Ski over 130 degrees F = temporary rocker change

[Dirt]

A very knowledgeable person in the ski Mfg business said that when the ski gets over 130 F, the rocker changes. He said that it takes a couple PASSES in the cooler water before the rocker returns to normal. Another thought he said it takes a couple SETS before the rocker returns to normal. He was telling this to the next skier up who's ski was on the starting dock waiting for the skier on the water to fall or miss. He said that short time in the sun was enough to change rocker if the temp got high enough.

I try to keep my ski out of the sun but didn't realize how fast it could damage it. Has anyone else ever heard this?

[Horton]

Not sure it is that simple. Carbon fibers are shorter at room temp - longer at high temp.

 

D3 lets skis sit for 3 days (something like that) before final QC because things can change if the skis has not cooled all the way and things have settled.

 

Keep MY A2 out of the sun.

[skidawg]

and don't forget to close your tailgate :-)

[Horton]

Wow that hurts. I can almost laugh about that now and it has been a year.

[wlrottge]

The boat that I race is 100% carbon and we have to be careful of a couple of things (20' long, 8 1/2' wide, 38' mast, 265 lbs!). Depending on the resin used, a carbon part could have issues if you get it too hot. Some resins will start to deform at 150F. If you apply any pressure and change the shape, it's changed and won't return on its own.

 

Repeated heating to temperatures above the glassing temperature can/will cause changes in the crystaline and chemical structure of the resin. The carbon is your strength, the resin holds it in place. If you have a degredation in the resin, it can become more brittle and crack. You will also have oxidation and end up looking like the "clear coat" has hazed and is flaking off. That's the outermost layer of resin... NOT good.

 

I have a pair of sandles that I left in the car this summer. The glue got hot enough to allow the sandle to come apart. I have no doubt that if you let a glass ski get that hot you'd have similar problems.

 

I buy that if it gets too hot you can screw it up, but I disagree that it will return to normal after X number of passes or .....

[Dirt]

He said they have done testing. I was just surprised at the low temperature to cause a rocker change. A black top carbon ski in direct sunlight on a 105F day would get to 130F very quickly. In 60 minutes on a 90F day the interior of a car gets to 133F.

[Horton]

Keep my A2 in the ac!

[Horton]

I think we should all start calling u dirt in real life.

[eleeski]

I was able to cure prepreg carbon by leaving it in my desert sun for a short time . The thermometer said 170F! Why do manufacturers paint their skis any color other than black?

 

I had a black ski totally delaminate in the backseat of a convertible on a not uncomfortable drive. Last non white ski I ever built.

 

Tha ambient temperture can go as high as 130F in my desert. It goes from hot to scorching over a few hours. I have never had a problem with a hot ski that heated slowly and evenly. As long as both top and bottom skins heat at the same rate there should not be too much added stress to the ski. Bringing your ski out of the AC to heat while you get ready then cool again in the water might add more stress to the ski than a ski that comes from the ambient (shaded) temperture. General warmth is OK, rapid unequal (solar) heating is not.

 

I screwed up a ski. My repair involved heating the ski with a heat gun until I could force it to the desired shape. The repair worked until it got really hot. The ski went back to the old unrepaired shape when it got heat stressed. If a ski is finish stress cured to change the rocker, heat will change the ski. Probably permanently.

 

Eric

[ForrestGump]

This brings up a good question, Eric. Greg Badal had MAD11 send an A2 back to him so he could change the rocker. MAD11 says it was definitely changed. Do they do that with heat?

[eleeski]

Heat can certainly be used to reset rocker. This would be a very effective tool for the testing and development process. But a ski that had heat changed rocker could have some residual stress. Resins do soften with heat - even moderate heat. Moderate heat could relieve stress in a ski and cause the rocker to change permanently. A ski with a reset rocker would be a likely candidate to change with time and temperature - but not guaranteed to change.

 

I don't know what resins and cores HO uses. Some resins and cores are designed for working temperatures well above the hottest ambient temperatures. My resins are OK to 50C (125F+). I used to use higher temp resins but ended cooking my cores too much. Plus a room temperature cure is easy to work with.

 

I radically change rocker with a saw in the core, resin and a mold reset. For more subtle rocker tuning, I add some Superfil to the appropriate places on the ski. Or I have a frustrating run and just take a grinder to the ski and make something completely different. Very entertaining!

 

Eric