them. And I'm really interested in the home resin infusion!

    Also your plan to control variables is spot on. If you have evaluated the basic plug, that is an excellent baseline. Little changes in flex, weight, weight distribution, finish and many other variables can radically alter the feel of a ski. Control what you can.

    I'm not sure that my crazy shapes intended to be that way. OK, some did but I'm not sure any of those ever getting seriously used. Most of the unusual features ended up as a result of tuning. Not fin dialing but grinder tuning. Skis are expensive and time consuming. Grinders, Bondo and a Surform not so much. I'm cheap and lazy so I might work too hard to salvage a sketchy ski. And yes, I did originally start with a factory ski and now I copy the skis of my own that I like. There is a lot of post molding finish that I end up doing.

    My motivation was (and is) to push the limits of how light a ski could be. Perhaps if I had invested the time and money in more practice rather than building I'd have gained a couple of buoys or picked up another trick. But my recreational engineering has sure been fun. And maybe I'm actually a better skier because of my skis. At least I need to believe.

    And Adam by sharing his experience here is entertaining us. Thanks and keep it coming!

  • skirayskiray Posts: 173 Baller
    @AdamCord thank you for this post. I've always wanted to build a ski just for fun.

    Are you going to add any suggestions on where to get the materials needed? (Later in the process)
    Ron Ray
  • taptap Posts: 78 Solid Baller
    @gsm_peter‌ , if I read your post correctly I think what you are describing is a "wet bag" technique. A similar process to what @AdamCord‌ is getting after, but different. Wet bagging generally implies wetting out the fiber during the layup process then using ambient pressure, via use of a vacuum bag and consumable stack, to consolidate the layup and press out air and excess resin. @AdamCord‌ is hinting at using more of a vacuum assisted resin transfer process whereby the layup would be constructed dry, then the resin would be forced through the laminate using ambient pressure, via use of a vacuum bag or vacuum cavity.
  • DragoDrago Posts: 1,488 Mega Baller
    On # 2: there is a fabric you can run down the entire length that will distribute the vacuum (would pull the epoxy up around the edges to the top)
    SR SL Judge & Driver (“a driver who is super late on the wheel and is out of sync”)
  • bishop8950bishop8950 Posts: 1,104 Open or 55K Rated Skier
    Great thread, thanks Adam! I remember Jamie talking about how he wished there were more home grown garage operations like the snow ski industry. If Adam gets it working without CNCs and presses it will be interesting. Looking forward to the rest!
  • gsm_petergsm_peter Posts: 732 Crazy Baller
    Yes you a correct. Some difference.

    It was a looong time ago when I assisted him building epoxy (type 1983 or so).
    First vacuum machine came from an old fridge. Did not last so long.
    The water driven vacuum pump was expensive then (type 30 USD or so ;)

    The important hints are
    - Water driven vacuum pump are rather cheap and creates almost 'space vacuum'
    - Window glass is very flat and creates an excellent building surface.
    - Regular tape (example for use for 'moving paper boxes') can be used to seal plastic


    Life is too short not to enjoy every day!
  • AdamCordAdamCord Posts: 703 Open or 55K Rated Skier
    edited November 2014
    @eleeski that's interesting that you've focused on making the ski light. I notice very little difference between light and heavy skis and I would much prefer a ski that will never break/break down. I could also be a bit jaded though because I seem to have the unique ability to break skis at will. It's not as much fun as it sounds.

    @skiray good suggestion I'll definitely list the materials used for each step and where I got them.

    @Drago yes that's called flow mesh or flow media and it's very commonly used in large parts like boat hulls and wind turbine blades for infusion. I may use some of it around the edges of the ski but I don't want to use any on the part. A big part of the challenge of what I'm hoping to do is end up with a smooth surface on the top and bottom of the ski. That means using no peel ply or flow media on the ski itself. I will use a piece of 1/4" thick acrylic as the top half of the mold, which will give a nice smooth/flat surface finish.

    @bishop8950 what I REALLY want to do is build on of these! Then I could cut the mold, cut the core from PVC, possibly even do the finishing on CNC.
  • dbskidbski Posts: 255 Crazy Baller
    @AdamCord , have you checked out Shopbot CNC machines? I use one of their smaller machines to cut the graphics and smaller parts of my wood decorative skis. They are fairly reasonably priced. I find this thread really interesting as building things yourself whether its skis, boats, cars or houses is incrediably rewarding. Seems like this is common trait to alot of skiers.
    Rick Bohn
  • jimbrakejimbrake Posts: 1,278 Mega Baller
    @AdamCord‌ - there are a lot of surfboard shapers who use CNC machines to shape their blanks. I wonder if one of them would cut a water ski core if you provided the specs for their program. Hmmm. This has me thinking now.
    "...all of the basic fun banter"
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