Waxing & Humidity (was "waxing question")

Waxing & Humidity (was "waxing question")

Post by ruddoc » Wed, 20 Dec 1995 04:00:00


>Now for a new question.  So often waxing recommendations revolve around
>humidity.  But what is the recommended method of measuring it?  Everyone
>brings a thermometer or two to races, but how many do you see bring a
>hygrometer?  I know I'm getting pretty good at picking up a handful of
>snow, and from the look and feel pronouncing it "wet" or "dry".  (Hint:
>upstate New York almost never gets dry snow.)  But this is far from
>scientific.  And we don't confine ourselves to upstate New York, either.
>Is it just a simple matter of bringing a hygrometer along with you and
>sticking it out next to your thermometer?  I remember once hearing or
>reading somewhere a recommendation to fill a cup up with snow, let it
>melt and see how much water it turns into.  (Seems like a time-consuming

yes and no. This is the point where people start talking about the "art"
of waxing and it sounds more like the "magic" of waxing. The big three
factors that have to be taken into account are temperature, humidity and
snow structure/condition. Work with all three and waxing is a science,
leave one or more out and waxing starts to turn into magic.

Most hygrometers measure the relative humidity of air (or more precisely
the air surrounding the special coil). What the waxer is
really interested in is the humidity of the snow pack in the top 3-5cm.
There are a couple of ways to measure this. If you have a big budget
there's a device you can buy (the name of which I forget right now) that
measures the amount of free and vapour water with a laser. It's a real
cool device. You can also purchase an electronic hygrometer. Still
big bucks, but not as big as the laser (about $800US if I recall
correctly). The other is too use the $5.00 hygrometer from the greenhouse
store. When using this one some methods need to be followed to get
accurate and consistant measurements: the tool needs to cool in the shade
to the air temperature; the vents (that give access to the coil) need to
be exposed only to the snow pack (not the air) and be shaded (otherwise
the reading will get perturbed); needs to be left there for at least 30
minutes (the coil tends to change slowly at colder temps and the
equalibrium between snow pack and air gap around the coil has to happen).
Essentially the hygrometer will be in a closed environment with the snow
without the sun affecting it. These cheap hygrometers also have a habit
of becoming uncalibrated often (to the point a new one should be bought).
So cavet emptor on hygrometers.

Great. So why am I measuring the snow pack's humidity? Because that's
what the ski interfaces with. Skiing is the combination of dry and wet
friction, and a delicate balance at times too. When the water layer is
created between the snow and the skis it disappears into the snow pack.
It goes into the snow pack as free and vapour water. The more "porous"
the snow is the more water it can absorb. And the lower the snow's
humidity the more water it can absorb. The reverse also holds true: more
dense and/or higher humidity = less absorbed. Now when absorbtion is too
high you end up skiing with more dry friction. That's often that
styrofoam sound heard. When absorbtion is too low it means mostly wet
friction which is where the suction problem starts.

Snow structure and humidity go hand-in-hand. For example, last year at
the Canada Winter Games many coaches made some poor wax choices because
of the conditions for the biathlon relay: warm chinook came in bringing
temps to about -6, air humidity was normal/dry. Waxes of the day?
Streamline and C44. The snow was 20+ days old (machine groomed at that). It
was completely transformed. Any water under the skis had nowhere to go.
So a wax to remove the water from under the base faster was needed. Some
coaches chose Dibloc red, but it wasn't enough. In converse you can have a
humid day with fresh snow to negate it.

So look at the temperature, humidity and snow structure before cancelling
out _any_ waxes. These three measurements feed off of each other. The older
or more transformed the snow becomes (from fresh flake to granular) it is
like the humidity rising. If you have high humidity and old snow this can
be the same as a 5C to 7C temp rise. Similarly a low humidity, fresh snow
situation can be the same a 5C temp drop.

Different waxes are 'tuned' for different conditions. It is generally
understood that Swix is tuned for fresh snow while Ski*go is tuned
towards transformed snow. This why given the same temp and humidity C44
will be better than F1 (or FC100 as the marketeers have renamed it) some
days: the snow structure is different.

It's skiing; it's waxing; it's science!

Sorry this turned out so long.

- Rodney

Rodney Ruddock         =    "Barking at Airplanes"     =        voice & fax