Official word (from John Estle) on difficulty of 50 km Sonot Kkaazoot course

The courses on the attached maps (course maps on Sonot Kkaazoot website) were plotted in the same FIS Homologation Software (online software) used to generate the specs for our FIS-Homologated competition courses.  The elevation data was based on a digital elevation model (DEM) generated from “the National Map” a USGS-provided data set.  Using a DEM from the National Map is an accepted practice as part of the FIS course-homologation process.  TC = “Total Climb” – the sum of all the partial height differences of every elevation gain on the course.

Section 1 = TC 626m / 16,572m

Section 2 = TC 408m / 14,135m (1034m / 30,707m partial total)

Section 3 = TC 655m / 20,021m (1689m / 50, 728m total)


Total = 1689m

Those amounts work out to an average of 33.3m/Km of climbing.  FIS specs for race courses over 5Km in length are required to be in the range of 25m/Km to 42m/Km.  The Sonot course is 33% above the minimum.  That amount of climb per Km is a degree of “physical challenge” (a FIS term) that is not typical for “popular competitions” (how FIS would categorize the Sonot Kkaazoot were it a FIS competition).  Most 50Km popular competition fall below the lower limit of the FIS specs.  On the other hand . . . a course used for a World Cup 50Km would still be legal with 25% more climbing than the Sonot course.  And the top male skiers would probably do that under two hours on fast snow.

Black Funk 5Km, South Tower 5Km and the Tower Island-Surprise 1350m sprint course (courses used at the 2023 Junior Nationals) are among about 10 homologated courses at Birch Hill for which the course specs were generated from that same DEM/dataset.  No dataset is perfect, and there are always errors in measurements.  However, the FIS Homologation Committee believes that datasets such as the one I used for the Birch Hill courses is sufficient to use as a basis for certifying that the course is what the specs say it is.

You can find homologation info at > Cross Country > Homologations.  Use USA in the nation field and apply the filter and you can see all the homologated courses in the US.

There is no homologation certificate for the Birkie course.  However, you might try contacting Allan Serrano ( who was the FIS Homologation Inspector for a 30Km course at Seeley Hills, WI, part of which might be part of the BIrkie course.  He might be able to provide you with some approximate (or precise) specs for the Birkie course itself.

Can’t think of anything else informative to add.

-John Estle email to Eric Troyer on how the total climb for the 50 km course was calculated

1 thought on “Official word (from John Estle) on difficulty of 50 km Sonot Kkaazoot course

  1. Pingback: Lessons in finishing the Sonot Kkaazoot when you’re just SCUM | Sonot Kkaazoot

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