C's Skis - Foray into converting a foam core waterski into a hollow one

[CsSkis]

This one is just for entertainment!

 

Before Adam Cord developed the AM33, he was experimenting with how to build a hollow ski. So, as a starting point, he took one of his old Elite's and pulled a mold off the bottom of the ski. After he was done, the ski was a little "worn" looking and he let me have it for experimentation purposes.

 

My approach was a little different than his. I took a Dremel moto-tool and cut through the carbon top deck of the ski. I then peeled off the carbon layer and used a coarse grinder on a hand drill to remove the foam core - with some cleaning up required with the moto-tool. (You will note I left the inserts in place. Before grinding, I made a reference template of the insert locations.) I added a layer of carbon in the tip area to strengthen this section of the ski and used J-B Weld to build a small flat area on the outside edge of the tip section of the ski (these 2 steps were required due to limitations in the way in which the tip area of the Elite is formed).

 

In discussions with Adam, it was agreed that a single layer of carbon for the replacement top deck would not be sufficient and that two layers would be required. (That's one of the advantages of a foam core. It keeps the laminates from "oil canning" and less material is required.) So, I needed to lay up a carbon top deck........

 

I had "access" to a glass topped dining room table, as well as a couple of additional sheets of glass. After mixing up resin and laminating two layers of ski-sized carbon cloth, I laid the laminate between sheets of thick acetate, placed it on the dining room table, covered it with the additional glass, and weighted the whole thing down with canned goods from the pantry to squeeze out excess resin. (Yes, you can go ahead and laugh. At least I have a very understanding wife!)

 

I let the laminates cure for a day. (Without heat, the resin won't completely cure in a day. It will still be slightly flexible.)

 

The next day I peeled the laminated sheets off the acetate. (The acetate leaves a very nice finish.) and used J-B Weld to bond the top deck onto the "de-cored" ski. In order to get enough pressure, without distorting the top deck too much, I used plastic bags filled with water to hold the top deck down until the J-B Weld cured.

 

After everything was cured, I used a band-saw to rough cut the edges of the excess cloth and then a sander to clean up the edges. Using my insert template, I drilled through (just) the top deck to expose the original insert holes.

 

Done.

 

So, how much weight did I save? Maybe a 1/4 of a pound. The PVC cores are already very light!

So, how did it ski? It was so stiff that it had absolutely no "feel" through the feet and had zero shock absorbancy.

Was it worth it? See above comments. I think that you can figure that out for yourself.

Would I recommend anyone else trying it? No, but it was still fun to try it.

 

 

If you have any questions, just ask.

Chuck Illi

 

[thager]

@CsSkis Wow, and I thought I had too much time on my hands! Very cool!!

[MattP]

@CsSkis wow you are one brave guy... @Horton can you post Jody....

The core does more for flex than you think as well does the top sheet that you removed. Very cool idea.. I would like to throw it on a flex tester though.

@AdamCord is a very smart ski designer. I have own a few of his skis.

[eleeski]

Nobody can single me out for crazy ski ideas.

 

Here's why you want a core: any tiny defect or handle ding will allow water in and your ski will get full of water. Epoxies soften with water exposure and your ski will weaken. Your ski will get heavy. You will not end up with the same ski over time. Note that open cell honeycomb has the same faults. Fill the voids with lightweight foam.

 

Additionally, cores do add significant strength for very little weight. Theoretically a ski with a core should be lighter. Why did you want to go coreless?

 

Finally, a flat carbon topsheet will have trouble carrying the compressive loads that are transferred to the top sheet (carbon is rather weak in compression). Some contours on the top help the carbon. Or reinforce with Boron.

 

My 1/2" 6 pound density foam weighs about 10 ounces for a slalom blank. It is very strong. One ply of lightweight carbon is all the covering needed in the unreinforced areas.

 

What really matters is did the ski work better?

 

Eric

 

 

[CsSkis]

@eleeski: I second everything you stated. Personally, I just did it for fun. However, regarding hollow skis, I don't discount the work/accomplishment of Adam Cord with the AM33.

[eleeski]

@CsSkis Playing with skis for fun rocks!

 

Maherajah built a hollow ski - but it barely floated and did not make Horton's list of game changing skis. Durafiber made some of the best (and lightest) race snow skis hollow (but they might have used a light foam as a filler) - a game changer on the snow. Adam is a savvy guy and your project was interesting.

 

I've built skis with a variety of methods. While I currently use foam cores and exotic skins, the honeycomb class project got me started and a wood ski had the most magic. It really is " how does it work?"

 

Eric