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

[AdamCord]

@mack I definitely intend to keep documenting this process. I currently have enough materials for maybe 5 or 6 skis. Now that all the hard setup work is done building skis is the easy part.

 

You can definitely fix the blemishes. Surface porosity/voids can be filled pretty easily and sanded/painted. It's pretty much the same as doing body work. The easiest way to build an at home ski is probably to "wet bag" the ski, then do post work on the surface to get it cleaned up. I made a trick ski this way over the summer for a friend and it turned out pretty good, although trick skis are much simpler to make than slalom skis.

[AdamCord]

@Tyler_R you're probably right but then @mattP would never give it back.

[eleeski]

Adam, what about 1/8 polyethylene instead of the acrylic? It seems your acrylic is too stiff and creating pressure points where the resin can't flow. Maybe a layer of foam (yoga mat?) would even out the pressure under the acrylic. A bit tougher to watch the infusion.

 

The top of the ski is purely cosmetic. You want to make sure the bottom has proper resin and pressure so it produces the base of the ski you desired. If the top is too uneven, Superfil can take care of any issues for just a couple grams of weight and some easy sanding. Seeing the fabric and reinforcement lines on the top is actually kind of cool.

 

Note that I have to massively slit my cores to make them flexible enough to avoid areas that don't get enough pressure to bond properly. The resin fills the slits and makes a bit of a honeycomb effect adding some strength. Also the slits allow some resin flow out under the pressure for a drier layup (in for infusion?).

 

Trick skis are easier to make?! Only if you don't care about performance.

 

Eric

 

 

[AdamCord]

@eleeski yeah I was thinking the same thing. Using a softer material will decrease the pressure points on the ski. Using peel ply on the top might actually give it a nice "matte" look. Military spec ski.

 

And yes I agree, if you don't care about the performance of your slalom ski, you could build it as easily as a trick ski :wink:

[mack]

does superfil cure clear?

[mwetskier]

you might consider pre-wetting certain known problem areas before bagging and infusing. presumably if the resin doesnt kick too quickly the in flow of the rest of the resin plus the vacuum draw should reduce or even prevent over saturation.

[eleeski]

@mack Superfil is like Bondo. It a mixture of epoxy and microbaloons. It has a long (1 to 2 hour pot) working life, sticks well, doesn't shrink with age, overnight room temperture cure, when cured it is easy to work and finish and is very light weight. I've used microballons as filler but the Superfil is optimally mixed with a good resin to get the best fill at the least weight. Reasonably priced.

 

But it is not clear so you will have to paint the part...

 

Eric

[Intheday]

@AdamCord any news on ski number two

[AdamCord]

@Intheday I took my first sets in 5 months last week so I'm finally switching back to the ski season mindset. I need a decent ski to ride so I'm motivated to pump out some new ones soon.

[mack]

@AdamCord what kind of epoxy are you going to use? are you going to vacuum infuse? Or, will you wett out and vacuum press it? Will you document? I will be gell coating my plug tomorrow. I tried once already but it was way to cold out and the gell coat alligatored all over. i built a test core but had a lot of trouble sawing it flush. i got a few ideas from a snow ski site about building a core profiler and using a router to finish top of core . I think it'll work and be much easier than sawing and filing. I will have an opportunity in the next month or so to get a mold built by a cnc machine. If that happens............... i'll be geeked. Hmmmmm maby get some pvc foam and have them cut me a core at the same time............ i will post any progress, as it occurs. The gentleman that will cut a mold on the CNC machine mentioned something about making the mold out of urethane block that it would be about 1/3 the cost of aluminum. Have you ever worked with such a mold? would one be able to run such a mold thru a heat process? I would not even be considering a machine built mold but i have a chance to get it done for just the cost of material.

Mack

[AdamCord]

@mack I am using infusion epoxy from Ill Street Composites. I plan to infuse on any skis I build. It's a better process when it works. Also I've built skis about every way possible at this point, and infusion is just more interesting to me for an at home build.

 

Building a core profiler would definitely make your job easier. Please post pics if you do that!

 

As far as cutting PVC foam, cutting molds, etc, the issue isn't so much the cutting as it is getting the ski into CAD. Designing a ski in CAD is more art than science and it's really really tough to get it right on the first go. Many manufacturers cut and recut molds over and over until they get it right before releasing a ski. You can 3D scan a ski but for the number of skis you want to make it will be much easier to just build a plug and mold if your plan is to copy a ski you already have.

 

Also taking a ski in CAD and flattening it so that you can cut the shape from a flat sheet of foam is really really tricky. Whenever I do it I just plan that it will take at least 5 tries to get it right, which means wasting a lot of expensive foam.

 

So I guess what I'm saying is using a CNC makes sense if you are going into production, and it makes no sense if you're building a few skis at home.

[mack]

@Adam Cord when I get to the core profiler i will post some pics. As far as the CNC, my son in law is the president of a manufacturing firm that provides some of the hardware to our military. they just purchased a machine that is capable of turning out finished parts that are 6x4. he said that all he'd have to do is scan the plug and presto. well, however it turns out so be it. but, if they want to practice on my plug..... smiles i'm all for it. i have given a little thought about thermo forming a pvc piece of foam as a core. i'm not really sure if i'd be able to do it with the crude equipment [oven] that i would be building.

[AdamCord]

And.....we're back. It's finally warmed up in NY, which means I need a ski. The first ski I built was skiable but came out too stiff, so here goes ski number 2:

 

After consulting with @tap we decided to try a new approach with the infusion. Last time the resin inlet was at the perimeter/tail of the ski and vacuum was pulled in one place at the tip. This time the resin inlet will run down the length of the ski center and the vacuum will be pulled at the perimeter. This is accomplished by putting holes in the plexiglass on top of the ski and running a spiral tube feed line on top of those holes. The vacuum around the perimeter is separated into 4 zones to try and isolate them from each other.

 

In order to make this work I need to do a better job of perforating the core. I put holes every 2":

 

In order to soften the ski I use less unidirectional carbon this time, 20oz/sq yd top and bottom. I still use a weave as the exterior layer. Here you can see how the carbon is wrapped:

 

Then the top layer goes down:

 

Then goes the plexiglass and the feed/vacuum tubes. The feed line runs down the center of the ski and there are 4 vacuum zones at the perimeter:

 

This time I use a tube bag that envelopes the entire mold. While this material is better than the stretchlon I used last time, It can cause some problems as it is susceptible to leaks on the underside of the mold.

 

Here's what the setup looks like before I start the infusion:

 

Here is the resin starting to flow in through the ports in the plexiglass:

 

 

 

And...

[AdamCord]

The only problem I had was that the bag did develop a leak under the mold while I was infusing. I'm not sure if this was from where it was sitting on some blocks, if it was a sharp edge on the mold, or what, but I couldn't find it. While the resin was flowing I couldn't really flip the mold over and give it a good inspection. Luckily the leak was outside of the part area so it didn't cause too much of a problem. I did end up with some porosity but for the most part the ski came out really nice. It's definitely better looking than a lot of skis I've ridden!

 

 

 

 

 

If you're wondering about the areas where the resin ports were on the top, they broke off pretty cleanly as expected and with a little sanding you can barely tell they were there. The flex came out just on the soft side, which is perfect because I can easily stiffen the ski. Now I just need to cut a fin slot, mount it up, and take her for a spin!

[MattP]

@AdamCord were you able to take that ski out for a ride this weekend?

[mack]

@AdamCord was the plexiglass the same size as your prior infusion., or did you make it smaller? how far apart are the holes that run down the center? what size are the holes? Also did you enlarge the holes going thru the core material as well as close up their spacing?

Darn!!! that looks freaking good! will you document how you cut the fin slot?

[AdamCord]

@MattP I've got 2 sets on it so far. The thing about building your own ski is that there are no "stock settings", so it does take a bit to get it dialed. Once I get it working nicely I'll see if I can't get some video. One thing I'll say about this ski so far... it's much much faster than any production ski I've ever ridden. I ran a 32 where I swear I was taking the entire handle section outside of the buoy line. :smiley:

 

@mack The plexiglass was exactly the same size as last time. I used ~1/8" holes spaced 2" apart. I used the same drill bit for the holes in the core. I tried to line the center holes in the core up with the holes in the plexiglass. I don't think that part has to be perfect but it's good that it's close.

 

For the fin slot there is a right way to do it and then there's the way I do it. The correct way involves using a router with the properly sized bit and building a jig so that you keep the router centered when you make the cut. That's not how I do it.

 

I measure the centerline and mark it:

 

Then I get out my favorite tool in the world, the angle grinder. I use a metal cutting blade and I cut all the way through the ski right in the middle of the slot:

 

It's fairly easy to cut straight and right on the line if you just drop the grinder down into the top surface. If you try to cut the whole slot, on the other hand, the grinder wants to wander. That's when I get out my 2nd favorite tool, the jig saw. I use the jig saw to cut the ends of the slot, going very slowly and keeping it right on the line:

 

The jig saw blade is super narrow so I use the angle grinder to widen the slot a bit, then I do the the final touches with sand paper. Cutting the slot like this can be surprisingly accurate so long as you take your time. I usually get the slot just wide enough for the fin to fit, but so that it's tight. If it's loose then the fin will flex side to side in the ski. That's a topic for a different discussion but let's just say that's not what you want your fin doing too much of.

 

 

[Horton]

There is a method I would expect from Eric Lee

[Chef23]

Cutting a ski with an angle grinder would scare the hell out of me.

[eleeski]

Grinders for skis! I love it!

 

I'm not alone.

 

Eric

[AdamCord]

@Chef23 forget calipers. The grinder is the only precision tool you need. :)

[mack]

laughs.........more than one way to skin the cat

[JayG80]

So after the fin slot is cut in the tail of the ski - there is nothing applied to seal the PVC core from water in the fin box?

 

Over the years I've heard comments about the need to repair handle dings in ski so it does not become water logged. Ski myth?

[slow]

This guy should start a ski company

[AdamCord]

@JayG80 that is definitely a ski myth. Skis are built using closed cell foam, meaning the air cells in the foam are closed off from one another. The water can never make it past the outer surface of the foam. If they were built using an open cell foam not only would skis be a lot weaker, but they would all soak up moisture over time and get heavier.

[Justupright]

Great thread

I'm currently in the process of making a mold myself. Was wondering if you have ever used Kevlar in a ski and if you did what were the characteristics of it ?.

[Adam Caldwell]

@Justupright - Dont waste your time with kevlar

[eleeski]

Kevlar sucks. It doesn't bond well to any epoxy I've used. It's impossible to finish sand. It's hard to cut the cloth (dedicate scissors just for Kevlar). It's heavier than carbon and rather flexible. My Kevlar ski didn't survive one run - so not very strong for how I laid it up.

 

I still use it in my skis. Deep in the laminate only where I'm going to put screws or inserts. Tough stuff. It is really good for retaining the screws.

 

Eric

[CsSkis]

As both @adamhcaldwell and @eleeski said, forget Kevlar. @adamcord built some O'Brien Elites out of Kevlar (red and blue ones!). They looked really amazing in the sunlight, but were a real pain to put in inserts and to clean up around the fin slot. (As @eleeski said, the Kevlar fibers are very hard to drill, trim or sand cleanly. They just end up getting real "fuzzy".) These particular skis turned out fairly soft, as Adam was just trying out the material and didn't worry too much about flex. The one that Adam gave me skied well in rough water as it seemed to absorb vibration better than Carbon. (Of course, I didn't have a direct comparison to work with, so it just could have been all in my mind.) I passed the ski along to someone else after I was done "playing" with it and the individual that has it now is still enjoying the ride. (The individual had radical spine surgery a few years back - he had to travel to a specialist in Europe to get it - and appreciates the softness of the ski.) So, in this particular case, the ski turned out very durable.

[Than_Bogan]

@CsSkis I would say "durable" and "soft" are exactly what one should expect from a Kevlar composite. The point of that stuff is to take a beating, but it doesn't have the tensile rigidity ("I will not stretch!") that indirectly leads to glass and carbon composites being stiff.

[eleeski]

If the resin doesn't bond well with the fibers the ski won't be durable. Also it is weak in compression and will get overloaded by certain loads that glass can carry. Breaks prematurely. That's my experience.

 

With the proper resin (usually found in an expensive and hard to mold prepreg) and proper design, Kevlar parts can have acceptable properties. But who has a freezer and autoclave at home with their ski mold? And a big wad of cash to laminate.

 

That gets me thinking. People hassle me about my primer white graphics. Maybe I'll mold in a dollar bill as my finish. Increase the value of the ski?

 

Eric

[gsm_peter]

@eleeski

 

How about this Dollar?

Suites you skis perfect.

 

 

[aupatking]

I love that @AdamCord has his obsession-to-real life business documented here. At least, step 1 and step 3.

[BraceMaker]

An example of something that would do really well with kevlar would be a sledge hammer handle.

 

Better question is have you tried Basalt fiber yet?

 

[eleeski]

@BraceMaker I haven't tried basalt. It's been a few years since I looked at the properties and it didn't make the cut then. Besides, as a light freak, I can't have a ski made of basalt!

 

I do use boron fibers though. Magic stuff but the splinters are horrible to work with.

 

Eric

[Justupright]

How about hybrid twill carbon/Kevlar and carbon/glass

Just interested to know what other products people have toyed with and results they have got.

In the layup has anyone sprayed coloured gel coat first then lay up fibres before bagging, or would that process suit a neutral cure process?.

[eleeski]

@Justupright I haven't used gelcoat. Too much work to spray it. I tried tedlar film but I struggled with it. Mainly because my homemade skis take too much work after molding. I end up having to paint to cover up all the dings, fixes and non moldable work. I use too much Superfil. My skis are all experiments so primer white is the standard color.

 

Regarding the Kevlar Carbon cloth, I tried a sample of it in prepreg. I was just after the carbon at the time so I used it as a carbon unidirectional with some extra pain in the ass material to make it harder to cut. Worked OK but why? Prepreg has lots of disadvantages for a homebuild. My skis got lighter and stronger with a careful wet layup. And cheaper and easier to build.

 

Do be careful with carbon in compression loads. I used a hybrid of glass, balsa and carbon to carry the compressive loads. I earlier mentioned Boron fibers to replace all that and carry those loads brilliantly. I reordered more boron despite the cost and splinters because it worked magically.

 

High quality glass is surprisingly good. But carbon is affordable magic.

 

PVC cores rock. Divinycell is a good brand. Polyurethane broke down after a while. Honeycomb is hard to bond, picks up water and didn't seem to last well for me.

 

Applied Poleramic epoxy makes better parts than any of the other epoxies I tried. Epoxy was better than polyester resin.

 

Prepreg needs freezers, heated molds and money. Less time pressure on the actual layup but not worth it.

 

I would love to vacuum bag my skis instead of the pressure bladder I use but I haven't been able to make it work.

 

Molds are hard to make. I envy @AdamCord and @adamhcaldwell and their cnc molds. Reproducible and consistent. But my bondo and grinder method does lead to some very out of the box ideas to try.

 

Have fun with your efforts. Let us know what works for you.

 

Eric

[Justupright]

@eleeski

Thanks for your advice will put some pictures up of my progress just waiting for tooling gel coat to show up.

[Justupright]

So have been a little busy with work,kids and water ski racing but still managed to get a mold knocked up

Really appreciate all the helpful pointers

 

[eleeski]

I love the shape of the tail. Where have I seen that before?!!

 

Eric

[dchristman]

here, circa 1978?

 

[eleeski]

Or,

 

[Chef23]

I still love the look on Dave Goode's face in that picture.

[Justupright]

We are a bit more into hotdog style skiing and found this old ski boost really well off the wash but if you want cut hard it also does that, quite a spin out for a old tech water ski .

Will be making a insert and core soon.

Unfortunately its winter down here and 6 degrees celcius at night just doesn't create yo much enthusiasm for being in the shed.

 

[Justupright]

 

[Justupright]

 

[Justupright]

 

[Justupright]

So after going to the trouble of going all this I thought that I might try a little bit of gel coat on the deck.

 

Well let's just say that was a shit idea the glass and gel coat cured at different rates and all but delaminated the deck ??

 

Well I have different plans for the next lay up.

If you don't wreck something in the process of trying something new than are you even having a go.